Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-1

Lecture 4

Transistor as Switch

Jan. 13 2003

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-2

Topics

Transistor structures. Transistor as a switch

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Transistor structure

n-type transistor:

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-4

The Nobel Prize in Physics 1956

William Bradford Shockley – Semiconductor Laboratory of Beckman

Instruments, Inc. Mountain View, CA, USA

John Bardeen – University of Illinois Urbana, IL, USA

Walter Houser Brattain – Bell Telephone Laboratories Murray Hill, NJ,

USA

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-5

N Transistor

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-6

P Transistor

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Transistor

Digital: switch Analog: many characteristics

Example: inverter– P transistor + N transistor == one inverter

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-8

Inverter

a out

+

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Inverter layout

(tubs notshown)a out

+

transistors

GND

VDD

a out

tub ties

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Example 1

+

ba

out

Write the truth Table of this circuit?

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-11

NAND layout

+

ba

out

b

a

out

VDD

GND

tubties

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Example 2

+

b

a

out

Write the truth Table of this circuit?

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-13

NOR gate

+

b

a

out

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NOR layout

b

a

out

a

b

out

VDD

GND

tub ties

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Difference of digital and analog

Digital: switch– High level

Analog: characteristics of transistor – Low level

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Example 3

Transmission gate:

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Lecture 5

Transistor Fabrication Process

Jan. 15 2003

Modern VLSI Design 3e: Chapter 2 Partly from 2002 Prentice Hall PTRweek2-18

Topics

Transistor structure (switch) Basic fabrication steps.

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Transistor structure

n-type transistor:

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Fabrication services

Educational services:– U.S.: MOSIS– EC: EuroPractice– Taiwan: CIC– Japan: VDEC

Fab companies: mainly South Asia

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Fabrication processes

IC built on silicon substrate:– some structures diffused into substrate;– other structures built on top of substrate.

Substrate regions are doped with n-type and p-type impurities. (n+ = heavily doped)

Wires made of polycrystalline silicon (poly), multiple layers of aluminum (metal).

Silicon dioxide (SiO2) is insulator.

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Simple cross section

substraten+ n+p+

substrate

metal1

poly

SiO2

metal2

metal3

transistor via

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What is

N and P

Substrate Poly Well (tub) Metal Via

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Photolithography

Mask patterns are put on wafer using photo-sensitive material:

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Process steps

First place tubs to provide properly-doped substrate for n-type, p-type transistors:

p-tub p-tub

substrate

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Process steps, cont’d.

Pattern polysilicon before diffusion regions:

p-tub p-tub

poly polygate oxide

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Process steps, cont’d

Add diffusions, performing self-masking:

p-tub p-tub

poly poly

n+n+ p+ p+

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Process steps, cont’d

Start adding metal layers:

p-tub p-tub

poly poly

n+n+ p+ p+

metal 1 metal 1

vias

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Transistor structure

n-type transistor:

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Question

How many layers? Aluminum or copper? Technology is P-MOS or N-MOS? What is the purpose of silicon?

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A complete fabrication process

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Transistor structure (cont’d)

n-type transistor:

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Questions (cont’d)

Order of Poly !!!– Self-aligned

What is the carrier for N-transistor and P-transistor?

Complete inverter ? – Need metals and vias

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0.25 micron transistor (Bell Labs)

poly

silicide

source/drain

gate oxide

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Review

N transistor P transistor

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Examples

Switch Fabrication process