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

EE-612: Lecture 1: MOSFET Review Mark Lundstrom Electrical and Computer Engineering Purdue University West Lafayette, IN USA Fall 2006 NCN www.nanohub.org Lundstrom EE-612 F06 1

MOSFETs physical structure circuit schematic S G D G S D 65 nm technology node: = 35 nm L T ox = 1.2nm V DD = 1.2V Lundstrom EE-612 F06 2

common source characteristics D I D V G = V DD G S V GS 1) ground source V DS V DD 2) set V G 1 2 3) sweep V D from 0 to V DD 4) Step V G from 0 to V DD Lundstrom EE-612 F06 3

common source characteristics on current ( μ A/ μ m) I D V G = V DD output conductance V GS V DD V DS channel resistance = V DS / I DS Lundstrom EE-612 F06 4

transfer characteristics D high V D I D G S low V D 1) ground source V DD V GS 2) set V D 3) sweep V G from 0 to V DD Lundstrom EE-612 F06 5

transfer characteristics high V D I D low V D V DD V GS intercept gives V T (sat) < V T (lin) intercept gives V T (lin) slope is related to the effective mobility Lundstrom EE-612 F06 6

log 10 I D vs. V GS above D Log 10 I DS --> threshold G S V T V GS --> 1) ground source 2) set V D = V DD subthreshold 3) sweep V G from 0 to V DD region Lundstrom EE-612 F06 7

log 10 I D vs. V GS on-current V GS = V DS = V DD Log 10 I DS --> off-current V GS = 0 V DS = V DD V GS V DD subthreshold swing S > 60 mV/decade Lundstrom EE-612 F06 8

DIBL (drain-induced barrier lowering) Log 10 I DS --> V D = 1.0V V D = 0.05V V GS V DD DIBL mV/V V T (V D = 1.0V) < V T (V D = 0.05V) Lundstrom EE-612 F06 9

GIDL (gate-induced drain leakage) Log 10 I DS --> V D = 1.0V V GS V DD GIDL Lundstrom EE-612 F06 10

physics of MOSFETs E = − qV electron energy vs. position S G D V D ≈ 0V V D = V DD E.O. Johnson, RCA Review , 34 , 80, 1973 Lundstrom EE-612 F06 11

modern MOSFETs 130 nm technology (L G = 60 nm) PMOS NMOS I DS (mA/ μ m) Intel Technical J., Vol. 6, May 16, 2002. (low V T device) Lundstrom EE-612 F06 12

MOSFET IV: low V DS 0 V G V D I D V GS ( ) = − C ox V GS − V T − V ( x ) ( ) Q i x ( ) υ x ( x ) = W Q i 0 ( ) υ x (0) I D = W Q i x V DS ( ) μ eff E x I D = W C ox V GS − V T I D = W ( ) V DS L μ eff C ox V GS − V T E x = V DS L Lundstrom EE-612 F06 13

MOSFET IV: high V DS 0 V G V D I D V GS ( ) = V GS − V T ( ) V x ( ) υ x ( x ) = W Q i 0 ( ) υ x (0) I D = W Q i x V DS ( ) μ eff E x I D = W C ox V GS − V T E x ≈ V GS − V T I D = W ( ) L μ eff C ox V GS − V T 2 2 L Lundstrom EE-612 F06 14

velocity saturation L = 1.5V V DS 60nm ≈ 25 × 10 4 V/cm velocity cm/s ---> υ = υ sat 10 7 υ = μ E 10 4 electric field V/cm ---> Lundstrom EE-612 F06 15

MOSFET IV: velocity saturation 0 V G V D E x >> 10 4 ( ) υ x ( x ) = W Q i 0 ( ) υ x (0) I D = W Q i x 0 0.4 0.8 1.2 1.4 ( ) υ sat I D = W C ox V GS − V T ( ) I D = W C ox υ sat V GS − V T Lundstrom EE-612 F06 16

MOSFET IV: discussion ( ) ≈ ? Q i = − C ox V GS − V T V GS 1.2V Q i ≈ 2 × 10 − 6 C/cm 2 V T = 0.3V T ox = 1.5 nm Q i ≈ 1 × 10 13 /cm 2 q Lundstrom EE-612 F06 17

MOSFET IV: discussion 130 nm technology (L G = 60 nm) I D ≈ W Q i (0) υ sat ≈ 1.6 mA/ μ m Intel Technical J., Vol. 6, May 16, 2002 . Lundstrom EE-612 F06 18

MOSFET IV: velocity overshoot 3.0x10 7 V D = 0.8V V G -V T = 0.5V Velocity (cm/s) 2.0x10 7 1.0x10 7 V D = 0.8V V G -V T = 0.5V 0.0 0.0 0.01 0.02 0.03 0.04 0.05 0.0 0.01 0.02 0.03 0.04 0.05 Position along Channel ( μ m) Position along Channel (mm) Frank, Laux, and Fischetti, IEDM Tech. Dig., p. 553, 1992 Lundstrom EE-612 F06 19

MOSFET IV: Quantum effects L = 10 nm increased off-current Log I D vs. V GS n(x, E) classical quantum (quantum confinement reduced treated in both cases) on-current nanoMOS at www.nanohub.org I D vs. V DS Lundstrom EE-612 F06 20

Summary 1) A MOSFET’s I D = inversion layer charge times velocity 2) 2D electrostatics determine Q i 3) Carrier transport determines the velocity 4) Second order effects are becoming first order (e.g. leakage) Lundstrom EE-612 F06 21