Theory of the MOS transistor in weak inversion-new method to determine the number of surface states

Abstract

The drain current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> versus gate voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</inf> of an MOST operating in weak inversion, and the influence of surface potential fluctuations on this characteristic have been studied before [1], [2]. The purpose of this paper is to derive an expression of the drain current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> versus the drain voltage V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> for devices with a channel length not smaller than 20 µm. It is demonstrated that the surface potential fluctuations do not affect the slope of the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> -V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> curve, whereas the density N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ss</inf> of surface states strongly influences the slope for small drain voltages. This yields a simple and useful technique to determine N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ss</inf> on MOS transistors.