1. EE 5340 Semiconductor Device Theory Lecture 23 – Spring 2011
Professor Ronald L. Carter

2. Ideal 2-terminal MOS capacitor/diode
conducting gate,
area = LW
Vgate
-xox
SiO2 y L
silicon substrate
tsub
Vsub x
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3. Band models (approx. scale)
metal
silicon dioxide
p-type s/c Eo Eo Eo
qcox
~ 0.95 eV
qcSi= 4.05eV
qfm= 4.1 eV for Al Ec
qfs,p
Eg,ox
~ 8 eV
EFm Ec
EFp
EFi Ev Ev
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4. Flat band condition (approx. scale)
SiO2
p-Si
q(fm-cox)= 3.15 eV
q(cox-cSi)=3.1eV
Ec,Ox
qffp= 3.95eV
EFm Ec
Eg,ox~8eV
EFi
EFp Ev Ev
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5. Equivalent circuit for Flat-Band
Surface effect analogous to the extr Debye length = LD,extr = [eVt/(qNa)]1/2
Debye cap, C’D,extr = eSi/LD,extr
Oxide cap, C’Ox = eOx/xOx
Net C is the series comb
C’Ox
C’D,extr
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6. Accumulation for Vgate< VFB
-xox
SiO2
EOx,x<0
holes
p-type Si
tsub
Vsub = 0 x
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7. Accumulation p-Si, Vgs < VFB
Fig 10.4a*
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8. Equivalent circuit for accumulation
Accum depth analogous to the accum Debye length = LD,acc = [eVt/(qps)]1/2
Accum cap, C’acc = eSi/LD,acc
Oxide cap, C’Ox = eOx/xOx
Net C is the series comb
C’Ox
C’acc
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9. Depletion for p-Si, Vgate> VFB
-xox
SiO2
EOx,x> 0
Depl Reg
Acceptors
p-type Si
tsub
Vsub = 0 x
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10. Depletion for p-Si, Vgate> VFB
Fig 10.4b*
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11. References
* Semiconductor Physics & Devices, by Donald A. Neamen, Irwin, Chicago, 1997.
**Device Electronics for Integrated Circuits, 2nd ed., by Richard S. Muller and Theodore I. Kamins, John Wiley and Sons, New York, 1986
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