INVESTIGATION ON CNT BASED TRANSISTOR WITH COMPARATIVE ANALYSIS OF ZnO & Al 2 O 3 AS GATE DIELECTRICS

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 01, January 2019, pp , Article ID: IJMET_10_01_161 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed INVESTIGATION ON CNT BASED TRANSISTOR WITH COMPARATIVE ANALYSIS OF ZnO & Al 2 O 3 AS GATE DIELECTRICS S.K. Suresh Babu Centre for Research in Nanotechnology, Department of Nanoscience, VLSI Laboratory, Department of Electronics and Communication Engineering, Naveen Kumar Centre for Research in Nanotechnology, Department of Nanoscience, D. Jackuline Moni VLSI Laboratory, Department of Electronics and Communication Engineering, ABSTRACT The present study investigates on the single walled carbon nano tube (CNT) based transistor and with comparative analysis of Zinc Oxide (ZnO) and Aluminium Oxide (Al 2 O 3 ) as gate dielectric films. Structural properties of these gate dielectric films were analysed and reported. Array network of single walled carbon nanotube (SWCNT) was formed as a channel in field effect transistor (FET) by drop casting method. At room temperature gate dielectric (ZnO and Al 2 O 3 ) films were deposited by using pulsed laser deposition. Various electrical parameters were analysed for the fabricated SWCNT/Al 2 O 3 and SWCNT/ZnO FET s. The achieved threshold voltage (V TH ), I ON and I OFF are 0.6 Volts, -2.88mA and -2.19mA was observed for CNT/Al 2 O 3 FET and 0.2Volts, -2.19mA and -4.99mA was observed for CNT/ZnO FET respectively. Keywords: Carbon Nano Tube, Zinc Oxide, Aluminium Oxide, Drop casting, Pulsed laser deposition, Field effect transistor Cite this Article: S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni, Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al 2 O 3 as Gate Dielectrics, International Journal of Mechanical Engineering and Technology 10(1), 2019, pp editor@iaeme.com

2 S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni 1. INTRODUCTION In recent research, many researchers have shown attention towards carbon nanotube (CNT) based electronic devices due to its very good electrical and mechanical properties[1-3]. In this paper, CNT based transistor with two high K dielectric materials such as ZnO and Al 2 O 3 are fabricated as gate dielectric of FET and their DC characteristics are compared [4-7]. The highk material shows good impact on the replacement of SiO 2 used in the conventional transistor [8-9]. Single walled carbon nanotube is widely used as a channel, since it has remarkable properties like electrical, thermal conductivity, and good mechanical properties [10-11]. Single walled CNT is more suitable for the channel of thin film FET [12]. ZnO thin film acts as a good dielectric when it is deposited at room temperature (Amorphous) [13]. The amorphous Al 2 O 3 has high dielectric properties, low permittivity to impurities and high thermal conduction [14]. Pulsed laser deposition is another good technology tool used for the deposition of ZnO and Al 2 O 3 as gate dielectric films in the FET [15-16]. The atom from the target (Zno / Al 2 O 3 ) losses and collided with the high gas molecule (oxygen) and nucleation takes place, which results in deposition of ZnO / Al 2 O 3 thin film over the substrate. The source, drain and gate were deposited using gold by sputtering. 2. EXPERIMENTAL DETAILS: The used single walled CNT is less than of 90nm length and 99.9% of pure ZnO and Al 2 O 3 was obtained from Sigma-Aldrich, USA. ZnO and Al 2 O 3 are been made as pellet using pelletizer to use it as a target in PLD system to make films over the substrate. The gate dielectric materials ZnO and Al 2 O 3 are deposited as a thin film at room temperature [13-14]. (a) (b) editor@iaeme.com

3 Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al 2 O 3 as Gate Dielectrics (c) Figure 1 (a) XRD pattern of Al 2 O 3 thin film deposited using PLD at room temperature (b) XRD pattern of ZnO thin film deposited using PLD at room temperature (c) XRD pattern of CNT film prepared by drop casting method The amorphous nature of these films were confirmed with the obtained XRD results shown in figure 1(a),1(b) for XRD pattern of Al 2 O 3 and ZnO thin films respectively. Figure 1(c) shows that XRD pattern of SWCNT and Dimethylformamide (DMF) of film shows the crystalline structure. The peak was observed at 28, 47, 56 and hkl value was (002), (001), (400) respectively. Figure 2 (a) SEM image of Al 2 O 3 thin film Figure 2(b) SEM image of ZnO thin film Al 2 O 3 thin film deposited at room temperature using PLD shows uniformity deposition and cluster formation was observed in SEM image figure 2(a). From these results, it s clear that the film formation is all over the substrate. Figure 2 (b) shows the SEM image of ZnO thin film. It confirms the uniform deposition and spherical formational growth Device Fabrication The gold was used as a back gate for the CNT/Al 2 O 3 and CNT/ZnO fabricated FET s. ~50nm thickness of gold was deposited on a glass substrate by DC sputtering. ZnO (8.5) and editor@iaeme.com

4 S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni Al 2 O 3 (10) have good dielectric constant than the conventional gate dielectric constant of SiO 2 in FET. Approximately 45nm was deposited over the gate layer by Pulsed Laser Deposition with the following conditions: 3000 pulse of laser energy with vacuum condition of 9.6x10-6 Torr of base pressure under the oxygen environment. The Single walled Carbon Nanotube is used as a channel for the proposed fabrication of FET. These SWCNT are dispersed with dimethyformamide by 1:1 ratio and it has been deposited as channel by drop casting method on the glass substrate. It is one of the simplest and cost effective deposition methods of the channel. Figure 3(a) and (b) show the schematic structure of fabricating used fabricating CNT/Al 2 O 3 and CNT/ZnO FET. For both the devices all the fabrication steps are the same except the gate dielectric. Gate, Source and drain are deposited by gold by DC sputtering under the vacuum condition. It is deposited at the thickness of ~45 nm. (a) (b) Figure 3 Fabricated structure of carbon nanotube thin film FET with 2.2. Electrical Analysis of Fabricated FET (a) CNT/ Al 2 O 3 film and (b) CNT/ZnO film configuration Figure 4 Current Voltage characteristics of CNT film The resistance of the channel (CNT film) of the FET was observed after depositing source and drain which is shown in figure 4. This graph helps us to understand the channel was editor@iaeme.com

5 Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al 2 O 3 as Gate Dielectrics resistive and allow the electron to pass after the threshold voltage. This also proves that there is a interlink of carbon nano tubes between the source and drain. (a) (b) Figure 5 (a) Transfer characteristics of Al2O3/SWCNT FET (b) Transfer characteristics of ZnO/SWCNT FET The threshold voltage of the fabricated FET s was calculated from the transfer characteristics. To obrain the threshold the the square root of drain current was considered with the varying gate voltage (V GS ) and with constant drain voltage (V DS ). For CNT/Al 2 O 3 FET the threshold voltage was observed as 0.6 volts and CNT/ZnO FET as 0.2 Volts as shown in figure 5 and 6 respectively. From this results the ZnO/CNT has low threshold voltage than the CNT/Al 2 O 3 FET. Figure 6 Logarithmic scale of drain current (I D ) Vs gate source voltage: (a) CNT/Al 2 O 3 FET (b) CNT/ZnO FET The on current and off current of the fabricated devices were observed from the logarithmic scale of drain current to the gate voltage. There is good I ON and I OFF current was observed for the Al 2 O 3 /CNT FET than the ZnO/CNT FET. The electrical parameters of the Al 2 O 3 /CNT FET and ZnO/CNT FET were tabulated in Table editor@iaeme.com

6 S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni Table 1 Compartive electrical results of Al 2 O 3 /CNT FET and ZnO/CNT FET Threshold Voltage (V TH ) On current (I ON ) Off current (I OFF ) Al 2 O 3 ZnO Al 2 O 3 ZnO Al 2 O 3 ZnO 0.6V 0.2V ma ma -6 ma ma From the results obtained it is clear that the CNT/ZnO FET over performed in on current (I ON ) and threshold voltage (V TH ), but in the case of off current (I OFF ) CNT/ l 2 O 3 FET was observed good response than the CNT/ZnO FET. This is due to high dielectric constant of Al 2 O 3 than the ZnO. From the observed results CNT/ZnO FET shows better response in case of gate dielectric than the CNT/ Al 2 O CONCLUSIONS The XRD pattern of ZnO and Al 2 O 3 thin films obtained confirms that the films are in amorphous, which has better dielectric property than the other crystalline films. From SEM image the uniformity coating was observed for films. CNT/ZnO and CNT/ Al 2 O 3 FET s were been fabricated by various techniques like drop casting, pulsed laser deposition and sputtering. The comparative electrical studies of these FET were carried out and reported as threshold voltage (V TH ), I ON and I OFF are 0.6 Volts, -2.88mA and -2.19mA was observed for CNT/Al 2 O 3 FET and 0.2Volts, -2.19mA and -4.99mA was observed for CNT/ZnOT FET. Among these results, the CNT/ZnO FET shows better response than the CNT/ Al 2 O 3 FET in terms of high leakage current. REFERENCES [1] Sharma P, Ahuja P. Recent advances in carbon nanotube-based electronics. Materials Research Bulletin Oct 2;43(10): [2] Avouris P, Appenzeller J, Martel R, Wind SJ. Carbon nanotube electronics. Proceedings of the IEEE Nov;91(11): [3] Avouris P, Chen J. Nanotube electronics and optoelectronics. Materials Today Oct 1;9(10) pp: [4] Carcia PF, McLean RS, Reilly MH. High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition. Applied physics letters Mar 20;88(12): [5] Lee K, Kim JH, Im S, Kim CS, Baik HK. Low-voltage-driven top-gate ZnO thin-film transistors with polymer/high-k oxide double-layer dielectric. Applied Physics Letters Sep 25;89(13): [6] Xuan Y, Wu YQ, Shen T, Yang T, Ye PD. High performance submicron inversion-type enhancement-mode InGaAs MOSFETs with ALD Al2O3, HfO2 and HfAlO as gate dielectrics. IEDM Tech. Dig Dec 10;637:640. [7] Cheng CC, Chien CH, Luo GL, Liu JC, Kei CC, Liu DR, Hsiao CN, Yang CH, Chang CY. Characteristics of atomic-layer-deposited Al2O3 high-k dielectric films grown on Ge substrates. Journal of The Electrochemical Society Oct 1;155(10):G editor@iaeme.com

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