week21

1

• Lecture 4
• Transistor as Switch
• Jan. 13 2003

2
Topics

• Transistor structures.
• Transistor as a switch

3
Transistor structure

• n-type transistor

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

5
N Transistor
6
P Transistor
7
Transistor

• Digital switch
• Analog many characteristics
• Example inverter
• P transistor N transistor one inverter

8
Inverter

out
a
9
Inverter layout

(tubs not shown)
out
a
a
out
10
Example 1

out
b
a
Write the truth Table of this circuit?
11
NAND layout

out
out
b
a
b
a
12
Example 2

Write the truth Table of this circuit?
b
a
out
13
NOR gate

b
a
out
14
NOR layout
b
a
b
out
out
a
15
Difference of digital and analog

• Digital switch
• High level
• Analog characteristics of transistor
• Low level

16
Example 3

• Transmission gate

17

• Lecture 5
• Transistor Fabrication Process
• Jan. 15 2003

18
Topics

• Transistor structure (switch)
• Basic fabrication steps.

19
Transistor structure

• n-type transistor

20
Fabrication services

• Educational services
• U.S. MOSIS
• EC EuroPractice
• Taiwan CIC
• Japan VDEC
• Fab companies mainly South Asia

21
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.

22
Simple cross section
SiO2
metal3
metal2
metal1
poly
substrate
n
n
p
substrate
23
What is

• N and P
• Substrate
• Poly
• Well (tub)
• Metal
• Via

24
Photolithography

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

25
Process steps

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

p-tub
p-tub
substrate
26
Process steps, contd.

• Pattern polysilicon before diffusion regions

gate oxide
poly
poly
p-tub
p-tub
27
Process steps, contd

• Add diffusions, performing self-masking

poly
poly
p-tub
p-tub
n
n
p
p
28
Process steps, contd

• Start adding metal layers

metal 1
metal 1
vias
poly
poly
p-tub
p-tub
n
n
p
p
29
Transistor structure

• n-type transistor

30
Question

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

31
A complete fabrication process
32
Transistor structure (contd)

• n-type transistor

33
Questions (contd)

• Order of Poly !!!
• Self-aligned
• What is the carrier for N-transistor and
  P-transistor?
• Complete inverter ?
• Need metals and vias

34
0.25 micron transistor (Bell Labs)
gate oxide
silicide
source/drain
poly
35
Review

• N transistor
• P transistor

36
Examples

• Switch
• Fabrication process