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2 1 From Optical MEMS to Micromechanical Photonics
[1.8, 1.9] for optical and magnetic recording, and µ-TAS [1.10] for medical
treatment.
Advanced lithography has been applied not only to silicon (Si) but also
to thin film materials, includingdielectric [1.11], polyimide [1.12], and metal
[1.13] to offer unprecedented capabilities in extendingthe functionality and
miniaturization of electro-optical devices and systems. Group III–V com-
pounds, which include gallium arsenide (GaAs) [1.14] and indium phosphide
(InP) [1.15], are attractive for integrating optical and mechanical structures to
eliminate the need for optical alignment. In a tunable LD, the moving external
cavity mirror has been integrated with a surface-emitting LD [1.16]. A moving
cantilever has been integrated with edge-emitting LDs and a photodiode in a
resonant sensor [1.17]. Monolithic integration technologies are expanding the
field of micromechanical photonics.
Novel probingtechnologies such as the scanningtunnelingmicroscope
(STM) and optical tweezers have advanced our knowledge of surface sci-
ence [1.18, 1.19] and technology, which are important in microscale and
nanoscale mechanisms. Today’s science and technology requires the focus-
ing of multidisciplinary teams from engineering, physics, chemistry, and life
sciences in both universities and industry. In this chapter, I first review
fabrication methods of microstructures, then summarize some of the high-
lights in these attractive research fields, and then discuss the outlook for the
future.

1.2 Fabrication Methods

There are common steps in fabricatingoptical MEMS/micromechanical
devices: deposition, sputteringand etching, bulk micromachiningincluding
anisotropic etchingand etch stop, and surface micromachiningcharacterized
by sacrificed layers that are etched away to leave etch-resistant layers. The
fabrication methods of microstructures with optical elements are reviewed
in [1.1,1.2]. Miniaturization requires high aspect ratios and new materials. Re-
active ion beam etching(RIBE) precisely defines the features and the spacing
in deposited thin film and is of great importance in making high-aspect-ratio
microstructures.
Si has been the most commonly used in micromachining, and its good elec-
trical and mechanical properties have resulted in many commercially available
sensors and actuators. A diaphragm is fabricated by bulk micromachining
such as selective wet etching. Free-space micro-optical systems can be fabri-
cated by surface micromachining; this is very promising and will greatly enrich
the variety of integrated optical devices [1.20]. One choice is the silicon-on-
insulator (SOI) technology [1.21]. Advantages of the SOI technology are its
simplicity and small number of process steps.
Group III–V compounds, such as GaAs and InP, are attractive candidates
for monolithic integration of optical and mechanical structures [1.14, 1.15].
Concrete examples are given later.