A Study of APCVD-Deposited TiO2Characteristics in the Structure of a Tunneling Transistor
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A Study of APCVD-Deposited TiO2Characteristics in the Structure of a Tunneling Transistor A. Behnam, B. Hekmatshoar, S. Mohajerzadeh, B. Arvan, F. Karbassian and A. Khakifirooz Department of Electrical and Computer Engineering, Thin Film laboratory, University of Tehran, Tehran, Iran, +98-21 801 1235, e-mail: [email protected] ABSTRACT TiO2 and nickel-silicide layers are consequently deposited and micro machined to compose a mesa-structured tunneling transistor. The depositions are done with the RFsputtering method and the electrical and physical characteristics of the products are investigated. Transistors show an amplification coefficient of about 20. To improve the quality and coverage of the TiO2 layer, the oxide deposition is made by means of an APCVD reactor. The grown oxide shows a dielectric coefficient between 19 and 21 and its breakdown field is about 107 V/cm. 1. INTRODUCTION Nowadays integrated circuits are mostly designed and fabricated in CMOS technology process in which field effect transistors play the most crucial role. Reducing the power and increasing the number of transistors is achieved by means of scaling, which is the main interest of the industry. Scaling rules demand a decrease in the gateoxide thickness to values about 2-3 nanometers. This will increase the leakage current passing through the oxide, mainly consisted of the tunneling component, hampering the overall device performance. To overcome this problem, oxide composites like TiO2 and Zr2O3 with high dielectric coefficients are proposed. With these oxides, one can increase the thickness of the insulating layer hence reducing the leakage current. These insulator layers have band-gap properties similar to SiO2 and they are suitable for MOSFET fabrication. Although normally leakage mechanisms are disruptive, they are used in some other transistor families [1]. For instance, they can be used in erasable memories [5] as well as in the state-of-the-art quantum mechanical devices. There are reports about the proposed structures of the tunneling transistors and their related models [8, 9, 10]. Integration of these devices is the subject of some other articles [6, 7]. In this paper TiO2 oxide is used to fabricate a tunneling transistor with a simple and reproducible structure. The fabrication process and the electrical properties of tunneling transistors are described in sections 2 and 3, respectively. The chemical vapor deposition, as an alternative approach for growing titanium oxide on silicon substrate, is demonstrated in the following sections. This method seems suitable for a low temperature and high rate deposition process. Using this technique, one can fabricate tunneling transistors on plastic substrates like PET. The method of TiO2 deposition and the output quality are explained in the following sections.
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2. STRUCTURE OF TUNNELING TRANSISTORS Fig.1 shows a schematic view of the tunneling transistor, in which the TiO2 and Nickel-silicide layers are deposited one after the other in a multi-target RF sputterin
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