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EE 5340 Semiconductor Device Theory Lecture 24 – Spring 2011

EE 5340 Semiconductor Device Theory Lecture 24 – Spring 2011. Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc. Ideal 2-terminal MOS capacitor/diode. conducting gate, area = LW. V gate. - x ox. SiO 2. 0. y. 0. L. silicon substrate. t sub. V sub. x.

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EE 5340 Semiconductor Device Theory Lecture 24 – Spring 2011

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  1. EE 5340Semiconductor Device TheoryLecture 24 – Spring 2011 Professor Ronald L. Carter ronc@uta.edu http://www.uta.edu/ronc

  2. Ideal 2-terminalMOS capacitor/diode conducting gate, area = LW Vgate -xox SiO2 0 y 0 L silicon substrate tsub Vsub x

  3. Band models (approx. scale) metal silicon dioxide p-type s/c Eo Eo qcox ~ 0.95 eV Eo qcSi= 4.05eV qfm= 4.1 eV for Al Ec qfs,p Eg,ox ~ 8 eV Ec EFm EFi EFp Ev Ev

  4. Flat band condition (approx. scale) Al 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

  5. Depletion for p-Si, Vgate> VFB Vgate> VFB -xox SiO2 EOx,x> 0 0 DeplReg Acceptors p-type Si tsub Vsub= 0 x

  6. Depletion forp-Si, Vgate> VFB Fig 10.4b*

  7. Equivalent circuitfor depletion • Depl depth given by the usual formula = xdepl = [2eSi(Vbb)/(qNa)]1/2 • Depl cap, C’depl = eSi/xdepl • Oxide cap, C’Ox = eOx/xOx • Net C is the series comb C’Ox C’depl

  8. Inversion for p-SiVgate>VTh>VFB Vgate> VFB EOx,x> 0 e- e- e- e- e- Acceptors DeplReg Vsub= 0

  9. Inversion for p-SiVgate>VTh>VFB Fig 10.5*

  10. Approximation concept“Onset of Strong Inv” • OSI = Onset of Strong Inversion occurs when ns = Na = ppo and VG=VTh • Assume ns = 0 for VG<VTh • Assume xdepl= xd,max for VG = VTh and it doesn’t increase for VG > VTh • Cd,min= eSi/xd,max for VG > VTh • Assume ns > 0 for VG > VTh

  11. MOS Bands at OSIp-substr = n-channel Fig 10.9*

  12. Equivalent circuitabove OSI • Depl depth given by the maximum depl = xd,max = [2eSi|2fp|/(qNa)]1/2 • Depl cap, C’d,min = eSi/xd,max • Oxide cap, C’Ox = eOx/xOx • Net C is the series comb C’Ox C’d,min

  13. MOS surface states**p- substr = n-channel

  14. n-substr accumulation (p-channel) Fig 10.7a*

  15. n-substrate depletion(p-channel) Fig 10.7b*

  16. n-substrate inversion(p-channel) Fig 10.7*

  17. Values for gate workfunction, fm

  18. Values for fmswith metal gate

  19. Values for fmswith silicon gate

  20. fms (V) Fig 10.15* NB (cm-3) Typical fms values

  21. Flat band with oxidecharge (approx. scale) Al SiO2 p-Si +<--Vox-->- q(Vox) Ec,Ox q(ffp-cox) Ex q(fm-cox) Eg,ox~8eV Ec EFm EFi EFp q(VFB) Ev VFB= VG-VB, when Si bands are flat Ev

  22. 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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