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., ~IEEE TRAN SACTI 0 NS ON MICROWAVE THEORY AND TECHNIQUES NOVEMBER 1993 VOLUME 41 NUMBER 11 IETMAB (ISSN 0018-9480) A PUBLICATION OF THE IEEE MICROWAVE THEORY AND TECHNIQUES SOCIETY PAPERS Hybrid High Temperature Superconductor/GaAs 10-GHz Microwave Oscillator: Temperature and Bias Effects .................................................................................. N. J. Rohrer, G. J. Valeo, and K. B. Bhasin 1865 Spectral-Domain Analysis of Open and Shielded Slotlines Printed on Various Anisotropic Substrates .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Y. Chen and B. Beker 1872 Heating Characteristics of Thin Helical Antennas with Conducting Cores in a Lossy Medium-I: Noninsulated Antennas .................................................................. M. S. Mirotznik, N. Engheta, and K. R. Foster 1878 Identifisation of Propagation Regimes on Integrated Microstrip Transmission Lines ..................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. S. Bagby, C.-H. Lee, D. P. Nyquist, and Y. Yuan 1887 Reflection and Transmission of Guided Electromagnetic Waves at an Air-Chiral Interface and at a Chiral Slab in Parallel- Plate Waveguide ............................................................................. F. Mariotte and N. Engheta 1895 Calculation of the Fundamental Mode Sizes in Optical Channel Waveguides Using Gaussian Quadrature .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. A. F. Jaeger and B. P. C. Tsou 1907 Measurements on a 215-GHz Subharmonically Pumped Waveguide Mixer Using Planar Back-to-Back Air-Bridge Schottky Diodes ... P.H. Siegel, R. J. Dengler, I. Mehdi, J.E. Oswald, W. L. Bishop, T. W. Crowe, and R. J. Mattauch 1913 Single-Frequency Relative Q Measurements Using Perturbation Theory ......................... B. Tian and W.R. Tinga 1922 Large Signal Design of Broadband Monolithilc Microwave Frequency Dividers and Phase-Locked Oscillators ................................................. R, Quere, E. N oya, M. Camiade, A. Suarez, M. Hessane, and J. Obregon 1928 Hybrid Couplers in Bilevel Microstrip ................................................... M. D. Prouty and S. E. Schwarz 1939 Turnstile Reftecto-Polarimeter Using the Principal Incidence Method: Determination of Permittivities up to 1220°C and Industrial Applications ......................................................... A. Bretenoux, Cl. Marzat, and R. Sardos 1945 A Nonreciprocal Tunable Waveguide Directional Filter Using a Turnstile Open Gyromagnetic Resonator .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Helszajn, C. S. Cheng, and B. A. Wilcock 1950 Effects of Waveguide Wall Grooves Used to Hold Samples for Measurement of Permittivity and Permeabillity ................................................................................................................... R. Luebbers 1959 MFIE Analysis and Design of Ridged Waveguides ............................................. W. Sun and C. A. Balanis 1965 Rigorously Modeling Short Bent, Graded-Index Dielectric Slab Waveguides ............................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. J. M. Bastiaansen. J. M. van der Keur, and H. Blok 1972 Finite-Element Analysis of Axisymmetric Cavity Resonator Using a Hybrid Edge Element Technique ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J.-F. Lee, G. M. Wilkins, and R. Mittra 1981 (Continued on back cover) ~IEEE MICROWAVE THEORY AND TECHNIQUES SOCIETY The Microwave Theory and Techniques Society is an organization, within the framework of the IEEE, of members with principal professional interest in the field of microwave theory and techmques. All members of the IEEE are eligible for membership in the Society and will receive this TRANSACTIONS upon payment of the annual Society memoership fee of $20.00. Affiliate membership is available upon payment of the annual affiliate fee of $33.00, plus the Society fee of $20.00. For information onjoming write to the IEEE at the address below. Member copies of Transactions/Journals are for personal use only. 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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41 , NO. 11, NOVEMBER 1993 1865 Hybrid High Temperature Superconductor/GaAs 10 GHz Microwave Oscillator: Temperature and Bias Effects Norman J. Rohrer, George J. Valeo, and Kul B. Bhasin Abstract- Hybrid YBa2Cu;01-x superconductor/GaAs mi in a one hertz bandwidth can be given in dBc/Hz by [7] crowave oscillators have been d~signed, fabricated and char l acterized. The planar oscillators were built on a single L(fo) = 10 mm x 10 mm LaAI03 substrate. The active elements in the (ic) hybrid oscillators were G~ MESFETs. A ring resonator w11s lOlo [kTFG ~ kTFG 2 af'1 used to select and stabilize the frequency. A superconducting g P + 27r f o + 4PQi, fo + 87rQi,fg . ring resonator had a loaded 'Q at 77 K which was 8 times larger than the loaded Q of a ring resonator fabricated out (1) of copper. S-parameters of the GaAs FET were measured at cryogenic temperatures and used to design the oscillator, which Herek is Boltzmann's constant, Tis the temperature, Fis the had a reflection mode configuration. The transmission lines, r f noise figure associated with the negative resistance device, G chokes and bias lines were all fabricated from YBa2Cu307-x is the gain of the amplifier after it has reached a steady-state superconducting thin films. The performance of the oscillators oscillation, P is the output power, QL is the loaded Q of the was measured as a function of temperature. The rate of change resonator, and a is the combined flicker noise constant of the of the frequency as a function .of temperature was smaller for an oscillator patterned from a pulsed laser deposited film than for amplifier and the resonator. As can be seen from the third and an oscillator patterned from a. sputtered film. As a function of fourth terms, a largei: loaded Q will decrease the phase noise. bias at 77 K, the best circuit had an output power of H.5 dBm The hybrid oscillators employing high temperature super and a maximum efficiency of 11.7%. The power of the second conductors that have been published include a parallel feed harmonic was 25 dB to 35 dB below that of the fundamental, for back oscillator [8] and a series feedback oscillator [9]. For the every circuit. At 77 K, the best phase noise of the superconducti.ng oscillators was -68 dBc/Hz at an offset frequency of 10 kHz and parallel feedback oscillator, the feedback network consisted less than -93 dBc/Hz at an offset frequency of 100 kHz. At an of a superconducting linear resonator acting as a narrow band offset frequency of 10 kHz, the superconducting oscillator had pass filter. Only the feedback network was cooled to 77 K. The 12 dB less phase noise than the copper oscillator at 77 K. The amplifier was implemented in normal metals and operated at superconducting oscillators at 77 K had 26 dB less phase noise room temperature. This oscillator operated at 10 GHz and had than the copper oscillator operating at 300 K. an output power of 6.0 dBm when the resonator was cooled to 80 K. A highly integrated microwave system will require I. INTRODUCTION the whole oscillator to be operating at cryogenic temperatures on a single substrate. The series feedback oscillator fit on T HE APPLICATION of high temperature superconducting a 10 mm x 10 mm LaAI03 substrate with a coplanar res thin films to microwave circuits is advantageous since onator stabilizing the frequency at 6.5 GHz. It had an output the films have a lower surface resistance than gold or copper power of 4.9 dBm when immersed in liquid nitrogen. The at microwave frequencies. Some of the passive microwave power of the second harmonic was only 10 dB down. In this structures that have shown improved performance using high paper, we report on the design, fabrication and testing of temperature superconductors are ring resonators [1 ]-[3], mul microstrip hybrid oscillators. Each oscillator was fabricated tiple pole filters [4] narrowband filters [5], and antennas [6]. The advantage of using high temperature superconducting on a 10 mm x 10 mm LaAI03 substrate. The phase noise of the superconductor oscillators at 77 K is compared to a copper films for resonators is the 1arger quality factor (Q) values that oscillator at 77 K and 300 K. It would also be advantageous if superconducting resonators have compared to normal metal resonators. The larger loaded Q of a resonator has the potential the frequency of the oscillators were not sensitive to variations in . the temperature or bias .c onditions. The frequency and for lowering the phase· noise of oscillators. In the Leeson power of these circuits were measured as a function .of the model, the phase noise of a feedback oscillator when measured temperature and the bias conditions. Manuscript received April 13, 1992; revised December 10, 1992. This work was supported by NASA under Award NCC-3-197. II. DESIGN N. J. Rohrer and G. J. Valeo are with the Department of Electrical Engi neering, The Ohio State University, Columbus, OH 43210. Since our objective was to implement the entire oscillator K. B. Bhasin is with the National Aeronautics and Space Administration, on a single substrate to be operated at cryogenic temperatures, Lewis Research Center, Cleveland, OH 44135. IEEE Log Number 9210215. the S-parameters of the transistors at 77 K were obtained. 0018-9480/93$03.00 © 1993 IEEE 1866 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE I PERCENT CHANGE OF THE S-PARAMETERS FROM 300 K TO 77 KAT 10 GHz Su 522 magnitude phase magnitude phase magnitude phase magnitude phase 3.3% 19.3% 20.4% 8.8% 8.8% 6.7% 36.5% 37.8% 0 811at300K D 812 at 300K 0 822 at 300K D 821at300K t. 811at77K + 812 at 77K t. 822 at 77K + 821at77K Fig. 1. 5-parameters at 300 K and 77 K for S 11 and S 12 in the range of 4 to 15 GHz. Fig. 2. 5-parameters at 300 K and 77 K for 521 and 522 in the range of 4 to 15 GHz on a compressed Smith Chart. These S-parameters were used in the design of the oscillators. The design of the oscillators was performed using simulations on commercially available software (Touchstone™) [10]. The simulations were performed using the S-parameters obtained when the bias on the transistor was maintained at Vds = 3 V and Id = 10 mA and the temperature was 77 K. The design had a ring resonator which was parallel coupled to the transmission line in the matching network off the drain. A. Cryogenic S-Parameter Measurements The active devices used in the oscillators were Toshiba GaAs FETs (JS8830-AS). This transistor is a low noise MES FET with a 0.25 µm gate length and a gate width of 250 µm. The S-parameters of the FET for frequencies of 4 to 15 GHz were measured over a temperature range from room tem perature (300 K) to 40 K. The values for the S-parameters 08U/NA8A from 4 to 15 GHz are shown in Fig. 1 and Fig. 2 with the transistor biased at drain voltage Vds = 3 V and drain current Id = 10 mA at 300 K and 77 K. To achieve this drain current, Fig. 3. The physical layout of the reflection mode oscillator on a 1 cm2 the gate bias was adjusted to V = -1.04 at 300 K and 98 LaAI03 substrate. to V = -1.19 V at 77 K. Of the S-parameters, the largest 98 change in magnitude as a function of temperature occurred for FET was made very large by varying the length of open the S21 values. This was due to an increase in the electron's circuited transmission lines on the source and the gate. The mobility at the reduced temperatures. The variation in phase selected lengths of the transmission lines from the source and of Su and S22 was the only other major change. The percent the gate were 1.57 mm and 2.79 mm, respectively. The output change of the phase and magnitude of the S-parameters at of the oscillator was taken off the drain. The layout of the 10 GHz due to the change in temperature from 300 K to 77 K oscillator is shown in Fig. 3. This configuration is a reflection is listed in Table I. mode oscillator. The matching network, which included the ring resonator, B. Reflection Mode Oscillator was designed such that the magnitude of the real part of The design of the oscillator was performed using the small the impedance of the matching network was less than the signal S-parameters of the FET that were measured at 77 K. magnitude of the real part of the impedance looking into The input reflection coefficient looking into the drain of the the drain of the FET. The magnitude of the imaginary part ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1867 was equal to zero at the resonant frequency. To achieve converted to a bandwidth of 1 Hz through the following the impedance match, the ring resonator, with a fundamental equation [12]: resonant frequency of 10 GHz, was placed >./4 from the Phase Noise (dBc/Hz) = drain of the transistor. It was parallel coupled to the output + transmission line with a coupling gap that was 40 µm wide. Measured Value - 10 log(l.2 x 300) 2.5 (2) With the impedance criteria met, the oscillator will start upon proper biasing of the FET. The r f chokes have a half-moon In this equation, the measured value is the difference in dB between the peak power and the side-band power at a structure that is a large shunting capacitor to ground for the r f signal on the bias lines. They are a quarter wavelength specific offset frequency. The resolution bandwidth of 300 Hz is multiplied by 1.2 to account for filtering in the spectrum removed from the transmission lines by a high impedance line. analyzer. The additive term of 2.5 is a correction for the logarithmic amplification within the spectrum analyzer. When III. EXPERIMENTAL DETAILS phase noise measurements are performed in this manner, the measured phase noise may be limited by the phase noise of The YBa2Cu307_x superconducting thin films were de the internal oscillator of the spectrum analyzer. The phase posited by pulsed laser deposition (PLD). The substrate tem noise of a synthesized source was measured to check this. At perature during deposition was 805 °C while the oxygen offset frequencies greater than 10 kHz, the data presented for pressure was maintained at 170 mTorr. A KrF excimer laser the two superconducting oscillators approach the limit of this with a wavelength of 248 nm was used. The energy density of technique. The data presented for these two circuits at larger 2 the laser beam at the target was 0.8 J / cm . The pulse rate was offset frequencies is an upper limit on the phase noise. A de two per second. This deposition procedure has produced films block was located between the test fixture and the spectrum with a critical temperature of 90.5 K and a critical current analyzer for all measurements. density of greater than 2 x 106 A/ cm2 at 77 K. The effective surface resistance of a superconducting thin film patterned into a ring resonator was 1.36 mf! at 77 Kand 10 GHz [11]. The IV. RESULTS AND DISCUSSION superconducting films were patterned into the oscillators using A superconducting ring resonator patterned from a PLD film standard positive photolithographic techniques. The etchant had a loaded Q value of 940 and an unloaded Q value of 2100. used was a 100:1 solution of deionized water:H3P04. A copper ring resonator had loaded and unloaded Q values Three reflection mode oscillators were fabricated and tested. of 120 and 250, respectively, when measured at 77 K and The transmission lines, r f chokes, and bias lines were fabri 10 GHz. The effective surface resistance of the YBa2Cu307_x cated out of 2.4 µm thick copper for one circuit while the was 1.36 mf! at 77 K which was 19 times smaller than the other two circuits were fabricated out of YBa2Cu301-x high copper value of 25.8 mf! at 77 K. The rate of change of temperature superconducting thin films. One of the supercon the resonant frequency as a function of temperature for the ducting thin films was made by the pulsed laser deposition superconducting resonator was -1.25 MHz/K at 77 K. procedures described previously while the other film was a All three oscillators exhibited a 10 GHz signal and a much sputtered film purchased commercially. The sputtered film was weaker 20 GHz signal. The oscillators' power and frequency guaranteed to have a critical temperature of greater than 88 K were measured as a function of temperature at fixed bias. The and a surface resistance of less than 0.8 mf! at 77 K. Contacts temperature was raised from near 20 K until the oscillations to the superconductor for the output and wire bonding pads disappeared. A 77 K, the frequency and power were measured were made with silver with a gold overlayer, patterned by as a function of the gate and drain voltages. The single-sided lift-off photolithography. Wire bonding pads were located at phase noise of the oscillator made from the sputtered film the bias pads as well as the ends of the transmission lines was measured as a function of the drain bias at 77 K and the near the FET. The ground plane for the three oscillators was phase noise of all three oscillators was compared at a bias of 2.4 µm of copper with a 300 A titanium layer to promote Vds = 2.5 V and V = 0 V. 98 adhesion. The GaAs FET was epoxied onto the LaAI03 Figs. 4 and 5 show the oscillation frequency and power as substrate. Connections between the FET and transmission lines a function of temperature, respectively, for all three circuits. were made with 18 µm diameter gold wire by thermosonic The copper circuit was biased at Vds = 2.0 V, V = -1.0 V, 98 wirebonding. and Id = 29 mA. The oscillations could be maintained up to Measurements of the power and frequency as a function room temperature by increasing V to raise the drain current 98 of the temperature and bias conditions on the oscillator were to nearly 40 mA. The frequency of this oscillator changed very made with the oscillator mounted on a brass fixture inside a little. Its sensitivity to temperature was - 70 kHz/K over the closed cycle cryostat. The phase noise could not be measured temperature range of 25 K to 100 K. The power decreased with the sample mounted inside the cryostat since the vibration from 4.8 dBm at 25 K to 2.8 dBm at 100 K. At 77 K, the of the closed cycle refrigerator induced more than 1 MHz of signal power was 3.8 dBm at 10.074 GHz and the second jitter in the signal. Phase noise measurements were performed harmonic was reduced by 21 dB. The efficiency of the circuit with the oscillators mounted inside a sealed brass test fixture at these bias conditions at 77 K was 4.1 %. and submerged in liquid nitrogen. The single sided phase The PLD film used for the reflection mode oscillator had a noise was measured on a HP 8592A spectrum analyzer with critical temperature of 88.5 K. For the data presented in Figs. 4 a resolution bandwidth of 300 Hz. The measured data was and 5, this oscillator was biased with Vds = 3 V and V = 98 1868 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE II SUMMARY OF RESULTS AT 77 K FROM TEMPERATURE EXPERIMENTS Tc Frequency D..f/D..T vd Vg Id Power Circuit (K) (GHz) (kHz/K) (Volts) (Volts) (mA) (dBm) Cu 10.074 -70 2 -1 29 3.8 PLO 88.5 9.967 - 1, 500 3 0 22 5.4 Sputtered 88.6 10.058 -10, 000 2 -0.5 20 6.4 10.2..----------------0--'---Cu- - from a PLD film [11). The output power was 5.4 dBm at 77 K -fr-- Sc-A with the power of the second harmonic reduced by 29.2 dB. N' -a-- Sc-B The power decreased from 7.3 dBm to 5.0 dBm over the range I ~ 10.1 of 25 K to 79 K. The efficiency of the circuit at these bias >. conditions and 77 K was 5.4%. u c: For the measurements as a function of temperature, the Q) g:::J oscillator patterned from the commercially purchased sputtered 10.0 ..._ film, which had a critical temperature of 88.6 K, was biased LL at Vds = 2 V and V = - 0.5 V which gave a current 98 of Id = 20 mA at 77 K. The frequency of the signal was 9.9+----.---~--~--~------1 10.082 GHz with a power of 6.4 dBm at 77 K. The efficiency 0 20 40 60 80 100 was 10.4%. The power of the 20 GHz signal was 35.5 dB less Temperature (K) than the 10 GHz signal at 77 K. The power of the 10 GHz signal varied from 7.4 dBm at 25 K to 6.4 dBm at 81 Kand Fig. 4. Frequency as a function of temperature for all three oscillators. The then dropped sharply to 4.8 dBm at 83 K, beyond which the = = Cu oscillator's FET was biased at Vds 3.0 V and V9, 1.0 V. Sc-A is oscillation ceased. The frequency varied from 10.119 GHz to the sputtered film and Sc-B is the PLO film. The FETs were biased at Vds = 2.0 V and V9, = -0.5 V and at Vds = 3.0 V and V9, = 0.0 V, respectively. 10.008 GHz. The temperature at with the frequency started to decrease rapidly was 75 K. The sensitivity of the frequency to 10 temperature for this circuit was -10 MHz/K at 77 K, which ----0-'- Cu - ~ Sc-A is much larger than from any of the other circuits. Another 8 --0-- Sc-B oscillator patterned for a sputtered film had a comparable rate E of change for the frequency as a function of the temperature, Ill 6 -9.75 MHz/K at 77 K. ~ ..._ Table II shows a summary of the measurements at 77 K Q) ;: 4 from the temperature variation experiments for all three oscil a0. . lators. The rate of change of the frequency as a function of 2 temperature was determined by the film used for the microstrip transmission lines. The rate of change of the frequency with 0 temperature was the least for the oscillator made from copper. 0 20 40 60 80 100 The frequency of the oscillator patterned from the PLD films Temperature (K) was less sensitive to temperature than the sputtered oscillators by nearly a factor of eight. To decrease the sensitivity to the Fig. 5. Power as a function of temperature for all three oscillators. The Cu temperature, the temperature of operation could be decreased. oscillator's FET was biased at Vds = 3.0 V an=d V9, = -1.0 V=. Sc-A is For example, at 70 K, the rate of change for the frequency for athned oSscc-ilBla tios r tfhreo mo sscpilulattteorre df rofimlm thbeia sPeLdO a t fVilmds, bia2s.e0d Va t aVndd sV 9=, 3.0- 0V. 5an Vd· the PLD oscillator was -0.4 MHz/K and it was -1.4 MHz/K V9, = 0.0 V. for the sputtered oscillator. At 25 K, the rate of change of the frequency for both superconductor oscillators was nearly 0 V, which resulted in Id= 22 mA at 77 K. The temperature identical to the copper oscillator. was increased from 25 K until the oscillation disappeared. The Figure 6 shows the single sided phase noise of the three frequency decreased from 9.979 GHz to 9.964 GHz over this oscillators at 77 K and also for the copper oscillator at 300 K. range. 9 MHz of this 15 MHz drop occurred between 75 K For these measurements, all three oscillators were biased and 79 K. The dependence of the frequency on temperature is with Vds = 2.5 V and V = 0 V. The phase noise of the 95 typical of a change in the phase velocity of a superconductor superconducting oscillators was nearly identical at all offset resulting from a variation in the penetration depth as a function frequencies. They have phase noise values of -61 dBc/Hz at of temperature [1 ], [2], [13). The sensitivity of the frequency an offset of 10 kHz and -88 dBc/Hz at an offset of 100 kHz. of the oscillation to temperature was -1.50 MHz/K at 77 K. At an offset frequency of 10 kHz, the phase noise of the copper This is nearly identical to the rate of change of the frequency as oscillator when measured at 77 K and 300 K was 13 dB and a function of temperature of the ring resonator patterned from 32 dB higher, respectively. At an offset frequency of 100 kHz, the PLD film and of a series feedback oscillator, also patterned the difference was 6 dB and 22 dB, respectively. ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1869 - -20 ~ Sc-A 77 K 10.2..--------------0------Cu- .. ---0- Sc-8 77 K --t:r-- Sc-A N N' ·Io -40 ---0-..--- Cu 77K I --a- Sc-8 ca Cu 300 K ~ 10.1 ~ >. (.) Q) -60 c ·C5/J Q) z C:JT 10.0 .Q...). Q) C/J -80 LL ctl ..c a... 9.9-+--...--..---...--...--...--..---..----t -100 0 2 3 4 10 100 1000 Vds (Volts) Offset Frequency (kHz) Fig. 8. Frequency as a function of drain voltage for all three oscillators at Fig. 6. Single sided phase noise for the three oscillators. All three oscillators 77 K. The Cu oscillator was biased at Vgs = -1.0 V while the FETs in Sc-A wSce-rBe bisi atsheed PaLt DV dfsil m=. T2.h5e Vsi paenrdc oVn9dsu c=ti n0g Vos. cSilcla-Ato riss wtheer es phuetldte raetd 7 f7i lmK aanndd (atnhde astp uVtt9e8r ed= fi0lm.0) Va,n dr eSspce-Bct iv(tehley . PTLhDe fsiolmli)d wsyemreb boilass emda arkt Vth9e8 b=ia s- 0p.o5in Vts the Cu oscillator was measured at 77 K and 300 K. during the measurements as a function of temperature. -50 of the temperature. The drain voltage for each circuit was decreased from 4 V until the signal disappeared. Figure 8 u -60. shows the frequency of oscillation as a function of the drain OJ voltage. The solid symbols mark the drain voltages used during ~ the measurements as a function of temperature. The copper Q) -70 C/J oscillator and the oscillator patterned from the sputtered film "6 z had frequencies very near each other since the temperature was -80 Q) maintained at 77 K. This is near the crossover point for the C/J ctl two circuits in Fig. 4. For these two oscillators, the frequency ..c a... -90 --0- 10 kHz decreased 87 MHz for drain voltages of less than 1.5 V. Above --a- 100 kHz 1.5 V, the frequencies were less sensitive to drain voltage. -100 The frequency of the oscillator patterned from the PLD film 0 2 3 4 decreased 2 MHz as the drain voltage was decreased. The Vds (Volts) frequency was less sensitive to drain voltage at higher voltages for this circuit as well. Fig. 7. Single sided phase noise of the sputtered oscillator at offset frequen The power at 10 GHz as a function of drain voltage is shown cies of 10 kHz and 100 kHz as a function of the drain voltage. in Fig. 9 for all three circuits, with the solid symbols indicating the drain voltages used during the measurements as a function Fig. 7 shows the phase noise at offsets of 10 kHz and of temperature. For all three circuits, the power decreased as 100 kHz as a function of the drain voltage of the sputtered the drain voltage decreased, with the rate of decrease becoming oscillator. For these measurements, V = 0. As the drain large at smaller voltages. The drain currents are quite different 98 bias was increased from 2.5 V to 4.0 V, the power increased for the three curves shown in this figure. For example, at by 8 dB. At an offset frequency of 10 kHz, the phase noise Vds = 3 V the copper circuit had Id = 36 mA with V = 98 decreased by 15 dB while at an offset of 100 kHz, the phase -1.0 V, the sputtered deposited circuit had Id = 29 mA with noise decreased 9 dB. The decrease in the phase noise at an V = -0.5 V and the PLD circuit had Id = 22mA with 98 offset frequency of 10 kHz was faster than at 100 kHz because V = 0 V. The specified ranges for the pinch-off voltage 98 the influence of power on the phase noise at an offset of and saturated drain current for these transistors are -0.5 V 100 kHz was primarily through the floor noise, the first term of to -5 V and 20 mA to 70 mA, respectively, at Vds = 3 V. (1), while the phase noise at an offset of 10 kHz was affected The transistors used here had pinch-off voltages of -1.55 V, by the power through both the floor noise and the third term in -2.15 V, and -3.2 V for the YBa2Cu307_x PLD circuit, the (1). At large offset frequencies, the phase noise would decrease circuit fabricated from the sputtered film and the copper circuit, by the same amount that the output power increased. In our respectively. measurement, the power increased by 8 dB while the phase Figs. 10 and 11 show the frequency and power as a function noise decreased by 9 dB at an offset frequency of 100 kHz. of gate bias at 77 K for all three circuits. For each circuit, The frequency and power of the oscillators were also the drain voltage was held at the same value used during measured as a function of drain voltage at a temperature measurements as a function of temperature. The data points of 77 K. For these measurements, the gates were biased at at the gate biases used in those measurements are marked the same voltages used for the measurements as a function with solid symbols. The copper circuit oscillated for gate 1870 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE III SUMMARY OF RESULTS AT 77 K FOR Vds = 2.0 v Vg Id Power Frequency Efficiency Circuit (Volts) (mA) (dBm) (GHz) (%) Cu -1.4 22 0.6 10.095 2.6 PLD 0 18 0.9 9.949 3.3 Sputtered -0.6 18 5.2 10.092 9.3 20 10.2 -0-- Cu - 'N ~ Sc-A 10 ---0-- Sc-8 E I c:c 10.1 ~ ~ >. ..... 0 0 Q) c: ~ Q) a0. -0-- Cu :O:I" 10.0 -10 .Q...). ll Sc-A -0-- Sc-8 LL -20 9.9 0 2 3 4 -1.00 -0.75 -0.50 -0.25 0.00 Vds (Volts) Vgs (Volts) Fig. 9. Power as a function of drain voltage for all three oscillators at 77 K. Fig. 10. Frequency as a function of gate voltage for all three oscillators at = The Cu oscillator was biased at Vgs = -1.0 V while the FETs in Sc-A (the 77 K. The Cu oscillator was biased at Vds 2.0 V while the FETs in Sc-A sputtered film) and Sc-B (the PLD film) were biased at Vgs = -0.5 V and (the sputtered film) and Sc-B (the PLD film) were biased at Vds = 2.0 V and at Vgs = 0.0 V, respectively. The solid symbols mark the bias points during at V98 = 3.0 V, respectively. The solid symbols mark the bias points during the measurements as a function of temperature. the measurements as a function of temperature. voltages from 0 V to -1.4 V. The full ranges for the other 10 circuits are shown. The frequency increased 200 MHz as - V was decreased for the copper oscillator. The oscillator 98 5 patterned from the PLD film showed little variation, but the E c:c sputtered sample's frequency increased 170 MHz as the gate ~ bias decreased to -0.7 V. The frequency was more sensitive ..... 0 to variations in the gate bias than to the drain bias. For all Q) ~ three circuits, the power decreased as the gate bias decreased. a0. The power for the copper circuit decreased 6.7 dB as V -5 98 -0-- Cu was varied from 0 V to -1.4 V. Its drai.n current varied from --i:r-- Sc-A ---0-- Sc-8 62 mA to 22 mA over that range. The power of the oscillator -10+-.......................... .,...... ............" "T""...-.,......... ..........- r....,.......-.............. patterned from the PLD film decreased sharply as the gate -1.00 -0.75 -0.50 -0.25 0.00 voltage neared -0.4 V. Its drain current ranged from 22 mA Vgs (Volts) to 12 mA. Finally, the power of the oscillator patterned from the sputtered film decreased from 8.9 dBm to 5.2 dBm, while Fig. 11. Power as a function of gate voltage for all three oscillators at 77 K. its current ranged from 38 mA to 15 mA. The large differences The Cu oscillator was biased at Vd~ =2.0 V while the FET=s in Sc-A (the sputtered film) and Sc-B (the PLD film) were biased at Vds 2.0 V and at in currents are a result of the different pinch-off voltages of Vgs = 3.0 V, respectively. The solid symbols mark the bias points during the the transistors, as discussed in the previous paragraph. The measurements as a function of temperature. largest power output of any circuit was for the sputtered oscillator. It delivered 11.5 dBm with a bias of Vis = 4.0 V entire circuit operated at cryogenic temperatures. The and V = -0.5 V. S-parameters of the GaAs MESFET used in the design 98 Table III shows a summary of the results with Vds = of the oscillators were measured at 77 K. The design was 2.0 V and the gate voltage adjusted to give comparable drain a reflection mode oscillator and used a ring resonator to currents at 77 K. The different gate biases were a result of stabilize the frequency. The ring resonator was coupled to the the transistors having different pinch-off voltages. The largest output line off the drain of the FET. A YBa2Cu301-x ring power and the most efficient oscillator was the oscillator resonator, which was tested separately, had a loaded Q that fabricated from the sputtered film. was eight times larger than that of a copper ring resonator. V. CONCLUSION Three oscillators were fabricated and tested, one from copper Hybrid superconductor/GaAs oscillators were successfully and two from high temperature superconductors. All three implemented on 10 mm x 10 mm LaAI03 substrates. The exhibited both 10 GHz and 20 GHz oscillations. The power ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1871 of the 20 GHz oscillation was 20 dB to 35 dB lower than the 6.5 GHz on a single substrate," IEEE Microwave Guide Letts, vol. 2, power of the 10 GHz oscillation for these three circuits. The no. 1, p. 22, Jan. 1992. (10] EEsof, Westlake, CA 91632. lowest phase noise at 77 K of -68 dBc/Hz and -93 dBc/Hz [11] N.J. Rohrer, Ph.D. Dissertation, The Ohio State University, Columbus, at offset frequencies of 10 kHz and 100 kHz, respectively, OH, 1992. = (12] Hewlett Packard publication, "RF & microwave phase noise measure was obtained for the sputtered oscillator with Vds 4.0 V. ment seminar." Compared to the copper circuit, the superconducting oscillators (13] T. Van Duzer and C. W. Turner, Principles of Superconductive Devices had 12 dB less phase noise at an offset of 10 kHz and and Circuits. New York: Elsevier, 1981, p. 125. 26 dB less noise at an offset at 100 kHz. The sensitivity of the frequency to temperature at 77 K was -10 MHz/K for the sputtered oscillator, while that of the PLD circuit was -1.5 MHz/K. The stability, power, and efficiency improved Norman J. Rohrer received the B.S. degree in physics and mathematics from Manchester College, as the temperature was decreased. The output power and North Manchester, IN in 1987, and the M.S. and frequency were dependent upon the bias conditions. The Ph.D. degrees in electrical engineering from the frequency of the oscillators were less sensitive to the drain Ohio State University, Columbus, OH, in 1990 and 1992, respectively. voltage than to the gate voltage. The oscillator patterned from As a graduate student, he was recipient of a a sputtered film had the largest output power and the highest NASA Graduate Student Research Fellowship under efficiency. which he was able to complete his dissertation research on microwave oscillators. In 1992 he joined IBM Microelectronics, Burlington, VT, working on microprocessor subsystems. ACKNOWLEDGMENT The authors would like to thank Chris Chorey for his assistance in the testing of the transistor and oscillator at George J. Valeo received the B.S. and M.S. de cryogenic temperatures. grees in electrical engineering from Case Western Reserve University in 1979 and 1981, respectively. He received the Ph.D. in electrical engineering from REFERENCES the University of Cincinnati in 1986. In 1986 he joined the faculty of the Ohio State [1] N. J. Rohrer, H. Y. To, G. J. Valeo, K. B. Bhasin, C. Chorey, and J. D. University where he is currently an associate pro Warner, "Sequentially evaporated thin film YBa2Cu307_x supercon fessor of electrical engineering. His current re ducting microwave ring resonator," Science and Technology of Thin Film search interests are electronic applications of high Superconductors 2. R. C. McConnell and R. Noufi, editors, New York: temperature superconductors, electronic properties Plenum, 1990, p. 615. and applications of diamond films, and compound [2] C. M. Chorey, K. Kong, K. B. Bhasin, J. D. Warner, and T. ltoh, "YBCO semiconductor devices and technology. superconducting ring resonator at millimeter-wave frequencies," IEEE Trans. Microwave Theory Tech., vol. 39, no. 9, p. 1480, Sept. 1991. (3] P.A. Palokas, C. E. Rice, M. V. Schneider, and R. Trambarulo, "Elec trical characteristics of thin-film Ba2 YCu307 superconducting ring Kul B. Bhasin received the M.S. and Ph.D. from resonator," IEEE Microwave Guide Letts. Vol. 1, p. 54, Mar. 1991. Purdue University and the University of Missouri (4] R.R. Bonetti, et al., "Thin film superconducting filter design techniques; Rolla, respectively. microstrip filters in LaAI03 and LaGa03 substrates," IEEE Trans. Since 1983 he has been a Senior Research Sci Microwave Theory Tech., vol. MTT-S, no. 1, p. 269, 1990. entist in the Solid State Technology Branch of the [5] B. R. McAvoy, G. R. Wagner, J. D. Adam, J. Talvacchio, and Space Electronics Division of the NASA Lewis M. Driscoll, "Superconducting stripline resonator performance," IEEE Research Center in Cleveland, OH. Prior to joining Trans. Magn., vol. 25, pp. 1104, 1989. (6] M.A. Richard, K. B. Bhasin, C. Gilber, S. Metzler, G. Keopf, and P. C. NASA he was with Gould, Inc., from 1977 to 1983 Claspy, "Performance of a four-element Ka-band high temperature as Senior Scientist and Manager of Technology. superconducting microstrip antenna," IEEE Microwave Guide Letts., He is currently engaged in the development of vol. 2, no. 4, pp. 143, Apr. 1992. GaAs microwave devices and circuits, microwave [7] D. B. Leeson, "A simple model of feedback oscillator noise spectrum," photonics, and superconducting electronics for space applications. in Proc. IEEE, vol. 54, no. 2, p. 329, 1966. Dr. Bhasin has authored many publications and coedited the book Mi (8] A. P. S. Khanna, M. Schmidt, and R. B. Hammond, "A superconducting crowave Integrated Circuits. He is the recipient of the IR-100 Award, NASA resonator stabilized low noise oscillator," Microwave J., vol. 34, p. 127, Group Achievement Awards, and the Gould Scientific Achievement Award Feb. 1991. and he is on the editorial board of Microwave and Optical Technology Letters'. [9] R. Klieber, R. Ramisch, A. A. Valenzuela, R. Weigel, and R. Russer, He is a member of Sigma Xi and a Fellow of the International Society for "A coplanar transmission line high-Tc superconductive oscillator at Optical Engineers. 1872 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 Analysis of Open and Shielded Spectral~Domain Slotlines Printed on Various Anisotropic Substrates Yinchao Chen and Benjamin Beker, Member IEEE Abstract-A rigorous full-wave analysis based on the spectral It is known that open slotlines leak power into the dielectric domain approach for open and shielded slotline transmission filled parallel plate waveguide (PPW) regions. For electric lines is presented. The substrate materials under consideration (PEC) conductor-backed structures, the leakage is always are anisotropic, characterized by both their peQDittivity and present, but is small if appropriate values of medium parame permeability tensors. The formulation includes off-dia.gonal ten sor elements to represent gyroelectric media, Ferrites, or the ters and geometrical dimensions are employed [5]. The same misalignment between the principal axes of the substrate and the is also true for a magnetic (PMC) conductor-backed slotline, coordinate system of the waveguide. Dyadic admittance Green's with the only difference being that the modes of this parallel functions for every structure are obtained with the help of plate structure have a cuff-off frequency [4]. In this paper, differential matrix operators in the Fourier-transformed domain, all physical dimensions and medium parameters are chosen and the Galerkin method is employed to find the propagation constants numerically. so as to minimize the leakage effects, since the paper aims at emphasizing the influence of substrate anisotropy on the propagation characteristics of bilateral slotlines. I. INTRODUCTION In what follows, it is assumed that every MIC transmission T HE SHIELDED slotline (or finline) has been used at line is printed on a homogeneous anisotropic substrate that has microwave and millimeter-wave frequencies for quite its optical axes of the permittivity and permeability arbitrarily some time [1]. Its analog, the open slotline, has enjoyed wide oriented in the xz-plane, i.e., the plane of propagation. As a popularity in various applications at these frequencies as well result, the theory presented in this work encompasses a wide [2]. Desirable features of shielded slotlines· include reduced variety of guiding media, which can be either gyroelectric, size, weight, and ease of integration into the overall microwave Ferrite, or both. When off-diagonal tensor elements of [io] and integrated circuit (MIC). Advantages of open slotlines, which [µ] .are real, the tensors are symmetric, then misalignment be are often used in microstrip antenna feeding networks [3], tween coordinates of the waveguide and those of the material include reduction in the radiation level back to the feed tensors can be examined well. ing circuit. Dyadic admittance Green's functions for every transmission The majority of past and present work has focused on line are formulated using differential matrix operators [12], slotlines with isotropic substrates only (see [1 ], [2], and and the spectral-domain approach [13, Chapter 5]. The propa [4]-[6]). More recently however, anisotropic substrates have gation constants of dominant modes are obtained by using the Galerkin method. Both electric and magnetic wall symmetries been considered as well, including shielded. finlines [7], [8], (odd and even modes, respectively) for open structures and partially covered slotlines [9], as well as fully open struc tures [10], [11 ]. Although the cited references laid out the the magnetic wall symmetry for shielded bilateral slotlines are ground work for such structures, none of thein considered considered. The basis functions used to expand the field inside the slot are carefully chosen with build-in edge singularities. bilateral open slotlines printed on general anisotropic media The formulation and the numerical approach are validated in detail. against the available published data from references [4], [6], This paper presents the spectral-domain formulation and numerical results for the dispersive characteristics of open and [7]. as well as shielded slotline transmission lines. The odd and even modes of open bilateral slotlines are examined. The II. ADMITTANCE GREEN'S FUNCTIONS FOR former corresponds to the electric wall bisecting the plane of ANISOTROPIC SUBSTRATES symmetry, whereas the later considers the magnetic wall case: Crossectional view of waveguides that are under considera In addition, an analysis of shielded bilateral slotlines (finlines) tion in this paper are shown in Fig. l. The substrate material is also included to illustrate the similarities in their propagation is assumed to be characterized by the permittivity tensor characteristics compared to those of open structures. which can be either gyroelectric (Hermitian) or misaligned with thy coordinates of the structure in the xz-plane. For Manuscript received May 14, 1992; revised January 19, 1993. generality, the constitutive properties of the substrate also The authors are with the Department of Electrical and Computer Engineer- include the anisotropic nature of the permeability tensor, which ing, University of South Carolina, Columbia, SC, 29208. · IEEE Log Number 9210213. can represent a Ferrite or the rotation effects of its principal 0018-9480/93$03.00 © 1993 IEEE

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., ~IEEE TRAN SACTI 0 NS ON MICROWAVE THEORY AND TECHNIQUES NOVEMBER 1993 VOLUME 41 NUMBER 11 IETMAB (ISSN 0018-9480) A PUBLICATION OF THE IEEE MICROWAVE THEORY AND TECHNIQUES SOCIETY PAPERS Hybrid High Temperature Superconductor/GaAs 10-GHz Microwave Oscillator: Temperature and Bias Effects .................................................................................. N. J. Rohrer, G. J. Valeo, and K. B. Bhasin 1865 Spectral-Domain Analysis of Open and Shielded Slotlines Printed on Various Anisotropic Substrates .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Y. Chen and B. Beker 1872 Heating Characteristics of Thin Helical Antennas with Conducting Cores in a Lossy Medium-I: Noninsulated Antennas .................................................................. M. S. Mirotznik, N. Engheta, and K. R. Foster 1878 Identifisation of Propagation Regimes on Integrated Microstrip Transmission Lines ..................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. S. Bagby, C.-H. Lee, D. P. Nyquist, and Y. Yuan 1887 Reflection and Transmission of Guided Electromagnetic Waves at an Air-Chiral Interface and at a Chiral Slab in Parallel- Plate Waveguide ............................................................................. F. Mariotte and N. Engheta 1895 Calculation of the Fundamental Mode Sizes in Optical Channel Waveguides Using Gaussian Quadrature .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. A. F. Jaeger and B. P. C. Tsou 1907 Measurements on a 215-GHz Subharmonically Pumped Waveguide Mixer Using Planar Back-to-Back Air-Bridge Schottky Diodes ... P.H. Siegel, R. J. Dengler, I. Mehdi, J.E. Oswald, W. L. Bishop, T. W. Crowe, and R. J. Mattauch 1913 Single-Frequency Relative Q Measurements Using Perturbation Theory ......................... B. Tian and W.R. Tinga 1922 Large Signal Design of Broadband Monolithilc Microwave Frequency Dividers and Phase-Locked Oscillators ................................................. R, Quere, E. N oya, M. Camiade, A. Suarez, M. Hessane, and J. Obregon 1928 Hybrid Couplers in Bilevel Microstrip ................................................... M. D. Prouty and S. E. Schwarz 1939 Turnstile Reftecto-Polarimeter Using the Principal Incidence Method: Determination of Permittivities up to 1220°C and Industrial Applications ......................................................... A. Bretenoux, Cl. Marzat, and R. Sardos 1945 A Nonreciprocal Tunable Waveguide Directional Filter Using a Turnstile Open Gyromagnetic Resonator .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Helszajn, C. S. Cheng, and B. A. Wilcock 1950 Effects of Waveguide Wall Grooves Used to Hold Samples for Measurement of Permittivity and Permeabillity ................................................................................................................... R. Luebbers 1959 MFIE Analysis and Design of Ridged Waveguides ............................................. W. Sun and C. A. Balanis 1965 Rigorously Modeling Short Bent, Graded-Index Dielectric Slab Waveguides ............................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. J. M. Bastiaansen. J. M. van der Keur, and H. Blok 1972 Finite-Element Analysis of Axisymmetric Cavity Resonator Using a Hybrid Edge Element Technique ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J.-F. Lee, G. M. Wilkins, and R. Mittra 1981 (Continued on back cover) ~IEEE MICROWAVE THEORY AND TECHNIQUES SOCIETY The Microwave Theory and Techniques Society is an organization, within the framework of the IEEE, of members with principal professional interest in the field of microwave theory and techmques. All members of the IEEE are eligible for membership in the Society and will receive this TRANSACTIONS upon payment of the annual Society memoership fee of $20.00. Affiliate membership is available upon payment of the annual affiliate fee of $33.00, plus the Society fee of $20.00. For information onjoming write to the IEEE at the address below. Member copies of Transactions/Journals are for personal use only. ADMINISTRATIVE COMMITTEE P. W. STAECKER, President E. J. CRESCENZI, JR., Vice President M. J. SCHINDLER, Secretary R. E. BRYAN, Treasurer R.E.BRYAN R. H. JANSEN B. S. PERLMAN P. W. STAECKER J. W. WASSEL E.D.COHEN S. A. MAAS R. POLLARD R. SUDBURY E. YAMASHITA E. J. CRESCENZI, JR. M. A. MAURY, JR. J. E. RAUE D. G. SWANSON D. HORNBUCKLE R. A. MOORE E. REZAK G.THOREN Honorary Life Members Distinguished Lecturers Past Presidents A. C. BECK T. S. SAAD W. CURTICE R. KAGIWADA (1992) S. B. COHN K. TOMIY ASU P. GOLDSMITH F. !VANEK (1991) A. A. OLINER L. YOUNG F. !VANEK T. ITOH (1990) V. RIZZOLI J. R. WHINNERY S-MTT Chapter Chairmen Albuquerque: M. A. DrNALLO Israel: E. LEVINE Schenectady: R. J. GUTMANN Atlanta: A. J. GASlEWSKI Ithaca: L. PALMATEER Seattle: D. T. HARVEY Baltimore: S. L. ANTHONISEN Kitchner-Waterloo: C.R. SELVAKUMAR Seoul: J. s. MYUNG Beijing: Y.-R. ZHONG Y. L. CHOW Singapore: L. M. SENG Benelux: K. VAN T. KLOOSTER Los Angeles: H.J. DE Los SANTOS South Africa: A. J. 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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41 , NO. 11, NOVEMBER 1993 1865 Hybrid High Temperature Superconductor/GaAs 10 GHz Microwave Oscillator: Temperature and Bias Effects Norman J. Rohrer, George J. Valeo, and Kul B. Bhasin Abstract- Hybrid YBa2Cu;01-x superconductor/GaAs mi in a one hertz bandwidth can be given in dBc/Hz by [7] crowave oscillators have been d~signed, fabricated and char l acterized. The planar oscillators were built on a single L(fo) = 10 mm x 10 mm LaAI03 substrate. The active elements in the (ic) hybrid oscillators were G~ MESFETs. A ring resonator w11s lOlo [kTFG ~ kTFG 2 af'1 used to select and stabilize the frequency. A superconducting g P + 27r f o + 4PQi, fo + 87rQi,fg . ring resonator had a loaded 'Q at 77 K which was 8 times larger than the loaded Q of a ring resonator fabricated out (1) of copper. S-parameters of the GaAs FET were measured at cryogenic temperatures and used to design the oscillator, which Herek is Boltzmann's constant, Tis the temperature, Fis the had a reflection mode configuration. The transmission lines, r f noise figure associated with the negative resistance device, G chokes and bias lines were all fabricated from YBa2Cu307-x is the gain of the amplifier after it has reached a steady-state superconducting thin films. The performance of the oscillators oscillation, P is the output power, QL is the loaded Q of the was measured as a function of temperature. The rate of change resonator, and a is the combined flicker noise constant of the of the frequency as a function .of temperature was smaller for an oscillator patterned from a pulsed laser deposited film than for amplifier and the resonator. As can be seen from the third and an oscillator patterned from a. sputtered film. As a function of fourth terms, a largei: loaded Q will decrease the phase noise. bias at 77 K, the best circuit had an output power of H.5 dBm The hybrid oscillators employing high temperature super and a maximum efficiency of 11.7%. The power of the second conductors that have been published include a parallel feed harmonic was 25 dB to 35 dB below that of the fundamental, for back oscillator [8] and a series feedback oscillator [9]. For the every circuit. At 77 K, the best phase noise of the superconducti.ng oscillators was -68 dBc/Hz at an offset frequency of 10 kHz and parallel feedback oscillator, the feedback network consisted less than -93 dBc/Hz at an offset frequency of 100 kHz. At an of a superconducting linear resonator acting as a narrow band offset frequency of 10 kHz, the superconducting oscillator had pass filter. Only the feedback network was cooled to 77 K. The 12 dB less phase noise than the copper oscillator at 77 K. The amplifier was implemented in normal metals and operated at superconducting oscillators at 77 K had 26 dB less phase noise room temperature. This oscillator operated at 10 GHz and had than the copper oscillator operating at 300 K. an output power of 6.0 dBm when the resonator was cooled to 80 K. A highly integrated microwave system will require I. INTRODUCTION the whole oscillator to be operating at cryogenic temperatures on a single substrate. The series feedback oscillator fit on T HE APPLICATION of high temperature superconducting a 10 mm x 10 mm LaAI03 substrate with a coplanar res thin films to microwave circuits is advantageous since onator stabilizing the frequency at 6.5 GHz. It had an output the films have a lower surface resistance than gold or copper power of 4.9 dBm when immersed in liquid nitrogen. The at microwave frequencies. Some of the passive microwave power of the second harmonic was only 10 dB down. In this structures that have shown improved performance using high paper, we report on the design, fabrication and testing of temperature superconductors are ring resonators [1 ]-[3], mul microstrip hybrid oscillators. Each oscillator was fabricated tiple pole filters [4] narrowband filters [5], and antennas [6]. The advantage of using high temperature superconducting on a 10 mm x 10 mm LaAI03 substrate. The phase noise of the superconductor oscillators at 77 K is compared to a copper films for resonators is the 1arger quality factor (Q) values that oscillator at 77 K and 300 K. It would also be advantageous if superconducting resonators have compared to normal metal resonators. The larger loaded Q of a resonator has the potential the frequency of the oscillators were not sensitive to variations in . the temperature or bias .c onditions. The frequency and for lowering the phase· noise of oscillators. In the Leeson power of these circuits were measured as a function .of the model, the phase noise of a feedback oscillator when measured temperature and the bias conditions. Manuscript received April 13, 1992; revised December 10, 1992. This work was supported by NASA under Award NCC-3-197. II. DESIGN N. J. Rohrer and G. J. Valeo are with the Department of Electrical Engi neering, The Ohio State University, Columbus, OH 43210. Since our objective was to implement the entire oscillator K. B. Bhasin is with the National Aeronautics and Space Administration, on a single substrate to be operated at cryogenic temperatures, Lewis Research Center, Cleveland, OH 44135. IEEE Log Number 9210215. the S-parameters of the transistors at 77 K were obtained. 0018-9480/93$03.00 © 1993 IEEE 1866 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE I PERCENT CHANGE OF THE S-PARAMETERS FROM 300 K TO 77 KAT 10 GHz Su 522 magnitude phase magnitude phase magnitude phase magnitude phase 3.3% 19.3% 20.4% 8.8% 8.8% 6.7% 36.5% 37.8% 0 811at300K D 812 at 300K 0 822 at 300K D 821at300K t. 811at77K + 812 at 77K t. 822 at 77K + 821at77K Fig. 1. 5-parameters at 300 K and 77 K for S 11 and S 12 in the range of 4 to 15 GHz. Fig. 2. 5-parameters at 300 K and 77 K for 521 and 522 in the range of 4 to 15 GHz on a compressed Smith Chart. These S-parameters were used in the design of the oscillators. The design of the oscillators was performed using simulations on commercially available software (Touchstone™) [10]. The simulations were performed using the S-parameters obtained when the bias on the transistor was maintained at Vds = 3 V and Id = 10 mA and the temperature was 77 K. The design had a ring resonator which was parallel coupled to the transmission line in the matching network off the drain. A. Cryogenic S-Parameter Measurements The active devices used in the oscillators were Toshiba GaAs FETs (JS8830-AS). This transistor is a low noise MES FET with a 0.25 µm gate length and a gate width of 250 µm. The S-parameters of the FET for frequencies of 4 to 15 GHz were measured over a temperature range from room tem perature (300 K) to 40 K. The values for the S-parameters 08U/NA8A from 4 to 15 GHz are shown in Fig. 1 and Fig. 2 with the transistor biased at drain voltage Vds = 3 V and drain current Id = 10 mA at 300 K and 77 K. To achieve this drain current, Fig. 3. The physical layout of the reflection mode oscillator on a 1 cm2 the gate bias was adjusted to V = -1.04 at 300 K and 98 LaAI03 substrate. to V = -1.19 V at 77 K. Of the S-parameters, the largest 98 change in magnitude as a function of temperature occurred for FET was made very large by varying the length of open the S21 values. This was due to an increase in the electron's circuited transmission lines on the source and the gate. The mobility at the reduced temperatures. The variation in phase selected lengths of the transmission lines from the source and of Su and S22 was the only other major change. The percent the gate were 1.57 mm and 2.79 mm, respectively. The output change of the phase and magnitude of the S-parameters at of the oscillator was taken off the drain. The layout of the 10 GHz due to the change in temperature from 300 K to 77 K oscillator is shown in Fig. 3. This configuration is a reflection is listed in Table I. mode oscillator. The matching network, which included the ring resonator, B. Reflection Mode Oscillator was designed such that the magnitude of the real part of The design of the oscillator was performed using the small the impedance of the matching network was less than the signal S-parameters of the FET that were measured at 77 K. magnitude of the real part of the impedance looking into The input reflection coefficient looking into the drain of the the drain of the FET. The magnitude of the imaginary part ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1867 was equal to zero at the resonant frequency. To achieve converted to a bandwidth of 1 Hz through the following the impedance match, the ring resonator, with a fundamental equation [12]: resonant frequency of 10 GHz, was placed >./4 from the Phase Noise (dBc/Hz) = drain of the transistor. It was parallel coupled to the output + transmission line with a coupling gap that was 40 µm wide. Measured Value - 10 log(l.2 x 300) 2.5 (2) With the impedance criteria met, the oscillator will start upon proper biasing of the FET. The r f chokes have a half-moon In this equation, the measured value is the difference in dB between the peak power and the side-band power at a structure that is a large shunting capacitor to ground for the r f signal on the bias lines. They are a quarter wavelength specific offset frequency. The resolution bandwidth of 300 Hz is multiplied by 1.2 to account for filtering in the spectrum removed from the transmission lines by a high impedance line. analyzer. The additive term of 2.5 is a correction for the logarithmic amplification within the spectrum analyzer. When III. EXPERIMENTAL DETAILS phase noise measurements are performed in this manner, the measured phase noise may be limited by the phase noise of The YBa2Cu307_x superconducting thin films were de the internal oscillator of the spectrum analyzer. The phase posited by pulsed laser deposition (PLD). The substrate tem noise of a synthesized source was measured to check this. At perature during deposition was 805 °C while the oxygen offset frequencies greater than 10 kHz, the data presented for pressure was maintained at 170 mTorr. A KrF excimer laser the two superconducting oscillators approach the limit of this with a wavelength of 248 nm was used. The energy density of technique. The data presented for these two circuits at larger 2 the laser beam at the target was 0.8 J / cm . The pulse rate was offset frequencies is an upper limit on the phase noise. A de two per second. This deposition procedure has produced films block was located between the test fixture and the spectrum with a critical temperature of 90.5 K and a critical current analyzer for all measurements. density of greater than 2 x 106 A/ cm2 at 77 K. The effective surface resistance of a superconducting thin film patterned into a ring resonator was 1.36 mf! at 77 Kand 10 GHz [11]. The IV. RESULTS AND DISCUSSION superconducting films were patterned into the oscillators using A superconducting ring resonator patterned from a PLD film standard positive photolithographic techniques. The etchant had a loaded Q value of 940 and an unloaded Q value of 2100. used was a 100:1 solution of deionized water:H3P04. A copper ring resonator had loaded and unloaded Q values Three reflection mode oscillators were fabricated and tested. of 120 and 250, respectively, when measured at 77 K and The transmission lines, r f chokes, and bias lines were fabri 10 GHz. The effective surface resistance of the YBa2Cu307_x cated out of 2.4 µm thick copper for one circuit while the was 1.36 mf! at 77 K which was 19 times smaller than the other two circuits were fabricated out of YBa2Cu301-x high copper value of 25.8 mf! at 77 K. The rate of change of temperature superconducting thin films. One of the supercon the resonant frequency as a function of temperature for the ducting thin films was made by the pulsed laser deposition superconducting resonator was -1.25 MHz/K at 77 K. procedures described previously while the other film was a All three oscillators exhibited a 10 GHz signal and a much sputtered film purchased commercially. The sputtered film was weaker 20 GHz signal. The oscillators' power and frequency guaranteed to have a critical temperature of greater than 88 K were measured as a function of temperature at fixed bias. The and a surface resistance of less than 0.8 mf! at 77 K. Contacts temperature was raised from near 20 K until the oscillations to the superconductor for the output and wire bonding pads disappeared. A 77 K, the frequency and power were measured were made with silver with a gold overlayer, patterned by as a function of the gate and drain voltages. The single-sided lift-off photolithography. Wire bonding pads were located at phase noise of the oscillator made from the sputtered film the bias pads as well as the ends of the transmission lines was measured as a function of the drain bias at 77 K and the near the FET. The ground plane for the three oscillators was phase noise of all three oscillators was compared at a bias of 2.4 µm of copper with a 300 A titanium layer to promote Vds = 2.5 V and V = 0 V. 98 adhesion. The GaAs FET was epoxied onto the LaAI03 Figs. 4 and 5 show the oscillation frequency and power as substrate. Connections between the FET and transmission lines a function of temperature, respectively, for all three circuits. were made with 18 µm diameter gold wire by thermosonic The copper circuit was biased at Vds = 2.0 V, V = -1.0 V, 98 wirebonding. and Id = 29 mA. The oscillations could be maintained up to Measurements of the power and frequency as a function room temperature by increasing V to raise the drain current 98 of the temperature and bias conditions on the oscillator were to nearly 40 mA. The frequency of this oscillator changed very made with the oscillator mounted on a brass fixture inside a little. Its sensitivity to temperature was - 70 kHz/K over the closed cycle cryostat. The phase noise could not be measured temperature range of 25 K to 100 K. The power decreased with the sample mounted inside the cryostat since the vibration from 4.8 dBm at 25 K to 2.8 dBm at 100 K. At 77 K, the of the closed cycle refrigerator induced more than 1 MHz of signal power was 3.8 dBm at 10.074 GHz and the second jitter in the signal. Phase noise measurements were performed harmonic was reduced by 21 dB. The efficiency of the circuit with the oscillators mounted inside a sealed brass test fixture at these bias conditions at 77 K was 4.1 %. and submerged in liquid nitrogen. The single sided phase The PLD film used for the reflection mode oscillator had a noise was measured on a HP 8592A spectrum analyzer with critical temperature of 88.5 K. For the data presented in Figs. 4 a resolution bandwidth of 300 Hz. The measured data was and 5, this oscillator was biased with Vds = 3 V and V = 98 1868 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE II SUMMARY OF RESULTS AT 77 K FROM TEMPERATURE EXPERIMENTS Tc Frequency D..f/D..T vd Vg Id Power Circuit (K) (GHz) (kHz/K) (Volts) (Volts) (mA) (dBm) Cu 10.074 -70 2 -1 29 3.8 PLO 88.5 9.967 - 1, 500 3 0 22 5.4 Sputtered 88.6 10.058 -10, 000 2 -0.5 20 6.4 10.2..----------------0--'---Cu- - from a PLD film [11). The output power was 5.4 dBm at 77 K -fr-- Sc-A with the power of the second harmonic reduced by 29.2 dB. N' -a-- Sc-B The power decreased from 7.3 dBm to 5.0 dBm over the range I ~ 10.1 of 25 K to 79 K. The efficiency of the circuit at these bias >. conditions and 77 K was 5.4%. u c: For the measurements as a function of temperature, the Q) g:::J oscillator patterned from the commercially purchased sputtered 10.0 ..._ film, which had a critical temperature of 88.6 K, was biased LL at Vds = 2 V and V = - 0.5 V which gave a current 98 of Id = 20 mA at 77 K. The frequency of the signal was 9.9+----.---~--~--~------1 10.082 GHz with a power of 6.4 dBm at 77 K. The efficiency 0 20 40 60 80 100 was 10.4%. The power of the 20 GHz signal was 35.5 dB less Temperature (K) than the 10 GHz signal at 77 K. The power of the 10 GHz signal varied from 7.4 dBm at 25 K to 6.4 dBm at 81 Kand Fig. 4. Frequency as a function of temperature for all three oscillators. The then dropped sharply to 4.8 dBm at 83 K, beyond which the = = Cu oscillator's FET was biased at Vds 3.0 V and V9, 1.0 V. Sc-A is oscillation ceased. The frequency varied from 10.119 GHz to the sputtered film and Sc-B is the PLO film. The FETs were biased at Vds = 2.0 V and V9, = -0.5 V and at Vds = 3.0 V and V9, = 0.0 V, respectively. 10.008 GHz. The temperature at with the frequency started to decrease rapidly was 75 K. The sensitivity of the frequency to 10 temperature for this circuit was -10 MHz/K at 77 K, which ----0-'- Cu - ~ Sc-A is much larger than from any of the other circuits. Another 8 --0-- Sc-B oscillator patterned for a sputtered film had a comparable rate E of change for the frequency as a function of the temperature, Ill 6 -9.75 MHz/K at 77 K. ~ ..._ Table II shows a summary of the measurements at 77 K Q) ;: 4 from the temperature variation experiments for all three oscil a0. . lators. The rate of change of the frequency as a function of 2 temperature was determined by the film used for the microstrip transmission lines. The rate of change of the frequency with 0 temperature was the least for the oscillator made from copper. 0 20 40 60 80 100 The frequency of the oscillator patterned from the PLD films Temperature (K) was less sensitive to temperature than the sputtered oscillators by nearly a factor of eight. To decrease the sensitivity to the Fig. 5. Power as a function of temperature for all three oscillators. The Cu temperature, the temperature of operation could be decreased. oscillator's FET was biased at Vds = 3.0 V an=d V9, = -1.0 V=. Sc-A is For example, at 70 K, the rate of change for the frequency for athned oSscc-ilBla tios r tfhreo mo sscpilulattteorre df rofimlm thbeia sPeLdO a t fVilmds, bia2s.e0d Va t aVndd sV 9=, 3.0- 0V. 5an Vd· the PLD oscillator was -0.4 MHz/K and it was -1.4 MHz/K V9, = 0.0 V. for the sputtered oscillator. At 25 K, the rate of change of the frequency for both superconductor oscillators was nearly 0 V, which resulted in Id= 22 mA at 77 K. The temperature identical to the copper oscillator. was increased from 25 K until the oscillation disappeared. The Figure 6 shows the single sided phase noise of the three frequency decreased from 9.979 GHz to 9.964 GHz over this oscillators at 77 K and also for the copper oscillator at 300 K. range. 9 MHz of this 15 MHz drop occurred between 75 K For these measurements, all three oscillators were biased and 79 K. The dependence of the frequency on temperature is with Vds = 2.5 V and V = 0 V. The phase noise of the 95 typical of a change in the phase velocity of a superconductor superconducting oscillators was nearly identical at all offset resulting from a variation in the penetration depth as a function frequencies. They have phase noise values of -61 dBc/Hz at of temperature [1 ], [2], [13). The sensitivity of the frequency an offset of 10 kHz and -88 dBc/Hz at an offset of 100 kHz. of the oscillation to temperature was -1.50 MHz/K at 77 K. At an offset frequency of 10 kHz, the phase noise of the copper This is nearly identical to the rate of change of the frequency as oscillator when measured at 77 K and 300 K was 13 dB and a function of temperature of the ring resonator patterned from 32 dB higher, respectively. At an offset frequency of 100 kHz, the PLD film and of a series feedback oscillator, also patterned the difference was 6 dB and 22 dB, respectively. ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1869 - -20 ~ Sc-A 77 K 10.2..--------------0------Cu- .. ---0- Sc-8 77 K --t:r-- Sc-A N N' ·Io -40 ---0-..--- Cu 77K I --a- Sc-8 ca Cu 300 K ~ 10.1 ~ >. (.) Q) -60 c ·C5/J Q) z C:JT 10.0 .Q...). Q) C/J -80 LL ctl ..c a... 9.9-+--...--..---...--...--...--..---..----t -100 0 2 3 4 10 100 1000 Vds (Volts) Offset Frequency (kHz) Fig. 8. Frequency as a function of drain voltage for all three oscillators at Fig. 6. Single sided phase noise for the three oscillators. All three oscillators 77 K. The Cu oscillator was biased at Vgs = -1.0 V while the FETs in Sc-A wSce-rBe bisi atsheed PaLt DV dfsil m=. T2.h5e Vsi paenrdc oVn9dsu c=ti n0g Vos. cSilcla-Ato riss wtheer es phuetldte raetd 7 f7i lmK aanndd (atnhde astp uVtt9e8r ed= fi0lm.0) Va,n dr eSspce-Bct iv(tehley . PTLhDe fsiolmli)d wsyemreb boilass emda arkt Vth9e8 b=ia s- 0p.o5in Vts the Cu oscillator was measured at 77 K and 300 K. during the measurements as a function of temperature. -50 of the temperature. The drain voltage for each circuit was decreased from 4 V until the signal disappeared. Figure 8 u -60. shows the frequency of oscillation as a function of the drain OJ voltage. The solid symbols mark the drain voltages used during ~ the measurements as a function of temperature. The copper Q) -70 C/J oscillator and the oscillator patterned from the sputtered film "6 z had frequencies very near each other since the temperature was -80 Q) maintained at 77 K. This is near the crossover point for the C/J ctl two circuits in Fig. 4. For these two oscillators, the frequency ..c a... -90 --0- 10 kHz decreased 87 MHz for drain voltages of less than 1.5 V. Above --a- 100 kHz 1.5 V, the frequencies were less sensitive to drain voltage. -100 The frequency of the oscillator patterned from the PLD film 0 2 3 4 decreased 2 MHz as the drain voltage was decreased. The Vds (Volts) frequency was less sensitive to drain voltage at higher voltages for this circuit as well. Fig. 7. Single sided phase noise of the sputtered oscillator at offset frequen The power at 10 GHz as a function of drain voltage is shown cies of 10 kHz and 100 kHz as a function of the drain voltage. in Fig. 9 for all three circuits, with the solid symbols indicating the drain voltages used during the measurements as a function Fig. 7 shows the phase noise at offsets of 10 kHz and of temperature. For all three circuits, the power decreased as 100 kHz as a function of the drain voltage of the sputtered the drain voltage decreased, with the rate of decrease becoming oscillator. For these measurements, V = 0. As the drain large at smaller voltages. The drain currents are quite different 98 bias was increased from 2.5 V to 4.0 V, the power increased for the three curves shown in this figure. For example, at by 8 dB. At an offset frequency of 10 kHz, the phase noise Vds = 3 V the copper circuit had Id = 36 mA with V = 98 decreased by 15 dB while at an offset of 100 kHz, the phase -1.0 V, the sputtered deposited circuit had Id = 29 mA with noise decreased 9 dB. The decrease in the phase noise at an V = -0.5 V and the PLD circuit had Id = 22mA with 98 offset frequency of 10 kHz was faster than at 100 kHz because V = 0 V. The specified ranges for the pinch-off voltage 98 the influence of power on the phase noise at an offset of and saturated drain current for these transistors are -0.5 V 100 kHz was primarily through the floor noise, the first term of to -5 V and 20 mA to 70 mA, respectively, at Vds = 3 V. (1), while the phase noise at an offset of 10 kHz was affected The transistors used here had pinch-off voltages of -1.55 V, by the power through both the floor noise and the third term in -2.15 V, and -3.2 V for the YBa2Cu307_x PLD circuit, the (1). At large offset frequencies, the phase noise would decrease circuit fabricated from the sputtered film and the copper circuit, by the same amount that the output power increased. In our respectively. measurement, the power increased by 8 dB while the phase Figs. 10 and 11 show the frequency and power as a function noise decreased by 9 dB at an offset frequency of 100 kHz. of gate bias at 77 K for all three circuits. For each circuit, The frequency and power of the oscillators were also the drain voltage was held at the same value used during measured as a function of drain voltage at a temperature measurements as a function of temperature. The data points of 77 K. For these measurements, the gates were biased at at the gate biases used in those measurements are marked the same voltages used for the measurements as a function with solid symbols. The copper circuit oscillated for gate 1870 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 TABLE III SUMMARY OF RESULTS AT 77 K FOR Vds = 2.0 v Vg Id Power Frequency Efficiency Circuit (Volts) (mA) (dBm) (GHz) (%) Cu -1.4 22 0.6 10.095 2.6 PLD 0 18 0.9 9.949 3.3 Sputtered -0.6 18 5.2 10.092 9.3 20 10.2 -0-- Cu - 'N ~ Sc-A 10 ---0-- Sc-8 E I c:c 10.1 ~ ~ >. ..... 0 0 Q) c: ~ Q) a0. -0-- Cu :O:I" 10.0 -10 .Q...). ll Sc-A -0-- Sc-8 LL -20 9.9 0 2 3 4 -1.00 -0.75 -0.50 -0.25 0.00 Vds (Volts) Vgs (Volts) Fig. 9. Power as a function of drain voltage for all three oscillators at 77 K. Fig. 10. Frequency as a function of gate voltage for all three oscillators at = The Cu oscillator was biased at Vgs = -1.0 V while the FETs in Sc-A (the 77 K. The Cu oscillator was biased at Vds 2.0 V while the FETs in Sc-A sputtered film) and Sc-B (the PLD film) were biased at Vgs = -0.5 V and (the sputtered film) and Sc-B (the PLD film) were biased at Vds = 2.0 V and at Vgs = 0.0 V, respectively. The solid symbols mark the bias points during at V98 = 3.0 V, respectively. The solid symbols mark the bias points during the measurements as a function of temperature. the measurements as a function of temperature. voltages from 0 V to -1.4 V. The full ranges for the other 10 circuits are shown. The frequency increased 200 MHz as - V was decreased for the copper oscillator. The oscillator 98 5 patterned from the PLD film showed little variation, but the E c:c sputtered sample's frequency increased 170 MHz as the gate ~ bias decreased to -0.7 V. The frequency was more sensitive ..... 0 to variations in the gate bias than to the drain bias. For all Q) ~ three circuits, the power decreased as the gate bias decreased. a0. The power for the copper circuit decreased 6.7 dB as V -5 98 -0-- Cu was varied from 0 V to -1.4 V. Its drai.n current varied from --i:r-- Sc-A ---0-- Sc-8 62 mA to 22 mA over that range. The power of the oscillator -10+-.......................... .,...... ............" "T""...-.,......... ..........- r....,.......-.............. patterned from the PLD film decreased sharply as the gate -1.00 -0.75 -0.50 -0.25 0.00 voltage neared -0.4 V. Its drain current ranged from 22 mA Vgs (Volts) to 12 mA. Finally, the power of the oscillator patterned from the sputtered film decreased from 8.9 dBm to 5.2 dBm, while Fig. 11. Power as a function of gate voltage for all three oscillators at 77 K. its current ranged from 38 mA to 15 mA. The large differences The Cu oscillator was biased at Vd~ =2.0 V while the FET=s in Sc-A (the sputtered film) and Sc-B (the PLD film) were biased at Vds 2.0 V and at in currents are a result of the different pinch-off voltages of Vgs = 3.0 V, respectively. The solid symbols mark the bias points during the the transistors, as discussed in the previous paragraph. The measurements as a function of temperature. largest power output of any circuit was for the sputtered oscillator. It delivered 11.5 dBm with a bias of Vis = 4.0 V entire circuit operated at cryogenic temperatures. The and V = -0.5 V. S-parameters of the GaAs MESFET used in the design 98 Table III shows a summary of the results with Vds = of the oscillators were measured at 77 K. The design was 2.0 V and the gate voltage adjusted to give comparable drain a reflection mode oscillator and used a ring resonator to currents at 77 K. The different gate biases were a result of stabilize the frequency. The ring resonator was coupled to the the transistors having different pinch-off voltages. The largest output line off the drain of the FET. A YBa2Cu301-x ring power and the most efficient oscillator was the oscillator resonator, which was tested separately, had a loaded Q that fabricated from the sputtered film. was eight times larger than that of a copper ring resonator. V. CONCLUSION Three oscillators were fabricated and tested, one from copper Hybrid superconductor/GaAs oscillators were successfully and two from high temperature superconductors. All three implemented on 10 mm x 10 mm LaAI03 substrates. The exhibited both 10 GHz and 20 GHz oscillations. The power ROHRER et al.: HIGH TEMPERATURE SUPERCONDUCTOR 1871 of the 20 GHz oscillation was 20 dB to 35 dB lower than the 6.5 GHz on a single substrate," IEEE Microwave Guide Letts, vol. 2, power of the 10 GHz oscillation for these three circuits. The no. 1, p. 22, Jan. 1992. (10] EEsof, Westlake, CA 91632. lowest phase noise at 77 K of -68 dBc/Hz and -93 dBc/Hz [11] N.J. Rohrer, Ph.D. Dissertation, The Ohio State University, Columbus, at offset frequencies of 10 kHz and 100 kHz, respectively, OH, 1992. = (12] Hewlett Packard publication, "RF & microwave phase noise measure was obtained for the sputtered oscillator with Vds 4.0 V. ment seminar." Compared to the copper circuit, the superconducting oscillators (13] T. Van Duzer and C. W. Turner, Principles of Superconductive Devices had 12 dB less phase noise at an offset of 10 kHz and and Circuits. New York: Elsevier, 1981, p. 125. 26 dB less noise at an offset at 100 kHz. The sensitivity of the frequency to temperature at 77 K was -10 MHz/K for the sputtered oscillator, while that of the PLD circuit was -1.5 MHz/K. The stability, power, and efficiency improved Norman J. Rohrer received the B.S. degree in physics and mathematics from Manchester College, as the temperature was decreased. The output power and North Manchester, IN in 1987, and the M.S. and frequency were dependent upon the bias conditions. The Ph.D. degrees in electrical engineering from the frequency of the oscillators were less sensitive to the drain Ohio State University, Columbus, OH, in 1990 and 1992, respectively. voltage than to the gate voltage. The oscillator patterned from As a graduate student, he was recipient of a a sputtered film had the largest output power and the highest NASA Graduate Student Research Fellowship under efficiency. which he was able to complete his dissertation research on microwave oscillators. In 1992 he joined IBM Microelectronics, Burlington, VT, working on microprocessor subsystems. ACKNOWLEDGMENT The authors would like to thank Chris Chorey for his assistance in the testing of the transistor and oscillator at George J. Valeo received the B.S. and M.S. de cryogenic temperatures. grees in electrical engineering from Case Western Reserve University in 1979 and 1981, respectively. He received the Ph.D. in electrical engineering from REFERENCES the University of Cincinnati in 1986. In 1986 he joined the faculty of the Ohio State [1] N. J. Rohrer, H. Y. To, G. J. Valeo, K. B. Bhasin, C. Chorey, and J. D. University where he is currently an associate pro Warner, "Sequentially evaporated thin film YBa2Cu307_x supercon fessor of electrical engineering. His current re ducting microwave ring resonator," Science and Technology of Thin Film search interests are electronic applications of high Superconductors 2. R. C. McConnell and R. Noufi, editors, New York: temperature superconductors, electronic properties Plenum, 1990, p. 615. and applications of diamond films, and compound [2] C. M. Chorey, K. Kong, K. B. Bhasin, J. D. Warner, and T. ltoh, "YBCO semiconductor devices and technology. superconducting ring resonator at millimeter-wave frequencies," IEEE Trans. Microwave Theory Tech., vol. 39, no. 9, p. 1480, Sept. 1991. (3] P.A. Palokas, C. E. Rice, M. V. Schneider, and R. Trambarulo, "Elec trical characteristics of thin-film Ba2 YCu307 superconducting ring Kul B. Bhasin received the M.S. and Ph.D. from resonator," IEEE Microwave Guide Letts. Vol. 1, p. 54, Mar. 1991. Purdue University and the University of Missouri (4] R.R. Bonetti, et al., "Thin film superconducting filter design techniques; Rolla, respectively. microstrip filters in LaAI03 and LaGa03 substrates," IEEE Trans. Since 1983 he has been a Senior Research Sci Microwave Theory Tech., vol. MTT-S, no. 1, p. 269, 1990. entist in the Solid State Technology Branch of the [5] B. R. McAvoy, G. R. Wagner, J. D. Adam, J. Talvacchio, and Space Electronics Division of the NASA Lewis M. Driscoll, "Superconducting stripline resonator performance," IEEE Research Center in Cleveland, OH. Prior to joining Trans. Magn., vol. 25, pp. 1104, 1989. (6] M.A. Richard, K. B. Bhasin, C. Gilber, S. Metzler, G. Keopf, and P. C. NASA he was with Gould, Inc., from 1977 to 1983 Claspy, "Performance of a four-element Ka-band high temperature as Senior Scientist and Manager of Technology. superconducting microstrip antenna," IEEE Microwave Guide Letts., He is currently engaged in the development of vol. 2, no. 4, pp. 143, Apr. 1992. GaAs microwave devices and circuits, microwave [7] D. B. Leeson, "A simple model of feedback oscillator noise spectrum," photonics, and superconducting electronics for space applications. in Proc. IEEE, vol. 54, no. 2, p. 329, 1966. Dr. Bhasin has authored many publications and coedited the book Mi (8] A. P. S. Khanna, M. Schmidt, and R. B. Hammond, "A superconducting crowave Integrated Circuits. He is the recipient of the IR-100 Award, NASA resonator stabilized low noise oscillator," Microwave J., vol. 34, p. 127, Group Achievement Awards, and the Gould Scientific Achievement Award Feb. 1991. and he is on the editorial board of Microwave and Optical Technology Letters'. [9] R. Klieber, R. Ramisch, A. A. Valenzuela, R. Weigel, and R. Russer, He is a member of Sigma Xi and a Fellow of the International Society for "A coplanar transmission line high-Tc superconductive oscillator at Optical Engineers. 1872 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 41, NO. 11, NOVEMBER 1993 Analysis of Open and Shielded Spectral~Domain Slotlines Printed on Various Anisotropic Substrates Yinchao Chen and Benjamin Beker, Member IEEE Abstract-A rigorous full-wave analysis based on the spectral It is known that open slotlines leak power into the dielectric domain approach for open and shielded slotline transmission filled parallel plate waveguide (PPW) regions. For electric lines is presented. The substrate materials under consideration (PEC) conductor-backed structures, the leakage is always are anisotropic, characterized by both their peQDittivity and present, but is small if appropriate values of medium parame permeability tensors. The formulation includes off-dia.gonal ten sor elements to represent gyroelectric media, Ferrites, or the ters and geometrical dimensions are employed [5]. The same misalignment between the principal axes of the substrate and the is also true for a magnetic (PMC) conductor-backed slotline, coordinate system of the waveguide. Dyadic admittance Green's with the only difference being that the modes of this parallel functions for every structure are obtained with the help of plate structure have a cuff-off frequency [4]. In this paper, differential matrix operators in the Fourier-transformed domain, all physical dimensions and medium parameters are chosen and the Galerkin method is employed to find the propagation constants numerically. so as to minimize the leakage effects, since the paper aims at emphasizing the influence of substrate anisotropy on the propagation characteristics of bilateral slotlines. I. INTRODUCTION In what follows, it is assumed that every MIC transmission T HE SHIELDED slotline (or finline) has been used at line is printed on a homogeneous anisotropic substrate that has microwave and millimeter-wave frequencies for quite its optical axes of the permittivity and permeability arbitrarily some time [1]. Its analog, the open slotline, has enjoyed wide oriented in the xz-plane, i.e., the plane of propagation. As a popularity in various applications at these frequencies as well result, the theory presented in this work encompasses a wide [2]. Desirable features of shielded slotlines· include reduced variety of guiding media, which can be either gyroelectric, size, weight, and ease of integration into the overall microwave Ferrite, or both. When off-diagonal tensor elements of [io] and integrated circuit (MIC). Advantages of open slotlines, which [µ] .are real, the tensors are symmetric, then misalignment be are often used in microstrip antenna feeding networks [3], tween coordinates of the waveguide and those of the material include reduction in the radiation level back to the feed tensors can be examined well. ing circuit. Dyadic admittance Green's functions for every transmission The majority of past and present work has focused on line are formulated using differential matrix operators [12], slotlines with isotropic substrates only (see [1 ], [2], and and the spectral-domain approach [13, Chapter 5]. The propa [4]-[6]). More recently however, anisotropic substrates have gation constants of dominant modes are obtained by using the Galerkin method. Both electric and magnetic wall symmetries been considered as well, including shielded. finlines [7], [8], (odd and even modes, respectively) for open structures and partially covered slotlines [9], as well as fully open struc tures [10], [11 ]. Although the cited references laid out the the magnetic wall symmetry for shielded bilateral slotlines are ground work for such structures, none of thein considered considered. The basis functions used to expand the field inside the slot are carefully chosen with build-in edge singularities. bilateral open slotlines printed on general anisotropic media The formulation and the numerical approach are validated in detail. against the available published data from references [4], [6], This paper presents the spectral-domain formulation and numerical results for the dispersive characteristics of open and [7]. as well as shielded slotline transmission lines. The odd and even modes of open bilateral slotlines are examined. The II. ADMITTANCE GREEN'S FUNCTIONS FOR former corresponds to the electric wall bisecting the plane of ANISOTROPIC SUBSTRATES symmetry, whereas the later considers the magnetic wall case: Crossectional view of waveguides that are under considera In addition, an analysis of shielded bilateral slotlines (finlines) tion in this paper are shown in Fig. l. The substrate material is also included to illustrate the similarities in their propagation is assumed to be characterized by the permittivity tensor characteristics compared to those of open structures. which can be either gyroelectric (Hermitian) or misaligned with thy coordinates of the structure in the xz-plane. For Manuscript received May 14, 1992; revised January 19, 1993. generality, the constitutive properties of the substrate also The authors are with the Department of Electrical and Computer Engineer- include the anisotropic nature of the permeability tensor, which ing, University of South Carolina, Columbia, SC, 29208. · IEEE Log Number 9210213. can represent a Ferrite or the rotation effects of its principal 0018-9480/93$03.00 © 1993 IEEE

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