Presentation on theme: "MEMS Rigid Diaphragm Speaker"— Presentation transcript:
1 MEMS Rigid Diaphragm Speaker Scott MaghyTim HavardSanchit Sehrawat
2 Macro-scaleTry to make MEMS device based on same concept
3 Motivation Few similar products Small size Potential lower cost ClandestinePrivacyLow powerPotential lower costHighly customizable performanceNo surgery!
4 Current Hearing Devices Few speakers that fit completely inside the earSome piezoelectric speakersBone conduction speaker for above the ear: 1 inch longCMOS MEMS speakers exits, and are being developedSeveral hearing devicesDownsides:Require surgeryMuch largerCostComplexity
7 Piezoelectric Devices OperationAdvantage: inert in a magnetic fieldDisadvantage: Power output directly related to size of crystal.Example:Middle Ear Transducer (MET)Pass current into Piezoceramic CrystalCrystal changes volumeVibratory signal produced
8 Middle Ear TransducerTranslates electrical signals into mechanical motion to directly stimulate the ossicles
10 Electromagnetic Devices OperationSmall magnet is attached to vibratory structure in earOnly 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 closePass current into Electric CoilMagnetic Flux createdDrives adjacent magnet
13 MaterialsPolysilicon: structural material for cantilever and diaphragmSilicon Oxide: for sacrificial layersSilicon Nitride: isolation of waferGold: electrodes and electrical connections
14 Fabrication Deposit layers of Electrodes, oxide, and photoresist (as shown)Deposit Silicon Nitride LayerPattern photoresist & then etchelectrodes & oxide using RIEDeposit Oxide 2 layer
15 Fabrication Etch oxide 2, and make Poly-Si columns Coat columns with Photoresist andetch away remaining oxide 2Remove photoresist from electrode 2Etch oxide 2, and make Poly-Si columnsDeposit oxide 3 as shownRemove photoresist and deposit Poly-Si
16 FabricationMake Poly-Si diaphragm base thickerRelease oxide layers
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 sourcesound power Pac wattsRocket engine1,000,000 WTurbojet engine10,000 WSiren1,000 WMachine gun10 WJackhammer1 WChain saw0.1 WHelicopter0.01 WLoud speech, vivid children0.001 WUsual talking, Typewriter10−5 WRefrigerator10−7 W(Auditory threshold at 2.8 m)10-10 W(Auditory threshold at 28 cm)10-12 WDecreasing frequencyDevice is in the threshold of human hearing!
22 ImprovementsImplement a process that allows for sealing of speaker cone to supportThis would give better acoustic propertiesCould be accomplished by CMOS MEMS procedureFabricate 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 cantileversThis would allow greater diaphragm displacement and therefore greater intensityOther materials exist with lower Young’s modulus that would accomplish this but fabrication is suspectOther methods of securing the diaphragm“Spring” attachmentDecrease the mass of the diaphragm by altering fabrication process