MOS capacitorno contact

1
MOS capacitor-no contact
2
MOS capacitor-no gate voltage and no bias
QG
QD
3
MOS capacitor charges
VbiVs Vox
QGQDCoxVox
QG
4
MOS capacitor gate voltage and no bias
VS?VB
Depletion mode
5
MOS capacitor charges-depletion mode
VG VbiVs Vox
VG -VbiVs Vox
QGQDCoxVox
6
MOS capacitor gate voltage and no bias
VBltVslt2VB
Inversion mode
7
MOS capacitor in inversion mode fields and
charges
8
MOS capacitor-deep inversion
Vsgt2VB
Mobile inversion charge
9
MOS capacitor in deep inversion mode fields and
charges
10
MOS capacitor charges-deep inversion mode
VG VbiVs Vox
QGQDQiCoxVox
VT2VB-VbiQD,max/Cox
QiCox(VG-VT)
11
MOS capacitor-deep inversion bias
Vs,y2VBV(y)
Evac
e?s
eVs,y
Ec,y
e(VbiVG)
e?s
Ei,y
eVB
EFs
eVox,y
Ev,y
EF.y
eVsy
eV(y)
Ei,y
eVG
e?m
EFm
Ef,y-Ei,y?eVBeVs,y-VB-V(y)
12
MOS capacitor charges-bias
QGQDQiCoxVox
VG VbiVs,y Vox,y
Vs,y2VBV(y)
VT,y2VB-VbiQD,max,y,/Cox
Qi(y) CoxVG-VT,y-V(y)
13
I-V Characteristics
Triode mode
14
I-V Characteristics
Triode mode
Saturation mode
15
Fields and charges
16
Fields and charges
17
What happens at saturation?
18
C-V Characteristics
Cox
High f
19
Channel length modulation
Transconductance
20
Equivalent circuit
21
Frequency limitations
Current gain
Cut-off frequency
At saturation Vy,maxVGS-VT
Ideal FET
Same result as BJT
22
Short Channel Effects
Some of the channel is already depleted
VT2VB-VbiQD,max/Cox
QD,max?QD,max(LL)/2L
L
23
Subthreshold MOSFET
EF,sub EF,y eV(y) Eiy(x) EF,subeVB-eVs(x) EF,y
- Eiy(x) eVs(x)- eVB- eV(y)
At source EF,S- Ei,S(x) eVs(x)- eVB- eVS
At drain EF,D- Ei,D(x) eVs(x)- eVB- eVD
Fermi level is not pinned
24
Diffusion current
Jdiff
At source EF,S- Ei,S(x) eVs(x)- eVB- eVS
At drain EF,D- Ei,D(x) eVs(x)- eVB- eVD
EFy
Carrier concentration
eVs(x)eVs(1-x2/xd2)
25
Surface potential
QGQDCoxVox