The impact of MOSFET’s physical parameters on its threshold voltage MILAIM ZABELI, NEBI CAKA, MYZAFERE LIMANI, QAMIL KABASHI Faculty of Electrical and Computer Engineering University of Prishtina 10110 Prishtina, Fakulteti Teknik, Kodra e Diellit, p.n. KOSOVA milaimzabeli@yahoo.com Abstract: The aim of this paper is to research the impact of physical parameters which characterize the MOSFET transistors structure on the threshold voltage value. It is also analysed the role of substrate (the body effect) on the threshold voltage. The MOSFET threshold voltage value will have influence in the dynamic and static work regime (mode) of device. Based on the results obtained we can further see impact of each single physical parameter on the total value of threshold voltage. Moreover we can see which of these parameters will have significant and small impact on the threshold voltage. Hence, considering we can adjust the values of MOSFET physical parameters to reach the accepted threshold voltage. Key words: MOSFET parameters, threshold voltage, body effect, enhancement-type NMOS, doped density, short- channel, narrow-channel. 1 Introduction An important value which characterizes the MOSFET transistors is the value of threshold voltage. According to the MOSFET type the value of threshold voltage can take positive and negative value. This value can be controlled during the fabrication process of MOSFET transistors. The physical structure of n-channel enhancement-type MOSFET (or NMOS) is represented in Fig.1. Because the enhancement-type NMOS have advantage over other type of MOSFET transistors, hence in following we will analyze this. Terminals of MOSFET transistors are indicate with S (source), D (drain), G (gate) and B (body). The value of the gate-to-source voltage V GS needed to create (induced) the conducting channel (to cause surface inversion) is called the threshold voltage and denoted with V th or V t [1, 2, 3, 4]. The value of the threshold voltage is dependent from some physical parameters which characterize the MOSFET structure such as: the gate material, the thickness of oxide layer t ox , substrate doping concentrations (density) N A , oxide –interface fixed charge concentrations (density) N ox , channel length L, channel width W and the bias voltage V SB [2, 5]. Fig.1 The physical structure of an n-channel enhancement-type MOSFET: (a) perspective view; (b) cross-section. Proceedings of the 6th WSEAS International Conference on Microelectronics, Nanoelectronics, Optoelectronics, Istanbul, Turkey, May 27-29, 2007 54