© 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.