Micromechatronics Final Report (due 2015/2/10)send your answer (preferably in pdf) to <f3hisyo@iis.u-Tokyo.ac.jp>

(1) Design a thermo-bimorphic microactuator for pressing the square mirror down to the substrate. The chip plan view is shown in Fig. 1.

a. Design the device fit in the dark blue area to maximize the mirror size and complete the plan view. Length of the actuator should not be smaller than Lc/5. Note: longer suspension needs less power to bend.

b. Deduce the formula between mirror height, z, and applied voltage, V, to the pads assuming hinges are so thin that its bending stiffness can be ignored. Draw a curve of z vs. V.

c. Discuss why rounded ends are preferable than square ends for the hinge (Fig. 3). How can rounded ends be made?

d. Give the process chart and draw masks. Please consider two points: (1) lithography cannot be done after etching and (2) material compatibility when sacrificial etching is performed.

(2) Analyze an electrostatic microactuator to drive the square mirror toward the substrate. Details are given in slides 3 and 4.

(3) Compare those actuators in terms of fabrication, control and power consumption.• Please define dimensions and necessary material parameters and deduce formulas.

1

Fig. 3 Hinge part cross-sectionleft: square end, right: rounded endFig. 1 Chip plan view

Lp

Lc

Lp

Lc

Si

SiSiO2

W

Fig. 2 Actuator part cross-section

Bonding pads

mirror actuators

2

3

(1) Design a thermo-bimorphic microactuator for pressing the square mirror down to the substrate. The chip plan view is shown in Fig. 1.

(2) Analyze an electrostatic microactuator to drive the square mirror toward the substrate.First calculate the spring constant, k, of the suspension(quiz 2) and use it in answers of following questions.

a. If the voltage is applied to the suspended mirror shown in Fig. 4, the height of the mirror changes as the curve given in Fig. 5 (pull-in instability: see my lecture slides). If the charge, Q, is applied in stead of the voltage to the mirror, how does the curve of z vs. Q become?

b. Suppose that charge, Q1 , is given to the mirror and fixed as an electret and that the height of the mirror becomes z1. Then, voltage is given to the mirror. Deduce the formula between mirror height and applied voltage. Draw the curve of z vs. V. Calculate the pull-in voltage if there is any.

(3) Compare those actuators in terms of fabrication, control and power consumption.• Please define dimensions and necessary material parameters and deduce formulas.

• References:

M. Mita, Y. Mita, H. Toshiyoshi, H. Fujita: Multi-height Microstructures Fabricated by ICP-RIE and Embedded Masking Layers, Trans. IEE Japan, 120-E, 493 (2000).

T. Sugiyama, M. Aoyama, Y. Shibata, M. Suzuki, T. Konno, M. Ataka, H. Fujita, G. Hashiguchi: SiO2 Electret Generated by Potassium Ions on a Comb-Drive Actuator, App. Phys. Express, 4, 114103 (2011)

Lb

La

Lm

Wb

Fig. 5 Driven by voltage

Fig. 4 Suspended mirror device (z coordinate is also shown)

4

SiO2

Si

Si

Tb z0z

zV

GND

V

zz0 2z0/3

z

GND

+ + + + + + +- - - - - - -

Q

Fig. 6 Driven by charge