© Digital Integrated Circuits 2nd Devices Digital Integrated Digital Integrated Circuits Circuits A Design Perspective A Design Perspective The Devices The Devices Jan M. Rabaey Anantha Chandrakasan Borivoje Nikolic July 30, 2002 © Digital Integrated Circuits 2nd Devices Goal of this chapter Goal of this chapter Present intuitive understanding of device operation Introduction of basic device equations Introduction of models for manual analysis Introduction of models for SPICE simulation Analysis of secondary and deep-sub- micron effects Future trends © Digital Integrated Circuits 2nd Devices The Diode The Diode n p p n B A SiO 2 Al A B Al A B Cross-section of pn-junction in an IC process One-dimensional representation diode symbol Mostly occurring as parasitic element in Digital ICs © Digital Integrated Circuits 2nd Devices Depletion Region Depletion Region hole diffusion electron diffusion p n hole drift electron drift Charge Density Distance x+ - Electrical x Field x Potential V ξ ρ W 2 -W 1 ψ 0 (a) Current flow. (b) Charge density. (c) Electric field. (d) Electrostatic potential. © Digital Integrated Circuits 2nd Devices Diode Current Diode Current © Digital Integrated Circuits 2nd Devices Forward Bias Forward Bias x p n0 n p0 -W 1 W 2 0 p n (W 2 ) n-region p-region L p diffusion Typically avoided in Digital ICs © Digital Integrated Circuits 2nd Devices Reverse Bias Reverse Bias x p n0 n p0 -W 1 W 2 0 n-region p-region diffusion The Dominant Operation Mode © Digital Integrated Circuits 2nd Devices Models for Manual Analysis Models for Manual Analysis V D I D = I S (e V D / φ T – 1) + – V D + – + – V Don I D (a) Ideal diode model (b) First-order diode model © Digital Integrated Circuits 2nd Devices Junction Capacitance Junction Capacitance © Digital Integrated Circuits 2nd Devices Diffusion Capacitance Diffusion Capacitance [...]... Integrated Circuits2nd Devices Transistor Model for Manual Analysis © Digital Integrated Circuits2nd Devices The Transistor as a Switch VGS ≥ V T R on S ID ID V GS = VD D V GS = VD D D Rmid Rmid R 00 R V DS V DS VDD/2 VDD/2 © Digital Integrated Circuits2nd VDD VDD Devices The Transistor as a Switch 7 x 10 5 6 Req (Ohm) 5 4 3 2 1 0 0.5 1 1.5 2 2.5 VDD (V) © Digital Integrated Circuits2nd Devices The Transistor... Circuits2nd D B S NMOS with Bulk Contact Devices Threshold Voltage: Concept + S VGS - D G n+ n+ n-channel Depletion Region p-substrate B © Digital Integrated Circuits2nd Devices The Threshold Voltage © Digital Integrated Circuits2nd Devices The Body Effect 0.9 0.85 0.8 0.75 VT (V) 0.7 0.65 0.6 0.55 0.5 0.45 0.4 -2.5 -2 -1.5 -1 -0.5 0 VBS (V) © Digital Integrated Circuits2nd Devices Current-Voltage Relations... Breakdown © Digital Integrated Circuits2nd Devices Diode Model RS + VD ID CD - © Digital Integrated Circuits2nd Devices SPICE Parameters © Digital Integrated Circuits2nd Devices What is a Transistor? A Switch! An MOS Transistor VGS ≥ V T |VGS| R on S © Digital Integrated Circuits2nd D Devices The MOS Transistor Polysilicon © Digital Integrated Circuits2nd Aluminum Devices MOS Transistors Types and Symbols... Circuits2nd Devices Current-Voltage Relations The Deep-Submicron Era 2.5 x 10 -4 VGS= 2.5 V Early Saturation 2 VGS= 2.0 V ID (A) 1.5 VGS= 1.5 V 1 0.5 0 Linear Relationship VGS= 1.0 V 0 0.5 1 1.5 2 2.5 VDS (V) © Digital Integrated Circuits2nd Devices υ n (m/s) Velocity Saturation υsat = 105 Constant velocity Constant mobility (slope = µ) ξc = 1.5 © Digital Integrated Circuits2nd ξ (V/µm) Devices Perspective... Integrated Circuits2nd Devices Transistor in Linear S VGS VDS G n+ – V(x) ID D n+ + L x p-substrate B MOS transistor and its bias conditions © Digital Integrated Circuits2nd Devices Transistor in Saturation VGS VDS > VGS - VT G D S n+ - VGS - VT + n+ Pinch-off © Digital Integrated Circuits2nd Devices Current-Voltage Relations Long-Channel Device © Digital Integrated Circuits2nd Devices A model for manual... Integrated Circuits2nd 2 2.5 0 0 0.5 1 1.5 2 VDS(V) Short Channel Devices 2.5 A unified model for manual analysis G S D B © Digital Integrated Circuits2nd Devices Simple Model versus SPICE 2.5 x 10 -4 VDS=VDSAT 2 Velocity Saturated ID (A) 1.5 Linear 1 VDSAT=VGT 0.5 VDS=VGT 0 0 0.5 Saturated 1 1.5 2 2.5 VDS (V) © Digital Integrated Circuits2nd Devices A PMOS Transistor -4 0 x 10 VGS = -1.0V -0.2 VGS = -1.5V... device VGS = VDD Short-channel device V DSAT © Digital Integrated Circuits2nd VGS - V T VDS Devices ID versus VGS -4 6 x 10 -4 x 10 2.5 5 2 4 linear quadratic ID (A) ID (A) 1.5 3 1 2 0.5 1 0 0 quadratic 0.5 1 1.5 VGS(V) Long Channel © Digital Integrated Circuits2nd 2 2.5 0 0 0.5 1 1.5 2 2.5 VGS(V) Short Channel Devices ID versus VDS -4 6 -4 x 10 VGS= 2.5 V x 10 2.5 VGS= 2.5 V 5 2 Resistive Saturation... VDD VDD Devices The Transistor as a Switch 7 x 10 5 6 Req (Ohm) 5 4 3 2 1 0 0.5 1 1.5 2 2.5 VDD (V) © Digital Integrated Circuits2nd Devices The Transistor as a Switch © Digital Integrated Circuits2nd Devices . Integrated Circuits 2nd Devices The Threshold Voltage The Threshold Voltage © Digital Integrated Circuits 2nd Devices The Body Effect The Body Effect -2.5. Integrated Circuits 2nd Devices Digital Integrated Digital Integrated Circuits Circuits A Design Perspective A Design Perspective The Devices The Devices Jan M.