EE-612: Lecture 1: MOSFET Review Mark Lundstrom Electrical and - - PowerPoint PPT Presentation

Lundstrom EE-612 F06 1

EE-612: Lecture 1: MOSFET Review

Mark Lundstrom Electrical and Computer Engineering Purdue University West Lafayette, IN USA Fall 2006

www.nanohub.org

NCN

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S D G

MOSFETs

physical structure

S D G

circuit schematic 65 nm technology node: L = 35 nm Tox = 1.2nm VDD = 1.2V

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common source characteristics

S D G

1) ground source 2) set VG 3) sweep VD from 0 to VDD 4) Step VG from 0 to VDD ID VDS

VGS

VDD VG = VDD

1 2

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common source characteristics

ID VDS

VGS

VDD

channel resistance = VDS / IDS

VG = VDD

• n current (μA/μm)
• utput

conductance

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transfer characteristics

ID VGS

VDD

S D G

1) ground source 2) set VD 3) sweep VG from 0 to VDD

low VD high VD

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transfer characteristics

ID VGS

VDD low VD high VD intercept gives VT(lin) slope is related to the effective mobility intercept gives VT(sat) < VT(lin)

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log10 ID vs. VGS

VGS --> Log10 IDS-->

S D G

1) ground source 2) set VD = VDD 3) sweep VG from 0 to VDD

VT

subthreshold region above threshold

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log10 ID vs. VGS

VDD Log10 IDS--> VGS VGS = VDS = VDD

• n-current
• ff-current

VGS = 0 VDS = VDD

S > 60 mV/decade

subthreshold swing

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DIBL (drain-induced barrier lowering)

VDD Log10 IDS--> VGS VD = 0.05V VD = 1.0V

VT(VD = 1.0V) < VT(VD = 0.05V) DIBL mV/V

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GIDL (gate-induced drain leakage)

VDD Log10 IDS--> VGS VD = 1.0V

GIDL

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physics of MOSFETs

S D G VD= VDD

electron energy

• vs. position

VD≈ 0V

E = −qV

E.O. Johnson, RCA Review, 34, 80, 1973

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modern MOSFETs

Intel Technical J., Vol. 6, May 16, 2002. (low VT device)

130 nm technology (LG = 60 nm)

PMOS IDS (mA/μm) NMOS

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MOSFET IV: low VDS

VG VD

ID = W Qi x

( )υ x(x) = W Qi 0 ( )υ x(0)

ID = W Cox VGS −VT

( )μeffE x

E x = VDS L

Qi x

( )= −Cox VGS −VT −V(x) ( )

ID VDS

VGS

ID = W L μeffCox VGS −VT

( )VDS

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MOSFET IV: high VDS

VG VD

ID = W Qi x

( )υ x(x) = W Qi 0 ( )υ x(0)

ID = W Cox VGS −VT

( )μeffE x

V x

( )= VGS −VT ( )

VGS

ID VDS

ID = W L μeffCox VGS −VT

( )

2

2

E x ≈ VGS − VT L

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velocity saturation

electric field V/cm ---> velocity cm/s ---> 107 104

υ = μE υ = υsat

VDS L = 1.5V 60nm ≈ 25 ×104 V/cm

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MOSFET IV: velocity saturation

VG VD

ID = W Qi x

( )υ x(x) = W Qi 0 ( )υ x(0)

ID = W Cox VGS −VT

( )υ sat

ID = W Cox υsat VGS − VT

( )

E x >> 104

0.4 0.8 1.2 1.4

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MOSFET IV: discussion

Qi = −Cox VGS −VT

( ) ≈ ?

VGS 1.2V VT = 0.3V Tox = 1.5 nm

Qi ≈ 2 ×10−6 C/cm2

Qi q ≈1×1013 /cm2

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MOSFET IV: discussion

Intel Technical J., Vol. 6, May 16, 2002.

130 nm technology (LG = 60 nm)

ID ≈ W Qi(0)υ sat ≈1.6 mA/μm

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MOSFET IV: velocity overshoot

Frank, Laux, and Fischetti, IEDM Tech. Dig., p. 553, 1992 Velocity (cm/s) Position along Channel (mm)

0.0 0.01 0.02 0.03 0.04 0.05

VD = 0.8V VG-VT = 0.5V

0.0 1.0x107 2.0x107 3.0x107

Position along Channel (μm)

0.0 0.01 0.02 0.03 0.04 0.05

VD = 0.8V VG-VT = 0.5V

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MOSFET IV: Quantum effects

L = 10 nm

(quantum confinement treated in both cases)

n(x, E) ID vs. VDS

classical quantum

Log ID vs. VGS

reduced

• n-current

increased

• ff-current

nanoMOS at www.nanohub.org

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Summary

1) A MOSFET’s ID = inversion layer charge times velocity 2) 2D electrostatics determine Qi 3) Carrier transport determines the velocity 4) Second order effects are becoming first order (e.g. leakage)