This presentation discusses a capacitive silicon resonator structure with movable electrodes designed to reduce capacitive gap widths. The presentation includes sections on the introduction and motivation, principle of operation, purpose, design, experiment results, and conclusion. The key points are that movable electrodes allow the gap width to be reduced electrostatically, lowering the motional impedance and insertion loss compared to a standard resonator. Experimental results showed a 21 dB lower insertion loss and 7 times better frequency tuning capability compared to a resonator without movable electrodes. In conclusion, the design of movable electrodes improved performance for capacitive silicon resonators.

1. 按一下以編輯母片標題樣式
NATIONAL TSING HUA UNIVERSITY
National Tsing Hua University
HsinChu, Taiwan
Presenter : Wan-Cheng Chiu (邱萬誠)
Instructor : Cheng-Hsien Liu (劉承賢)
Midterm Project Presentation
-Presentation I-
April 22, 2014
NATIONAL TSING HUA UNIVERSITY
Capacitive Silicon Resonator Structure with Movable
Electrodes to Reduce Capacitive Gap Widths Based on
Electrostatic Parallel Plate Actuation

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• Introduction & Motivation
• Principle
• Purpose
• Method
• Design
• Experiment Results
• Conclusion
Outline

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•Resonator is a fundamental component in many MEMS devices.
•Small electromechanical structure that vibrate at high frequencies
Introduction
Mode Shape Mode Shape

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•These devices can be used as timing references, filters, sensors, and
so on.
•It has the possibility to replace quartz due to the capability for further
miniaturization.
Introduction & Motivation
Medical Ultrasonography
GPS
Smartphone

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•For two parallel plate:
Principle
+
V
-
g
Capacitance = εA/g
If one of the plate is free to move up
and down, then the capacitance can
vary.

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•For a single beam capacitive resonator, we can measure the response
of the device.
Principle
When a small signal vi
is applied, we will get a
frequency response.
Resonant
frequency
vi
Rm im
Vp
vo
Driving
electrode
Sensing
electrode
Resonator
body

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Principle
•Electrical System• Mechanical System
Lm = mr / ηe
2
Rm = cr / ηe
2
Cm = ηe
2 /kr
mr
kr = ωn
2mr
cr = (√krmr)/Q

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Principle
• Pull-In Effect
g0
2/3g0
•Spring Force:
Fspring = kδ
•Electrostatic Force:
Fe = εAV2/2(g- δ)2
Fnet = εAV2/2(g- δ)2 - kδ
•Pull-In Voltage:

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Purpose
•Electrical System
Lm = mr / ηe
2
Rm = cr / ηe
2
Cm = ηe
2 /kr
Rm is also known as motional impedance,
a low Rm device has a low insertion loss
and lower phase noise.
In this paper, the author focus on reducing
gap width to reduce the motional
impedance.

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Method
By making the electrodes movable,
when voltage is applied the electrodes
will move towards the resonator body
due to electrostatic force. Thus the gap
widths become smaller.
d Rm

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Design
•The electrodes are attached to spring,
which will make the electrodes movable.
•In the design stoppers are added to
prevent pull-in effect from occurring.
•The new gap width is equal to:
greduced = gB-B’ – gA-A’

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Experiment Results
•The image below is a SEM image of silicon resonator with movable electrodes.
A-A’ is the stopper gap = 400nm
B-B’ is the capacitive gap = 500nm
Final gap = 100nm
＊A same version of the silicon resonator without movable electrodes is also fabricated
for measurement comparison.

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Experiment Results
•The measurement was done inside a vacuum chamber with pressure of 0.01 Pa.
The resonator with movable
electrode shows lower insertion loss
and Rm.

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Experiment Results
• Loading Effect Qloaded:
Originally, the Q of the device can be calculated by:
However, when we measure a device, other resistances needs to be included:
Rm
R1 R2
Since the Rm of the movable electrode resonator is
smaller, the loading effect affects the Q more than
the other resonator.

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Experiment Results
•By applying different bias voltage, VDC, to the resonator we can observe the frequency
shift.
•The resonator with movable
electrode has a better tuning
capability than the other.
•This is an advantage because
due to fabrication process or
operation temperature the
resonant frequency may shift
from our desired frequency.

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Conclusion
• In this paper, capacitive silicon resonators with
movable electrodes was designed, fabricated,
and evaluated.
• The insertion loss increased by 21 dB, and the
motional impedance was reduced.
• The frequency tuning capability is also 7 times
better.

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~Thank you for your attention~