Page 167 - Mechatronics for Safety, Security and Dependability in a New Era

Ch31-I044963.fm Page 151 Tuesday, August 1, 2006 3:06 PM
Tuesday, August
3:06 PM
Page 151
1, 2006
Ch31-I044963.fm
151 - & •
151
[nm]
[nm]
[nm]
Δ ΔZ Z [nm] Δ ΔZ Z [nm] Δ ΔZ Z [nm]
3.5 I 12 5
3.5
3 10
4
2.5 8
J_
2 Simulation result 3
Simulation result
6 Simulation result
1.5
Simulation result
/ Simulation result 4 2
1
0.5 2 1
Fit ( 1∝ b )
0 0
0 0 200 400 600 800 1000 1200 0 0 10 10 20 30 30 40 50 50 0
400
200
1000
1200
600
800
40
20
6
8
4
l (beam length) [μm] b (beam width) [μm] 0 2 h (thickness) [μm] 10 12
/ (beam length) [μm]
b (beam width) [μm]
h (thickness) [μm]
Figure2: Relationship Figure3: Relationship Figure4: Relationship
between AZ and / between AZ and b between AZ and h
beam is efficient as compared with other beam shapes in order to form a long beam structure in a
limited space.
RESONAT FREAQUENCY MEASUREMENT
Next, the resonant frequencies of Parylene suspended structures are investigated experimentally. Free
standing Parylene suspended structures are fabricated. The process flow is shown in Fig. 5. A SEM
images of fabricated structures are shown in Fig. 6. And, a rotation tip is also employed in order to
check the actual tensile stress as shown in Fig. 7 [4], and tensile stress is proved to be about 30 MPa.
Resonant frequencies of the fabricated structures are measured. The structures are shaken by a
piezoelectric actuator and the out-of-plane vibrations of them are observed by a LDV (Laser Doppier
Vibrometer). A vacuum chamber is specially developed in order to decrease the influence of air
damping. This vacuum pressure is about 0.8 Pa during measurement. The measured structures are the
same as shown in Fig. 6. Changing the driving frequency of the piezoelectric actuator, the amplitude of
the center of the plate is measured. The result of the frequency response is shown in Fig. 8. From the
results of this figure, it is found that the resonant frequency of normal straight beam structure is 24
kHz and that of spiral shaped beam structure is 12 kHz. From simulation results (omitted from the
want of space), the resonant frequencies of these structures under tensile stress of 30 MPa are 26 kHz
and 11 kHz respectively. Considering that the experimental resonant frequencies agree with simulated
Sputter Si (2|xm)
13npp
0)
Sputter sacrificial silicon and pattern it by SF ( , gas
Anchor Mass Beam Parylene(5u.m)
(2) l^rtfrM
Mass:1000xl000|im Mass:1000xl000|am
Deposit Parylene and pattern it by O 2 plasma length of beam: 300 (am length of beam: 1500 urn
width of beam : 100 Jim width of beam : 100 nm
(3) a) The structure with normal b) The structure with spiral
straight beams shaped beams
Etch sacrificial silicon by XeF 2 gas Figure 6: SEM image of fabricated structure
Figure 5: Fabrication process flow of
suspended structure

- &