J. Semicond. > Volume 35 > Issue 12 > Article Number: 124002

Impact of source and drain contact thickness on the performance of organic thin film transistors

Poornima Mittal 1, 3, , , Y.S. Negi 2, and R.K. Singh 3,

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Abstract: This paper analyzes the impact of source (ts) and drain (td) contact thicknesses on top contact (TC) and bottom contact (BC) organic thin film transistors (OTFTs) with a gate in the bottom, using a benchmarked industry standard Atlas 2-D numerical device simulator. The parameters including drive current (Ids), mobility (μ), threshold voltage (Vt) and current on-off ratio (ION/IOFF) are analyzed from the device physics point of view on different electrode thicknesses, ranging from infinitesimal to 50 nm, for both top and bottom contact structures. Observations demonstrate that the performance of the BC structure is more affected by scaling of ts/d in comparison to its counterpart. In the linear region, the mobility is almost constant at all the values of ts/d for both structures. However, an increment of 18% and 83% in saturation region mobility is found for TC and BC structures, respectively with scaling down ts/d from 50-0 nm. Besides this, the current on-off ratio increases more sharply in the BC structure. This analysis simplifies a number of issues related to the design and fabrication of organic material based devices and circuits.

Key words: contact thicknessorganic semiconductororganic thin film transistorbottom contacttop contact structure

Abstract: This paper analyzes the impact of source (ts) and drain (td) contact thicknesses on top contact (TC) and bottom contact (BC) organic thin film transistors (OTFTs) with a gate in the bottom, using a benchmarked industry standard Atlas 2-D numerical device simulator. The parameters including drive current (Ids), mobility (μ), threshold voltage (Vt) and current on-off ratio (ION/IOFF) are analyzed from the device physics point of view on different electrode thicknesses, ranging from infinitesimal to 50 nm, for both top and bottom contact structures. Observations demonstrate that the performance of the BC structure is more affected by scaling of ts/d in comparison to its counterpart. In the linear region, the mobility is almost constant at all the values of ts/d for both structures. However, an increment of 18% and 83% in saturation region mobility is found for TC and BC structures, respectively with scaling down ts/d from 50-0 nm. Besides this, the current on-off ratio increases more sharply in the BC structure. This analysis simplifies a number of issues related to the design and fabrication of organic material based devices and circuits.

Key words: contact thicknessorganic semiconductororganic thin film transistorbottom contacttop contact structure



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ATLAS user's manual, device simulation software, Santa Clara, Silvaco International, 2012

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Jung K D, Kim Y C, Kim B J. An analytic current-voltage equation for top contact organic thin film transistors including the effects of variable series resistance[J]. Jpn J Appl Phys, 2008, 47: 3174. doi: 10.1143/JJAP.47.3174

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Resendiz L, Estrada M, Cerdeira A. Effect of active layer thickness on the electrical characteristics of polymer thin film transistors[J]. Org Electron, 2010, 11(9): 1920.

[28]

Zhang X A, Zhang J W, Zhang W F. Fabrication and comparative study of top-gate and bottom-gate ZnO-TFTs with various insulator layers[J]. J Mater Sci Mater Electron, 2010, 21(7): 671. doi: 10.1007/s10854-009-9975-3

[29]

Street R A, Salleo A. Contact effects in polymer transistors[J]. Appl Phys Lett, 2002, 81(15): 2887. doi: 10.1063/1.1512950

[30]

Mittal P, Kumar B, Kaushik B K. Organic thin film transistor architecture, parameters and their applications[J]. Proc IEEE Int Conf on Communication Systems and Network Technologies, Katra, 2011: 436.

[31]

Hill G. Numerical simulations of contact resistance in organic thin-film transistors[J]. Appl Phys Lett, 2005, 87(16): 163505. doi: 10.1063/1.2112189

[32]

Kano M, Minari T, Tsukagoshi K. Control of device parameters by active layer thickness in organic thin film transistors[J]. Appl Phys Lett, 2011, 98(7): 073307. doi: 10.1063/1.3555463

[33]

Pernstich K P, Haas S, Oberhoff D. Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator[J]. J Appl Phys, 2004, 96(11): 6431. doi: 10.1063/1.1810205

[34]

Sirringhaus H, Friend R H, Li X C. Bis (dithienothiophene) organic field effect transistors with a high ON/OFF ratio[J]. Appl Phys Lett, 1997, 71(26): 3871. doi: 10.1063/1.120529

[1]

Tobjork D, Osterbacka R. Paper electronics[J]. Adv Mater, 2011, 23(17): 1935. doi: 10.1002/adma.201004692

[2]

Marien H, Steyaert M S J, Veenendaal E V. A fully integrated ΣADC in organic thin film transistor technology on flexible plastic foil[J]. IEEE J Solid-State Circuits, 2011, 46: 276. doi: 10.1109/JSSC.2010.2073230

[3]

Lee J B, Subramanian V. Organic transistors on fiber:a first step toward electronic textiles[J]. IEDM Tech Dig, 2003: 8.3.1.

[4]

Ohode Y, Negi Y S, Suzuki Y, et al. Polyimide, polyamide-imide, polyamide-liquid crystal orienting film and display using same. Patent No. JP 4-055495 A2, Jpn Kokai Tokkyo Koho, 1992

[5]

Takamiya M, Sekitani T, Kato Y. An organic FET SRAM with back gate to increase static noise margin and its application to braille sheet display[J]. IEEE J Solid-State Circuits, 2007, 42(1): 93. doi: 10.1109/JSSC.2006.886578

[6]

Weimer P K. The TFT-a new thin-film transistor[J]. Proc IRE, 1962, 50: 1462. doi: 10.1109/JRPROC.1962.288190

[7]

LeComber P G, Spear W E, Ghaith A. Amorphous-silicon field-effect device and possible application[J]. Electron Lett, 1979, 15(6): 179. doi: 10.1049/el:19790126

[8]

Luo M F C, Chen I, Genovese F C. A thin film transistor for flat planel displays[J]. IEEE Trans Electron Devices, 1981, 28(6): 740. doi: 10.1109/T-ED.1981.20422

[9]

Waldrop J R. Electrical properties of ideal metal contacts to GaAs:Schottky-barrier height[J]. J Vac Sci Technol B, 1984, 2(3): 445. doi: 10.1116/1.582892

[10]

Warta W, Stehle R, Karl N. Ultrapure, high mobility organic photoconductors[J]. Appl Phys A, 1985, 36(3): 163. doi: 10.1007/BF00624938

[11]

Assadi A, Svensson C M, Willander O I. Field-effect mobility of poly (3-hexylthiophene)[J]. Appl Phys Lett, 1988, 53(3): 195. doi: 10.1063/1.100171

[12]

Kumar P, Jain S C, Kumar V. A model for the J-V characteristics of P3HT:PCBM solar cells[J]. J Appl Phys, 2009, 105(10): 104507. doi: 10.1063/1.3129320

[13]

Brianda D, Opreab A, Courbata J. Making environmental sensors on plastic foils[J]. Mater Today, 2011, 14(9): 416. doi: 10.1016/S1369-7021(11)70186-9

[14]

Liu P T, Chu LW. Innovative voltage driving pixel circuit using organic thin-film transistor for AMOLEDs[J]. J Display Technol, 2009, 5(6): 224. doi: 10.1109/JDT.2008.2005071

[15]

Guerin M, Daami A, Jacob S. High gain fully printed organic complementary circuits on flexible plastic foils[J]. IEEE Trans Electron Devices, 2011, 58(10): 3587. doi: 10.1109/TED.2011.2162071

[16]

Gupta D, Katiyar M, Gupta D. An analysis of the difference in behavior of top and bottom contact organic thin film transistors using device simulation[J]. Org Electron, 2012, 10(9): 775.

[17]

Li C, Pan F, Wang X. Effect of the work function of gate electrode on hysteresis characteristics of organic thin-film transistors with Ta2O5/polymer as gate insulator[J]. Org Electron, 2009, 10(5): 948. doi: 10.1016/j.orgel.2009.05.001

[18]

Li L, Chung K S, Jang J. Field effect mobility model in organic thin film transistor[J]. Appl Phys Lett, 2011, 98: 023305. doi: 10.1063/1.3543900

[19]

ATLAS user's manual, device simulation software, Santa Clara, Silvaco International, 2012

[20]

Shim C H, Maruoka F, Hattori R. Structural analysis on organic thin film transistor with device simulation[J]. IEEE Trans Electron Devices, 2010, 57(1): 195. doi: 10.1109/TED.2009.2035540

[21]

Horowitz G. Organic field-effect transistors[J]. Adv Mater, 1998, 10(5): 365. doi: 10.1002/(ISSN)1521-4095

[22]

Klauk H, Halik M, Zschieschang U. Pentacene organic transistors and ring oscillators on glass and on flexible polymeric substrates[J]. Appl Phys Lett, 2003, 82: 4175. doi: 10.1063/1.1579870

[23]

Watkins N J, Gao Y. Vacuum level alignment of pentacene on LiF/Au[J]. J Appl Phys, 2003, 94: 1289. doi: 10.1063/1.1585112

[24]

Jung K D, Kim Y C, Park B G. Modeling and parameter extraction for the series resistance in thin-film transistors[J]. IEEE Trans Electron Devices, 2009, 56: 431. doi: 10.1109/TED.2008.2010579

[25]

Jung K D, Kim Y C, Kim B J. An analytic current-voltage equation for top contact organic thin film transistors including the effects of variable series resistance[J]. Jpn J Appl Phys, 2008, 47: 3174. doi: 10.1143/JJAP.47.3174

[26]

Chiang C S, Martin S, Kanicki J. Top-gate staggered amorphous silicon thin-film transistors:series resistance and nitride thickness effects[J]. Jpn J Appl Phys, 1998, 37: 5914. doi: 10.1143/JJAP.37.5914

[27]

Resendiz L, Estrada M, Cerdeira A. Effect of active layer thickness on the electrical characteristics of polymer thin film transistors[J]. Org Electron, 2010, 11(9): 1920.

[28]

Zhang X A, Zhang J W, Zhang W F. Fabrication and comparative study of top-gate and bottom-gate ZnO-TFTs with various insulator layers[J]. J Mater Sci Mater Electron, 2010, 21(7): 671. doi: 10.1007/s10854-009-9975-3

[29]

Street R A, Salleo A. Contact effects in polymer transistors[J]. Appl Phys Lett, 2002, 81(15): 2887. doi: 10.1063/1.1512950

[30]

Mittal P, Kumar B, Kaushik B K. Organic thin film transistor architecture, parameters and their applications[J]. Proc IEEE Int Conf on Communication Systems and Network Technologies, Katra, 2011: 436.

[31]

Hill G. Numerical simulations of contact resistance in organic thin-film transistors[J]. Appl Phys Lett, 2005, 87(16): 163505. doi: 10.1063/1.2112189

[32]

Kano M, Minari T, Tsukagoshi K. Control of device parameters by active layer thickness in organic thin film transistors[J]. Appl Phys Lett, 2011, 98(7): 073307. doi: 10.1063/1.3555463

[33]

Pernstich K P, Haas S, Oberhoff D. Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator[J]. J Appl Phys, 2004, 96(11): 6431. doi: 10.1063/1.1810205

[34]

Sirringhaus H, Friend R H, Li X C. Bis (dithienothiophene) organic field effect transistors with a high ON/OFF ratio[J]. Appl Phys Lett, 1997, 71(26): 3871. doi: 10.1063/1.120529

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P Mittal, Y.S. Negi, R.K. Singh. Impact of source and drain contact thickness on the performance of organic thin film transistors[J]. J. Semicond., 2014, 35(12): 124002. doi: 10.1088/1674-4926/35/12/124002.

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Manuscript received: 01 June 2014 Manuscript revised: 15 July 2014 Online: Published: 01 December 2014

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