1. Tunneling Accelerometers Samantha Cruz Kevin Lee Deepak Ponnavolu ME 381 Final Presentation December 6, 2004

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

3. Concept Sensor Basics (a)On acceleration, the proof mass moves (b)This changes distance which changes tunneling current (c)Feedback circuit fights to maintain the same tunneling current by changing voltage of electrode (d)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 (a)e - beam evaporation (b)SiO 2 deposition and etching (c)SOI (d)removal of back Si, tip mold etched (e)e - beam evaporation (f)mask and ion milling (g)cantilever release

6. Microfabrication

7. Sensing  I t = V B *exp(α I √Φ*x tg ) Where V B = tunneling bias across electrode gap α I = 1.025(Å-1eV-0.5) Φ = height of tunneling barrier x tg = minimum tunneling gap I t = tunneling current

8. Feedback Control Feedback Circuit (a)Operational Amplifier controls the tunneling Current (b)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 √((4*k B *T*ω o )/(m p *Q)) Where, k B = Boltzmann constant T = Temperature ω o = Resonant frequency of proof mass m p = 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 ???