sensing and actuation in miniaturized systems _ midterm presentation

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


Capacitive Silicon Resonator Structure with Movable

Electrodes to Reduce Capacitive Gap Widths Based on

Electrostatic Parallel Plate Actuation


National Tsing Hua University

2

• Introduction & Motivation

• Principle

• Purpose

• Method

• Design

• Experiment Results

• Conclusion

Outline



3

•Resonator is a fundamental component in many MEMS devices.

•Small electromechanical structure that vibrate at high frequencies

Introduction

Mode Shape Mode Shape



4

•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 UltrasonographyGPS

Smartphone



5

•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.



6

•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



7

Principle

•Electrical System• Mechanical System

Lm = mr / ηe2

Rm = cr / ηe2

Cm = ηe2 /kr

mr

kr = ωn2mr

cr = (√krmr)/Q



8

Principle

• Pull-In Effect

g02/3g0

•Spring Force:

Fspring = kδ

•Electrostatic Force:

Fe = εAV2/2(g- δ)2

Fnet = εAV2/2(g- δ)2 - kδ

•Pull-In Voltage:



9

Purpose

•Electrical System

Lm = mr / ηe2

Rm = cr / ηe2

Cm = ηe2 /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.



10

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



11

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’



12

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 = 500nmFinal gap = 100nm

＊A same version of the silicon resonator without movable electrodes is also fabricated

for measurement comparison.



13

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.



14

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.



15

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.



16

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.



17

~Thank you for your attention~

sensing and actuation in miniaturized systems _ midterm presentation

Engineering