International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 01, January 2019, pp. 1581–1587, Article ID: IJMET_10_01_161 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=1 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed INVESTIGATION ON CNT BASED TRANSISTOR WITH COMPARATIVE ANALYSIS OF ZnO & Al2O3 AS GATE DIELECTRICS S.K. Suresh Babu Centre for Research in Nanotechnology, Department of Nanoscience, Karunya Institute of Technology and Sciences, India VLSI Laboratory, Department of Electronics and Communication Engineering, Karunya Institute of Technology and Sciences, India Naveen Kumar Centre for Research in Nanotechnology, Department of Nanoscience, Karunya Institute of Technology and Sciences, India D. Jackuline Moni VLSI Laboratory, Department of Electronics and Communication Engineering, Karunya Institute of Technology and Sciences, India 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 (Al2O3) 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 Al2O3) films were deposited by using pulsed laser deposition. Various electrical parameters were analysed for the fabricated SWCNT/Al2O3 and SWCNT/ZnO FET’s. The achieved threshold voltage (VTH), ION and IOFF are 0.6 Volts, -2.88mA and -2.19mA was observed for CNT/Al2O3 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 & Al2O3 as Gate Dielectrics, International Journal of Mechanical Engineering and Technology 10(1), 2019, pp. 1581–1587. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=1 http://www.iaeme.com/IJMET/index.asp 1581 editor@iaeme.com 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 Al2O3 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 SiO2 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 Al2O3 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 Al2O3 as gate dielectric films in the FET [15-16]. The atom from the target (Zno / Al2O3) losses and collided with the high gas molecule (oxygen) and nucleation takes place, which results in deposition of ZnO / Al2O3 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 Al2O3was obtained from Sigma-Aldrich, USA. ZnO and Al2O3 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 Al2O3 are deposited as a thin film at room temperature [13-14]. (a) (b) http://www.iaeme.com/IJMET/index.asp 1582 editor@iaeme.com Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al2O3 as Gate Dielectrics (c) Figure 1 (a) XRD pattern of Al2O3 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 Al2O3 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 Al2O3 thin film Figure 2(b) SEM image of ZnO thin film Al2O3 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. 2.1. Device Fabrication The gold was used as a back gate for the CNT/Al2O3 and CNT/ZnO fabricated FET’s. ~50nm thickness of gold was deposited on a glass substrate by DC sputtering. ZnO (8.5) and http://www.iaeme.com/IJMET/index.asp 1583 editor@iaeme.com S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni Al2O3(10) have good dielectric constant than the conventional gate dielectric constant of SiO2 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/Al2O3 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 (a) CNT/ Al2O3 film and (b) CNT/ZnO film configuration 2.2. Electrical Analysis of Fabricated FET 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 http://www.iaeme.com/IJMET/index.asp 1584 editor@iaeme.com Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al2O3 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 (VGS) and with constant drain voltage (VDS). For CNT/Al2O3 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/Al2O3 FET. Figure 6 Logarithmic scale of drain current (ID) Vs gate source voltage: (a) CNT/Al2O3 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 ION and IOFF current was observed for the Al2O3/CNT FET than the ZnO/CNT FET. The electrical parameters of the Al2O3/CNT FET and ZnO/CNT FET were tabulated in Table 1. http://www.iaeme.com/IJMET/index.asp 1585 editor@iaeme.com S.K. Suresh Babu, Naveen Kumar, D. Jackuline Moni Table 1 Compartive electrical results of Al2O3/CNT FET and ZnO/CNT FET Threshold Voltage (VTH) On current (ION) Off current (IOFF) Al2O3 ZnO Al2O3 ZnO Al2O3 ZnO 0.6V 0.2V -2.88 mA -2.19 mA -6 mA -4.99 mA From the results obtained it is clear that the CNT/ZnO FET over performed in on current (ION) and threshold voltage (VTH), but in the case of off current (IOFF) CNT/ l2O3 FET was observed good response than the CNT/ZnO FET. This is due to high dielectric constant of Al2O3 than the ZnO. From the observed results CNT/ZnO FET shows better response in case of gate dielectric than the CNT/ Al2O3. 3. CONCLUSIONS The XRD pattern of ZnO and Al2O3 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/ Al2O3 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 (VTH), ION and IOFF are 0.6 Volts, -2.88mA and -2.19mA was observed for CNT/Al2O3 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/ Al2O3 FET in terms of high leakage current. REFERENCES [1] Sharma P, Ahuja P. Recent advances in carbon nanotube-based electronics. Materials Research Bulletin. 2008 Oct 2;43(10):2517-26. [2] Avouris P, Appenzeller J, Martel R, Wind SJ. Carbon nanotube electronics. Proceedings of the IEEE. 2003 Nov;91(11):1772-84. [3] Avouris P, Chen J. Nanotube electronics and optoelectronics. Materials Today. 2006 Oct 1;9(10) pp:46-54. [4] Carcia PF, McLean RS, Reilly MH. High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition. Applied physics letters. 2006 Mar 20;88(12):123509. [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. 2006 Sep 25;89(13):133507. [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. 2007 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. 2008 Oct 1;155(10):G203-8. http://www.iaeme.com/IJMET/index.asp 1586 editor@iaeme.com Investigation on CNT Based Transistor with Comparative Analysis of ZnO & Al2O3 as Gate Dielectrics [8] Vellianitis G, Apostolopoulos G, Mavrou G, Argyropoulos K, Dimoulas A, Hooker JC, Conard T, Butcher M. MBE lanthanum-based high-k gate dielectrics as candidates for SiO2 gate oxide replacement. Materials Science and Engineering: B. 2004 Jun 15;109(13):85-8. [9] Chau R. Advanced Metal Gate/High-K Dielectric Stacks for High-Performance CMOS Transistors. InAVS 5th Int. Microelectronics Interfaces Conf 2004 Mar 1 (pp. 3-5). [10] Allaoui A, Bai S, Cheng HM, Bai JB. Mechanical and electrical properties of a MWNT/epoxy composite. Composites science and technology. 2002 Nov 1;62(15):19938. [11] Flahaut E, Peigney A, Laurent C, Marliere C, Chastel F, Rousset A. Carbon nanotube– metal–oxide nanocomposites: microstructure, electrical conductivity and mechanical properties. Acta Materialia. 2000 Sep 4;48(14):3803-12. [12] Kang SJ, Kocabas C, Ozel T, Shim M, Pimparkar N, Alam MA, Rotkin SV, Rogers JA. High-performance electronics using dense, perfectly aligned arrays of single-walled carbon nanotubes. Nature nanotechnology. 2007 Apr;2(4):230. [13] Fortunato EM, Barquinha PM, Pimentel AC, Gonçalves AM, Marques AJ, Martins RF, Pereira LM. Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature. Applied Physics Letters. 2004 Sep 27;85(13):2541-3. [14] Klein TM, Niu D, Epling WS, Li W, Maher DM, Hobbs CC, Hegde RI, Baumvol IJ, Parsons GN. Evidence of aluminum silicate formation during chemical vapor deposition of amorphous Al2O3 thin films on Si (100). Applied Physics Letters. 1999 Dec 20;75(25):4001-3. [15] Craciun V, Elders J, Gardeniers JG, Boyd IW. Characteristics of high quality ZnO thin films deposited by pulsed laser deposition. Applied physics letters. 1994 Dec 5;65(23):2963-5. [16] Willmott PR, Huber JR. Pulsed laser vaporization and deposition. Reviews of Modern Physics. 2000 Jan 1;72(1):315. http://www.iaeme.com/IJMET/index.asp 1587 editor@iaeme.com