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
Lc
Si
W
SiO2
mirror
actuators
Lc
Si
Fig. 2 Actuator part cross-section
Lp
Lp
Bonding pads
Fig. 1 Chip plan view
Fig. 3 Hinge part cross-section
left: square end, right: rounded end
2
(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)
3
V
z
Wb
Lb
GND
z
z0
2z0/3
Lm
z
Tb
Si
V
Fig. 5 Driven by voltage
z0 La
SiO2
Si
z
Q+ + + + + + +
- - - - - - -
Fig. 4 Suspended mirror device
(z coordinate is also shown)
GND
Fig. 6 Driven by charge
4