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?