1. ECE 875: Electronic Devices
Prof. Virginia Ayres
Electrical & Computer Engineering
Michigan State University

2. Lecture 29, 24 Mar 14
Chp 04: metal-insulator-semiconductor junction: GATES
Q, E , V/y: WD , Vi
Capacitances
VM Ayres, ECE875, S14

3. Lec 26: p-type Si Use energy band diagram to find:
Electron concentration in channel
V requirements: battery = $
E –field/Vi across the insulator: breakdown not good
VM Ayres, ECE875, S14

4. 3: @ ys for known condition 1. Know substrate doping NA or ND2
Or nn0
Or nn0
Or pp0/nn0
ys for known condition
1. Know substrate doping NA or ND
VM Ayres, ECE875, S14

5. From Lec 26-27 example: Known condition: n-channel in p-substrate:
VM Ayres, ECE875, S14

6. From Lec 27 example: Known condition: p-channel in n-substrate:

7. Have: values for ys and Qs :
Therefore have potential drop across the dielectric: Vi = |Qs| d ei
Makes sense to evaluate this in strong inversion/accumulation
Therefore have battery V

8. Example: is this an n-channel or p-channel device?

9. Answer: is this an n-channel in p-substrate (NA)

10. Lec 26: p-type Si Use energy band diagram to find:
Electron concentration in channel
V requirements: battery = $
E –field/Vi across the insulator: breakdown not good
VM Ayres, ECE875, S14

11. Qs = Qn + Qdepletion = Qn + q (NA or ND) WD

12. Qs = Qn + Qdepletion = Qn + q (NA or ND) WD

13. Lecture 29, 24 Mar 14
Chp 04: metal-insulator-semiconductor junction: GATES
Q, E , V/y: WD , Vi
Capacitances
VM Ayres, ECE875, S14

14. ON to OFF: n-channel in a p-substrate:
VM Ayres, ECE875, S14

15. OFF to ON: n-channel in a p-substrate:
ON: Strong inversion
Going OFF: intrinsic
OFF: Strong accumulation
Going OFF: Flatband
VM Ayres, ECE875, S14

16. Fig 07: n-channel in p-substrate:
OFF ON
C / Ci
VM Ayres, ECE875, S14

17. Intermediate: 1 kHz - 1 MHz High: > 1 MHz
Fig. 07 shows all behaviors. Complication: C-V curves depend on frequency of voltage sweep.
Gate voltage:
Sweeping Vgate for example ± 4 Volts over and over to turn the channel OFF and ON: binary logic
Low: 1- 1 kHz
Intermediate: 1 kHz - 1 MHz
High: > 1 MHz
VM Ayres, ECE875, S14

18. Low frequency C-V curves
Start:
Low frequency C-V curves
VM Ayres, ECE875, S14

19. Example: what values are easiest to determine experimentally?
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20. Answer: @OFF, @ON and minimum
Example: Why so?
Answer: compare to slide 18, works for now
VM Ayres, ECE875, S14

21. Total C: Ci and CD are in series
Note that Qn can be big number
Units = C/cm2
E (x) = constant
|| plate capacitor Ci
E (x) = distributed capacitor CD = dQs/dys
Total C: Ci and CD are in series
VM Ayres, ECE875, S14

22. VM Ayres, ECE875, S14

23. Also true in strong inversion
CD = dQs/dys = large
neglect
C ≈ Ci
Also true in strong inversion
VM Ayres, ECE875, S14

24. OFF ON C / Ci Can normalize curve to Ci 1.0
I will continue with experimental readings in F/cm2. Fancy C means Farads/Area.
OFF ON
1.0
C / Ci
VM Ayres, ECE875, S14

25. OFF ON Ci = eie0 d C (x 10-7 F/cm2) 2.0 1.73 1.0 0.5
C-V curve for an n-channel in a p-type Si block
Low frequency curve: 1 Hz
Ci = eie0 d
Units: F/cm2
VM Ayres, ECE875, S14

26. Ci = eie0 => d = eie0 d Ci OFF ON C (x 10-7 F/cm2)
Important: Use C-V reading to experimentally solve for the gate oxide thickness d:
Ci = eie0 => d = eie0
d Ci
OFF ON
2.0
1.73
1.0
C (x 10-7 F/cm2)
0.5
C-V curve for an n-channel in a p-type Si block
Low frequency curve: 1 Hz
VM Ayres, ECE875, S14

27. Next: Cmin is easy to identify on the experimental curve:
VM Ayres, ECE875, S14