Page 168 - Mechatronics for Safety, Security and Dependability in a New Era

Ch31-I044963.fm Page 152 Tuesday, August 1, 2006 3:06 PM
Ch31-I044963.fm
152
152 Page 152 Tuesday, August 1, 2006 3:06 PM
results, the FEM simulation taking account of intrinsic tensile stress in this study is thought to have
good validity. It is surely confirmed theoretically and experimentally that the a spiral beam is effective
for lowering the resonant frequency of /,., which leads to the sensitivity of accelerometer of
2
l/(2^) .
Amplitude [nm]
Amplitude [nm]
10 10
The structure with normal
9
straight beams
8
7
From rotation angle, it is proved 6
actual tensile stress is 30 MPa 5 The structure with spiral
Figure 7: Optical microscope view image of 4 shaped beams
Rotation Tip
3
Theoretical Theoretical
2
11kHz 26kHz
1
12kHz 24kHz
0
20
10 15 15 20 25
Freaquency[kHz]
Freaquency[kHz]
Figure 8: Result of frequency response
CONCULUSION
An accelerometer made of Parylene, which comprises a proof mass and support beam, has been
developed now. In this study, the stiffness and the resonant frequency of suspended microstructures
under tensile stress are investigated. The summary is as follows:
1) It is proved by FEM simulation that the stiffness is decreased in proportion to the first power of the
beam length, while it is decreased in proportional to the third power of it under no stress according
to the theory of strength of materials. Therefore, the structure with spiral beam is proposed.
2) Free standing Parylene suspended structures are fabricated by a micromachining process. The
vibrations of these structures are observed by using a LDV and resonant frequencies of them are
obtained. It is found that the resonant frequency of the structure with spiral beams is lower than
that with straight beams, which shows the effectiveness of spiral beams for obtaining high
sensitivity of accelerometer.

ACKNOWLEDGEMENT
This work was mainly supported by JSPS (Japan Society for the Promotion of Science).KAKENHT
(16310103). This work was also partially supported by MEXT (Ministry of Education, Culture, Sports,
Science and Technology). KAKENH1 (17656090), "High-Tech Research Center" Project for Private
Universities: Matching Fund Subsidy from MEXT, 2000-2004 and 2005-2009, the Kansai University
Special Research Fund, 2004 and 2005.

REFERENCE

[1] Tai Y. C. (2003). Parylene MEMS: Material, Technology and Application. Proc. 20th Sensor
Symposium, 1-8.
[2] Aoyagi S. and Tai Y. C. (2003). Development of Surface Micromachinable Capacitive
Accelerometer Using Fringe Electrical Field. Proc. Transducers'03, 1383-1386.
[3] Harder T. A., Yao T. J., He Q., Shih C. Y. and Tai Y. C. (2002). Residual Stress in Thin-Film
Parylene-C. Proc. MEMS'02, 435-438.