EE4353_Lecture_4_SCE_Velocity_Saturation

# EE4353_Lecture_4_SCE - EE 4353 Lecture 4 Short Channel MOSFET Professor Hsing-Huang Tseng Sep 7 2011 Short Channel Effects(SCE Geometry effects

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EE 4353 Lecture 4 Short Channel MOSFET Professor Hsing-Huang Tseng Sep. 7, 2011

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Short Channel Effects (SCE) Geometry effects: Gate length dependence (with a fixing high drain voltage V d ) Drain voltage dependence: larger V d results in bigger SCE
V t Roll-off 65nm technology. EOT=1.2nm, V dd =1V K. Goto et al., (Fujitsu) IEDM 2003 V t roll-off : V t decreases with decreasing L g . • It determines the minimum acceptable L g because I off is too large if V t becomes too small. 0.01 0.1 1 -0.25 -0.20 -0.15 -0.10 -0.05 0.00 Vds = 50mV Vds = 1.0V Vt Roll-off (V) Lg (um)

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Reverse-biased PN junction, Apply Vr on N-side 1. W dep = [2 e s ( f bi + Vr )/(qN)] 1/2 where 1/N = 1/Nd + 1/Na 2. Increase Vr W dep increase Ec at the N-junction lowers. (lower than the build-in potential when Vr= 0) W dep REVIEW W dep,bi Vr=0 Vr>0
Vd: + Answer: DIBL: Drain induced barrier lowering Q: Why Vt ↓ as L ↓ N + p Depletion layer p N + N + N + p

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Drain Voltage Effects on Short Channel Vt Subthreshold characteristics of ( a ) a long-channel and (b) a short-channel NMOSFET. For short L, larger V d leads to bigger V t drop stronger short channel effects Vt shifts can be used to quantify DIBL Long Channel Vt ≠ f( Vd) Short Channel Vt = f(Vd)
Increased I dst V t1 Decreases V t Increases I off Consequence of V t becomes too low I off is too large Slope = 1 / S Q: do we want to have small or large slope? Larger slope

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Short channel subthreshold characteristics of an n -channel MOSFET with V DS = 0.1, 1, and 4 V.
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## This note was uploaded on 09/22/2011 for the course EE 4353 taught by Professor Tseng during the Spring '11 term at Texas State.

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EE4353_Lecture_4_SCE - EE 4353 Lecture 4 Short Channel MOSFET Professor Hsing-Huang Tseng Sep 7 2011 Short Channel Effects(SCE Geometry effects

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