Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-02-19
2001-04-24
Williams, Hezron (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S654000
Reexamination Certificate
active
06220096
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of accelerometers, and particularly to enhancing the high frequency capabilities of accelerometers, and to differential measurement capabilities of accelerometers.
BACKGROUND OF THE INVENTION
The concept of a moveable gate Field Effect Transistor (FET) has been extensively studied and reported in literature. A number of devices have been disclosed that make use of a moveable gate FET for building accelerometers.
Force balance feedback control of vibration sensors has been used in seismometers and in accelerometers for attaining increased bandwidth and dynamic range. A number of devices using this approach have been routinely demonstrated and its theory of operation is well understood. Several seismometer and accelerometer manufacturers base their designs on this principle.
The fabrication of a silicon accelerometer using wafer bonding techniques is disclosed in great detail in U.S. Pat. No. 5,095,752 and No. 5,417,312. In these invention disclosures a relatively large mass made of silicon is encapsulated in a cavity formed by electrodes made out of glass on silicon. The accelerometer is operated using an active feedback loop, in which control voltages are applied to the upper and lower electrodes. The displacement of the free mass under acceleration requires compensation through changes in the voltage applied between the upper and lower electrodes and the moving mass.
Utilizing the FET concept, the feedback bulk silicon micromachined accelerometer disclosed in U.S. Pat. No. 5,205,171 makes use of a feedback loop and at least one pair of dual electrodes acting as capacitive transducers. Differential sensing of the beam-gate capacitance variations is used to generate a null feedback signal used to modulate the voltage applied to electrodes in order to prevent them from moving. Based on the similar concept of using a FET, a device with acceleration dependent gain is disclosed in U.S. Pat. No. 5,103,279 and a device that uses a piezoelectric device to generate voltage for the gate is disclosed in U.S. Pat. No. 4,873,871.
The type of accelerometers mentioned above have good sensitivity at low frequencies but limited sensitivity at high frequencies, although they result in higher bandwidth devices than open loop devices. In addition, due to mechanical and electronic manufacturing variations from one accelerometer to the next, the process of calibrating any given accelerometer to detect vibration as differentiated against a “zero” vibration level is difficult without means to establish such a differential reading.
One fundamental problem of implementing a vibration sensor is that most of the time the fabrication process used to implement the sensor is incompatible with the most common processes used to implement the standard electronics associated with the sensor. To solve this incompatibility, it is often preferred to fabricate the sensor in a separate die from the electronic circuitry. This type of multi-die implementation, however, results in higher costs and lower yield since a more complex multi-die packaging is needed. In some cases cost considerations might advise the use of a monolithic (single-dye) implementation in which the sensor and accompanying electronics reside in the same die.
OBJECTS OF THE INVENTION
It is an object of the invention disclosed herein to provide an accelerometer featuring a force balanced feedback loop in which the electrodes are used as actuating elements in the control loop and the sensing element utilizes a FET having a moveable gate. Variations in the geometric configuration of the gate can also be used to increase capacitance and hence sensitivity. This approach enables increased sensitivity and greater maximum signal range resulting in an increased bandwidth and dynamic range typical of a force balance system. Furthermore, the disclosed accelerometer is compatible with microelectromechanical systems processing.
It is also an object of the invention to provide said accelerometer with an associated mechanical and electrical reference to allow true calibration of vibration measurements.
It is also an object of the invention to provide a means of overcoming the usual incompatibilities between sensor fabrication and an electronic device fabrication processes.
SUMMARY OF THE INVENTION
The present invention provides a high sensitivity wideband MEMS (Microelectromechanical Systems) acceleration sensor of the force balanced type based on the use of a closed feedback loop for attaining maximum bandwidth for the sensed variables. The vibration sensor operates through the action of forces applied electrostatically between a pair of fixed electrodes and the suspended mass configured to form a closed feedback loop. The most useful form of control is negative feedback which is intended to keep the mass in a nearly fixed position with respect to the electrodes and substrate, making the suspension appear more stiff and increasing the natural frequency.
The operation of the wideband vibration sensor is based on a feedback loop which includes a moveable gate FET otherwise known as a MGT (Moveable Gate Transistor) as the sensor element. The MGT offers the best means for detecting out-of-plane oscillations in a very small area, since it relies on capacitance per unit area (as opposed to total capacitance).
An important embodiment of the invention includes an associated mechanical and electrical reference structure to allow for differential measurements with the accelerometer. The use of a reference allows calibration of the sensor to an electronic and mechanical “zero” of vibration. This simplified measurement approach eliminates costly precision tuning of individual units and allows for cost effective, automated self-calibration during operation.
REFERENCES:
patent: 3585466 (1971-06-01), Davis, Jr. et al.
patent: 4841775 (1989-06-01), Ikeda et al.
patent: 4873871 (1989-10-01), Bai et al.
patent: 5001933 (1991-03-01), Brand
patent: 5095752 (1992-03-01), Suzuki et al.
patent: 5103279 (1992-04-01), Gutteridge
patent: 5205171 (1993-04-01), O'Brien et al.
patent: 5345824 (1994-09-01), Sherman et al.
patent: 5417312 (1995-05-01), Tsuchitani et al.
patent: 5456111 (1995-10-01), Hulsing
patent: 5540095 (1996-07-01), Sherman et al.
patent: 5587343 (1996-12-01), Kano et al.
patent: 5619050 (1997-04-01), Uenoyama et al.
patent: 5818093 (1998-10-01), Gutteridge et al.
patent: 5874675 (1999-02-01), Emans et al.
Harvey C. Nathanson, William E. Newell, Robert A Wickstrom, & John R. Davis, Jr., “The Resonant Gate Transistor”, IEEE Transactions on Electron Devices, Mar. 1967, pp. 117-133, vol. Ed-14, No. 3.
M.J. Usher, I.W. Buckner, & R.F. Burch, “A Miniature Wideband horizontal-component feedback seismometer”, Journal of Physics E: Scientific Instruments, 1977, pp. 1253-1260, vol. 10, Great Britian.
Kevin E. Burcham, Gregory N. DeBrabander, & Joseph T. Boyd, “Micromachined Silicon Cantilever Beam Accelerometer Incorporating an Integrated Optical Waveguide”, Pro. of Integrated Optics and Microstructures 1992, pp. 12-18, SPIE vol. 1793.
Takashi Yoshida, Takahiro Kudo, Satoshi Kato, Shun-Ichi Miyazaki, Shinjiro Kiyono & Kyoichi Ikeda, “Strain Sensitive Resonant Gate Transistor”, IEEE Proceedings of MEMS95, Amsterdam, 1995, pp. 316-321.
Shun-Ichi Miyazaki, Takashi Yoshida, & Kyoichi Ikeda, “Strain Sensitive Resonant Gate Transistor”, Proceedings of Micromachined Devices and Components II, SPIE vol. 2882, 1996, pp. 278-285.
Adolfo Gutierrez, Daniel Edmans, Chris Cormeau, Gernot Seidler, Dave DeAngelis, & Edward Maby, “Si Micromachined Sensor for Broadband Vibration Analysis”, Pro of Int'l Conf. on Int. Micro/Nanotechnology for Space App., 1995, Houston, TX.
E.W. Maby, C.M. Cormeau, D.M. Edmans, & J.G. Fiorenza, “Micro-microphones for Insect Detection”, Proceedings of the Second Symposium on Agroacoustics, National Center for Physical Acoustics, University of Mississippi, May 1996, pp. 1-8.
E.W. Maby, C.M. Cormeau, D.M. Edmans, & J.G. Fiorenza, “Micro-microphones for Insect Detection”, Abstracts, Second Symposium on
Cormeau Christopher
Edmans Daniel M.
Gutierrez Adolfo O.
InterScience, Inc.
Miller Rose M.
Williams Hezron
Yablon Jay R.
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