Introduction to MEMS Design and Fabrication

1
Introduction to MEMS Design and Fabrication

• Kristofer S.J. Pister
• Berkeley Sensor and Actuator Center
• UC Berkeley

2
A brief history of MEMS

• 1750s first electrostatic motors (Benjamin
  Franklin, Andrew Gordon)
• 1824 Silicon discovered (Berzelius)
• 1927 Field effect transistor patented
  (Lilienfield)
• 1947 invention of the transistor (made from
  germanium)
• 1954 Smith, C.S., "Piezoresistive effect in
  Germanium and Silicon, Physical Review, 94.1,
  April 1954.
• 1958 silicon strain gauges commercially available
• 1961 first silicon pressure sensor demonstrated
  (Kulite)
• 1967 Invention of surface micromachining
  (Nathanson, Resonant Gate Transistor)
• 1970 first silicon accelerometer demonstrated
  (Kulite)
• 1977 first capacitive pressure sensor (Stanford)
• 1980 Petersen, K.E., "Silicon Torsional Scanning
  Mirror", IBM J. RD, v24, p631, 1980.
• 1982 disposable blood pressure transducer
  (Foxboro/ICT, Honeywell, 40)
• 1982 active on-chip signal conditioning
• 1984? First polysilicon MEMS device (Howe, Muller
  )
• 1988 Rotary electrostatic side drive motors (Fan,
  Tai, Muller)
• 1989 Lateral comb drive (Tang, Nguyen, Howe)
• 1991 polysilicon hinge (Pister, Judy, Burgett,
  Fearing)
• 1992 Grating light modulator (Solgaard, Sandejas,
  Bloom)
• 1992 MCNC starts MUMPS

3
References

• Books
• Elwenspoek and Jansen, Silicon Micromachining,
  Cambridge
• Keller, Microfabricated High Aspect Ratio Silicon
  Flexures, MEMS Precision Instruments
• Kovacs, Micromachined Transducers Sourcebook,
  McGraw-Hill
• Madou, Fundamentals of Microfabrication, CRC
• Maluf, An Introduction to Microelectromechanical
  Systems Engineering, Artech House
• Ristic, Sensor Technology and Devices, Artec
  House
• Senturia, Microsystem Design, Kluwer
• Sze, Semiconductor Sensors, Wiley

4
References

• Conferences
• Sensors and Actuators Workshop (Hilton Head),
  even years, Hilton Head Island, SC. N. America
  only
• IEEE MEMS workshop, annual, 00 Japan, 01 Europe,
  02 U.S.
• Intl. Conf. Solid State Sensors and Actuators
  (Transducers), odd years, 99 Japan, 01 Europe, 03
  U.S.
• MOEMS, 97 Japan, 98 U.S. (LEOS), 99 Germany
• SPIE, annual, San Jose, CA. (formerly Austin, TX)
• LEOS, OSA, CLEO
• ASME

5
References

• Periodicals
• IEEE/ASME, JMEMS
• Sensors and Actuators A/B
• J. Micromechanics and Microengineering
• Sensors and Materials
• Articles
• Petersen, Silicon as a Mechanical Material, Proc.
  IEEE, V70 pp.420-457, 1982.
• Proc. IEEE V86N8, 1998 Special issue on MEMS
• Wu, Micromachining for Optical and Optoelectronic
  Systems, Proc. IEEE V85N11 pp.1833-1856, 1997.

6
References
Http//www.memsnet.org - probably the best
overall MEMS site on the web. Materials
database, bibliography are great.
7
Early Semiconductor Fabrication
J. Bardeen, W.H. Brattain, The first transistor,
a semiconductor triode, Phys. Rev., 74, 230
(1948).
8
Intel 133 MHzPentium Processor 3.3 million
transistors0.35 micron lithography4 layer
metalizationFirst silicon May 1995
9
Fabrication

• IC Fabrication
• Deposition
• Lithography
• Removal
• Bulk micromachining
• Crystal planes
• Anisotropic etching
• Deep Reactive Ion Etching
• Surface micromachining
• Sacrificial etching
• Molding
• Bonding

10
Process Flow

• Integrated Circuits and MEMS identical
• Process comlexity/yield related to trips
  through central loop

11
Materials

• Metals
• Al, Au, Cu, W, Ni, TiNi, NiFe,
• Insulators
• SiO2 - thermally grown or vapor deposited (CVD)
• Si3N4 - CVD
• Polymers
• The King of Semiconductors Silicon
• stronger than steel, lighter than aluminum
• single crystal or polycrystalline
• 10nm to 10mm

12
Applications

• Pressure sensors
• Automotive, Medical, Industrial,
• Accelerometers
• Automotive, Medical, Industrial
• Gyros
• Automotive
• Displays
• TI DMD, SLM GLV
• Fiber optics
• Switches, attenuators, alignment
• RF components
• Relays, filters, tunable passive elements
• Biomedicine
• Drug delivery, DNA sequencing, chemical analysis

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Course content

• Fabrication
• Materials, geometry
• Compatibility, integration
• Physics
• Beam theory, electrostatics, thermal, fluidic,
• Design
• Combs, springs, hinges
• Resonators, accelerometers, gyros
• Scanning mirrors

14
Design

• To conceive invent contrive (American Heritage
  Dictionary)
• MEMS Design
• Process
• Device
• System
• Application

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IntelliSuite
16
IntelliSuite
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IntelliSuite
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SUGAR Spice-like environment
Simulation Engine
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Input Netlist
uses mumps.net v1 Vsrc n1 g V10 e1
eground g a1 anchor p1 n1
l5e-6 w10e-6 oz180 R100 b1 beam2de p1 n1
n2 l1e-4 w2e-6 oz0 R1000 g1 gap2de p1 n2
n3 n4 n5 l1e-4 w11e-5 w22e-6
gap2e-6 R1100 R2100 oz0 a2 anchor p1
n4 l5e-6 w1e-5 oz-90 R100 e2 eground
n4 a3 anchor p1 n5 l5e-6 w1e-5
oz-90 R100 e3 eground n5
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Y-axis Accelerometer
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Netlist of Y-axis Accelerometer
uses mumps.net subnet XSusp B susp_len
angle a1 anchor parent A l10u w10u h6u
oz90angle b1 beam3d parent A a1 lsusp_len
w2u h6u oz0angle b2 beam3d parent a1 a2
l10u w2u h6u oz-90angle b3 beam3d parent
a2 B lsusp_len w2u h6u oz180angle b4
beam3d parent A a3 lsusp_len w2u h6u
oz180angle b5 beam3d parent a3 a4 l10u
w2u h6u oz-90angle b6 beam3d parent a4 B
lsusp_len w2u h6u oz0angle subnet XMass
A B finger_len b1 beam3d parent A b1
l25u w50u h6u oz-90 b2 beam3d parent b1
B l25u w50u h6u oz-90 b3 beam3d parent b1
b2 lfinger_len w2u h6u oz0 b4 beam3d
parent b1 b3 lfinger_len w2u h6u
oz180 XSusp p1 c(1) susp_len200u
angle0 for k110 mass(k) XMass p1 c(k)
c(k1) finger_len100u XSusp p1 c(11)
susp_len200u angle180
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Static Simulation Example

• Test structures are fabricated by MCNC
• Beam Nominal Lb100um, w2um, h2um. Measured
  L100um, w1.74um, h2.003um
• Gap plate Lg100um, w10um, h2.003um.
• Youngs Modulus assume 165GPa.
• Simulation was done by considering
  fringing-field effects
• Contact force model was used to get pull-in
  voltage

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Steady State Simulation Examples

• Simulation of a linear multiple mode resonator by
  Reid Brennen. Sugar results match his
  measurements within 5.

The response of vertical displacement of mass
The response of induced current in lower comb
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TA / Gap-Closing Actuator
A)
B)
Transient response of a gap-closing actuator. A)
shows a plot of displacement as a function of
time. The voltage ramps from 5V at t5usec to 12V
at t500usec, and then releases. As the voltage
increases linearly during this time interval, the
space between the gap decreases at a nonlinear
rate due to electrostatic forces likewise, the
period of oscillation decreases. The amplitude of
oscillations decrease exponentially due to the
viscous layer of air between the device and
substrate.
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What is MEMS?

• MEMS is Micro ElectroMechanical Systems
• Integrated circuit processing micromachining
• Sensors, Motors, Structures, Electronics
• ? Systems on a micron to centimeter scale

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Foundry Services and Standard Processes

• MUMPS
• 3 level poly, no electronics
• started in 1992, now 6? runs per year
• LIGAMUMPS
• single level metal, no electronics
• Sandia
• 5 level poly, no electronics
• 1 level poly w/ quality CMOS
• CMOS post-processing
• EDP, TMAH, XeF2 (Parameswaran)
• Plasma (Fedder)

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MUMPS process flow
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MUMPS process flow
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MUMPS process flow
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Sandia National Lab 5 layer polysilicon
5-Level Polysilicon surface Micromachine
Technology Application to Complex Mechanical
Systems M. Steven Rodgers and Jeffry J. Sniegowski
Solid-State Sensor and Actuator Workshop Hilton
Head 1998

31
Planarized, translating gear trains
Sandia National Lab
Solid-State Sensor and Actuator Workshop Hilton
Head 1998

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Most complex mechanical system to date in MEMS?

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2D beam scanning
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8mm3 laser scanner
Two 4-bit mechanical DACs control mirror scan
angles. 6 degrees azimuth, 3 elevation
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MicroOptical Bench (Ming Wu, UCLA)
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LIGA synchrotron lithography,electroplated metal
Closed Loop Controlled, Large Throw, Magnetic
Linear Microactuator with 1000 mm Structural
Height H. Guckel, K. Fischer, and E. Stiers U.
Wisconsin
Micro Electro Mechanical Systems Jan., 1998
Heidelberg, Germany

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Spectacular assembly!
U. Wisconsin
Fig. 2 shows a detailed view of an assembled
actuator.
Micro Electro Mechanical Systems Jan., 1998
Heidelberg, Germany

38
Magnetic Actuation in LIGA
U. Wisconsin
Micro Electro Mechanical Systems Jan., 1998
Heidelberg, Germany

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Tuneable RF components Inductors and Variable
Capacitors
UCLA

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Fiber Attenuator
Bell Labs

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Residual stress gradients
More tensile on top
More compressive on top
Just right! The bottom line anneal poly between
oxides with similar phosphorous content. 1000C
for 60 seconds is enough.
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Residual stress gradients
A bad day at MCNC (1996).
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MEMS Gyroscope Chip
Sense Circuit
Proof Mass
Rotation induces Coriolis acceleration
Electrostatic Drive Circuit
J. Seeger, X. Jiang, and B. Boser
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MEMS Gyroscope Chip
J. Seeger, X. Jiang, and B. Boser
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Digital Light Processor(Texas Instruments)