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MEMS Rigid Diaphragm Speaker

MEMS Rigid Diaphragm Speaker. Scott Maghy Tim Havard Sanchit Sehrawat. Macro-scale. Try to make MEMS device based on same concept. Motivation. Few similar products Small size Clandestine Privacy Low power Potential lower cost Highly customizable performance No surgery!.

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MEMS Rigid Diaphragm Speaker

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  1. MEMS Rigid Diaphragm Speaker Scott Maghy Tim Havard SanchitSehrawat

  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. Cochlear Implants Auditory Brainstem Implants Source: http://www.nidcd.nih.gov/health/hearing/coch.asp

  7. Piezoelectric Devices • Operation • Advantage: inert in a magnetic field • Disadvantage: Power output directly related to size of crystal. Example: • Middle Ear Transducer (MET)

  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

  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 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 Force balance: Fspring + +/- Felect 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 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

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