Tunneling Accelerometers

1
Tunneling Accelerometers
ME 381 Final Presentation December 6, 2004

• Samantha Cruz
• Kevin Lee
• Deepak Ponnavolu

2
Introduction
High sensitivity Low range
Applications Underwater acoustic
detection. Seismology Micro-g measurements.
3
Concept

• Sensor Basics
• On acceleration, the proof mass moves
• This changes distance which changes tunneling
  current
• Feedback circuit fights to maintain the same
  tunneling current by changing voltage of
  electrode
• The force required to keep it at the same
  position is used to figure out acceleration

4
Microfabrication

• Counter-electrode cantilever
• (a) e- beam evaporation,
• (b) lithography and ion milling
• (c) ion milling
• (d) sacrificial layer
• (e) masking and metal evaporation
• (f) cantilever release

5
Microfabrication

• Tunneling electrode cantilever
• e- beam evaporation
• SiO2 deposition and etching
• SOI
• removal of back Si, tip mold etched
• e- beam evaporation
• mask and ion milling
• cantilever release

6
Microfabrication
7
Sensing

• It VBexp(aIvFxtg)
• Where
• VB tunneling bias across electrode gap
• aI 1.025(Å-1eV-0.5)
• F height of tunneling barrier
• xtg minimum tunneling gap
• It tunneling current

8
Feedback Control

• Feedback Circuit
• Operational Amplifier controls the tunneling
  Current
• High Voltage supply is used to correct for change
  in deflection voltage for proper separation of
  the proof mass and tip drifts slowly over time

9
Noise Correction

• Equivalent acceleration error v((4kBT?o)/(mpQ)
  )
• Where,
• kB Boltzmann constant
• T Temperature
• ?o Resonant frequency of proof mass
• mp mass of proof mass
• Q Mechanical quality factor

10
Conclusion

• Amazing Sensitivity
• Great range
• High Bandwidth
• ONLY FOR APPLICATIONS THAT REQUIRE HIGH
  SENSITIVITY

11
Questions ???