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Lundstrom EE-612 F06 1
EE-612:Lecture 1: MOSFET Review
Mark LundstromElectrical and Computer Engineering
Purdue UniversityWest Lafayette, IN USA
Fall 2006
www.nanohub.orgNCN
Lundstrom EE-612 F06 2
S DG
MOSFETs
physical structure
S D
G
circuit schematic
65 nm technology node:L = 35 nmTox = 1.2nmVDD = 1.2V
Lundstrom EE-612 F06 3
common source characteristics
S
D
G
1) ground source2) set VG3) sweep VD from 0 to VDD4) Step VG from 0 to VDD
ID
VDS
VGS
VDD
VG = VDD
1 2
Lundstrom EE-612 F06 4
common source characteristics
ID
VDS
VGS
VDD
channel resistance = VDS / IDS
VG = VDD
on current (μA/μm)
outputconductance
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transfer characteristics
ID
VGSVDD
S
D
G
1) ground source2) set VD3) sweep VG from 0 to VDD
low VD
high VD
Lundstrom EE-612 F06 6
transfer characteristics
ID
VGSVDD
low VD
high VD
intercept gives VT(lin)slope is related to the effective mobility
intercept givesVT(sat) < VT(lin)
Lundstrom EE-612 F06 7
log10 ID vs. VGS
VGS -->Lo
g 10
I DS-
->
S
D
G
1) ground source2) set VD = VDD3) sweep VG from 0 to VDD
VT
subthresholdregion
above threshold
Lundstrom EE-612 F06 8
log10 ID vs. VGS
VDD
Log 1
0I D
S-->
VGS
VGS = VDS = VDD
on-current
off-currentVGS = 0 VDS = VDD
S > 60 mV/decadesubthreshold swing
Lundstrom EE-612 F06 9
DIBL (drain-induced barrier lowering)
VDD
Log 1
0I D
S-->
VGS
VD = 0.05V
VD = 1.0V
VT(VD = 1.0V) < VT(VD = 0.05V)
DIBL mV/V
Lundstrom EE-612 F06 10
GIDL (gate-induced drain leakage)
VDD
Log 1
0I D
S-->
VGS
VD = 1.0V
GIDL
Lundstrom EE-612 F06 11
physics of MOSFETs
S DG
VD= VDD
electron energyvs. 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)
PMOSI D
S(m
A/μm
)NMOS
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MOSFET IV: low VDS
VG VD0
ID =W Qi x( )υ x (x) =W Qi 0( )υ x (0)
ID =W Cox VGS −VT( )μeffEx
Ex =
VDS
L
Qi x( )= −Cox VGS −VT −V (x)( )
ID
VDS
VGS
ID =WLμeff Cox VGS −VT( )VDS
Lundstrom EE-612 F06 14
MOSFET IV: high VDS
VG VD0
ID =W Qi x( )υ x (x) =W Qi 0( )υ x (0)
ID =W Cox VGS −VT( )μeffEx
V x( )= VGS −VT( )
VGS
ID
VDS
ID =WLμeff Cox VGS −VT( )2
2 E x ≈
VGS −VT
L
Lundstrom EE-612 F06 15
velocity saturation
electric field V/cm --->
velo
city
cm
/s --
->
107
104
υ = μE
υ =υ sat
VDS
L=
1.5V60nm
≈ 25 ×104 V/cm
Lundstrom EE-612 F06 16
MOSFET IV: velocity saturation
VG VD0
ID =W Qi x( )υ x (x) =W Qi 0( )υ x (0)
ID =W Cox VGS −VT( )υ sat
ID = W Coxυsat VGS −VT( )
E x >> 104
0 0.4 0.8 1.2 1.4
Lundstrom EE-612 F06 17
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
Lundstrom EE-612 F06 18
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
Lundstrom EE-612 F06 19
MOSFET IV: velocity overshoot
Frank, Laux, and Fischetti, IEDM Tech. Dig., p. 553, 1992
Veloc
ity (c
m/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
Lundstrom EE-612 F06 20
MOSFET IV: Quantum effectsL = 10 nm
(quantum confinementtreated in both cases)
n(x, E)
ID vs. VDS
classical
quantum
Log ID vs. VGS
reducedon-current
increasedoff-current
nanoMOS at www.nanohub.org
Lundstrom EE-612 F06 21
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)
