MOSFET MODELING & BSIM3 USER’S GUIDE

TroyGong

MOSFET MODELING &
BSIM3 USER’S GUIDE
by
Yuhua Cheng
Conexant Systems, Inc.
and
Chenming Hu
University of California, Berkeley
KLUWER ACADEMIC PUBLISHERS
NEW YORK, BOSTON , DORDRECHT, LONDON, MOSCOW

Contents
Contents .................................................................................................. v
Preface .................................................................................................... xiii
Chapter 1 Introduction ......................................................................1
1.1 Compact MOSFET Modeling for Circuit Simulation....................................1
1.2 The Trends of Compact MOSFET Modeling.......................................................5
1.2.1 Modeling new physical effects ................................................................................5
1.2.2 High frequency (HF) analog compact models ........................................................6
1.2.3 Simulation robustness and efficiency ...............................................................7
1.2.4 Model standardization ........................................................................................8
References ....................................................................................................8
Chapter 2 Significant Physical Effects In Modern MOSFETs ...13
2.1 MOSFET Classification and Operation .......................................................13
2.1.1 Strong inversion region (Vgs>Vth) ..................................................................17
2.1.2 Weak and moderate inversion or the subthreshold region..............................18
2.2 Effects Impacting the Threshold Voltage .....................................................18
2.2.1 Non-uniform doping effects ..............................................................................19
2.2.2 Normal short channel effects ...........................................................................23


2.2.3 Reverse short channel effects ........................................................................... 23
2.2.4 Normal narrow-width effects ........................................................................... 25
2.2.5 Reverse narrow-width effects ........................................................................... 27
2.2.6 Body bias effect and bulk charge effect............................................................28
2.3 Channel Charge Theory ................................................................................ 30
2.3.1 Accumulation.................................................................................................... 33
2.3.2 Depletion .......................................................................................................... 33
2.3.3 Inversion ........................................................................................................... 34
2.4 Carrier Mobility............................................................................................ 37
2.5 Velocity Saturation ....................................................................................... 39
2.6 Channel Length Modulation ......................................................................... 41
2.7 Substrate Current Due to Impact Ionization .................................................44
2.8 Polysilicon Gate Depletion........................................................................... 48
2.9 Velocity Overshoot Effects ........................................................................... 51
2.10 Self-heating Effect ........................................................................................ 53
2.11 Inversion Layer Quantization Effects ...........................................................55
References .................................................................................................... 57
Chapter 3 Threshold Voltage Model .............................................65
3.1 Threshold Voltage Model for Long Channel Devices ..................................65
3.2 Threshold Voltage Model with Short Channel Effects .................................67
3.2.1 Charge sharing model...................................................................................... 68
3.2.2 Quasi 2-D models for drain induced barrier lowering effect .......................... 71
3.3 Narrow Width Effect Model .........................................................................77
3.4 Threshold Voltage Model in BSIM3v3 ........................................................80
3.4.1 Modeling of the vertical non-uniform doping effects ....................................... 80
3.4.2 Modeling of the RSCE due to lateral non-uniform channel doping................ 83
3.4.3 Modeling of the short channel effect due to drain induced barrier lowering .. 85
3.4.4 Modeling of the narrow width effects ............................................................... 88
3.4.5 Complete Vth model in BSIM3v3 ..................................................................... 90
3.5 Helpful Hints ................................................................................................92
References ...................................................................................................... 101
Chapter 4 I-V Model.....................................................................105
4.1 Essential Equations Describing the I-V Characteristics .............................105