Analysis And Parameter Extraction of Organic Transistor At PTAA With Different Organic Materials Anuradha Yadav, Savita Yadav, Sanjay Singh, Nishant Tripathi Abstract The Organic thin film transistor has made significant progress in the recent past in achieving high performance in terms of mobility, I on/i off current ratio, threshold voltage, sub threshold voltage and transconductance, still faces a number of challenges at the fabrication, materials and device physics level. In this paper we are using PTAA with different insular combination and form organic transistor and compare other material in basis of mobility, threshold voltage, and transconductance, on/off ratio, Sub-threshold slope, ID min and ID max. Index Terms PTAA, OSC, OTET, P3HT, dielectric, transconductance, sub-threshold voltage. 1 INTRODUCTION Recently there has been remarkable interest on organic electronics because of their unique advantages such as low cost fabrication, light weight and mechanical flexibility. The contemporary portable communication and computing devices need light weight, high image quality, thin and low power flat panel displays. The answer to this need is Organic Thin Film Transistor (OTFT). It is likely to have suitable applications requiring large area coverage, structural flexibility and low cost which was not possible with crystalline silicon [1].However, the innovative human mind soon searched a novel class of TFTs based on organic or polymeric semiconductor as active layer material that shows amazing possibility for integration onto flexible plastic substrates, thus giving the world an idea of futuristic technology of low cost, thin, printable electronics, flexible and light weight displays [2]. Organic thin film transistors (OTFT) have made impressive progress over the last decade. Organic electronics allows us the option of making devices that are cheap, flexible and just smart enough to perform the task in hand. Electronic price tags, chemical sensors, information displays, electronic paper and low cost microelectronics are among potential applications. 2 PTAA WITH DIFFERENT INSULATOR COMBINATION Here the dimension of device kept same, but the organic semiconductor and dielectric material has been changed. PTAA is used as OSC in place of P3HT. The band gap of PTAA is taken as 3.3eV, density of both valance band (NV) and conduction band (NC) states as 2.88*1021 cm3, mobility of holes and electrons as 0.7 and 5*10-5cm2/V-sec. 2.1 PTAA with Al2O3+SAM dielectric Fig.1(a) Simulated Structure (b) Output characteristics Anuradha Yadav is currently pursuing masters degree program in ED&T in NIELIT Gorakhpur, India PH-07428683431. E-mail: anuec25@gmail.com Savita Yadav is currently pursuing masters degree program in ED&T in NIELIT Gorakhpur, India PH-09198853333. E-mail: savi07a@gmail.com Sanjay Singh is currently working as a Assistant Professor in BIT GIDA Gorakhpur, India PH-09450890613. E-mail: dcsanjaypm@gmail.com Nishant Tripathi is currently working as a Scientist-B in NIELIT Gorakhpur, India PH-099838200621. E-mail: nishanttri@gmail.com The dimension of device is same as discussed above, only gate dielectric has been changed. In Fig.1 (a) Al2O3+SAM layer has chosen as dielectric, which has dielectric constant of 4.5 and due to which capacitance of dielectric has been also changed i.e. 0.7 µf/cm2. Fig.1 (b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vg sis kept constant and curves are drawn for Vgs 0V,-1.5V, - 1.8V, -2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -6.10*10-21 Amp. at constant Vgs 0V and max current is -1.44*10-08Amp. at constant Vgs -3V. 108
Fig.2 (a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.2 (a) shows the transfer characteristic of top contact constant at -1.5 V. Here It can be seen from fig.2 (b) log 10Id vsvgs curve, that Vgs is varied with a step of -0.5 V from -3V to -0V and Id varies from -4.54*10-24Amp to -1.40*10-08 Amp. This curve is drawn in saturation region, keeping Vds 2.2 PTAA with HfO2 dielectric Fig.4 (a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.4(a) shows the transfer characteristic of top contact bottom gate organic thin film transistor with gate voltage Vgs varying with step 0.5 V from 0V to -3V and Vds is kept constant at -1.5 V. Here It can be seen from fig 4.16.2 (b) log 10Id vsvgs curve, that Vgs is varied with a step of -0.5 V from -3V to -0V and Id varies from - 1.67*10-24Amp to -6.35*10-08 Amp.This curve is drawn in saturation region, keeping Vds 2.3 PTAA with Fluor polymer dielectric The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.5(a) Fluor polymer layer has chosen as dielectric, which has dielectric constant of 2.1 and due to which capacitance of dielectric has been also changed i.e. 0.33 µf/cm 2. Fig.3 (a) Simulated Structure (b) Output characteristics The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.3 (a) HfO2 layer has chosen as dielectric, which has dielectric constant of 22 and due to which capacitance of dielectric has been also changed i.e. 3.4 µf/cm2. Fig.3(b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgsis kept constant and curves are drawn for Vgs 0V,-1.5V, - 1.8V, -2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -4.06*10-21 Amp. at constant Vgs 0V and max current is -6.46*10-08Amp. at constant Vgs -3V. Fig.5 (a) Simulated Structure (b) Output characteristics Fig.5(b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgs is kept constant and curves are drawn for Vgs 0V,-1.5V, -1.8V, - 2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -8.6*10-21 Amp. at constant Vgs 0V and max current is -4.16*10-09Amp. at constant Vgs -3V. 109
Fig,6 (a) Transfer characteristics (Id - Vgs) at Vds= - 1.5 V Fig.6(a) shows the transfer characteristic of top contact bottom gate organic thin film transistor with gate voltage Vgs varying with step 0.5 V from 0V to -3V and Vds is kept constant at -1.5 V. Here It can be seen from fig.6(b) log 10Id vsvgs curve, that Vgs is varied with a step of - 0.5 V from -3V to -0V and Id varies from -2.21*10-22Amp to -4.03*10-09 Amp.This curve is drawn in saturation region, keeping Vds Fig.8(a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.8(a) shows the transfer characteristic of top contact bottom gate organic thin film transistor with gate voltage Vgs varying with step 0.5 V from 0V to -3V and Vds is kept constant at -1.5 V. Here It can be seen from fig.8(b) log 10 Id vsvgs curve, that Vgs is varied with a step of -0.5 V from -3V to -0V and Id varies from -5.47*10-23 Amp to -5.92*10-09 Amp.This curve is drawn in saturation region, keeping Vds 2.5 PTAA with CYTOP dielectric 2.4 PTAA with PMMA dielectric Fig.9(a) Simulated Structure (b) Output characteristics (I d- V d ) for different constant Vgs values Fig.7(a) Simulated Structure (b) Output characteristics The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.7(a) PMMA layer has chosen as dielectric, which has dielectric constant of 3.5 and due to which capacitance of dielectric has been also changed i.e. 0.54 µf/cm 2. Fig.7(b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgs is kept constant and curves are drawn for Vgs 0V,-1.5V, -1.8V, - 2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -4.59*10-21 Amp. at constant Vgs 0V and max current is -6.11*10-09 Amp. at constant Vgs -3V. The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.9(a) CYTOP layer has chosen as dielectric, which has dielectric constant of 2.2 and due to which capacitance of dielectric has been also changed i.e. 0.34 µf/cm 2. Fig.9(b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgsis kept constant and curves are drawn for Vgs 0V,-1.5V, -1.8V, - 2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -7.37*10-22 Amp. at constant Vgs 0V and max current is -4.31*10-09 Amp. at constant Vgs -3V. 110
Fig.10(a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.10(a) shows the transfer characteristic of top contact constant at -1.5 V. Here It can be seen from fig 4.19.2 (b) log 10Id vsvgs curve, that Vgs is varied with a step of -0.5 V from - 3V to -0V and Id varies from -2.14*10-22 Amp to -4.17*10-09 Amp.This curve is drawn in saturation region, keeping Vds 2.6 PTAA with SiO2 dielectric The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.11 (a) SiO2 layer has chosen as dielectric, which has dielectric constant of 3.9 and due to which capacitance of dielectric has been also changed i.e. 0.61 µf/cm 2. Here Si is used as contacts in place of Al, which has work function of 4.6 ev. Fig.12 (a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.12 (a) shows the transfer characteristic of top contact constant at -1.5 V. Here It can be seen from fig.12 (b) log 10 Id vsvgs curve, that Vgs is varied with a step of -0.5 V from -3V to -0V and Id varies from -1.87*10-20 Amp to -1.93*10-08 Amp.This curve is drawn in saturation region, keeping Vds 2.7 PTAA with Al2O3 dielectric Fig.13 (a) Simulated Structure (b) Output characteristics (I d- V d ) for different constant Vgs values Fig.11 (a) Simulated Structure (b) Output characteristics Fig.11 (b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to -0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgsis kept constant and curves are drawn for Vgs 0V,-1.5V, -1.8V, -2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -5.08*10-21 Amp. at constant Vgs 0V and max current is -2.03*10-08 Amp. at constant Vgs -3V. The dimension of device is kept same as discussed above, only gate dielectric has been changed. In Fig.13 (a) Al2O3 layer has chosen as dielectric, which has dielectric constant of 9.1 and due to which capacitance of dielectric has been also changed i.e. 1.41 µf/cm 2. Fig.13 (b) shows the output characteristics for top contact bottom gate organic thin film transistor with drain voltage varying with step of -0.05V from 0 to - 0.5V then vary the step with 0.5 from 0.5 to -3V. Here Vgsis kept constant and curves are drawn for Vgs 0V,-1.5V, -1.8V, -2.1V, 2.4V, 2.7V, 3V. The drain source voltage Vds is varied. In this curve, the lowest current is -8.62*10-22 Amp. at constant Vgs 0V and max current is -2.82*10-08 Amp. at constant Vgs -3V. 111
Fig.14 (a) Transfer characteristics (Id - Vgs) at Vds= -1.5 V Fig.14(a) shows the transfer characteristic of top contact constant at -1.5 V. Here It can be seen from fig 4.21.2 (b) log 10Id vs Vgs curve, that Vgs is varied with a step of -0.5 V from -3V to -0V and Id varies from -1.80*10-23 Amp to -2.74*10-08 Amp.This curve is drawn in saturation region, keeping Vds 3 PARAMETER EXTRACTION FOR DIFFERENT DIELECTRIC MATERIAL COMBINATION WITH PTAA The performance parameters such as mobility, threshold voltage, Sub-threshold slope, transconductance, ON/OFF current ratio are extracted from characteristic plots of various OTFT structures. The resulting characteristics parameter values are presented in following table. combination 2 is much higher than other material combinations and I d(min) in material combination 2 is much lower than other material combinations even with the same channel length, width and other dimension. The linear mobility, saturation mobility and transconductance values are higher in material combination 2 than other combinations. Subthreshold voltage and threshold values are lower for material combination 2 and material combination 6.I on /I off current ratio is highest for material combination 2.So high I on /I off current ratio is required to fabricate and designing display and memory devices. So from the table, It can be concluded that the material combination 2 shows better performance as compared to other material combinations in terms of drain current, mobility, transconductance and I on /I off current ratio and sub-threshold voltage 4 CONCLUSION This paper describes about the simulated device structure and output characteristics (I d-v d) for different constant Vgs values. This also describes transfer characteristics (Id-Vgs) at Vds=-1.5V and Log 10 Id Vs Vgs curve at Vds = -1.5 V. These simulated structures and characteristics are drawn for pentacene with different insulators, PTAA with different insulators. A comparative analysis of various OTFTs with different material combination has been done using Silvaco ATLAS two dimensional finite element dependent numerical device simulations. The performance of material combination pentacene-hfo2-au-al is better in terms of Max. I on, Max. transconductance g m, Max. µ sat, Max. µ lin and material combination PTAA-HfO2-Au-Al is better in terms of Min. I off, Max. I on/i off ratio, Min. Sub-threshold slope voltage SS but material combination Pentacene-SiO2-Au-Si is better than other material combinations in terms of Min. V T. Now a particular material combination can be chosen according to our application The above table summarizes the extracted parameters for different dielectric material combination with P3HT.It is noted from the table that the max current I d(max) in material ACKNOWLEDGMENT I feel a sense of deep self-satisfaction and a great experience of having accomplished my paper entitled DESIGN OF PI CONTROLLER TO MINIMIZE THE SPEED ERROR OF D.C. SERVO MOTOR. I would like to extend my gratitude and my sincere thanks to my honorable Sh.H.P.Shukla, Director in NIELIT, Gorakhpur, U.P., India 273010. I am also grateful to Sh.S.K.Singh, HOD of ED&T in NIELIT, Gorakhpur, U.P., India 273010, for providing a solid background for my studies and research thereafter. I feel pleasure to express my profound gratitude to Sh.Nishant Tripathi for their valuable encouragement, timely suggestions and continuous support and providing me with all the necessary information. REFERENCES [1] O. Marinov and M. Jamal Deen, Performance of Organic thin film transistors, J. Vac. Sci. Technol. B. vol. 24, no. 4, 2006. [2] M. J. Deen, M. H. Kazemeini, and S. Holdcroft, Contact effects and extraction of intrinsic parameters in poly (3- alkylthiophene) P3AT thin-film field effect transistors, J. Appl. Phys., vol 103, no. 12, pp. 124 509 (1-7), Jun. 2008. [3] Poornima Mittal, Brijesh Kumar, B.K. Kaushikand Y.S. Negi, Organic Thin Film Transistor Architecture, Parameters and their Applications, Proc. IEEE Int. Conf. 112
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