Reducing Anchor Loss in MEMS Resonators
Noah TovaresOccidental College
SUNFEST 2010NSF REU Site
Micro-electro-mechanical Systems (MEMS) Micro electro mechanical Systems (MEMS) Uses
Mechanical switchesMechanical switchesResonatorsAccelerometersSensors
AdvantagesSystem-on-a-chip SizePower efficiencyPower efficiency
MEMS Resonators as RF FiltersMEMS Resonators as RF FiltersPiezoelectricityEngineered to have a given resonant frequencyEngineered to have a given resonant frequency
Act as band pass filter for that frequencyVibration at resonant frequency amplifiedVibration at resonant frequency amplifiedInduce the reverse piezoelectric effect Electrodes on resonator route signal to external gcircuitries
AlN Contour-Mode MEMS ResonatorsAlN Contour Mode MEMS ResonatorsAlN film sandwiched between metal film Utilizes the lateral piezoelectric coefficient (d31) R t f iResonant frequency is determined by lateral dimensions LC circuit
Resonant circuitV liVery appealing
Easy fabricationsLarge arrays g y
HurdlesHurdlesQuality factor
Measure of energy lost by resonatorMeasure of energy lost by resonatorEnergy Loss
Air damping p gThermo-elastic dissipationMaterial lossPhonon-phonon interactionsAnchor loss
Anchor loss is most significantAnchor loss is most significant
Anchor LossAnchor LossEscape of energy from the resonator to the substrate through the anchorthrough the anchorWaves that travel to the substrate via the tether are considered lost energy Waves must be stopped!
Wave propagation( h i l(mechanical energy loss)
COMSOL FEM Software and PML COMSOL FEM Software and PML Finite Element MethodSimulationsSimulationsPerfectly matched layer
Artificial layerArtificial layerAbsorbs all incoming radiationSemi-infinite domain representingsilicon substrateAllows for more accurate simulations
D t i t f t PMLDetermine parameters for accurate PML
COMSOL ModelCOMSOL ModelPML WidthPML Mesh DensityPML Mesh DensitySubstrate SizeSubstrate Mesh DensitySubstrate Mesh DensityBase Parameters
2-micron wide tether10 micron mesh element size40 i l th Substrate40 micron wavelength
PMLTether
ResonatorBodyy
PML Width SimulationsPML Width SimulationsVary PML width from 5 microns to 35 micronsto 35 micronsConstant
PML Mesh SizeSubstrate SizeSubstrate Mesh DensityT th WidthTether WidthTether Length
PML Width Simulation ResultsPML Width Simulation ResultsThe average quality factor
46563 246563.2Standard deviation
2260.9 5%
Quality factor has little dependence on PML width
PML Mesh SimulationsPML Mesh SimulationsVary maximum mesh element size in the PML sub-domainsize in the PML sub domain from 6 to 15 micronsConstant
PML widthSubstrate SizeS b t t M h D itSubstrate Mesh DensityTether WidthTether LengthTether Length
PML Mesh Simulation ResultsPML Mesh Simulation ResultsThe average quality factor
46594 946594.9Standard deviation
2824.76%
Quality factor has little dependence on PML mesh density
Substrate/Tether SimulationsSubstrate/Tether SimulationsSimilar simulations done with substrate
Vary substrate sizeyVary substrate mesh density
Same conclusions: Little affect on quality factorU b d d l i h ff f h hUse bade model to examine the effect of the tether on the quality factor. Tether lengthsTether lengths
1/8 λ1/4 λ3/8 λ3/8 λ
Tether widths2 and 5 microns2 and 5 microns
Tether ResultsTether ResultsWider and thinner tether is betterbetter1/8
20% drop form 2 to 5 micron1/4
25% drop form 2 to 5 micron3/8
Increase form 2 to 5 micronExplored in futureExplored in future
Further WorkFurther WorkExplore length, width, and number of branchesNo branchesNo branches
Lengths ofλ/8, λ/4, and 3λ/8Width of 2 and 5 microns
1 branchLengths λ/4Width of 2 and 5 microns
2 branchesL th λ/4Lengthsλ/4Width of 2 and 5 microns
ConclusionConclusionCreated a base model
Not affected by PMLNot affected by PMLCan be modified to simulate novel resonators designsSave time and money
Shorter and thinner tethersHigher quality factor
AcknowledgementsAcknowledgementsDr. Gianluca Piazza
Assistant Professor AdvisorAssistant Professor, AdvisorDr. Songbing Gong
Post-Doc PMaNS labNick Kuo
PhD Student PMaNS labDr. Jan Van Der Spiegel
Director, SUNFESTSNational Science Foundation
Thanks for Listening!Thanks for Listening!Questions?
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