Lundstrom ECE 305 F16
ECE-305: Spring 2016
MOS Capacitance vs. Voltage
Professor Mark Lundstrom Electrical and Computer Engineering
Purdue University, West Lafayette, IN USA [email protected]
4/5/16
Pierret, Semiconductor Device Fundamentals (SDF) pp. 584-599
MOS capacitor
2
p-Si
vS sinωt
+ VG
+
-
-
VG + vS sinωt
~
Lundstrom ECE 305 F16
MOS capacitor in depletion
3
VG
p-Si
W φS( ) W VG( )
Lundstrom ECE 305 F16
4
MOS capacitor in depletion
xo
W φS( )
KO
KS
C = ?
Gate
Undepleted P-type semiconductor
CS =KSε0W φS( )
Cox =KOε0xo
1C
=1Cox
+1CS
C =CSCox
CS + Cox
C =Cox
1+ Cox CS
result
xo
W φS( )
κ ox
κ Si
C = Cox
1+KOW φS( )KSxo
VG
Cox
CS
φS
Lundstrom ECE 305 F16 5
6
s.s. gate capacitance vs. d.c. gate bias
C
VG′
C = Cox
1+KOW φS( )KSxo
accumulation depletion
inversion
VT′
flat band
Cox
Lundstrom ECE 305 F16
7
s.s. gate capacitance vs. d.c. gate bias
C
VG′C = Cox
1+KOW φS( )KSxo
accumulation
depletion
inversion
VT′
flat band
Cox
high frequency
Lundstrom ECE 305 F16
8
capacitance vs. gate voltage
C
VG
C = Cox
1+KOW φS( )KSxo
accumulation
depletion
inversion
VT
flat band
Cox
VFB = φms
Lundstrom ECE 305 F16
9
high frequency vs. low frequency
C
VG′
C = Cox
1+KOW φS( )KSxo
accumulation depletion
inversion
VT′
flat band
Cox
high frequency
low frequency
Lundstrom ECE 305 F16
10
high frequency vs. low frequency
p-Si
n+-Si n+-Si
MOS capacitor
11
CV measurements as an analysis tool
C
VG
C = Cox
1+KOW φS( )KSxo
accumulation
depletion
inversion VT
Cox
C = Cox =K0ε0xo
C = Cox
1+KOW 2φF( )
KSxo
flat band
VFB = φms
Lundstrom ECE 305 F16
12
CV measurements as an analysis tool
source drain S
iO2
Si
S DG
(Texas Instruments, ~ 2000)
• Oxide thickness • Flatband voltage • Doping density