Short-channel MOSFET VT-VDScharacteristics model based on a point charge and its mirror images

Abstract

Short-channel MOS transistor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV_{T}/dV_{DS}</tex> characteristics are expressed by an analytic function of fundamental device parameters. The expression is derived from a simple model of short-channel MOS transistors in threshold condition, which is based on a point charge and its mirror images. With this expression, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV_{T}/dV_{DS}</tex> is found to be proportional to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/L^{2}-1/L^{4}</tex> , where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</tex> is channel length. Following factors are also found, wherein the source and drain junction depth effect is only logarithmic on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV_{T}/dV_{DS}</tex> characteristics, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV_{T}/dV_{SUB}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dV_{T}/dV_{DS}</tex> are closely related in short-channel MOS transistors, and short-channel effects are expected to be smaller in MOS transistors on SOS than on bulk silicon, due to a large number of Si/sapphire interface states. This model is simple, and it can be applied to short-channel MOS transistor designing and circuit simulations.