Transcript Spintronics Integrating magnetic materials with semiconductors

Case Studies in MEMS
Case study
Pressure sensor
Technology
Bulk micromach.
+ bipolar circuitry
Transduction
Packaging
Piezoresistive sensing
of diaphragm deflection
Plastic
Accelerometer
Surface micromach.
Capacitive detection of
proof of mass motion
Metal can
Electrostatic
projection displays
Surface micromach.
+ XeF2 release
Electrostatic torsion of
suspended tensile beams
Glass bonded
Optical MEMS
Why are MEMS used here?
- Structures are the same dimensions as the wavelength
- Small displacement has a large effect, can be used for SWITCHING
* Interferometric devices
* Scanning devices
- A photon has no mass, easy to deflect light
-Can fabricate large-scale systems,
(e.g. 1000 X 1000 displays as in the
Digital Micro-mirror device)
Courtesy: H. Toshiyoshi
Applications of Electrostatic projection displays
Courtesy: H. Toshiyoshi
Applications of Electrostatic projection displays
Control of light through:
(1) Reflection : Texas Instruments
(DMD: Digital Micromirror Device)
(2) Diffraction: Silicon light Machines
(GLV: Grating Light Valve)
Texas Instruments’ Digital Micro-mirror Device (DMD)
The most advanced display technology to date
- Each rotatable mirror is a pixel
- 1024 shades of gray and 35 trillion colors possible
- use in projection systems, TV and theaters
Distinguishing features of a DMD
• Gray scale achieved by digital and analog modulation
- Digital: Pulse Width Modulation (PWM)
- Analog: Spatial Light Modulation (SLM)
• Compact, low weight and low power  Portable system
H. Toshiyoshi
• Higher brightness and contrast
History (1): Si cantilever based light modulator
Petersen, K.E., “Micromechanical light modulator array fabricated on Silicon”,
Applied Physics Letters, 31, pp. 521-523, 1977
• Electrically actuated, individually addressable cantilevers
• Pull -in
• SiO2 structural layer
• Si sacrificial layer
History(2): Torsional electrostatic light modulator
Petersen, K.E., “Silicon torsional scanning mirror”,
IBM Journal of Research & Dev., 24, pp. 631-637, 1980
• Electrically actuated torsion mirrors
• 1012 cycles, with ± 1o rotation
• Bulk micromachining of Silicon
History (3): Deformable Mirror Devices
L. Hornbeck, “Deformable Mirror Spatial Light Modulator”,
SPIE, vol. 1150, p.86, 1989
Elastomer based
Cantilever based
Membrane based
Torsion: Amplitude dependent modulation
Cantilever based: Phase dependent modulation
Digital Micro-mirror device
www.dlp.com
DMD Fabrication (6 photomask layers)
DMD superstructure on CMOS circuitry
• Surface micromachining process
• Hinge: Aluminum alloy (Al, Ti, Si)
(50-100 nm thick)
• Mirror: Aluminum (200-500 nm thick)
• Aluminum : structural material
• DUV hardened photoresist: sacrificial material
• Dry release (plasma etching) reduces stiction
Courtesy: H. Toshiyoshi
Texas Instruments DMD characteristics
Digital Micro-mirror device
www.dlp.com
Principle of Operation
Balancing electrical torque with mechanical torque
Telectrical is proportional to (voltage)2
Tmechanical is proportional to (deflection, a)
a
Electrostatic model of a torsion mirror
d
a  rθ  (
 x)θ
sinθ
V
V
E 
a ( d  x )
sin 
Arc length
Electric field
Mirror

a
d
V
Torsion beam
-Neglect fringing electric field
-Neglect any residual stress
Electrostatic model of a torsion mirror
Electrostatic torque (Telec) =
1 2
1 2
x
dx
 2εE Wxdx  2 εV W d
(
- x)2
sin 
Mechanical torque (Tmech) =
e.g. polysilicon, G = 73 GPa
r 2.35 g/cm3
Mirror

a
d
V
Torsion beam
W: width
L: length
t: thickness
Balancing electrical and mechanical Torques
Graph Courtesy, M. Wu
Operation of torsion mirror based DMD
DMD bias cycles
Energy domain model
The torsion mirror as a capacitive device
Calculation of capacitance
From: M. Wu and S. Senturia
Approximate solution
- stable angle and pull-in voltage
From: M. Wu and S. Senturia
Schemes of Torsion Mirror operation
Pull-in voltage
Single side drive
Low
a

Scan angle
Angle-voltage
Small
Non-linear
Large
Linear
d
(V  v)2  (V  v)2 α V.v
V
Push-pull drive
High
d
a

V+v
Bias voltages
V-v
(V  v)  (V  v) α V.v
2
2
Digital Micro-mirror Device (Texas Instruments)
1-DMD chip system
- Can create 1024 shades of gray
- used in projectors, TVs and home theater systems
2-DMD chip system
- Can create 16.7 million shades of color
- used in projectors, TVs and home theater systems
3-DMD chip system is used for higher resolutions
-For movie projection and other high end applications
(35 trillion colors can be generated)
Courtesy: M.C. Wu
Grating Light Valve (GLV)
- Silicon Light Machines (www.siliconlight.com)
Reflection : broad band
Diffraction :Wavelength (l) dependent
1 mirror/pixel (2-D array)
6 ribbons/pixel (1-D array)
Larger displacements
(msec time response)
Displacement: l/4
(nanosecond response)
Voltage controlled
A fixed angle
Constant intensity
Diffracted intensity varied by voltage
Mode of Operation
A diffraction grating of 6 beams  1 pixel
1 pixel in the GLV: 6 ribbons wide
By using a different spacing between ribbons, one can create
different color-oriented pixels
MEMS in Optical Communications
- Very quick switching (> 100 kHz), low losses,
- Low cost, batch fabrication
1 X 2 Optical switch
Optical fibers
Optical Micro-mirrors used
with Add-Drop multiplexers
Bell Labs research
MEMS Micro Optical Bench
Integrable Micro-Optics
MEMS Actuators
Opto MEMS
Slide courtesy: H. Toshiyoshi
Scratch Drive Actuator
Akiyama, J. MEMS, 2, 106, 1993
- Large total displacements can be achieved (1 mm) @ 100 Hz – 100 KHz
- Increments / forward movement as small as 10 nm
- voltages required are large
Scratch actuator movement
Voltage applied
MEMS in 3-dimensions
“Microfabricated hinges”, K. Pister et al, Sensors & Actuators A, vol. 33, pp. 249-256, 1992
-Assembly of three-dimensional structures
- Large vertical resolution and range
Surface micromachining based
Other variants of the hinge
H. Toshiyoshi
MEMS in Optical Communications
- Very quick switching (> 100 kHz), low losses,
- Low cost, batch fabrication
1 X 2 Optical switch
Optical fibers
Optical Micro-mirrors used
with Add-Drop multiplexers
Bell Labs research