Transcript Team-based design and CAD modelling using Lego in first year

ES050 – Introductory Engineering
Design and Innovation Studio
ECE Case Study
Accelerometers in Interface
Design – Part II
Prof. Ken McIsaac
2008 11 21
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Outline
Review of generated concepts
 Introduction to electronics
 The microelectronics process
 MEMS
 MEMS Accelerometer

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Accelerometer Theory
Accelerometer for into plane acceleration or
pitch
Strain gauge
3
Wii First Proposal
We can build something like this:
Computer monitors
and integrates
acceleration data
Acc 1
Acc 3
Acc 2
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Introduction to electronics

It all started with the vacuum tube
Amplification mode (eg:
radio)
 Switching mode (eg:
computing)
 They are inefficient,
bulky and slow

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Introduction to electronics
In the late 1940s, we moved to
semiconductor technology
 The primary semiconductor is silicon

Pure silicon crystal
Single silicon wafer
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Introduction to electronics

Silicon forms a crystal lattice structure
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
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Introduction to electronics

n-type doping with (eg) Phosphorus
Si
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si

Free electrons
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Introduction to electronics

n-type doping with (eg) Phosphorus
-
Si
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
Electric field
+
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Introduction to electronics

n-type doping with (eg) Phosphorus
-
Si
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
Electric field
+
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Introduction to electronics

n-type doping with (eg) Phosphorus
-
Si
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
P
Si
P
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
P
Si
Si
Si
Electric field
+
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Introduction to electronics

p-type doping with (eg) Boron
Si
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
Si
Si

Free holes
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Introduction to electronics

p-type doping with (eg) Boron
+
Si
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
Si
Si
Electric field
13
Introduction to electronics

p-type doping with (eg) Boron
+
Si
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
B
Si
B
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
Si
B
Si
Si
Si
Electric field
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Introduction to electronics
Once we have n-type and p-type silicon,
we have electronics
 These devices do everything tubes do,
only faster, cheaper and smaller

p
n
n
p
n
Diode
p
n
p
Transistor
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Microelectronics Process

The real breakthrough was the monolithic
(integrated) circuit
p
n
p
n
Integrated circuits are built onto a single
silicon substrate, not from discrete parts
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Microelectronics Process

Integrated circuits are created using a
process called lithography
Resist
Lithography uses masks and resists to
dope and create circuit elements
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Microelectronics Process

Masks define the locations of circuit
elements and light (or other beam) cures
the resist
Mask
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Microelectronics Process

Uncured resist can be washed away,
leaving only cured resist behind
Cured resist
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Microelectronics Process

Dopants can then be flooded over the
wafer. They will only penetrate where they
should
Boron solution
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Microelectronics Process

Finally, the resist can be removed, to yield
doped silicon
P-type silicon
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Microelectronics Process

A second sequence (with different mask)
continues to build the circuit
Resist
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Microelectronics Process

A second sequence (with different mask)
continues to build the circuit
Mask
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Microelectronics Process

A second sequence (with different mask)
continues to build the circuit
Cured resist
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Microelectronics Process

A second sequence (with different mask)
continues to build the circuit
Phosphorus solution
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Microelectronics Process

A second sequence (with different mask)
continues to build the circuit
Integrated diode
p
n
p
n
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Microelectronics Process

Devices can be made as small as we can
focus the exposing beam (~ 20 nm)

We can make as many simultaneously as
will fit on a wafer
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Introduction to MEMS

That’s nice, but what does this have to do
with accelerometers?

It turns out that silicon can also be etched,
vertically or at a 55 degree angle

This allows us to build
microelectromechanical systems (MEMS)
using the lithography process
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Accelerometer Theory
Suppose we want to build this accelerometer
Strain gauge
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Accelerometer Theory
First, we create the negative of the shape as a
mask
Strain gauge
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Accelerometer Theory
If we use this mask in the lithography process
then etch, we can cut away the center portion
with vertical etching
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Accelerometer Theory
Edge regions
Central regions
Next, an anisotropic wet (KOH) etch from
the bottom creates the thin beam
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Accelerometer Theory
Thin, flexible support beam
Edge regions
Large inertial mass
Central regions
Next, an anisotropic wet (KOH) etch from
the bottom creates the thin beam
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Accelerometer Theory
The strain gauges are not required, because
the resistance of silicon depends on stress
Piezoresistors
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Wii First Proposal
Recall that we needed a computer to process
the data
Computer monitors
and integrates
acceleration data
Acc 1
Acc 3
Acc 2
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Accelerometer Theory
But this is still silicon. So, we can just build the
electronics on the same wafer, using more steps of the
same process.
Control circuit
Accelerometer
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MEMS Process

Devices can be made as small as
practical, given the needed function

We can still make as many simultaneously
as will fit on a wafer!

We can build the needed electronics (to
communicate with Wii, for example) right
on the same chip.
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MEMS Process

Can you think of other applications for the
MEMS accelerometer?

Can you think of other applications for
MEMS?
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