xiii
Contents
9. Compact Models for Ultrathin Body FETs ............................................ 313
9.1
Introduction .....................................................................................313
9.2
Multigate Device Structures ......................................................... 314
9.2.1
Bulk-Multigate Device Structure ................................... 314
9.2.2
UTB-SOI Device Structure ............................................. 317
9.3
Common Multiple-Gate FinFET Model....................................... 318
9.3.1
Core Model: Poisson-Carrier Transport ....................... 318
9.3.1.1
Electrostatics ................................................... 318
9.3.1.2
Drain Current Model ..................................... 325
9.3.2
Modeling Physical Effects of Real Device .................... 328
9.3.2.1
Short Channel Effects .................................... 329
9.3.2.2
Quantum Mechanical Effects ...................... 330
9.3.2.3
Mobility Degradation .................................... 331
9.3.2.4
Series Resistances........................................... 332
9.4
Independent Multiple-Gate FET Model ...................................... 332
9.4.1
Electrostatics .................................................................... 333
9.4.2
Drain Current Model ...................................................... 335
9.5
Dynamic Model .............................................................................. 336
9.5.1
Common Multigate C–V Model .................................... 336
9.5.2
Independent Multigate C–V Model .............................. 338
9.6
Summary ......................................................................................... 341
Exercises ........................................................................................................ 341
10. Beyond-CMOS Transistor Models: Tunnel FETs .................................343
10.1
Introduction .....................................................................................343
10.2
Basic Features of TFETs .................................................................. 344
10.3
Basic Theory of TFET Operation ..................................................346
10.3.1 Energy Band Diagram ....................................................346
10.3.2 Tunneling Mechanism ....................................................348
10.3.3 Device Characteristics .....................................................351
10.3.4 Subthreshold Swing ........................................................353
10.4
TFET Design Considerations ........................................................ 355
10.5
Compact TFET Models................................................................... 357
10.5.1 Threshold Voltage Model ............................................... 358
10.5.2 Drain Current Model ...................................................... 360
10.5.2.1 Ideal Drain Current Model ........................... 361
10.5.2.2 Modeling the Channel Transports
Using Drain MOSFET....................................364
10.5.2.3 Modeling the Channel Transports
Using Source Resistance ............................... 366
10.6
Summary ......................................................................................... 367
Exercises ........................................................................................................ 367