Implantable Left Ventricular Pressure Sensor Chenyang Wu
Gary Fedder
Jeyanandh Paramesh Heartfailure,whichiscausedbytheheartfailingtopumpenoughbloodtothebody,affects
about2%ofadultpopulationandisamaincauseofdeath.Leftventricularpressureisa
significantparameterneededfortheclinicaldiagnosisofheartdiseases.Constant
monitoringofLVpressureinpatientscanprovideearlywarningsbeforeacuteheartfailure
occur,thusreducingtheneedforhospitalizationandalsoloweringmortalityrates.
TheMEMScapacitivepressuresensorhasthefeaturesofultrasmallsize,lowpower‐
dissipationandabsolutepressuresensing.ThecapacitorisfabricatedonaCMOSdie,along
withthecircuitstomeasurethecapacitance.Theintegrationofthecapacitorandcircuits
leadstohigh‐precisionmeasurement.Thisdeviceaimstomeasuretheleftventricularend
diastolicpressureoftheheart,thenormalrangeofwhichis3‐12mmHg,andforpatients
withheartfailure,thisvalueisusuallyabove12mmHgbutlessthan30mmHg,which
meansthattheheartpressurevalueisonlyasmallfractionoftheatmosphericpressure.
Usingproperformulas,thecapacitancecanbenon‐linearlyrelatedtopressure.However,
withinthevarianceoftargetedheartpressure,thecapacitancevarieslinearlywithrespect
toheartpressure,makingthedevicealinearsystem.
Thefabricationprocessisillustratedinfigure1.Cross‐sectionsareshownhere.Thereare4
metallayersinaCMOSdie,whichareseparatedbyoxidelayersandconnectedbyvias.The
gapin(4)highlightedbyaredcircleistheareathatformsthecapacitor.Inthefirststep
(2),oxideetchisdonefromthetopsurfacetothemetallayerthatwilleventuallybeetched
awaytoformthecapacitor.Inthesecondstep(3),theexposedmetallayerwillbeetched
bywetetching,exceptthattheadhesionlayerswillstayintact,andformagapbetween
them.Thenin(4),theboundaryofthegapwill
besealedusingtwodistinctdepositing
techniques.Thetoppartofthestructurewill
nowbendduetothepressuredifferenceon
bothsides,andthereforethismakesapressure
sensor.
(Theprojectispartofalargercollaborative
effortontheentireheartpressuresensor
systeminvolvingECEgraduatestudents
AhmadKhairiandYouLiangLionelWong,
RoboticsProfessorLeeWeiss,ICESProfessor
PhilCampbellandDr.DavidSchwartzmannof
UPMC.)
Fig 1: Fabrication process 75 | Emerging