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MEMS Rigid Diaphragm Speaker Scott Maghy Tim Havard Sanchit Sehrawat.

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Presentation on theme: "MEMS Rigid Diaphragm Speaker Scott Maghy Tim Havard Sanchit Sehrawat."— Presentation transcript:

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 – 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 Source: Cochlear Implants Auditory Brainstem Implants

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 MET Implant Charger Remote Middle Ear Transducer

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 Silicon Nitride Layer Deposit layers of Electrodes, oxide, and photoresist (as shown) 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 Deposit oxide 3 as shownRemove photoresist and deposit Poly-Si

16 Fabrication Make Poly-Si diaphragm base thickerRelease oxide layers

17 Performance and Optimization

18 Speaker Mechanics whereand Setting + +/- Force balance:

19 Acoustic Modeling Sinusoidal input voltage: Which causes sound intensity: Drives diaphragm displacement: 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 P ac watts Rocket engine1,000,000 W TurbojetTurbojet engine10,000 W Siren1,000 W Machine gun10 W Jackhammer1 W Chain saw0.1 W Helicopter0.01 W Loud speech, vivid children 0.001 W Usual talking, Typewriter Typewriter 10 −5 W Refrigerator10 −7 W (Auditory threshold at 2.8 m)Auditory threshold10 -10 W (Auditory threshold at 28 cm)Auditory threshold10 -12 W Device is in the threshold of human hearing! Decreasing frequency

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


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