Page 224 -

6

Answers, Hints and Solutions

Chapter 1

A1.1 There are several aspects in comparingthe fabrication methods for
microstructures: productivity, thickness, structure, and material used. Pho-
tolithography and LIGA will be used for mass production, but photoforming
will be used for small-scale production and also for fabricatinga complicated
3-D structure. An EBL, which has high resolution and does not require masks,
will be used for fabricatingmicrostructures less than 1 µm thick. Photolitho-
graphy will be used for fabricating microstructures less than several 10 µm,
and LIGA less than several 100 µm. The latter two require the use of masks
for the etching. Groups III–V compound materials are used to integrate an
LD and a PD.
A1.2 A sacrificed layer is the layer that is etched away, whereby the
microstructure is undercut, leavingit freely suspended (see Sect. 1.2.1).
A1.3 Friction-less and contact sticking-free structures are needed for optical
MEMS because of the increase of the surface effect. Refer to the scalinglaw
(see Sect. 1.3.1).
3
A1.4 The moment of inertia of the mirror is I 1 = ρab t/12.I 2 with a 50%
3
reduction in the dimensions is I 2 /I 1 =(0.5)(0.5) (0.5) = 3.1%.
2
3
A1.5 Response time is proportional to [mass/frictional force], i.e., [L /L ]=
[L], which leads to faster response as L decreases.
A1.6 See Sect. 1.5.