Short-Channel Organic Thin-Film Transistors: Fabrication, Characterization, Modeling and Circuit Demonstration

232 Pages·2015·15.82 MB·English

by  Tarek Zaki (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Tarek Zaki

Short-Channel
Organic Thin-Film
Transistors
Fabrication, Characterization,
Modeling and Circuit
Demonstration
Springer Theses
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Tarek Zaki
Short-Channel Organic
Thin-Film Transistors
Fabrication, Characterization, Modeling
and Circuit Demonstration
Doctoral Thesis accepted by
the University of Stuttgart, Germany
123
Author Supervisor
Dr. Tarek Zaki Prof. Joachim N.Burghartz
Institute for Microelectronics Stuttgart Institute for Microelectronics Stuttgart
Stuttgart Stuttgart
Germany Germany
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-319-18895-9 ISBN978-3-319-18896-6 (eBook)
DOI 10.1007/978-3-319-18896-6
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Parts of this thesis have been published in the following journal articles:
1. J.Milvich,T.Zaki,M.Aghamohammadi,R.Röodel,U.Kraft,H.Klauk,and
J. N. Burghartz, “Flexible low-voltage organic phototransistors based on air-
stable dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene,” Organic Electronics,
vol. 20, pp. 63–68, May 2015.
2. U. Kraft, M. Sejfić, M. J. Kang, K. Takimiya, T. Zaki, F. Letzkus,
J. N. Burghartz, E. Weber, and H. Klauk, “Flexible low-voltage organic
complementary circuits: Finding the optimum combination of semiconductors
and monolayer gate dielectrics,” Advanced Materials, vol. 27, no. 2, pp. 207–
214, Jan. 2015.
3. S.Scheinert,T.Zaki,R.Rödel,I.Hörselmann,H.Klauk,andJ.N.Burghartz,
“Numerical analysis of capacitance compact models for organic thin-film
transistors,” Organic Electronics, vol. 15, no. 7, pp. 1503–1508, Jul. 2014.
4. T. Zaki, S. Scheinert, I. Hörselmann, R. Rödel, F. Letzkus, H. Richter, U.
Zschieschang, H.Klauk, and J. N.Burghartz,“Accurate capacitance modeling
and characterization of organic thin-film transistors,” IEEE Transactions on
Electron Devices, vol. 61, no. 1, pp. 98–104, Jan. 2014.
5. R. Rödel, F. Letzkus, T. Zaki, J. N. Burghartz, U. Kraft, U. Zschieschang, K.
Kern, and H. Klauk, “Contact properties of high-mobility, air-stable, low-
voltage organic n-channel thin-film transistors based on a naphthalene tetra-
carboxylic diimide,” Applied Physics Letters, vol. 102, no. 233303,
pp. 233303-1–233303-5, Jun. 2013.
6. U.Zschieschang,R.Hoffmockel,R.Rödel,U.Kraft,M.J.Kang,K.Takimiya,
T. Zaki, F. Letzkus, J. Butschke, H. Richter, J. N. Burghartz, and H. Klauk,
“Megahertz operation of flexible low-voltage organic thin-film transistors,”
Organic Electronics, vol. 14, no. 6, pp. 1516–1520, Jun. 2013.
7. T. Zaki, R. Rödel, F. Letzkus, H. Richter, U. Zschieschang, H. Klauk, and
J. N. Burghartz, “AC characterization of organic thin-film transistors with
asymmetric gate-to-source and gate-to-drain overlaps,” Organic Electronics,
vol. 14, no. 5, pp. 1318–1322, May 2013.
8. T. Zaki, R. Rödel, F. Letzkus, H. Richter, U. Zschieschang, H. Klauk, and
J. N. Burghartz, “S-parameter characterization of submicrometer low-voltage
organic thin-film transistors,” IEEE Electron Device Letters, vol. 34, no. 4,
pp. 520–522, Apr. 2013.
9. T. Zaki, F. Ante, U. Zschieschang, J. Butschke, F. Letzkus, H. Richter, H.
Klauk, and J. N. Burghartz, “A 3.3 V 6-bit 100 kS/s current-steering D/A
converter using p-type organic thin-film transistors on glass,” IEEE Journal of
Solid-State Circuits, vol. 47, no. 1, pp. 292–300, Jan. 2012.
10. F. Ante, D. Kälblein, T. Zaki, U. Zschieschang, K. Takimiya, M. Ikeda, T.
Sekitani, T. Someya, J. N. Burghartz, K. Kern, and H. Klauk, “Contact resis-
tance and megahertz operation of aggressively scaled organic transistors,”
Small,vol.8,no.1,pp.73–79,Jan.2012.
Dedicated to my beloved parents
’
Supervisor s Foreword
Theyear2015marksthe50thanniversaryofGordonMoore’s1965predictionthat
miniaturizationofmicroelectronicswouldfollowanexponentialgrowthpathwitha
doubleddensityonchipevery24months,widelyknownasMoore’slaw.Thishas
fostered tremendous growth in consumer and industrial electronics applications.
Electronic chips have become increasingly complex and are commonly realized
while minimizing chip area and, thus, cost. Chips are, therefore, miniature size
products by nature and are unsuitable for use in any large-area and mechanically
flexible electronic applications, such as flexible or curved displays, photovoltaics,
and certain sensor as well as life style devices.
It was not surprising that after the discovery of conductive polymers in the
1970s, researchers in academia and industry envisioned a tremendous opportunity
in developing electronic products that are macrosize by nature. The Nobel Prize
awarded to Heeger, MacDiarmid, and Shirakawa in 2000 for their work on con-
ductive polymers has even more ignited enthusiasm in this field. Organic photo-
voltaics and organic displays, in particular, are manufactured in large volumes
today and feature superiority to other technological solutions in terms of perfor-
mance and cost. However, organic electronic circuits are still far from industrial
applications, which is mainly due to the low carrier mobility of organic semicon-
ductors, falling two orders of magnitudes behind the silicon value. Also, operating
voltages for organic field-effect transistors (OTFTs) are in the tens of volts and
OTFTsare,thus, notwell suitable for battery-powereddeviceswhichare thebasis
forenteringthepromisingindustrialmarkets.Therefore,thereishighneedforlow-
voltage OTFT technology which will also enable flexible electronic systems that
utilize both high-performance ultra-thin silicon chips and large-area organic elec-
tronics, which we recently proposed as hybrid systems-in-foil (HySiF).
This thesis addresses the main shortcomings of current OTFT technology by
aiming at increasing the performance level of OTFTs at a voltage supply that is
compatible with that of modern silicon chips. The use of stencil masks for pat-
terning OTFTs at submicrometer channel lengths not only greatly advances OTFT
performance but also offers an insight at the parasitic effects that become apparent
ix
x Supervisor’sForeword
when OTFT technology will advance to that level of miniaturization in the future.
Stencil mask patterning also leads to far better device matching which allows for
exploiting circuit topologies known from silicon electronics. S-parameter charac-
terizationonindividualOTFTs,whichisfirstdemonstratedinthisthesis,willhelp
to advance OTFT compact modeling and, thus, circuit design to pave the way to
viable electronic products realized in organic or HySiF technologies.
Stuttgart Prof. Joachim N. Burghartz
January 2015
Abstract
Plasticelectronicsbased onorganicthin-filmtransistors (OTFTs)pavethewayfor
cheap, flexible, and large-area products. Over the past few years, OTFTs have
undergone remarkable progress in terms of reliability, performance and scale of
integration. This work takes advantage of high-resolution silicon stencil masks to
buildair-stablecomplementaryOTFTsusingalow-temperaturefabricationprocess.
Manyfactorscontributetotheallureofthistechnology;themasksexhibitexcellent
stiffness and stability, thus allowing to pattern the OTFTs with submicrometer
channel lengths andsuperb device uniformity. Furthermore,theOTFTsemployan
ultra-thingatedielectricthatprovidesasufficientlyhighcapacitanceoftheorderof
1 μF/cm2 to enable the transistors to operate at voltages as low as 3 V.
The critical challenges in this development are the subtle mechanisms that
govern the properties of the aggressively scaled OTFTs. These mechanisms, dic-
tated by device physics, have to be described and implemented into circuit design
toolstoensureadequatesimulationaccuracy.Thisisparticularlybeneficialtogain
deeperinsightintomaterials-relatedlimitations.Theprimaryobjectiveofthiswork
is to bridge the gap between device modeling and mixed-signal circuits by estab-
lishinganOTFTcompactmodel,togetherwithrealizingtheworld’sfastestorganic
digital-to-analog converter (DAC).
A unified model that captures the essence in the static/dynamic behavior of the
OTFTs is derived. Approaches to incorporate the implicit bias-dependent parasitic
effectsinthemodelareelucidatedandaccordinglyareliablefittoexperimentaldata
of OTFTs with different dimensions is obtained. It is demonstrated that the charge
storagebehaviorintheintrinsicOTFTsagreesverywellwithMeyer’scapacitance
model. Moreover, the first comprehensive study of the frequency response of
OTFTs using S-parameter characterization is presented. In view of the low supply
voltageandairstability,arecordcutofffrequencyof3.7MHzforachannellength
of 0.6 μm and a gate overlap of 5 μm is accomplished. Finally, a 6-bit current-
steering DAC, comprising as many as 129 OTFTs, is designed. The converter
achieves a 1000-fold faster update rate (100 kS/s) than prior state of the art.
xi