1 / 17

ECE 875: Electronic Devices

ECE 875: Electronic Devices. Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu. Lecture 37, 11 Apr 14. Chp 06: MOSFETs Aspects of realistic MOSFET operation (n-channel p-substrate) Comment on 2D mobility m Use of field oxide in CMOS

pete
Download Presentation

ECE 875: Electronic Devices

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


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

  2. Lecture 37, 11 Apr 14 • Chp 06: MOSFETs • Aspects of realistic MOSFET operation (n-channel p-substrate) • Comment on 2D mobility m • Use of field oxide in CMOS • Short channel effects on ON operation: • high E (y) => velocity saturation => lower IDS • micron-scale = worst • nano-scale = not so bad • scaling • Good test for future ON/OFF operation: sub-threshold (not fully ON) swing VM Ayres, ECE875, S14

  3. Problem: if you reduce just L while keeping all other fabrication and operating parameters the same: performance degrades: RHS: VM Ayres, ECE875, S14

  4. Diagnose the problem: assuming that Z is still effectively the same, that leaves Qn(y) and <vel> as possible causes: Lec 36: we noted that <vel> has a saturation effect at high E Also: expect higher E (y) when same VDS is applied across a shorter length. Check this possibility out

  5. Previous steps leading to eq’n (23) for ID: VM Ayres, ECE875, S14

  6. No restrictions on E (y): can go all the way up to pinch-VDsat / L: Result: VM Ayres, ECE875, S14

  7. Repeat with new <vel>: much more complicated mathematically: VM Ayres, ECE875, S14

  8. Simpler mathematics:for n-channel in Si: using green line or blue line approximation for realistic red line to get simpler v(E ): <vel> E (y) that increases along L VM Ayres, ECE875, S14

  9. Simpler mathematics: Goal: find new VDsat. Then draw ID as in saturation after that point. Up to new lower VDsat continue to use: VM Ayres, ECE875, S14

  10. Simpler mathematics: Also: replace Qn eq’n 20 with something simpler: eq’n (32): VM Ayres, ECE875, S14

  11. Find ID: But goal was: find new VDsat VM Ayres, ECE875, S14

  12. Find ID E (y) = Ecritical where velocity saturation becomes a problem: VM Ayres, ECE875, S14

  13. Dyi (y) Dyi (y = L) = (VatD – VatS) – (VatS – VatS) = VDS = Sze VD VM Ayres, ECE875, S14

  14. VM Ayres, ECE875, S14

  15. Accomplished goal in terms of Ec E c for Si is pretty well known: 1 x 107 cm/s

  16. Compare: With Constant mobility assumption: Pinch- With field dependent mobility assumption in the two-piece linear approximation: Velocity saturation- VM Ayres, ECE875, S14

  17. Pinch-VDsat > Velocity saturation-VDsat Therefore: Pinch-ID > Velocity saturation-ID Pinch-VDsat Velocity saturation-VDsat VM Ayres, ECE875, S14

More Related