NASA Technical Reports Server (NTRS) 20110011901: Characterization of 720 and 940 MHz Oscillators with Chip Antenna for Wireless Sensors from Room Temperature to 200 and 250 deg C

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by  NASA Technical Reports Server (NTRS)

Characterization of 720 and 940 MHz Oscillators with Chip
Antenna for Wireless Sensors from Room Temperature to 200 and
250 ºC
Maximilian C. Scardelletti and George E. Ponchak
NASA Glenn Research Center, 21000 Brookpark Rd. Cleveland, Ohio, 44135
[email protected]

Abstract — Oscillators that operate at 720 and 940 MHz making it much more applicable for miniaturized wireless
and characterized over a temperature range of 25 ºC to 200 sensor applications that operate at high temperatures.
ºC and 250 ºC, respectively, are presented. The oscillators are
designed on alumina substrates with typical integrated circuit
fabrication techniques. Cree SiC MESFETs, thin film metal- II. DESIGN AND FABRICATION
insulator-metal capacitors and spiral inductors, and Johanson
miniature chip antennas make-up the circuits. The output The oscillators are based on a conventional Clapp
power and phase noise are presented as a function of oscillator design, which is shown in Fig. 1. The values of
temperature and frequency.
C , C , C and L are given in Table 1 for both the 720 and
T 1 2 T
Index Terms — MESFETS, chip antennas, oscillators SiC
940 MHz designs. The method of design is illustrated in
alumina.
[6].
V
I. INTRODUCTION DS
The need for electronics that operate at high
temperatures is growing in both commercial and
CC LL
government applications. The automobile industry uses a TT TT
variety of electronics that operate at high temperatures
VV
including power brake (140 ºC), on-engine (150 ºC) and GGSS
exhaust sensors (850 ºC) [1]. The oil and natural gas
industry require high temperature wireless sensors for
CC
drilling and monitoring wells up to 360ºC [2]. NASA’s 11
planned missions to Venus will require electronic systems CC
22
for probes and robotic landers on the surface that could
reach as high as 500 ºC [3]. Mechanisms for exploring the

atmosphere of Venus may consist of small airplanes, but
Figure 1: Schematic of Clapp oscillator.
sophisticated electronics will be required to navigate the

vessel in temperatures up to 320 ºC [4].
Table1. Passive component values.
NASA Glenn Research Center is developing high

temperature electronics for wireless sensing applications
Oscillator C (pF) C (pF) C (pF) L (nH)
[5, 6]. Oscillators that incorporate a capacitive pressure T 1 2 T
720 MHz 10 4 4 8.5
sensor have been developed [7]. The pressure was varied
940 MHz 5 10 10 10.5
and the oscillation frequency shifted according to the

change in capacitance at 300 ºC. The oscillator/pressure
Figures 2 and 3 are photographs of the fabricated
senor was coupled to a square ring antenna, which radiated
oscillators. The oscillators are fabricated on 99.9 %
its power over a distance of one meter.
alumina substrates that are 500 µm thick and have a
In this paper, two oscillators that operate over a
dielectric constant of 9.9. A Cree SiC MESFET, model
temperature range of 25 to over 200 ºC are presented.
number CRF24010D, is used in both oscillators with thin
Both oscillators utilize a miniature chip antenna that
film metal-insulator-metal (MIM) capacitors and spiral
radiates to a receive antenna 1.7 m away. The miniature
inductors. The metallization of the underlying first metal
chip antenna greatly reduces the overall size of the circuit,
of the MIMs is Cr/Au (25/500 nm). A 1.6 µm thick silicon
dioxide layer is used as the insulator; the dielectric
constant of the silicon dioxide is approximately 4.3. The and has a gain of 2.3 and 4.0 dBi at 720 and 940 MHz,
top electrode metallization is Ti/Au (25 nm/1.7 µm) and respectively. The oscillators with chip antennas are
finally a third layer of 1.7 m Au, for a total metal separated from the receive antenna by 1.7 m. Between the
thickness of 3.9 m, is used to decrease the resistive oscillator and ceramic heater are four, 500 m thick
losses. The thin film spiral inductor has 1.5 turns for the alumina wafers to minimize the effects the heating element
720 MHz design and 1.9 turns for the 940 MHz design, in the ceramic heater has on the circuits. A thermocouple
which results in an inductance of 8.5 and 10.5 nH, is placed on the circuit substrate near the oscillator to
respectively, according to Sonnet simulations. The accurately record the temperature of the circuit. The
miniature chip antennas, model number 0920AT50A080, temperature of the ceramic heater is varied with a Labveiw
were provided by Johanson Technology. The antennas controlled power source. An Agilent E4440A spectrum
resonate at approximately 920 MHz, which matched well analyzer is used to record the spectrum and phase noise at
the 940 MHz oscillator design, thus no matching circuit temperature increments of 25 ºC starting at room
required. To better match the chip antenna to the 720 MHz temperature and ending when the oscillator fails. Before
design, a 2 pF chip capacitor was placed in series with the each measurement, the temperature is held constant with
input of the antenna to resonate with the series inductance the oscillator operating for 10 minutes to assure thermal
of the antenna. Wire bonds were used to connect the drain, equilibrium is reached. The gate voltage was varied as the
gate and source of the transistor to DC bias pads. temperature is varied to keep the drain current constant at
100 mA for both designs. For the 720 MHz circuit, the
CCrreeee SSiiCC MMEESSFFEETT drain voltage is 6 V, and for the 940 MHz design, the
drain voltage is 8.8 V.
CChhiipp AAnntteennnnaa
The measured spectrum for the 720 MHz design at 25
and 200 ºC is shown in Fig. 4. It is seen that the frequency
DDCC BBiiaassiinngg PPaaddss of oscillation and transmitted power decrease with
temperature. The oscillation frequency decreases from
726.2 MHz at 25 ºC to 720 MHz at 200 ºC, which is less
than a 1% change. The transmitted power decreases from -
CChhiipp CCaappaacciittoorr
22.1 dBm at 25 ºC to -27.9 dBm at 175 ºC, which is only a
decrease of 3 dBm, but it decreases to -34.4 dBm at 200
ºC. Just beyond 200 ºC, the 720 MHz oscillator seizes to
operate. Figure 5 shows the frequency and transmitted
Figure 2: Photograph of 720 MHz circuit. power received at every temperature setting.
0
T=25C
-20 T=200C
CChhiipp AAnntteennnnaa
-40
m)
B
d
er ( -60
CCrreeee SSiiCC MMEESSFFEETT w
DDCC BBiiaassiinngg PPaaddss Po -80
-100
-120
660 680 700 720 740 760 780 800
Figure 3: Photograph of 940 MHz circuit.
Frequency (MHz)
Figure 4: Measured spectrum for the 720 MHz circuit at
III. OSCILLATOR CHARACTERIZATION
25 and 200 ºC.
The oscillators were characterized in an anechoic
Figure 6 displays the spectrum at 25ºC and 250ºC for
chamber. All of the test equipment is outside the room to
the 940 MHz oscillator design. The figure shows the
eliminate interference from the equipment. The oscillators
oscillation frequency and transmitted power decrease
are clamped to a ceramic heater that is placed on a
similar to the 720 MHz design. The frequency decreases
rotational stage so that a 180º radiation pattern can be
from 940.2 MHz at 25ºC to 932.2 MHz at 250ºC, which is
measured. A wideband horn is used as the receive antenna
less than a 1% change. The transmitted power decreases
from -27.6 dBm at 25ºC to -32.9 dBm at 175ºC. Beyond The measured phase noise of the 940 MHz design at 25
this, the power decreases more rapidly to -41.7 dB at and 250 ºC is shown in Fig. 8. The phase noise increases at
250ºC. Just above 250 ºC the 940 MHz oscillator seizes higher temperatures far from the carrier frequency, which
operation. Figure 7 shows the frequency and transmitted is expected. Figure 9 shows the phase noise at 100 kHz
power received at every temperature setting. offset over the temperature range from 25 to 250 ºC. The
phase noise increases as temperature increases, which is
727 -20
expected. The 720 MHz circuit had similar phase noise
726 -22
characteristics.
725 -24
z) -20
Frequency (MH 777222234 Freq (MHz) ---322086 Pout (dBm) Bc/Hz) --6400 TT==2255 0CC
721 Pout -32 se (d -80
720 -34 oi
N
e
719 -36 s -100
a
0 20 40 60 80 100 120 140 160 180 200 220 h
P
Temperature (C) -120
Figure 5: Measured received power and frequency for the
720 MHz circuit as a function of temperature.
-140
102 103 104 105 106 107
-20
Offset Frequency (Hz)
Figure 8: Measured phase noise of the 940 MHz circuit at
T=25C
-40
T=250C 25 and 250 ºC.
m) -60 -100
B
d
er ( -105
w
o -80 z)
P H
c/
dB -110
-100 e (
s
oi
-120 se N -115
930 932 934 936 938 940 942 Pha Phase Noise at
Frequency (MHz) -120 100 kHz Offset
Figure 6: Measured spectrum of the 940 MHz circuit at 25
and 250 ºC.
-125
0 50 100 150 200 250 300
942 -26
Temperature (C)
-28
940 Figure 9: Measured phase noise of the 940 MHz circuit at
-30 100 kHz offset frequency as a function of temperature.
Hz) 938 -32
M m)
ency ( 936 --3364 ut (dB deTsihgen sm aerea ssuhroewd nr aind iFatiigosn. 1p0a tatenrdn s1 1o. fB tohteh tgwraop hoss ccillelaatrolyr
u o
q P demonstrate how the transmitted power decreases as
Fre 934 FProeuqt (MHz) -38 temperature increases. More important, the radiation
-40
932 patterns for both designs change very little over the
-42 temperature ranges.
930 -44
0 50 100 150 200 250 300
Temperature (C)
Figure 7: Measured received power and frequency for the
940 MHz circuit as a function of temperature.
respectively. Both designs have a frequency shift less than
90 1% over there designated temperature ranges. The
-15
120 60 transmitted power varies little till the oscillators reach the
temperature just before they stop operation, then the power
-20
decreases significantly. Radiation patterns demonstrate
that there is no significant change in the radiation patterns
150 -25 30 and that the chip antennas may be used to at least 250 ºC.
T=25 C The circuits and their characteristics demonstrate that the
T=50 C -30 technology permits wireless sensors operating through 250
T=75 C
T=100 C ºC by replacing the MIM capacitor, CT, by a capacitive
180 T=125 C--3355 0 pressure sensor as was done in [7].
T=150 C
-15 -20 -25 -30 --3355 -30 -25 -20 -15
T=175 C
T=200 C
-30 ACKNOWLEDGEMENT
This work was supported by the NASA Integrated
210 -25 330
Vehicle Health Management (IVHM) program. The
authors thank Nicholas C. Varaljay and Elizabeth A.
-20
McQuaid for fabricating the circuits.
240 300
-15
270 REFERENCES
Figure 10: Measured radiation pattern of the 720 MHz
circuit as a function of temperature. [1] R. W. Johnson, J. L. Evans, P. Jacobsen. J. R. Thompson
and M. Christopher, “The changing automotive
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150 -30 30 Geothermal Reservoir Engineering, Stanford Univ.,
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T=75 C -35 McNutt, S. M. Lal and A. Mantooth, “Silicon-Carbide
T=100 C
(SIC) Semiconductor Power Electronics for Extreme High-
T=125 C
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180 T=150 C --4400 0
-20 -25 -30T=175- 3C5 --4400 -35 -30 -25 -20 Vol. 4, 2004, pp. 2538 – 2555.
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T=250 C Vol. IE-29, Iss. 2, 1982, pp. 107-111.
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210 -30 330 1 GHz oscillator-type active antenna,” IET Electronics
Letters, Vol. 45, Issue 8, April 9, 2009, pp. 386-387.
-25 [6] G. E. Ponchak, M. C. Scardelletti and J. L. Jordan, “30 and
90 MHz Oscillators Operating Through 450 and 470ºC for
240 300 High Temperature Wireless Sensors,” Asia-Pacific
-20
Microwave Conference, Yokohama, Japan December 7 -10,
270
Figure 11: Measured radiation pattern of the 940 MHz 2010. Submitted on June, 2010.
circuit as a function of temperature. [7] G. W. Hunter, G. M. Beheim, G .E. Ponchak, M. C.
Scardelletti, R. D. Meredith, F. W. Dynys, P. G. Neudeck, J.
L. Jordan and L. Y. Chen, “Development of High
IV. CONCLUSIONS Temperature Wireless Sensor Technology Based on Silicon
Carbide Electronics,” submitted to ECS Transactions , Las
Oscillators that utilize miniature chip antennas have
Vegas, NV, October 10-15, 2010.
been presented. They were operated at 720 and 940 MHz
over a temperature range from 25 to 200 and 250ºC,