Tunneling Tunneling AccelerometersAccelerometers
Samantha CruzSamantha Cruz
Kevin LeeKevin Lee
Deepak PonnavoluDeepak Ponnavolu
ME 381Final PresentationDecember 6, 2004
IntroductionIntroduction
High sensitivity
Low range
Applications:
Underwater acoustic detection.
Seismology
Micro-g measurements.
ConceptConcept
Sensor BasicsSensor Basics
(a)(a) On acceleration, the proof On acceleration, the proof mass movesmass moves
(b)(b) This changes distance which This changes distance which changes tunneling currentchanges tunneling current
(c)(c) Feedback circuit fights to Feedback circuit fights to maintain the same tunneling maintain the same tunneling current by changing voltage current by changing voltage of electrodeof electrode
(d)(d) The force required to keep it The force required to keep it at the same position is used at the same position is used to figure out accelerationto figure out acceleration
MicrofabricationMicrofabrication
Counter-electrode Counter-electrode cantilever cantilever
(a) e- beam evaporation, (a) e- beam evaporation,
(b) lithography and ion (b) lithography and ion milling milling
(c) ion milling(c) ion milling
(d) sacrificial layer(d) sacrificial layer
(e) masking and metal (e) masking and metal evaporationevaporation
(f) cantilever release(f) cantilever release
MicrofabricationMicrofabricationTunneling electrode cantileverTunneling electrode cantilever
(a)(a) ee-- beam evaporation beam evaporation
(b)(b) SiOSiO22 deposition and deposition and
etchingetching
(c)(c) SOISOI
(d)(d) removal of back Si, tip removal of back Si, tip mold etchedmold etched
(e)(e) ee-- beam evaporation beam evaporation
(f)(f) mask and ion millingmask and ion milling
(g)(g) cantilever releasecantilever release
MicrofabricationMicrofabrication
SensingSensing
IItt = V = VBB*exp(α*exp(αII√Φ*x√Φ*xtgtg))
WhereWhere
VVBB = tunneling bias across electrode gap = tunneling bias across electrode gap
ααII = 1.025(Å-1eV-0.5) = 1.025(Å-1eV-0.5)
ΦΦ = height of tunneling barrier = height of tunneling barrier
xxtgtg = minimum tunneling gap = minimum tunneling gap
IIt t = tunneling current = tunneling current
Feedback ControlFeedback Control
Feedback CircuitFeedback Circuit
(a)(a) Operational Amplifier Operational Amplifier controls the tunneling controls the tunneling CurrentCurrent
(b)(b) High Voltage supply is High Voltage supply is used to correct for change used to correct for change in deflection voltage for in deflection voltage for proper separation of the proper separation of the proof mass and tip drifts proof mass and tip drifts slowly over timeslowly over time
Noise CorrectionNoise Correction
Equivalent acceleration error Equivalent acceleration error √((4*k√((4*kBB*T*ω*T*ωoo)/(m)/(mpp*Q))*Q))
Where,Where,
kkBB = Boltzmann constant = Boltzmann constant
T = TemperatureT = Temperature
ωωoo = Resonant frequency of proof mass = Resonant frequency of proof mass
mmpp = mass of proof mass = mass of proof mass
Q = Mechanical quality factorQ = Mechanical quality factor
ConclusionConclusion
Amazing SensitivityAmazing Sensitivity Great rangeGreat range High BandwidthHigh Bandwidth
ONLY FOR APPLICATIONS THAT ONLY FOR APPLICATIONS THAT REQUIRE HIGH SENSITIVITYREQUIRE HIGH SENSITIVITY
Questions ???Questions ???