J. Semicond. > 2014, Volume 35 > Issue 12 > 124002, doi: 10.1088/1674-4926/35/12/124002
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SEMICONDUCTOR DEVICES

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

Poornima Mittal1, 3, , Y.S. Negi2 and R.K. Singh3

+ Author Affiliations

 Corresponding author: Poornima Mittal, Email:poornima2822@gmail.com

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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 thickness, organic semiconductor, organic thin film transistor, bottom contact, top contact structure



[1]
Tobjork D, Osterbacka R. Paper electronics. Adv Mater, 2011, 23(17):1935 doi: 10.1002/adma.201004692
[2]
Marien H, Steyaert M S J, Veenendaal E V, et al. A fully integrated ΣADC in organic thin film transistor technology on flexible plastic foil. 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. 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, et al. An organic FET SRAM with back gate to increase static noise margin and its application to braille sheet display. 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. 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. 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. 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 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. 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). Appl Phys Lett, 1988, 53(3):195 doi: 10.1063/1.100171
[12]
Kumar P, Jain S C, Kumar V, et al. A model for the J-V characteristics of P3HT:PCBM solar cells. J Appl Phys, 2009, 105(10):104507 doi: 10.1063/1.3129320
[13]
Brianda D, Opreab A, Courbata J, et al. Making environmental sensors on plastic foils. 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 Display Technol, 2009, 5(6):224 doi: 10.1109/JDT.2008.2005071
[15]
Guerin M, Daami A, Jacob S, et al. High gain fully printed organic complementary circuits on flexible plastic foils. 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. Org Electron, 2012, 10(9):775
[17]
Li C, Pan F, Wang X, et al. Effect of the work function of gate electrode on hysteresis characteristics of organic thin-film transistors with Ta2O5/polymer as gate insulator. 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. 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. IEEE Trans Electron Devices, 2010, 57(1):195 doi: 10.1109/TED.2009.2035540
[21]
Horowitz G. Organic field-effect transistors. Adv Mater, 1998, 10(5):365 doi: 10.1002/(ISSN)1521-4095
[22]
Klauk H, Halik M, Zschieschang U, et al. Pentacene organic transistors and ring oscillators on glass and on flexible polymeric substrates. 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 Appl Phys, 2003, 94:1289 doi: 10.1063/1.1585112
[24]
Jung K D, Kim Y C, Park B G, et al. Modeling and parameter extraction for the series resistance in thin-film transistors. IEEE Trans Electron Devices, 2009, 56:431 doi: 10.1109/TED.2008.2010579
[25]
Jung K D, Kim Y C, Kim B J, et al. An analytic current-voltage equation for top contact organic thin film transistors including the effects of variable series resistance. Jpn J Appl Phys, 2008, 47:3174 doi: 10.1143/JJAP.47.3174
[26]
Chiang C S, Martin S, Kanicki J, et al. Top-gate staggered amorphous silicon thin-film transistors:series resistance and nitride thickness effects. Jpn J Appl Phys, 1998, 37:5914 doi: 10.1143/JJAP.37.5914
[27]
Resendiz L, Estrada M, Cerdeira A, et al. Effect of active layer thickness on the electrical characteristics of polymer thin film transistors. Org Electron, 2010, 11(9):1920
[28]
Zhang X A, Zhang J W, Zhang W F, et al. Fabrication and comparative study of top-gate and bottom-gate ZnO-TFTs with various insulator layers. 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. Appl Phys Lett, 2002, 81(15):2887 doi: 10.1063/1.1512950
[30]
Mittal P, Kumar B, Kaushik B K, et al. Organic thin film transistor architecture, parameters and their applications. 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. Appl Phys Lett, 2005, 87(16):163505 doi: 10.1063/1.2112189
[32]
Kano M, Minari T, Tsukagoshi K, et al. Control of device parameters by active layer thickness in organic thin film transistors. Appl Phys Lett, 2011, 98(7):073307 doi: 10.1063/1.3555463
[33]
Pernstich K P, Haas S, Oberhoff D, et al. Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator. J Appl Phys, 2004, 96(11):6431 doi: 10.1063/1.1810205
[34]
Sirringhaus H, Friend R H, Li X C, et al. Bis (dithienothiophene) organic field effect transistors with a high ON/OFF ratio. Appl Phys Lett, 1997, 71(26):3871 doi: 10.1063/1.120529
Fig. 1.  Bottom gate OTFT schematics with (a) BGTC and (b) BGBC OTFT structures.

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Fig. 2.  Equivalent circuit of OTFT, demonstrating source, drain, bulk and channel resistances along with internal source ($V'_{\rm s})$ and drain ($V'_{\rm d})$ voltages at the channel ends[24].

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Fig. 3.  Output characteristics for (a) top and (b) bottom contact OTFT structures.

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Fig. 4.  Output characteristics for (a) BGTC and (b) BGBC structure with $t_{\rm s/d}$ varying from 0 to 50 nm at $V_{\rm gs}$ $=$ -40 V.

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Fig. 5.  Linear and saturation region mobility of (a) top and (b) bottom contact structures as a function of $t_{\rm s/d}$.

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Fig. 6.  Characteristic plot of $V_{\rm t, lin}$ and $V_{\rm t, sat}$ for top and bottom contact structures as a function of $t_{\rm s/d}$.

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Fig. 7.  $I_{\rm ON}$/$I_{\rm OFF}$ as a function of $t_{\rm s/d}$ for top and bottom contact structures at $V_{\rm gs}$ $=$ $-40$ V.

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Table 1.   Device dimensions and materials of BGTC and BGBC OTFTs[20].

Table 2.   entacene semiconductor, insulator and contact electrode material properties used for simulation of top and bottom contact OTFTs.
[1]
Tobjork D, Osterbacka R. Paper electronics. Adv Mater, 2011, 23(17):1935 doi: 10.1002/adma.201004692
[2]
Marien H, Steyaert M S J, Veenendaal E V, et al. A fully integrated ΣADC in organic thin film transistor technology on flexible plastic foil. 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. 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, et al. An organic FET SRAM with back gate to increase static noise margin and its application to braille sheet display. 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. 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. 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. 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 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. 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). Appl Phys Lett, 1988, 53(3):195 doi: 10.1063/1.100171
[12]
Kumar P, Jain S C, Kumar V, et al. A model for the J-V characteristics of P3HT:PCBM solar cells. J Appl Phys, 2009, 105(10):104507 doi: 10.1063/1.3129320
[13]
Brianda D, Opreab A, Courbata J, et al. Making environmental sensors on plastic foils. 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 Display Technol, 2009, 5(6):224 doi: 10.1109/JDT.2008.2005071
[15]
Guerin M, Daami A, Jacob S, et al. High gain fully printed organic complementary circuits on flexible plastic foils. 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. Org Electron, 2012, 10(9):775
[17]
Li C, Pan F, Wang X, et al. Effect of the work function of gate electrode on hysteresis characteristics of organic thin-film transistors with Ta2O5/polymer as gate insulator. 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. 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. IEEE Trans Electron Devices, 2010, 57(1):195 doi: 10.1109/TED.2009.2035540
[21]
Horowitz G. Organic field-effect transistors. Adv Mater, 1998, 10(5):365 doi: 10.1002/(ISSN)1521-4095
[22]
Klauk H, Halik M, Zschieschang U, et al. Pentacene organic transistors and ring oscillators on glass and on flexible polymeric substrates. 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 Appl Phys, 2003, 94:1289 doi: 10.1063/1.1585112
[24]
Jung K D, Kim Y C, Park B G, et al. Modeling and parameter extraction for the series resistance in thin-film transistors. IEEE Trans Electron Devices, 2009, 56:431 doi: 10.1109/TED.2008.2010579
[25]
Jung K D, Kim Y C, Kim B J, et al. An analytic current-voltage equation for top contact organic thin film transistors including the effects of variable series resistance. Jpn J Appl Phys, 2008, 47:3174 doi: 10.1143/JJAP.47.3174
[26]
Chiang C S, Martin S, Kanicki J, et al. Top-gate staggered amorphous silicon thin-film transistors:series resistance and nitride thickness effects. Jpn J Appl Phys, 1998, 37:5914 doi: 10.1143/JJAP.37.5914
[27]
Resendiz L, Estrada M, Cerdeira A, et al. Effect of active layer thickness on the electrical characteristics of polymer thin film transistors. Org Electron, 2010, 11(9):1920
[28]
Zhang X A, Zhang J W, Zhang W F, et al. Fabrication and comparative study of top-gate and bottom-gate ZnO-TFTs with various insulator layers. 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. Appl Phys Lett, 2002, 81(15):2887 doi: 10.1063/1.1512950
[30]
Mittal P, Kumar B, Kaushik B K, et al. Organic thin film transistor architecture, parameters and their applications. 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. Appl Phys Lett, 2005, 87(16):163505 doi: 10.1063/1.2112189
[32]
Kano M, Minari T, Tsukagoshi K, et al. Control of device parameters by active layer thickness in organic thin film transistors. Appl Phys Lett, 2011, 98(7):073307 doi: 10.1063/1.3555463
[33]
Pernstich K P, Haas S, Oberhoff D, et al. Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator. J Appl Phys, 2004, 96(11):6431 doi: 10.1063/1.1810205
[34]
Sirringhaus H, Friend R H, Li X C, et al. Bis (dithienothiophene) organic field effect transistors with a high ON/OFF ratio. Appl Phys Lett, 1997, 71(26):3871 doi: 10.1063/1.120529

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    Received: 01 June 2014 Revised: 15 July 2014 Online: Published: 01 December 2014

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      Article Navigation >  Journal of Semiconductors  > 2014  >  35(12): 124002
      Poornima Mittal, Y.S. Negi, R.K. Singh. Impact of source and drain contact thickness on the performance of organic thin film transistors[J]. Journal of Semiconductors, 2014, 35(12): 124002. doi: 10.1088/1674-4926/35/12/124002 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.Export: BibTex EndNote
      Citation:
      Poornima Mittal, Y.S. Negi, R.K. Singh. Impact of source and drain contact thickness on the performance of organic thin film transistors[J]. Journal of Semiconductors, 2014, 35(12): 124002. doi: 10.1088/1674-4926/35/12/124002

      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.
      Export: BibTex EndNote
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      Impact of source and drain contact thickness on the performance of organic thin film transistors

      doi: 10.1088/1674-4926/35/12/124002
      • 1.

        Department of Electronics & Communication Engineering, Graphic Era University, Dehradun-248002, India

      • 2.

        Department of Polymer and Process Engineering, Indian Institute of Technology, Roorkee-246776, India

      • 3.

        Department of Electronics & Communication Engineering, Uttarakhand Technical University, Dehradun-248002, India

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      • Corresponding author: Poornima Mittal, Email:poornima2822@gmail.com
      • Received Date: 2014-06-01
      • Revised Date: 2014-07-15
      • Published Date: 2014-12-01

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