Introduction to MEMS
Bruce K. Gale Mechanical Engineering Department BIOEN 6421, ELEN 5221, MEEN 5960 and 6960
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Overview
What is micromanufacturing and MEMS? ! Why the interest in MEMS? ! IC Fabrication Processes ! Bulk Micromachining Processes ! Surface Micromachining Processes ! Combined Processes ! References
MEMS - evolved from the Microelectronics Revolution IC Industry Timeline
1947 1958 1999
So what exactly is MEMS?
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common substrate through the utilization of microfabrication technology or microtechnology.
single transistor
first IC
10 million transistors
MEMS Examples
pressure sensors accelerometers flow sensors inkjet printers deformable mirror devices gas sensors micromotors microgears lab-on-a-chip systems
1980
MEMS Timeline
1999
Bulk micromachined pressure sensor
2030
TI DMD
(1.3 million micro-mirrors)
The Opportunity of MEMS Technology
General MEMS Advantages
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Batch fabrication
Reduced cost
Reduced size
Is everything better smaller?
Reduced power ! High precision ! New capabilities? ! Improved performance?
The MicroTechnology/MEMS Tool Set
Cleanroom plus microfab processes !
Micromachining Processes
Standard Integrated Circuit (IC) Processes
Identical to those used in IC fabrication Generally used for surface micromachining
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Surface Micromachining
Additive processes
Bulk Micromachining
Subractive Process
Dividing line can become very blurry
Standard IC Processes
Standard IC Processes Photolithography
Source: Jaeger
Source: CWRU Source: Jaeger
Standard IC Processes
Standard IC Processes
1) Deposit/Grow Thin Films
Sputtering Evaporation Thermal Oxidation CVD Spinning Epitaxy
2) Pattern Thin Films
Lithography Etching Techniques (wet, dry, RIE)
Standard IC Processes 3) Introduce Dopants (to form electrically-active regions for diodes, transistors, etc.)
Thermal Diffusion Ion Implantation
Micromachining Processes Bulk Micromachining
wet vs dry isotropic vs anisotropic subtractive process
Micromachining Processes Bulk Micromachining
Micromachining Processes Deep Reactive Ion Etching (DRIE)
Source: Madou
high density ICP plasma high aspect ratio Si structures cost: $500K
Source: LucasNova
Source: Maluf
Source: Maluf
Source: STS
Source: STS
Source: AMMI
Micromachining Processes Wafer-Level Bonding
glass-Si anodic bonding Si-Si fusion bonding eutectic bonding low temp glass bonding
MEMS Examples Pressure Sensor (conventional)
Source: NovaSensor
60
Output Voltage (m V)
50 40 30 20 10 0
Source: Maluf
Source: EV
Source: UofL
20
40
60
80
100
120
Pressure (PSI)
Micromachining Processes Surface Micromachining
additive process structural & sacrificial layers
Micromachining Processes LIGA (lithographie, galvanoformung, abformtechnik)
uses x-ray lithography (PMMA), electrodeposition and molding to produce very high aspect ratio (>100) microstructures up to 1000 um tall (1986)
Source: Sandia
Source: Madou
Source: Kovacs
MEMS Examples Micro-structures using LIGA
Micromachining Processes Poor Mans LIGA
uses optical epoxy negative-resist (SU-8) developed by IBM to produce high aspect ratio micro-structures (1995)
UofL Micro-reaction wells: 150 um wide, 120 um tall, 50 um wall thickness Source: UW Source: Maluf
MEMS Examples Micromotors
MEMS Examples Optical MEMS (MOEMS)
Source: MIT and Berkeley
Source: NIST, Simon Fraser, UCLA, and MCNC
MEMS Examples Pressure Sensor (ultra-miniature)
MEMS Examples Lab-on-a-Chip Systems
separation dilution mixing and dispensing analysis
Source: NovaSensor
Source: Caliper
Integration
Micromachining processes may be integrated ! Both bulk and surface micromachining may be performed on a single substrate ! Micromachined structures may be integrated with ICs
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EFFF Fabrication 1
Anisotropic etching of input and output ports in 20% KOH at 65 C with Si3N4 mask Deposit and pattern Ti/Au electrodes on front of wafer Thick photosensitive polyimide or SU-8 used to define flow channels
Silicon Au
Conta ct
Detect or Silicon Polyimide Silicon
Ti
EFFF Fabrication 2
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EFFF Fabrication 3
Output Port Input Port
Remove Si3N4 membrane Deposit and pattern Ti/Au electrode on glass substrate Bond glass substrate to polyimide using biocompatible UV curable adhesive
Silicon Glass Au Glass Silicon Ti
Completed channel looking from the top
Channel Polyimide Detector Electrode Channel Electrod
Cross section through channel showing electrodes, polyimide and substrates
Completed Cross Section
Results- Section Fabrication
Glass substrate with titanium, gold, and platinum electrode Silicon substrate with input/output ports, gold electrodes and patterned SU-8
ResultsSystem Assembly
Above- Complete device with input/output port connections Right- Complete systems with sample and buffer input, -EFFF system, and detectors
MEMS Examples
Fabrication Results
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Micromachined Tips for FEDs and AFMs
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Micrograph of detector wire across channel defined by polyimide Wire is 19 m wide Location of wire eliminates all end effects
Detection Wire
Output Port Channel Sidewalls
Source: Micron (?) Source: IBM
MEMS Examples Neural Probes
MEMS Examples Neural Interface Chip
Source: Mich (K. Wise)
Source: Stanford
MEMS Examples Micro-Grippers Micro-Tweezers
MEMS Examples
Source: Berkeley
Source: MEMS Precision Instruments
MEMS Examples Optical MEMS (MOEMS) Accelerometers
MEMS Examples
Source: IMC (Sweden), Maluf and TI
Sources: Analog Devices, Lucas NovaSensor, and EG&G IC Sensors
MEMS Examples Channels, Nozzles, Flow Structures, and Load Cells
MEMS References
Fundamentals of Microfabrication; Marc J. Madou Micromachined Transducers Sourcebook; G. Kovacs An Introduction to MEMS Engineering; by Nadim Maluf Silicon Micromachining; by Elwenspoek and Jansen Microsensors; by Richard S. Muller, Roger T. Howe, Stephen D. Senturia, R. Smith (Editors) Micromechanics and Mems : Classic and Seminal Papers to 1990; by W. Trimmer (Editor)
Source: EG&G IC Sensors
MEMS WWW Bookstore: http://mems.isi.edu/bookstore/
