MEMS Tuning-Fork Gyroscope
Group 8:
Amanda Bristow
Travis Barton
Stephen Nary
What is a MEMS Gyroscope?
A small, silicon device
that senses rotation
●
Benefits:
●Small size
●Low power
●Cheap to mass produce
●
MEMS Gyroscope viewed under a microscope
Where is it Used?
Used in devices
requiring detection of
rotational motion:
●
IPhone 4
●
Wii Motion Plus
accessory
●
iPhone 4
Wii Motion Plus
Purpose
To refine an existing MEMS Gyroscope design to improve
accuracy
●
To examine the method of fabrication for MEMS devices
●
To gain practical experience with the testing of MEMS devices
using the existing design
●
Structure of a MEMS Gyroscope
Symmetric mechanical
structure
●
Gyroscope structure
free to move, except at
anchors
Sense
electrodes
●
Proof mass
Proof mass
Comb Drive
Transducers used to
drive proof masses
●
Sense electrodes used
to detect rotation
●
Gyroscope Structure
Drive Mode
Structure made to vibrate
at natural frequency
●
Vibration of proof mass
provides necessary
velocity for Coriolis
Acceleration
●
Drive Mode Vibration
Sense Mode
When rotation is
applied, Coriolis force
causes proof mass
direction to change
●
Coriolis Acceleration
ac  2  V
Sense Mode Vibration
Optimization of Mechanical
Structure
Ideal frequency range: 15
kHZ – 30 kHz
●
L2
Ideal difference between
drive mode and sense mode:
50 Hz – 100 Hz
●
L1
Key Dimensions for
adjusting frequency:
●L2 → Sense Mode
●L1 → Drive Mode
●
Key Dimensions
Optimization of Mechanical
Structure
Trial L1, μm Drive L2, μm Sense Difference
4
530 14598.075
620 15888.053 1289.978
5
520 14924.587
620 15904.967 980.381
6
510 15281.028
620 15922.051 641.023
7
500 15653.750
620 15942.423 288.673
8
499 15694.665
620 15943.953 249.289
9
498 15730.412
620 15944.225 213.813
10
497 15759.223
620 15944.581 185.358
11
496 15809.871
620 15947.541 137.670
12
495 15832.345
620 15948.254 115.910
13
494 15872.906
620 15951.401
78.495
14
493 15911.840
620 15953.967
42.127
15
492 15951.379
620 15951.931
0.552
Optimization of Mechanical
Structure
Comb Drive Transducers
Form capacitors with proof
masses
●
Use “fingers” to increase
surface area
●
Proof mass
AC voltage applied to one
transducer to excite proof
masses to vibrate
●
Other transducer used to
monitor drive mode
vibration
Proof mass
●
Comb Drive
Transducers
Designing the Comb Drive
Transducers
Proof Mass Vibration Amplitude
VDC
2nε 0 hVDC v AC
q0 =
Q
gk
~
vAC
Voltage Sources
Magnified View: Proof Mass and
Comb Drive Fingers
CAD Model for Mask
-Calculations determine structure
dimensions
-Total of 25 fingers on proof
mass
-2 micron interference for comb
transducers
-3 micron sense gap
Manufacturing of MEMS Gyroscope
1. Design is laser etched onto a chrome plated mask.
2. Align mask above silicon wafer.
3. Expose wafer and mask to UV light.
Mask
Photo resist
Silicon
substrate
Manufacturing of MEMS Gyroscope
5. Developing
Manufacturing of MEMS Gyroscope
Mechanical structure needs to move freely. Therefore special wafer is
used.
6. Etch SiO2
Note: HF does not etch away all
SiO2
Planned Work
Complete Sense Mode
Calculations
●
Complete AutoCAD drawing for
gyroscope die
●
Connect PCBs for testing
●
Learn testing procedure
●
Learn to interpret data
●
PCB
Questions?