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BSIM3v3.2.2 MOSFET Model - The University of Texas at Dallas

BSIM3v3.2.2 MOSFET Model - The University of Texas at Dallas

BSIM3v3.2.2 MOSFET Model - The University of Texas at Dallas

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Non-Uniform Doping and Small Channel Effects on Threshold VoltageEqu<strong>at</strong>ion (2.1.1) assumes th<strong>at</strong> the channel is uniform and makes use <strong>of</strong> the onedimensional Poisson equ<strong>at</strong>ion in the vertical direction <strong>of</strong> the channel. This modelis valid only when the substr<strong>at</strong>e doping concentr<strong>at</strong>ion is constant and the channellength is long. Under these conditions, the potential is uniform along the channel.Modific<strong>at</strong>ions have to be made when the substr<strong>at</strong>e doping concentr<strong>at</strong>ion is notuniform and/or when the channel length is short, narrow, or both.2.1.1 Vertical Non-Uniform Doping Effect<strong>The</strong> substr<strong>at</strong>e doping pr<strong>of</strong>ile is not uniform in the vertical direction asshown in Figure 2-1.N chN subFigure 2-1. Actual substr<strong>at</strong>e doping distribution and its approxim<strong>at</strong>ion.<strong>The</strong> substr<strong>at</strong>e doping concentr<strong>at</strong>ion is usually higher near the Si/SiO 2interface (due to V th adjustment) than deep into the substr<strong>at</strong>e. <strong>The</strong>distribution <strong>of</strong> impurity <strong>at</strong>oms inside the substr<strong>at</strong>e is approxim<strong>at</strong>ely a half<strong>BSIM3v3.2.2</strong> Manual Copyright © 1999 UC Berkeley 2-3

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