1. MEMS Rigid Diaphragm Speaker
Scott Maghy
Tim Havard
Sanchit Sehrawat

2. Macro-scale
Try to make MEMS device based on same concept

3. Motivation Few similar products Small size Potential lower cost
Clandestine
Privacy
Low power
Potential lower cost
Highly customizable performance
No surgery!

4. Current Hearing Devices
Few speakers that fit completely inside the ear
Some piezoelectric speakers
Bone conduction speaker for above the ear: 1 inch long
CMOS MEMS speakers exits, and are being developed
Several hearing devices
Downsides:
Require surgery
Much larger
Cost
Complexity

5. Implantable Hearing Devices
Cochlear Implants
Auditory Brainstem implants
Implantable Middle-ear devices
Piezoelectric devices
Electromagnetic devices

6. Auditory Brainstem Implants
Cochlear Implants
Auditory Brainstem Implants
Source:

7. Piezoelectric Devices
Operation
Advantage: inert in a magnetic field
Disadvantage: Power output directly related to size of crystal.
Example:
Middle Ear Transducer (MET)
Pass current into Piezoceramic Crystal
Crystal changes volume
Vibratory signal produced

8. Middle Ear Transducer
Translates electrical signals into mechanical motion to directly stimulate the ossicles

9. Middle Ear Transducer
Remote
MET Implant
Charger

10. Electromagnetic Devices
Operation
Small magnet is attached to vibratory structure in ear
Only partially implantable – coil must be housed externally. Sizes of coil & magnet restricted by ear anatomy.
Power decreases as the square of the distance between coil & magnet – coil & magnet must be close
Pass current into Electric Coil
Magnetic Flux created
Drives adjacent magnet

11. Vibrant Soundbridge
Magnet surrounded by coil

12. Ridged Diaphragm MEMS Speaker

13. Materials
Polysilicon: structural material for cantilever and diaphragm
Silicon Oxide: for sacrificial layers
Silicon Nitride: isolation of wafer
Gold: electrodes and electrical connections

14. Fabrication Deposit layers of Electrodes, oxide,
and photoresist (as shown)
Deposit Silicon Nitride Layer
Pattern photoresist & then etch
electrodes & oxide using RIE
Deposit Oxide 2 layer

15. Fabrication Etch oxide 2, and make Poly-Si columns
Coat columns with Photoresist and
etch away remaining oxide 2
Remove photoresist from electrode 2
Etch oxide 2, and make Poly-Si columns
Deposit oxide 3 as shown
Remove photoresist and deposit Poly-Si

16. Fabrication
Make Poly-Si diaphragm base thicker
Release oxide layers

17. Performance and Optimization

18. Speaker Mechanics Fspring Felect Force balance: + +/- where and
Setting

19. Acoustic Modeling Sinusoidal input voltage:
Drives diaphragm displacement:
Which causes sound intensity:
Acoustic power can then be obtained:
Note: system parameters can be tailored to be significantly below the resonant frequency.

20. Observed Acoustic Power
Sound intensity decays quadratically with distance
 This results in limited effective speaker range

21. Comparison of Acoustic Sound Power
Situation and sound source
sound power Pac watts
Rocket engine
1,000,000 W
Turbojet engine
10,000 W
Siren
1,000 W
Machine gun
10 W
Jackhammer
1 W
Chain saw
0.1 W
Helicopter
0.01 W
Loud speech, vivid children
0.001 W
Usual talking, Typewriter
10−5 W
Refrigerator
10−7 W
(Auditory threshold at 2.8 m)
10-10 W
(Auditory threshold at 28 cm)
10-12 W
Decreasing frequency
Device is in the threshold of human hearing!

22. Improvements
Implement a process that allows for sealing of speaker cone to support
This would give better acoustic properties
Could be accomplished by CMOS MEMS procedure
Fabricate cone shape with stamping method to achieve better shape and more cost effective fabrication

23. Improvement Cont.
Further research into materials for the cantilevers to decrease stiffness of cantilevers
This would allow greater diaphragm displacement and therefore greater intensity
Other materials exist with lower Young’s modulus that would accomplish this but fabrication is suspect
Other methods of securing the diaphragm
“Spring” attachment
Decrease the mass of the diaphragm by altering fabrication process

24. QUESTIONS