<s>
MEMS	B-Architecture
(	O
Microelectromechanical	B-Architecture
systems	I-Architecture
)	O
is	O
the	O
technology	O
of	O
microscopic	O
devices	O
incorporating	O
both	O
electronic	O
and	O
moving	O
parts	O
.	O
</s>
<s>
MEMS	B-Architecture
are	O
made	O
up	O
of	O
components	O
between	O
1	O
and	O
100	O
micrometers	O
in	O
size	O
(	O
i.e.	O
,	O
0.001	O
to	O
0.1mm	O
)	O
,	O
and	O
MEMS	B-Architecture
devices	O
generally	O
range	O
in	O
size	O
from	O
20	O
micrometres	O
to	O
a	O
millimetre	O
(	O
i.e.	O
,	O
0.02	O
to	O
1.0mm	O
)	O
,	O
although	O
components	O
arranged	O
in	O
arrays	O
(	O
e.g.	O
,	O
digital	O
micromirror	O
devices	O
)	O
can	O
be	O
more	O
than	O
1000mm2	O
.	O
</s>
<s>
They	O
usually	O
consist	O
of	O
a	O
central	O
unit	O
that	O
processes	O
data	O
(	O
an	O
integrated	O
circuit	O
chip	O
such	O
as	O
microprocessor	B-Architecture
)	O
and	O
several	O
components	O
that	O
interact	O
with	O
the	O
surroundings	O
(	O
such	O
as	O
microsensors	B-Application
)	O
.	O
</s>
<s>
Because	O
of	O
the	O
large	O
surface	O
area	O
to	O
volume	O
ratio	O
of	O
MEMS	B-Architecture
,	O
forces	O
produced	O
by	O
ambient	O
electromagnetism	O
(	O
e.g.	O
,	O
electrostatic	O
charges	O
and	O
magnetic	O
moments	O
)	O
,	O
and	O
fluid	O
dynamics	O
(	O
e.g.	O
,	O
surface	O
tension	O
and	O
viscosity	B-Application
)	O
are	O
more	O
important	O
design	O
considerations	O
than	O
with	O
larger	O
scale	O
mechanical	O
devices	O
.	O
</s>
<s>
MEMS	B-Architecture
technology	O
is	O
distinguished	O
from	O
molecular	O
nanotechnology	O
or	O
molecular	B-Algorithm
electronics	I-Algorithm
in	O
that	O
the	O
latter	O
two	O
must	O
also	O
consider	O
surface	O
chemistry	O
.	O
</s>
<s>
MEMS	B-Architecture
became	O
practical	O
once	O
they	O
could	O
be	O
fabricated	O
using	O
modified	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
technologies	O
,	O
normally	O
used	O
to	O
make	O
electronics	O
.	O
</s>
<s>
These	O
include	O
molding	O
and	O
plating	O
,	O
wet	B-Algorithm
etching	I-Algorithm
(	O
KOH	O
,	O
TMAH	O
)	O
and	O
dry	B-Algorithm
etching	I-Algorithm
(	O
RIE	B-Algorithm
and	O
DRIE	B-Algorithm
)	O
,	O
electrical	O
discharge	O
machining	O
(	O
EDM	O
)	O
,	O
and	O
other	O
technologies	O
capable	O
of	O
manufacturing	O
small	O
devices	O
.	O
</s>
<s>
An	O
early	O
example	O
of	O
a	O
MEMS	B-Architecture
device	O
is	O
the	O
resonant-gate	O
transistor	O
,	O
an	O
adaptation	O
of	O
the	O
MOSFET	O
,	O
developed	O
by	O
Harvey	O
C	O
.	O
Nathanson	O
in	O
1965	O
.	O
</s>
<s>
During	O
the	O
1970s	O
to	O
early	O
1980s	O
,	O
a	O
number	O
of	O
MOSFET	O
microsensors	B-Application
were	O
developed	O
for	O
measuring	O
physical	O
,	O
chemical	O
,	O
biological	O
and	O
environmental	O
parameters	O
.	O
</s>
<s>
The	O
term	O
"	O
MEMS	B-Architecture
"	O
was	O
introduced	O
in	O
1986	O
.	O
</s>
<s>
Wood	O
(	O
Co-PI	O
)	O
introduced	O
the	O
term	O
“	O
MEMS	B-Architecture
”	O
by	O
way	O
of	O
a	O
proposal	O
to	O
DARPA	O
(	O
15	O
July	O
1986	O
)	O
,	O
titled	O
"	O
Micro	B-Architecture
Electro-Mechanical	I-Architecture
Systems	I-Architecture
(	O
MEMS	B-Architecture
)	O
"	O
,	O
granted	O
to	O
the	O
University	O
of	O
Utah	O
.	O
</s>
<s>
The	O
term	O
“	O
MEMS	B-Architecture
”	O
was	O
presented	O
by	O
way	O
of	O
an	O
invited	O
talk	O
by	O
S.C.	O
Jacobsen	O
,	O
titled	O
“	O
Micro	B-Architecture
Electro-Mechanical	I-Architecture
Systems	I-Architecture
(	O
MEMS	B-Architecture
)	O
”	O
,	O
at	O
the	O
IEEE	O
Micro	O
Robots	O
and	O
Teleoperators	O
Workshop	O
,	O
Hyannis	O
,	O
MA	O
Nov	O
.	O
9-11	O
,	O
1987	O
.	O
</s>
<s>
The	O
term	O
“	O
MEMS	B-Architecture
”	O
was	O
published	O
by	O
way	O
of	O
a	O
submitted	O
paper	O
by	O
J.E.	O
</s>
<s>
There	O
are	O
two	O
basic	O
types	O
of	O
MEMS	B-Architecture
switch	O
technology	O
:	O
capacitive	O
and	O
ohmic	O
.	O
</s>
<s>
A	O
capacitive	O
MEMS	B-Architecture
switch	O
is	O
developed	O
using	O
a	O
moving	O
plate	O
or	O
sensing	B-Application
element	I-Application
,	O
which	O
changes	O
the	O
capacitance	O
.	O
</s>
<s>
Ohmic	O
MEMS	B-Architecture
switches	O
can	O
fail	O
from	O
metal	O
fatigue	O
of	O
the	O
MEMS	B-Architecture
actuator	B-Algorithm
(	O
cantilever	O
)	O
and	O
contact	O
wear	O
,	O
since	O
cantilevers	O
can	O
deform	O
over	O
time	O
.	O
</s>
<s>
The	O
fabrication	B-Architecture
of	O
MEMS	B-Architecture
evolved	O
from	O
the	O
process	O
technology	O
in	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
,	O
i.e.	O
</s>
<s>
the	O
basic	O
techniques	O
are	O
deposition	O
of	O
material	O
layers	O
,	O
patterning	O
by	O
photolithography	B-Algorithm
and	O
etching	B-Algorithm
to	O
produce	O
the	O
required	O
shapes	O
.	O
</s>
<s>
The	O
economies	O
of	O
scale	O
,	O
ready	O
availability	O
of	O
inexpensive	O
high-quality	O
materials	O
,	O
and	O
ability	O
to	O
incorporate	O
electronic	O
functionality	O
make	O
silicon	O
attractive	O
for	O
a	O
wide	O
variety	O
of	O
MEMS	B-Architecture
applications	O
.	O
</s>
<s>
Semiconductor	B-Algorithm
nanostructures	I-Algorithm
based	O
on	O
silicon	O
are	O
gaining	O
increasing	O
importance	O
in	O
the	O
field	O
of	O
microelectronics	O
and	O
MEMS	B-Architecture
in	O
particular	O
.	O
</s>
<s>
Silicon	B-Algorithm
nanowires	I-Algorithm
,	O
fabricated	O
through	O
the	O
thermal	B-Algorithm
oxidation	I-Algorithm
of	O
silicon	O
,	O
are	O
of	O
further	O
interest	O
in	O
electrochemical	O
conversion	O
and	O
storage	O
,	O
including	O
nanowire	O
batteries	O
and	O
photovoltaic	O
systems	O
.	O
</s>
<s>
MEMS	B-Architecture
devices	O
can	O
be	O
made	O
from	O
polymers	O
by	O
processes	O
such	O
as	O
injection	O
molding	O
,	O
embossing	O
or	O
stereolithography	O
and	O
are	O
especially	O
well	O
suited	O
to	O
microfluidic	O
applications	O
such	O
as	O
disposable	O
blood	O
testing	O
cartridges	O
.	O
</s>
<s>
Metals	O
Metals	O
can	O
also	O
be	O
used	O
to	O
create	O
MEMS	B-Architecture
elements	O
.	O
</s>
<s>
Metals	O
can	O
be	O
deposited	O
by	O
electroplating	O
,	O
evaporation	B-Algorithm
,	O
and	O
sputtering	O
processes	O
.	O
</s>
<s>
Ceramics	O
The	O
nitrides	O
of	O
silicon	O
,	O
aluminium	O
and	O
titanium	O
as	O
well	O
as	O
silicon	O
carbide	O
and	O
other	O
ceramics	O
are	O
increasingly	O
applied	O
in	O
MEMS	B-Architecture
fabrication	B-Architecture
due	O
to	O
advantageous	O
combinations	O
of	O
material	O
properties	O
.	O
</s>
<s>
AlN	O
crystallizes	O
in	O
the	O
wurtzite	O
structure	O
and	O
thus	O
shows	O
pyroelectric	O
and	O
piezoelectric	O
properties	O
enabling	O
sensors	B-Application
,	O
for	O
instance	O
,	O
with	O
sensitivity	O
to	O
normal	O
and	O
shear	O
forces	O
.	O
</s>
<s>
TiN	O
,	O
on	O
the	O
other	O
hand	O
,	O
exhibits	O
a	O
high	O
electrical	O
conductivity	O
and	O
large	O
elastic	O
modulus	O
,	O
making	O
it	O
possible	O
to	O
implement	O
electrostatic	O
MEMS	B-Architecture
actuation	O
schemes	O
with	O
ultrathin	O
beams	O
.	O
</s>
<s>
The	O
figure	O
shows	O
an	O
electron-microscopic	O
picture	O
of	O
a	O
MEMS	B-Architecture
biosensor	O
with	O
a	O
50nm	O
thin	O
bendable	O
TiN	O
beam	O
above	O
a	O
TiN	O
ground	O
plate	O
.	O
</s>
<s>
When	O
a	O
fluid	O
is	O
suspended	O
in	O
the	O
cavity	O
its	O
viscosity	B-Application
may	O
be	O
derived	O
from	O
bending	O
the	O
beam	O
by	O
electrical	O
attraction	O
to	O
the	O
ground	O
plate	O
and	O
measuring	O
the	O
bending	O
velocity	O
.	O
</s>
<s>
One	O
of	O
the	O
basic	O
building	O
blocks	O
in	O
MEMS	B-Architecture
processing	O
is	O
the	O
ability	O
to	O
deposit	O
thin	O
films	O
of	O
material	O
with	O
a	O
thickness	O
anywhere	O
from	O
one	O
micrometre	O
to	O
about	O
100	O
micrometres	O
.	O
</s>
<s>
Techniques	O
to	O
do	O
this	O
include	O
the	O
process	O
of	O
sputtering	O
,	O
in	O
which	O
an	O
ion	O
beam	O
liberates	O
atoms	O
from	O
a	O
target	O
,	O
allowing	O
them	O
to	O
move	O
through	O
the	O
intervening	O
space	O
and	O
deposit	O
on	O
the	O
desired	O
substrate	B-Architecture
,	O
and	O
evaporation	B-Algorithm
,	O
in	O
which	O
a	O
material	O
is	O
evaporated	O
from	O
a	O
target	O
using	O
either	O
heat	O
(	O
thermal	O
evaporation	B-Algorithm
)	O
or	O
an	O
electron	O
beam	O
(	O
e-beam	O
evaporation	B-Algorithm
)	O
in	O
a	O
vacuum	O
system	O
.	O
</s>
<s>
Chemical	B-Algorithm
deposition	I-Algorithm
techniques	O
include	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
(	O
CVD	O
)	O
,	O
in	O
which	O
a	O
stream	O
of	O
source	O
gas	O
reacts	O
on	O
the	O
substrate	B-Architecture
to	O
grow	O
the	O
material	O
desired	O
.	O
</s>
<s>
This	O
can	O
be	O
further	O
divided	O
into	O
categories	O
depending	O
on	O
the	O
details	O
of	O
the	O
technique	O
,	O
for	O
example	O
LPCVD	B-Algorithm
(	O
low-pressure	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
)	O
and	O
PECVD	O
(	O
plasma-enhanced	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
)	O
.	O
</s>
<s>
Oxide	O
films	O
can	O
also	O
be	O
grown	O
by	O
the	O
technique	O
of	O
thermal	B-Algorithm
oxidation	I-Algorithm
,	O
in	O
which	O
the	O
(	O
typically	O
silicon	O
)	O
wafer	B-Architecture
is	O
exposed	O
to	O
oxygen	O
and/or	O
steam	O
,	O
to	O
grow	O
a	O
thin	O
surface	O
layer	O
of	O
silicon	O
dioxide	O
.	O
</s>
<s>
Patterning	O
in	O
MEMS	B-Architecture
is	O
the	O
transfer	O
of	O
a	O
pattern	O
into	O
a	O
material	O
.	O
</s>
<s>
Lithography	O
in	O
a	O
MEMS	B-Architecture
context	O
is	O
typically	O
the	O
transfer	O
of	O
a	O
pattern	O
into	O
a	O
photosensitive	O
material	O
by	O
selective	O
exposure	O
to	O
a	O
radiation	O
source	O
such	O
as	O
light	O
.	O
</s>
<s>
This	O
exposed	O
region	O
can	O
then	O
be	O
removed	O
or	O
treated	O
providing	O
a	O
mask	O
for	O
the	O
underlying	O
substrate	B-Architecture
.	O
</s>
<s>
Photolithography	B-Algorithm
is	O
typically	O
used	O
with	O
metal	O
or	O
other	O
thin	O
film	O
deposition	O
,	O
wet	O
and	O
dry	B-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
Sometimes	O
,	O
photolithography	B-Algorithm
is	O
used	O
to	O
create	O
structure	O
without	O
any	O
kind	O
of	O
post	O
etching	B-Algorithm
.	O
</s>
<s>
Electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
(	O
often	O
abbreviated	O
as	O
e-beam	B-Architecture
lithography	I-Architecture
)	O
is	O
the	O
practice	O
of	O
scanning	O
a	O
beam	O
of	O
electrons	O
in	O
a	O
patterned	O
fashion	O
across	O
a	O
surface	O
covered	O
with	O
a	O
film	O
(	O
called	O
the	O
resist	O
)	O
,	O
(	O
"	O
exposing	O
"	O
the	O
resist	O
)	O
and	O
of	O
selectively	O
removing	O
either	O
exposed	O
or	O
non-exposed	O
regions	O
of	O
the	O
resist	O
(	O
"	O
developing	O
"	O
)	O
.	O
</s>
<s>
The	O
purpose	O
,	O
as	O
with	O
photolithography	B-Algorithm
,	O
is	O
to	O
create	O
very	O
small	O
structures	O
in	O
the	O
resist	O
that	O
can	O
subsequently	O
be	O
transferred	O
to	O
the	O
substrate	B-Architecture
material	O
,	O
often	O
by	O
etching	B-Algorithm
.	O
</s>
<s>
The	O
primary	O
advantage	O
of	O
electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
is	O
that	O
it	O
is	O
one	O
of	O
the	O
ways	O
to	O
beat	O
the	O
diffraction	O
limit	O
of	O
light	O
and	O
make	O
features	O
in	O
the	O
nanometer	O
range	O
.	O
</s>
<s>
This	O
form	O
of	O
maskless	B-Algorithm
lithography	I-Algorithm
has	O
found	O
wide	O
usage	O
in	O
photomask-making	O
used	O
in	O
photolithography	B-Algorithm
,	O
low-volume	O
production	O
of	O
semiconductor	O
components	O
,	O
and	O
research	O
&	O
development	O
.	O
</s>
<s>
The	O
key	O
limitation	O
of	O
electron	B-Architecture
beam	I-Architecture
lithography	I-Architecture
is	O
throughput	O
,	O
i.e.	O
,	O
the	O
very	O
long	O
time	O
it	O
takes	O
to	O
expose	O
an	O
entire	O
silicon	B-Architecture
wafer	I-Architecture
or	O
glass	O
substrate	B-Architecture
.	O
</s>
<s>
X-ray	B-Algorithm
lithography	I-Algorithm
is	O
a	O
process	O
used	O
in	O
the	O
electronic	O
industry	O
to	O
selectively	O
remove	O
parts	O
of	O
a	O
thin	O
film	O
.	O
</s>
<s>
It	O
uses	O
X-rays	O
to	O
transfer	O
a	O
geometric	O
pattern	O
from	O
a	O
mask	O
to	O
a	O
light-sensitive	O
chemical	O
photoresist	O
,	O
or	O
simply	O
"	O
resist	O
"	O
,	O
on	O
the	O
substrate	B-Architecture
.	O
</s>
<s>
Diamond	O
patterning	O
is	O
a	O
method	O
of	O
forming	O
diamond	O
MEMS	B-Architecture
.	O
</s>
<s>
It	O
is	O
achieved	O
by	O
the	O
lithographic	O
application	O
of	O
diamond	O
films	O
to	O
a	O
substrate	B-Architecture
such	O
as	O
silicon	O
.	O
</s>
<s>
There	O
are	O
two	O
basic	O
categories	O
of	O
etching	B-Algorithm
processes	O
:	O
wet	B-Algorithm
etching	I-Algorithm
and	O
dry	B-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
Wet	O
chemical	O
etching	B-Algorithm
consists	O
of	O
the	O
selective	O
removal	O
of	O
material	O
by	O
dipping	O
a	O
substrate	B-Architecture
into	O
a	O
solution	O
that	O
dissolves	O
it	O
.	O
</s>
<s>
The	O
chemical	O
nature	O
of	O
this	O
etching	B-Algorithm
process	O
provides	O
good	O
selectivity	O
,	O
which	O
means	O
the	O
etching	B-Algorithm
rate	O
of	O
the	O
target	O
material	O
is	O
considerably	O
higher	O
than	O
the	O
mask	O
material	O
if	O
selected	O
carefully	O
.	O
</s>
<s>
Wet	B-Algorithm
etching	I-Algorithm
can	O
be	O
performed	O
using	O
either	O
isotropic	O
wet	O
etchants	O
or	O
anisotropic	O
wet	O
etchants	O
.	O
</s>
<s>
Etching	B-Algorithm
progresses	O
at	O
the	O
same	O
speed	O
in	O
all	O
directions	O
.	O
</s>
<s>
Some	O
single	O
crystal	O
materials	O
,	O
such	O
as	O
silicon	O
,	O
will	O
have	O
different	O
etching	B-Algorithm
rates	O
depending	O
on	O
the	O
crystallographic	O
orientation	O
of	O
the	O
substrate	B-Architecture
.	O
</s>
<s>
This	O
is	O
known	O
as	O
anisotropic	O
etching	B-Algorithm
and	O
one	O
of	O
the	O
most	O
common	O
examples	O
is	O
the	O
etching	B-Algorithm
of	O
silicon	O
in	O
KOH	O
(	O
potassium	O
hydroxide	O
)	O
,	O
where	O
Si	O
<111>	O
planes	O
etch	O
approximately	O
100	O
times	O
slower	O
than	O
other	O
planes	O
(	O
crystallographic	O
orientations	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
etching	B-Algorithm
a	O
rectangular	O
hole	O
in	O
a	O
(	O
100	O
)	O
-Si	O
wafer	B-Architecture
results	O
in	O
a	O
pyramid	O
shaped	O
etch	O
pit	O
with	O
54.7	O
°	O
walls	O
,	O
instead	O
of	O
a	O
hole	O
with	O
curved	O
sidewalls	O
as	O
with	O
isotropic	O
etching	B-Algorithm
.	O
</s>
<s>
Hydrofluoric	O
acid	O
is	O
commonly	O
used	O
as	O
an	O
aqueous	O
etchant	O
for	O
silicon	O
dioxide	O
(	O
,	O
also	O
known	O
as	O
BOX	O
for	O
SOI	O
)	O
,	O
usually	O
in	O
49%	O
concentrated	O
form	O
,	O
5:1	O
,	O
10:1	O
or	O
20:1	O
BOE	O
(	O
buffered	O
oxide	O
etchant	O
)	O
or	O
BHF	O
(	O
Buffered	B-Algorithm
HF	I-Algorithm
)	O
.	O
</s>
<s>
They	O
were	O
first	O
used	O
in	O
medieval	O
times	O
for	O
glass	O
etching	B-Algorithm
.	O
</s>
<s>
It	O
was	O
used	O
in	O
IC	O
fabrication	B-Architecture
for	O
patterning	O
the	O
gate	O
oxide	O
until	O
the	O
process	O
step	O
was	O
replaced	O
by	O
RIE	B-Algorithm
.	O
</s>
<s>
Hydrofluoric	O
acid	O
is	O
considered	O
one	O
of	O
the	O
more	O
dangerous	O
acids	O
in	O
the	O
cleanroom	B-Application
.	O
</s>
<s>
Electrochemical	O
etching	B-Algorithm
(	O
ECE	O
)	O
for	O
dopant-selective	O
removal	O
of	O
silicon	O
is	O
a	O
common	O
method	O
to	O
automate	O
and	O
to	O
selectively	O
control	O
etching	B-Algorithm
.	O
</s>
<s>
In	O
combination	O
with	O
wet	O
anisotropic	O
etching	B-Algorithm
as	O
described	O
above	O
,	O
ECE	O
has	O
been	O
used	O
successfully	O
for	O
controlling	O
silicon	O
diaphragm	O
thickness	O
in	O
commercial	O
piezoresistive	O
silicon	O
pressure	O
sensors	B-Application
.	O
</s>
<s>
Xenon	O
difluoride	O
(	O
)	O
is	O
a	O
dry	O
vapor	O
phase	O
isotropic	O
etch	O
for	O
silicon	O
originally	O
applied	O
for	O
MEMS	B-Architecture
in	O
1995	O
at	O
University	O
of	O
California	O
,	O
Los	O
Angeles	O
.	O
</s>
<s>
Models	O
of	O
the	O
etching	B-Algorithm
action	O
are	O
available	O
,	O
and	O
university	O
laboratories	O
and	O
various	O
commercial	O
tools	O
offer	O
solutions	O
using	O
this	O
approach	O
.	O
</s>
<s>
Modern	O
VLSI	O
processes	O
avoid	O
wet	B-Algorithm
etching	I-Algorithm
,	O
and	O
use	O
plasma	B-Algorithm
etching	I-Algorithm
instead	O
.	O
</s>
<s>
Ordinary	O
plasma	B-Algorithm
etching	I-Algorithm
operates	O
between	O
0.1	O
and	O
5	O
Torr	O
.	O
</s>
<s>
The	O
plasma	O
produces	O
energetic	O
free	O
radicals	O
,	O
neutrally	O
charged	O
,	O
that	O
react	O
at	O
the	O
surface	O
of	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
Since	O
neutral	O
particles	O
attack	O
the	O
wafer	B-Architecture
from	O
all	O
angles	O
,	O
this	O
process	O
is	O
isotropic	O
.	O
</s>
<s>
Plasma	B-Algorithm
etching	I-Algorithm
can	O
be	O
isotropic	O
,	O
i.e.	O
,	O
exhibiting	O
a	O
lateral	O
undercut	O
rate	O
on	O
a	O
patterned	O
surface	O
approximately	O
the	O
same	O
as	O
its	O
downward	O
etch	O
rate	O
,	O
or	O
can	O
be	O
anisotropic	O
,	O
i.e.	O
,	O
exhibiting	O
a	O
smaller	O
lateral	O
undercut	O
rate	O
than	O
its	O
downward	O
etch	O
rate	O
.	O
</s>
<s>
Such	O
anisotropy	O
is	O
maximized	O
in	O
deep	B-Algorithm
reactive	I-Algorithm
ion	I-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
The	O
use	O
of	O
the	O
term	O
anisotropy	O
for	O
plasma	B-Algorithm
etching	I-Algorithm
should	O
not	O
be	O
conflated	O
with	O
the	O
use	O
of	O
the	O
same	O
term	O
when	O
referring	O
to	O
orientation-dependent	O
etching	B-Algorithm
.	O
</s>
<s>
Ion	O
milling	O
,	O
or	O
sputter	O
etching	B-Algorithm
,	O
uses	O
lower	O
pressures	O
,	O
often	O
as	O
low	O
as	O
10−4	O
Torr	O
(	O
10	O
mPa	O
)	O
.	O
</s>
<s>
It	O
bombards	O
the	O
wafer	B-Architecture
with	O
energetic	O
ions	O
of	O
noble	O
gases	O
,	O
often	O
Ar+	O
,	O
which	O
knock	O
atoms	O
from	O
the	O
substrate	B-Architecture
by	O
transferring	O
momentum	O
.	O
</s>
<s>
Because	O
the	O
etching	B-Algorithm
is	O
performed	O
by	O
ions	O
,	O
which	O
approach	O
the	O
wafer	B-Architecture
approximately	O
from	O
one	O
direction	O
,	O
this	O
process	O
is	O
highly	O
anisotropic	O
.	O
</s>
<s>
Reactive-ion	B-Algorithm
etching	I-Algorithm
(	O
RIE	B-Algorithm
)	O
operates	O
under	O
conditions	O
intermediate	O
between	O
sputter	O
and	O
plasma	B-Algorithm
etching	I-Algorithm
(	O
between	O
10	O
–	O
3	O
and	O
10−1	O
Torr	O
)	O
.	O
</s>
<s>
Deep	B-Algorithm
reactive-ion	I-Algorithm
etching	I-Algorithm
(	O
DRIE	B-Algorithm
)	O
modifies	O
the	O
RIE	B-Algorithm
technique	O
to	O
produce	O
deep	O
,	O
narrow	O
features	O
.	O
</s>
<s>
In	O
reactive-ion	B-Algorithm
etching	I-Algorithm
(	O
RIE	B-Algorithm
)	O
,	O
the	O
substrate	B-Architecture
is	O
placed	O
inside	O
a	O
reactor	O
,	O
and	O
several	O
gases	O
are	O
introduced	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
the	O
chemical	O
part	O
of	O
reactive	B-Algorithm
ion	I-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
It	O
is	O
a	O
very	O
complex	O
task	O
to	O
develop	O
dry	O
etch	O
processes	O
that	O
balance	O
chemical	O
and	O
physical	O
etching	B-Algorithm
,	O
since	O
there	O
are	O
many	O
parameters	O
to	O
adjust	O
.	O
</s>
<s>
By	O
changing	O
the	O
balance	O
it	O
is	O
possible	O
to	O
influence	O
the	O
anisotropy	O
of	O
the	O
etching	B-Algorithm
,	O
since	O
the	O
chemical	O
part	O
is	O
isotropic	O
and	O
the	O
physical	O
part	O
highly	O
anisotropic	O
the	O
combination	O
can	O
form	O
sidewalls	O
that	O
have	O
shapes	O
from	O
rounded	O
to	O
vertical	O
.	O
</s>
<s>
Deep	B-Algorithm
reactive	I-Algorithm
ion	I-Algorithm
etching	I-Algorithm
(	O
DRIE	B-Algorithm
)	O
is	O
a	O
special	O
subclass	O
of	O
RIE	B-Algorithm
that	O
is	O
growing	O
in	O
popularity	O
.	O
</s>
<s>
Currently	O
,	O
there	O
are	O
two	O
variations	O
of	O
the	O
DRIE	B-Algorithm
.	O
</s>
<s>
The	O
creates	O
a	O
polymer	O
on	O
the	O
surface	O
of	O
the	O
substrate	B-Architecture
,	O
and	O
the	O
second	O
gas	O
composition	O
(	O
and	O
)	O
etches	O
the	O
substrate	B-Architecture
.	O
</s>
<s>
The	O
polymer	O
is	O
immediately	O
sputtered	O
away	O
by	O
the	O
physical	O
part	O
of	O
the	O
etching	B-Algorithm
,	O
but	O
only	O
on	O
the	O
horizontal	O
surfaces	O
and	O
not	O
the	O
sidewalls	O
.	O
</s>
<s>
Since	O
the	O
polymer	O
only	O
dissolves	O
very	O
slowly	O
in	O
the	O
chemical	O
part	O
of	O
the	O
etching	B-Algorithm
,	O
it	O
builds	O
up	O
on	O
the	O
sidewalls	O
and	O
protects	O
them	O
from	O
etching	B-Algorithm
.	O
</s>
<s>
As	O
a	O
result	O
,	O
etching	B-Algorithm
aspect	O
ratios	O
of	O
50	O
to	O
1	O
can	O
be	O
achieved	O
.	O
</s>
<s>
The	O
process	O
can	O
easily	O
be	O
used	O
to	O
etch	O
completely	O
through	O
a	O
silicon	O
substrate	B-Architecture
,	O
and	O
etch	O
rates	O
are	O
3	O
–	O
6	O
times	O
higher	O
than	O
wet	B-Algorithm
etching	I-Algorithm
.	O
</s>
<s>
After	O
preparing	O
a	O
large	O
number	O
of	O
MEMS	B-Architecture
devices	O
on	O
a	O
silicon	B-Architecture
wafer	I-Architecture
,	O
individual	O
dies	O
have	O
to	O
be	O
separated	O
,	O
which	O
is	O
called	O
die	O
preparation	O
in	O
semiconductor	O
technology	O
.	O
</s>
<s>
For	O
some	O
applications	O
,	O
the	O
separation	O
is	O
preceded	O
by	O
wafer	B-Algorithm
backgrinding	I-Algorithm
in	O
order	O
to	O
reduce	O
the	O
wafer	B-Architecture
thickness	O
.	O
</s>
<s>
Wafer	B-Algorithm
dicing	I-Algorithm
may	O
then	O
be	O
performed	O
either	O
by	O
sawing	O
using	O
a	O
cooling	O
liquid	O
or	O
a	O
dry	O
laser	O
process	O
called	O
stealth	O
dicing	O
.	O
</s>
<s>
Bulk	O
micromachining	O
is	O
the	O
oldest	O
paradigm	O
of	O
silicon-based	O
MEMS	B-Architecture
.	O
</s>
<s>
The	O
whole	O
thickness	O
of	O
a	O
silicon	B-Architecture
wafer	I-Architecture
is	O
used	O
for	O
building	O
the	O
micro-mechanical	O
structures	O
.	O
</s>
<s>
Silicon	O
is	O
machined	O
using	O
various	O
etching	B-Algorithm
processes	O
.	O
</s>
<s>
Bulk	O
micromachining	O
has	O
been	O
essential	O
in	O
enabling	O
high	O
performance	O
pressure	O
sensors	B-Application
and	O
accelerometers	O
that	O
changed	O
the	O
sensor	O
industry	O
in	O
the	O
1980s	O
and	O
90	O
's	O
.	O
</s>
<s>
Surface	O
micromachining	O
uses	O
layers	O
deposited	O
on	O
the	O
surface	O
of	O
a	O
substrate	B-Architecture
as	O
the	O
structural	O
materials	O
,	O
rather	O
than	O
using	O
the	O
substrate	B-Architecture
itself	O
.	O
</s>
<s>
Surface	O
micromachining	O
was	O
created	O
in	O
the	O
late	O
1980s	O
to	O
render	O
micromachining	O
of	O
silicon	O
more	O
compatible	O
with	O
planar	O
integrated	O
circuit	O
technology	O
,	O
with	O
the	O
goal	O
of	O
combining	O
MEMS	B-Architecture
and	O
integrated	O
circuits	O
on	O
the	O
same	O
silicon	B-Architecture
wafer	I-Architecture
.	O
</s>
<s>
The	O
original	O
surface	O
micromachining	O
concept	O
was	O
based	O
on	O
thin	O
polycrystalline	O
silicon	O
layers	O
patterned	O
as	O
movable	O
mechanical	O
structures	O
and	O
released	O
by	O
sacrificial	O
etching	B-Algorithm
of	O
the	O
underlying	O
oxide	O
layer	O
.	O
</s>
<s>
This	O
MEMS	B-Architecture
paradigm	O
has	O
enabled	O
the	O
manufacturing	O
of	O
low	O
cost	O
accelerometers	O
for	O
e.g.	O
</s>
<s>
Analog	O
Devices	O
has	O
pioneered	O
the	O
industrialization	O
of	O
surface	O
micromachining	O
and	O
has	O
realized	O
the	O
co-integration	O
of	O
MEMS	B-Architecture
and	O
integrated	O
circuits	O
.	O
</s>
<s>
Wafer	B-Architecture
bonding	O
involves	O
joining	O
two	O
or	O
more	O
substrates	B-Architecture
(	O
usually	O
having	O
the	O
same	O
diameter	O
)	O
to	O
one	O
another	O
to	O
form	O
a	O
composite	O
structure	O
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
wafer	B-Architecture
bonding	O
processes	O
that	O
are	O
used	O
in	O
microsystems	O
fabrication	B-Architecture
including	O
:	O
direct	O
or	O
fusion	O
wafer	B-Architecture
bonding	O
,	O
wherein	O
two	O
or	O
more	O
wafers	B-Architecture
are	O
bonded	O
together	O
that	O
are	O
usually	O
made	O
of	O
silicon	O
or	O
some	O
other	O
semiconductor	O
material	O
;	O
anodic	O
bonding	O
wherein	O
a	O
boron-doped	O
glass	O
wafer	B-Architecture
is	O
bonded	O
to	O
a	O
semiconductor	B-Architecture
wafer	I-Architecture
,	O
usually	O
silicon	O
;	O
thermocompression	O
bonding	O
,	O
wherein	O
an	O
intermediary	O
thin-film	O
material	O
layer	O
is	O
used	O
to	O
facilitate	O
wafer	B-Architecture
bonding	O
;	O
and	O
eutectic	O
bonding	O
,	O
wherein	O
a	O
thin-film	O
layer	O
of	O
gold	O
is	O
used	O
to	O
bond	O
two	O
silicon	B-Architecture
wafers	I-Architecture
.	O
</s>
<s>
Most	O
wafer	B-Architecture
bonding	O
processes	O
rely	O
on	O
three	O
basic	O
criteria	O
for	O
successfully	O
bonding	O
:	O
the	O
wafers	B-Architecture
to	O
be	O
bonded	O
are	O
sufficiently	O
flat	O
;	O
the	O
wafer	B-Architecture
surfaces	O
are	O
sufficiently	O
smooth	O
;	O
and	O
the	O
wafer	B-Architecture
surfaces	O
are	O
sufficiently	O
clean	O
.	O
</s>
<s>
The	O
most	O
stringent	O
criteria	O
for	O
wafer	B-Architecture
bonding	O
is	O
usually	O
the	O
direct	O
fusion	O
wafer	B-Architecture
bonding	O
since	O
even	O
one	O
or	O
more	O
small	O
particulates	O
can	O
render	O
the	O
bonding	O
unsuccessful	O
.	O
</s>
<s>
In	O
comparison	O
,	O
wafer	B-Architecture
bonding	O
methods	O
that	O
use	O
intermediary	O
layers	O
are	O
often	O
far	O
more	O
forgiving	O
.	O
</s>
<s>
Both	O
bulk	O
and	O
surface	O
silicon	O
micromachining	O
are	O
used	O
in	O
the	O
industrial	O
production	O
of	O
sensors	B-Application
,	O
ink-jet	O
nozzles	O
,	O
and	O
other	O
devices	O
.	O
</s>
<s>
A	O
new	O
etching	B-Algorithm
technology	O
,	O
deep	B-Algorithm
reactive-ion	I-Algorithm
etching	I-Algorithm
,	O
has	O
made	O
it	O
possible	O
to	O
combine	O
good	O
performance	O
typical	O
of	O
bulk	O
micromachining	O
with	O
comb	O
structures	O
and	O
in-plane	O
operation	O
typical	O
of	O
surface	O
micromachining	O
.	O
</s>
<s>
The	O
materials	O
commonly	O
used	O
in	O
HAR	O
silicon	O
micromachining	O
are	O
thick	O
polycrystalline	O
silicon	O
,	O
known	O
as	O
epi-poly	O
,	O
and	O
bonded	O
silicon-on-insulator	O
(	O
SOI	O
)	O
wafers	B-Architecture
although	O
processes	O
for	O
bulk	O
silicon	B-Architecture
wafer	I-Architecture
also	O
have	O
been	O
created	O
(	O
SCREAM	O
)	O
.	O
</s>
<s>
Bonding	O
a	O
second	O
wafer	B-Architecture
by	O
glass	O
frit	O
bonding	O
,	O
anodic	O
bonding	O
or	O
alloy	O
bonding	O
is	O
used	O
to	O
protect	O
the	O
MEMS	B-Architecture
structures	O
.	O
</s>
<s>
Some	O
common	O
commercial	O
applications	O
of	O
MEMS	B-Architecture
include	O
:	O
</s>
<s>
MEMS	B-Architecture
gyroscopes	O
in	O
remote	O
controlled	O
,	O
or	O
autonomous	O
,	O
helicopters	O
,	O
planes	O
and	O
multirotors	O
(	O
also	O
known	O
as	O
drones	O
)	O
,	O
used	O
for	O
automatically	O
sensing	O
and	O
balancing	O
flying	O
characteristics	O
of	O
roll	O
,	O
pitch	O
and	O
yaw	O
.	O
</s>
<s>
MEMS	B-Architecture
magnetic	O
field	O
sensor	O
(	O
magnetometer	O
)	O
may	O
also	O
be	O
incorporated	O
in	O
such	O
devices	O
to	O
provide	O
directional	O
heading	O
.	O
</s>
<s>
MEMS	B-Architecture
inertial	O
navigation	O
systems	O
(	O
INSs	O
)	O
of	O
modern	O
cars	O
,	O
airplanes	O
,	O
submarines	O
and	O
other	O
vehicles	O
to	O
detect	O
yaw	O
,	O
pitch	O
,	O
and	O
roll	O
;	O
for	O
example	O
,	O
the	O
autopilot	O
of	O
an	O
airplane	O
.	O
</s>
<s>
Accelerometers	O
in	O
consumer	O
electronics	O
devices	O
such	O
as	O
game	O
controllers	O
(	O
Nintendo	B-Operating_System
Wii	I-Operating_System
)	O
,	O
personal	O
media	O
players	O
/	O
cell	O
phones	O
(	O
virtually	O
all	O
smartphones	O
,	O
various	O
HTC	O
PDA	O
models	O
)	O
,	O
augmented	B-General_Concept
reality	I-General_Concept
(	O
AR	O
)	O
and	O
virtual	B-Application
reality	I-Application
(	O
VR	O
)	O
devices	O
,	O
and	O
a	O
number	O
of	O
digital	O
cameras	O
(	O
various	O
Canon	B-Application
Digital	I-Application
IXUS	I-Application
models	O
)	O
.	O
</s>
<s>
MEMS	B-Architecture
microphones	O
in	O
portable	O
devices	O
,	O
e.g.	O
,	O
mobile	O
phones	O
,	O
head	O
sets	O
and	O
laptops	O
.	O
</s>
<s>
Bio-MEMS	O
applications	O
in	O
medical	O
and	O
health	O
related	O
technologies	O
including	O
lab-on-a-chip	O
(	O
taking	O
advantage	O
of	O
microfluidics	O
and	O
micropumps	O
)	O
,	O
biosensors	O
,	O
chemosensors	O
as	O
well	O
as	O
embedded	O
components	O
of	O
medical	O
devices	O
e.g.	O
</s>
<s>
Micromachined	O
ultrasound	B-Algorithm
transducers	I-Algorithm
.	O
</s>
<s>
The	O
global	O
market	O
for	O
micro-electromechanical	B-Architecture
systems	I-Architecture
,	O
which	O
includes	O
products	O
such	O
as	O
automobile	O
airbag	O
systems	O
,	O
display	O
systems	O
and	O
inkjet	O
cartridges	O
totaled	O
$40	O
billion	O
in	O
2006	O
according	O
to	O
Global	O
MEMS/Microsystems	O
Markets	O
and	O
Opportunities	O
,	O
a	O
research	O
report	O
from	O
SEMI	O
and	O
Yole	O
Development	O
and	O
is	O
forecasted	O
to	O
reach	O
$72	O
billion	O
by	O
2011	O
.	O
</s>
<s>
Companies	O
with	O
strong	O
MEMS	B-Architecture
programs	O
come	O
in	O
many	O
sizes	O
.	O
</s>
<s>
Smaller	O
firms	O
provide	O
value	O
in	O
innovative	O
solutions	O
and	O
absorb	O
the	O
expense	O
of	O
custom	O
fabrication	B-Architecture
with	O
high	O
sales	O
margins	O
.	O
</s>
<s>
Both	O
large	O
and	O
small	O
companies	O
typically	O
invest	O
in	O
R&D	O
to	O
explore	O
new	O
MEMS	B-Architecture
technology	O
.	O
</s>
<s>
The	O
market	O
for	O
materials	O
and	O
equipment	O
used	O
to	O
manufacture	O
MEMS	B-Architecture
devices	O
topped	O
$1	O
billion	O
worldwide	O
in	O
2006	O
.	O
</s>
<s>
Materials	O
demand	O
is	O
driven	O
by	O
substrates	B-Architecture
,	O
making	O
up	O
over	O
70	O
percent	O
of	O
the	O
market	O
,	O
packaging	O
coatings	O
and	O
increasing	O
use	O
of	O
chemical	O
mechanical	O
planarization	O
(	O
CMP	O
)	O
.	O
</s>
<s>
While	O
MEMS	B-Architecture
manufacturing	O
continues	O
to	O
be	O
dominated	O
by	O
used	O
semiconductor	O
equipment	O
,	O
there	O
is	O
a	O
migration	O
to	O
200mm	O
lines	O
and	O
select	O
new	O
tools	O
,	O
including	O
etch	O
and	O
bonding	O
for	O
certain	O
MEMS	B-Architecture
applications	O
.	O
</s>
