1 / 15

MOSCAP Non-idealities

MOSCAP Non-idealities. Effect of oxide charges Poly-Si gate depletion effect V T adjustment HW9. Oxide Charges. Within the oxide: Trapped charge Q ot High-energy electrons and/or holes injected into oxide Mobile charge Q M

jillian-bond
Download Presentation

MOSCAP Non-idealities

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. MOSCAP Non-idealities • Effect of oxide charges • Poly-Si gate depletion effect • VT adjustment • HW9

  2. Oxide Charges • Within the oxide: • Trapped charge Qot • High-energy electrons and/or holes injected into oxide • Mobile charge QM • Alkali-metal ions, which have sufficient mobility to drift in oxide under an applied electric field • At the interface: • Fixed charge QF • Excess Si (?) • Trapped charge QIT • Dangling bonds

  3. Threshold Voltage Shift (x is defined to be 0 at metal-oxide interface) Fixed charge: Mobile charge: Trapped charge:

  4. Oxide Charge Effect on CV Mobile ion: Trapped charge:

  5. + + + + + + + + - - - - - - - - - Gate Depletion and Inversion Gauss’s Law dictates that Wpoly = eoxEox / qNpoly n+ poly-Si Cpoly Cox N+ p-type Si Inversion layer thickness:

  6. Effective Oxide Capacitance, Coxe

  7. VT Adjustment • A relatively small dose NI(units: ions/cm2) of dopant atoms is implanted into the near-surface region of the semiconductor that shifts the threshold voltage in the desired direction.

  8. The MOSFET Non-idealities • Velocity saturation • Short channel effect • HW11

  9. Velocity Saturation • Velocity saturation limits IDsat in sub-micron MOSFETS • Simple model: • Esat is the electric field at velocity saturation: for e < esat for eesat

  10. MOSFET I-V with Velocity Saturation In the linear region: EE130/230M Spring 2013 Lecture 22, Slide 10

  11. Short- vs. Long-Channel NMOSFET For very short L:

  12. The Short Channel Effect (SCE) i) VT roll-off ii) DIBL ii) Degraded SS

  13. The Short Channel Effect (SCE) iv) Punch-through

  14. Hot carriers and SD structure • The lateral electric field peaks at the drain end of the channel. • High E-field causes: • Damage to oxide interface & bulk (trapped oxide charge  VT shift) • substrate current due to impact ionization: LDD structure:

  15. Current and voltage with Parasitic SD Resistance G RD RS S D • For short-channel MOSFET, IDsat0 VGS– VT, so that •  IDsatis reduced by ~15% in a 0.1 mm MOSFET. • VDsatis increased to VDsat0+IDsat(RS+ RD)

More Related