Project

Micro-Systems & Control Laboratory, NTHU

 

Stanford Micro Structures & Sensors Lab

Quantum Electron Tunneling Sensor

Objectives:

High-precision accelerometers are widely required in applications such as microgravity measurements, acoustic measurements, seismology for oil exploration, earthquake prediction, platform stabilization in space, and navigation and guidance.  Since the first MEMS accelerometer was developed at Stanford Integrated Circuit Laboratory for biomedical applications in 1978, many MEMS accelerometers have been developed with different operating principles and designs.  Constrained by scaling laws, these miniature accelerometers generally suffer from either poor resolution or very narrow measurement bandwidth. It has proven difficult to make miniaturized accelerometers based on piezoresistive, piezoelectric or capacitive transducers with sub-micro-g resolution and 1 kHz bandwidth. Our development of Quantum Electron Tunneling Accelerometers has been motivated by the Office of Naval Research (ONR) requirement for underwater acoustics applications. These performance specifications for the ONR application include:

¨    Resolution: The miniature accelerometers are required to feature resolution approaching 10 nano-g/.

¨    Bandwidth: The intended measurement frequency band is from 5 Hz to 1 kHz.

¨    Size and weight: The accelerometer is intended to be packaged in an 8-cm3 sphere volume with a total mass of 8 grams to allow neutral buoyancy.

Technical Approach:

Fig. 1 shows the typical signal output responding to 1 milli-g acceleration at 700 Hz for a commercial MEMS accelerometer from Analog Devices Inc.  The sensor resolution is far away from ONR specification.

Fig. 1: ADXL05 output signal responding to 100 mg acceleration at 700 Hz

Displacement transducers based on quantum electron tunneling have been demonstrated in variety of physical sensors as well as well-known scanning tunneling microscope, which brings Binnig and Rohrer the Nobel Prize in Physics, because of their high position sensitivity.  Displacement resolution approaching 10-4 Å/ has been shown for tunneling transducers.  Due to the capability for high displacement resolution, quantum tunneling accelerometers can have better performance (resolution, sensitivity), smaller size, and lighter mass than conventional piezoresistive or capacitive accelerometers. In this research, we utilize quantum electron tunneling to approach high-resolution accelerometer with miniaturized size.  Analysis of tunneling sensors shows that the ONR performance specifications should be accessible, but practical problems in sensor construction, operation as well as high nonlinearity near atom-scale hard-contact gap have always prevented this goal from being met. With sophisticated feedback control, we demonstrated the quantum electron tunneling accelerometers with the high resolution of of 20 nano-g/ 2^(1/2)and a 5 Hz-1.5 kHz bandwidth that had never been approached before when the results was published on Journal of MicroElectroMechanical Systems.  Fig. 2 shows the illustration for an example of control design by using Mu-synthesis to enhance the robustness performance of the quantum electron tunneling accelerometers.  Fig. 3 shows an early prototype tunneling accelerometers developed at Jet Propulsion Laboratory, USA.  Fig. 4 shows the typical signal output comparison between commercial ADXL05 (green) and our quantum electron tunneling accelerometer (red) responding to the same periodical excitation input signal.  Fig. 5 shows the performance comparison for updating miniaturized accelerometers, which is published on my Journal of MicroElectroMechanical Systems paper.

Fig. 2: Robust control design by using Mu-Synthesis with the mixed real/complex

structured uncertainty.

Fig. 3: An early prototype quantum electron tunneling accelerometers

Fig. 4: A typical signal output comparison between commercial ADXL05 (green) and our quantum electron tunneling accelerometer (red) responding to the same periodical excitation input signal

Fig. 5: Comparison of micromachined accelerometers based on reported performance.  + These are not MEMS accelerometers, and the GURALP is a very large device.

 

References:

1.      Cheng-Hsien Liu and T.W. Kenny, "A High-Precision, Wide-Bandwidth Micromachined Tunneling Accelerometer", Journal of Microelectromechanical Systems, Vol.10, No.3, pp. 425-433, Sept 2001.

  1. Liu, C. H., Rockstad, H. K. and Kenny, T. W., “Robust controller design via mu-synthesis for high-performance micromachined tunneling accelerometers,” American Control Conference, pp. 247-252, 1999

3.      Liu, C. H., Barzilai, A. M., Reynolds, J. K., Partridge, A, Grade, J. D., Rockstad, H. K. and Kenny, T. W., “Characterization of a high-sensitivity micromachined accelerometer with micro-g resolution,” Journal of MicroElectroMechanical System, Vol. 7, n. 2, pp. 235-244, June 1998.

4.      Grade, J. D., Barzilai, A. M., Reynolds, J. K., Liu, C. H., Partridge, A., Kenny, T. W., Miller, L. M., Podosek, J. A., “Low frequency drift in tunneling sensors,” Solid-State Sensors and Actuators (Transducers ’97), pp. 871-874, 1997.

5.      Liu, C. H., Grade, J. D., Barzilai, A. M., Reynolds, J. K., Partridge, A., Rockstad, H. K., and Kenny, T. W., “Characterization of a high-sensitivity micromachined tunneling accelerometer,” Solid-State Sensors and Actuators (Transducers ’97), pp. 471-472, 1997.

Collaboration:

·         Dr. J. K. Reynolds

·         Dr. J. D. Grade

·         Dr. A. M.  Barzilai

·         Rockstad et. al. at Jet Propulsion Laboratory

Contact Information :

·         Cheng-Hsien Liu   liuch@pme.nthu.edu.tw

·         Tom Kenny  kenny@cdr.stanford.edu

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