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ECE 875: Electronic Devices

ECE 875: Electronic Devices. Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu. Lecture 27, 19 Mar 14. Chp 04: metal-insulator-semiconductor junction: GATES Examples. VM Ayres, ECE875, S14. VM Ayres, ECE875, S14. Chp. 04: MOS: Gate.

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ECE 875: Electronic Devices

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

  2. Lecture 27, 19 Mar 14 • Chp 04: metal-insulator-semiconductor junction: GATES • Examples VM Ayres, ECE875, S14

  3. VM Ayres, ECE875, S14

  4. Chp. 04: MOS: Gate Chp. 03: Interconnect Chp. 01: Si Chp. 02: pn VM Ayres, ECE875, S14

  5. p-type Si Use energy band diagram to find: VM Ayres, ECE875, S14

  6. 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

  7. Usual approach: Q(x) E (x) V  y(x) Everything else VM Ayres, ECE875, S14

  8. Usual approach: The total charge density is The Electric field is a function of the charge density. The potential is proportional to the Electric field The surface charge is: = d E dx ∞ means deep in substrate VM Ayres, ECE875, S14

  9. Example 01 (will be a continuing problem): + VM Ayres, ECE875, S14

  10. Answer: = 2.32 x 104 cm-3 In forward bias: b = 38.6 V-1 @ r.t. VM Ayres, ECE875, S14

  11. Example: what is the electron concentration at x = 0? = 2.32 x 104 cm-3 In forward bias: b = 38.6 V-1 @ r.t. VM Ayres, ECE875, S14

  12. Answer: need yp =yp(x) = 2.32 x 104 cm-3 In forward bias: b = 38.6 V-1 @ r.t. VM Ayres, ECE875, S14

  13. Can find potential yp(at x=0) using strong inversion condition: 2 x yBp = VM Ayres, ECE875, S14 ys = yp(x=0)

  14. Example: Evaluate ys in strong inversion condition for example problem 01 with NA = 4 x 1015 cm-3 VM Ayres, ECE875, S14

  15. Answer: yp(x = 0) = VM Ayres, ECE875, S14

  16. To find yp(x) (and therefore concentration) must use this approach: Q(x) E (x) V  y(x) Everything else Will get E -field first and also wanted to know that VM Ayres, ECE875, S14

  17. Electric field and potentials: in inversion: Breakdown info here concentration info here New: the potential drop across the (ideal) insulator Vi Metal = battery potential: V p-type Semiconductor potential: yp(x) Semiconductor surface potential: ys = yp(x=0) VM Ayres, ECE875, S14

  18. VM Ayres, ECE875, S14

  19. LD : the Debye length VM Ayres, ECE875, S14

  20. Example: VM Ayres, ECE875, S14

  21. Answer: VM Ayres, ECE875, S14

  22. Can easily find E (x=0) = Es: Take the square root of E2 in eq’n 10 and use yp(x=0) = ys to evaluate: VM Ayres, ECE875, S14

  23. Can easily find Q(x=0) = Qs: VM Ayres, ECE875, S14

  24. Example: Evaluate Qs for ys = 0.67 V VM Ayres, ECE875, S14

  25. Answer: VM Ayres, ECE875, S14

  26. VM Ayres, ECE875, S14

  27. VM Ayres, ECE875, S14

  28. s VM Ayres, ECE875, S14

  29. Note that an important part of the concentration we’d like to know could be defined as charge/area under the Gate (different than usual units) VM Ayres, ECE875, S14

  30. Example: VM Ayres, ECE875, S14

  31. Answer: VM Ayres, ECE875, S14

  32. VM Ayres, ECE875, S14

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