MEMS Applications –Lecture 1 (J. Ahmed)
I.
Introduction
a. The definition of MEMS is changing
i. The field no longer dominated by mechanical devices.
ii. new fields include
1. BIOMEMS
2. Optical MEMS
3. radio frequency MEMS
4. Much more alphabet soup
iii. Europe has adopted the term MST (MicroSystems
Technology)
b. Why use miniaturization technology? (excerpt from Table 10.4)
i. Minimization of energy and materials use in manufacture
ii. Integration with electronics (systems are simpler)
iii. Reduction of power consumption
iv. Advantages of scaling (e.g. speed, temperature)
v. Minimally invasive.
vi. Improved reproducibility
vii. Improved accuracy and reliability
II.
There are 6 main areas of growth for MEMS devices (see
Table 10.6)
a. Automotive
b. Environmental monitoring
c. Industrial/automation
d. IT/peripheral
e. Medical/biochemical
f. Telecommunications
III. MEMs in the automotive industry
a. There are many different areas in which MEMS devices can be used in
automotive design. (Fig 10.11)
i. pressure measurement
ii. accelerometer
1. High-G models are used in triggering of airbag
deployment
a. resulted in a cost reduction from $15 per unit to
< $2 per unit
b. basis of operation
(from Analog Devices AXDL150 Data Sheet)
2. Low-G models are used in triggering ABS/ Dynamic
Stability Control systems
IV.
Electrostatic Projection Displays
a. The Digital Micromirror Device

The DMD consists of a 2-D array of micromirrors, each of which can
have their angle switched between two positions (±10°)
i. Function of the DMD device
ii. How DMDs can be used in projector
b. The Grating-Light-Valve Display
i. Structure

The GLV consists of a linear array of deformable
mirrors. Each mirror is essentially a beam supported at
both ends, and is electrostatically deformed using a
capacitive actuator.

When activated, alternate mirrors are deformed,
resulting in a diffracted reflection of the incident light.

Peak diffraction occurs at angle θ, where
sin  


2W
The optimal deformation distance, d, at which the
amplitude of the diffracted waveform is maximal is
given by
d

4
ii. Microfabrication of the GLV device.

Silicon Light Machines claims that it can produce a
GLV ribbon in a 2 mask process (this process is
proprietary)

Possible fabrication steps
o Start with bare silicon wafer
o Thermal formation of SiO2 on surface
o Deposition of a layer of polysilicon using LPCVD
(This is a sacrificial layer)
o Deposition of a layer of silicon nitride using
LPCVD (This forms the beams)
o Deposition of a layer of aluminum using PVD
(evaporation)
o Etching away of polysilicon sacrificial layer using
XeF2 (dry etching, avoids stiction problems).
iii. Packaging of the GLV
V.
Performance of the GLV
c. Liquid Crystal on Silicon
i. Background on Liquid Crystals (Courtesy Wikipedia)
1 Vertical filter film to polarize the
light as it enters.
2 Glass substrate with ITO
electrodes. The shapes of these
electrodes will determine the dark
shapes that will appear when the
LCD is turned on. Vertical ridges
are etched on the surface so the
liquid crystals are in line with the
polarized light.
3 Twisted nematic liquid crystals.
4 Glass substrate with common electrode film (ITO) with horizontal ridges to line
up with the horizontal filter.
5 Horizontal filter film to block/allow through light.
6 Reflective surface to send light back to viewer.
ii. theoretical function of LCOS
1. Controls reflection of light by using liquid crystals
iii. structure of the LCOS chip
1. important features
a. liquid crystal layer
b. reflective electrode
c. transparent (Indium Tin Oxide) electrode
iv. advantages of the LCOS
1. gray-scale is determined by LCD voltage, not by duty
cycle.
2. allows extremely high resolution, contrast, and brightness
v. Disadvantages of LCOS
1. very difficult to make (Intel gave up!)
vi. use of the LCOS to generate color images
vii. LCOS projection systems on the market
1. SONY SXRD
2. JVC D-ILA