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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

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MOSCAP Non-idealities

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Moscap non idealities

MOSCAP Non-idealities

  • Effect of oxide charges

  • Poly-Si gate depletion effect

  • VT adjustment

  • HW9

Oxide charges

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

Threshold voltage shift

Threshold Voltage Shift

(x is defined to be 0 at metal-oxide interface)

Fixed charge:

Mobile charge:

Trapped charge:

Oxide charge effect on cv

Oxide Charge Effect on CV

Mobile ion:

Trapped charge:

Gate depletion and inversion


















Gate Depletion and Inversion

Gauss’s Law dictates that Wpoly = eoxEox / qNpoly

n+ poly-Si




p-type Si

Inversion layer thickness:

Effective oxide capacitance c oxe

Effective Oxide Capacitance, Coxe

V t adjustment

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.

The mosfet non idealities

The MOSFET Non-idealities

  • Velocity saturation

  • Short channel effect

  • HW11

Velocity saturation

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

Mosfet i v with velocity saturation

MOSFET I-V with Velocity Saturation

In the linear region:

EE130/230M Spring 2013

Lecture 22, Slide 10

Short vs long channel nmosfet

Short- vs. Long-Channel NMOSFET

For very short L:

The short channel effect sce

The Short Channel Effect (SCE)

i) VT roll-off

ii) DIBL

ii) Degraded SS

The short channel effect sce1

The Short Channel Effect (SCE)

iv) Punch-through

Hot carriers and sd structure

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:

Current and voltage with parasitic sd resistance

Current and voltage with Parasitic SD Resistance






  • 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)

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