Tuyển tập công trình Hội nghị Cơ điện tử toàn quốc lần thứ 6 459
Mã bài: 108
Nghiên cứu thiết kế và chế tạo con quay vi cơ fork tuning
có độ nhạy cao
Design and Fabrication of an Enhanced Sensitivity Tuning Fork
Micro-Gyroscope
Nguyen Quang Long
1
, Chu Manh Hoang
1,

, Trinh Quang Thong
2
,
Chu Duc Trinh
3
and Vu Ngoc Hung
1

1
International Training Institute for Materials Science, Hanoi University of Science and Technology
2
The Institute of Engineering Physics, Hanoi University of Science and Technology
3
MEMS Dept., Faculty of Electronics and Telecommunications, University of Engineering and Technology,
Vietnam National University
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Tóm tắt:
Chúng tôi trình bày kết quả nghiên cứu thiết kế và chế tạo cảm biến con quay vi cơ fork tuning có độ nhạy
cao. Độ nhạy vận tốc góc của cảm biến được khuếch đại bởi hệ số phẩm chất của mốt nhạy khi điều kiện cộng
hưởng cơ trong mốt nhạy và mốt chấp hành được thỏa mãn. Cấu trúc điện cực răng lược trong mốt nhạy cũng

possible to reject common-mode acceleration
inputs by a differential Coriolis measurement [2].
However, the detection of the sensor signal in
micromachined gyroscopes is quite challenging

due to small output capacitance signal. In order to
improve the sensitivity of a vibratory gyroscope,
the driving and sensing vibration modes of the
gyroscope need designed and fabricated with the
matched resonant frequencies [3]. When driven at
the resonant condition, the amplitude of sensing
mode vibration is amplified by its mechanical
quality factor. In [4], the sensing-mode quality
factor is increased by eliminating the energy
dissipation through the substrate using the anti-
phase operation of a dual mass tuning fork
gyroscope architecture and the mode-matching
operation in vacuum condition. In a latest report
[5], the research showed that the tuning fork
gyroscopes having decoupled sense and drive
masses with an anchored drive mass is less
460 Nguyen Quang Long, Chu Manh Hoang, Trinh Quang Thong, Chu Duc Trinh, Vu Ngoc Hung

VCM2012
sensitive to vibration than tuning fork gyroscope
designs featured in literature. To increase signal to
noise ratio, the mass and capacitance of a
capacitive type gyroscope are also required to be
as large as possible.
In this paper, design and fabrication of a


The main structure of the Turning Fork Gyroscope
design comprises two proof masses, each of which
includes the outer frame for driving and the inner
one for sensing. The drive comb electrode set is
attached to the outer frame and designed such that
in driving mode the masses oscillate in opposite
direction along x-axis due to electrostatics force.
The rotation rate is measured by a capacitance
change. A pair of sense electrode set using the
balanced scheme is placed symmetrically within
each inner mass frame. In order to increase the
change of capacitance, we here design four comb
banks each side of sense electrode set. The
dimension of comb finger is 30 μm length and 3
μm width. The gap between two adjacent fingers is
2.5 μm. Upon the rotation the Coriolis force
excites these mass frames in out of plane motion
that the differential capacitance can be detected.
This design also employs the folded beams for
suspension. The suspensions of the proof mass are
designed to allow the structure to oscillate in two
orthogonal modes.
After we have the designed model, the sensor was
verified by finite element analysis (FEA) using
ANSYS software. In this case, SOLID45 element
was employed for modeling and simulation. The
dimension parameters of the proof mass and the
suspension beam were investigated to have the
optimal the designed mechanical structure of the
Tuyển tập công trình Hội nghị Cơ điện tử toàn quốc lần thứ 6 461
Mã bài: 108 Fig. 2 FEA result of gyros obtained by ANSYS, (a)
sensing and (b) driving mode
3. Fabrication process
The gyroscope has been fabricated by SOI-based
MEMS technology as shown schematically in Fig.
3. The main steps in the fabrication process are
described as follows. The 4-inches Silicon-On-
Insulator (SOI) wafer was used for fabrication
with thickness of a device layer is 30 µm, buried
silicon dioxide layer is 4 µm and substrate is about
500 µm (Fig. 3 (a)). First, the SOI wafer has been
cleaned by SC process. Next, the sensors patterns
were transferred to the surface of SOI wafer after
photolithography and developing processes (Fig. 3
(b)) with positive photoresist layer. This layer has
a role as protecting mask, which used for DRIE
process in next step.

Fig. 3 Main steps of the fabrication process

Then, DRIE process was performed to a depth of
30 µm to reach the buried dioxide layer of SOI
wafer (Fig. 3 (c)). The SOI wafer was then diced
to separate each sensor. Vapor HF etching process

Figure 4 shows SEM pictures of gyroscope after
fabrication process. The pictures show that the
good fabrication process has been achieved. All
the moving parts seem to be released. The edges
are very well etched and not broken or damaged in
structure and sensing electrodes.
Packaging is a final step to complete the fabricated
sensors. Firstly, the sensor chip is glued on a
device holder using two components epoxy, which
may be either made of hard plastic or metal with
pins for use. Next step is wire bonding process. In
this work, the Westbond 7400C was used to
package the device.
Figure 5 shows a picture of packaged device.
When the fabrication period is finished, basic tests
are performed on capacitive micromachined
sensors. Fig. 5 Sensor after packaging

Fig. 6 The 1-port actuation and detection scheme
for frequency response extraction
These are the stiction test, short circuit test, and
capacitance test. These basic tests were carried out
using probe station equiped a microscope, a
milimeter and an impedance analyzer.
In order to improve the sensitivity of a vibratory
gyroscope, the driving and sensing vibration
modes of the gyroscope need fabricated with the

Design and fabrication of a symmetric tuning fork
gyroscope with enhanced sensitivity were
presented. The closely matched resonant
Tuyển tập công trình Hội nghị Cơ điện tử toàn quốc lần thứ 6 463
Mã bài: 108
frequencies were obtained for the driving and
sensing vibration modes of the gyroscope. In order
to enhance the sensitivity of the gyroscope,
parallel-plate sensing comb structure with
increasing number of comb electrodes was also
designed. The gyroscope was fabricated by SOI-
based high-aspect ratio micromachining process.

Acknowledgement
This work is supported by the Ministry of Science
and Technology (MOST), Vietnam under the
NAFOSTED project coded MS 103.02-2010.23.

References
[1] Yazdi, N.; Ayazi, F.; Najafi, K.;
Micromechanical inertial sensors, in :
Proceedings of the IEEE, pp. 1640-1659, 1998
[2] Weinberg, M.S.; Kourepenis, A.; Error sources
in in-plane silicon tuning-fork MEMS
gyroscopes, J. Microelectromech. Syst. 15 (3),
pp. 479-491, 2006
[3] Maenaka, K., Fujita, T.; Konish, Y.; Maeda;
M.; Analysis of hightly sensitive silicon
gyroscope with cantilever beam as vibratin,g
mass, Sen. Actuators A, 54, pp. 568-573, 1996

School of Mechanical Engineering, Tohoku
University, Japan, in 2011. He was a Fellow of the
Japanese Society for the Promotion of Science
from April 2010 to March 2012.
Since September 2012, Dr. Chu is a lecturer at
Hanoi University of Science and Technology. His
current research interests are MEMS inertial
sensors, micro-mirrors, and nanophotonic. He is a
reviewer for several international journals. Thong Quang Trinh received his
PhD degree in electrical
engineering from Dresden
University of Technology,
Germany, in 2006. From 1986 to
1999 he worked in the field of
applied physics at the Institute for
Applied Physics at Vietnamese Academy of
Science and Technology (VAST). Since 2000 he
has been Senior Scientist at Hanoi University of
Science and Technology (HUST). His current
research interests are focused on the design of
sensors and sensor systems including the
simulation of their components as well as
development of MEMS mechanical sensors for
different applications. Chu Duc Trinh received the B.S.

Workshop on Micromechanics Best Poster Award
in 2006. He is guest editor of the Special Issue of
“Microelectromechanical systems” Vietnam
journal of Mechanics, in 2012. Hung Ngoc Vu received the B.S. degree in physics
from Kishinev University (USSR), in 1979 and the
Ph.D. degree from Hanoi
University of Technology
(Vietnam), in 1991. His doctoral
thesis dealt with the
xeroradiography. At present, he is
an Associate Professor with the
International Training Institute for
Materials Science (ITIMS), Hanoi
University of Technology. His current research
interests are in the area of MEMS inertial sensors
and PiezoMEMS.