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MEMS Fabrication 63

material selectivity is necessary to make useful devices. Commercial applications
utilizing bulk micromachining are available such as accelerometers and ink-jet
nozzles.
LIGA is a fabrication technology that utilizes x-ray synchrotron radiation, a
thick resist material and electroplating technology to produce high aspect ratio
metallic devices.
Surface micromachining is a technology that uses thick films and processes
from the microelectronic industry to produce devices. Surface micromachining
employs two types of materials, a sacrificial material and a structural material, in
alternating layers. A release process removes the sacrificial material in the last step
in the process, which produces free function structural devices. Surface microma-
chining enables large arrays of devices since no assembly is required. Surface
micromachining is also integratable with microelectronic for sensing and control.
Two notable commercial applications of surface micromachining are the TI DMD
and the Analog Devices ADXL accelerometers.
New materials are being developed to enhance MEMS applications. For ex-
ample, silicon carbide is a hard, high-temperature material, which can withstand
harsh environments. Silicon–germanium and diamond are materials that can be
deposited at low temperatures, which enable increased MEMS process flexibility.
SU-8 is an epoxy photo resin that can be used to produce high aspect ratio channels
and molds.

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