Micromechanical accelerometer

Details Micromechanical accelerometer Micromechanical accelerometer

1997-10-03

1999-08-17

Williams, Herzon

Measuring and testing

Speed, velocity, or acceleration

Acceleration determination utilizing inertial element

7351432, 738665, G01P 1508

Patent

active

059396326

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

This invention relates to a micromechanical accelerometer, that is an accelerometer constructed, preferably from silicon, using micromechanical techniques.


BACKGROUND OF THE INVENTION

Silicon microfabricated accelerometers are being intensively developed because of the possibility of low cost batch fabrication. Such accelerometers include a seismic or proof mass which is anchored to a silicon substrate by a micromechanical suspension system. In one commercially available chip (ADXL50), the position of the proof mass is detected by a differential capacitance measurement. Using a force-balance configuration, the proof mass deflects in response to acceleration to which the chip is subjected, a sense signal arising from the differential capacitance measurement is amplified and fed back to electrostatically deflect the proof mass and counteract the effect of the acceleration. The output from the accelerometer is the required feedback voltage to counteract the effect of the acceleration.
Tunnel based accelerometers have also been proposed, in which the sense signal is derived from a tunnel current between a sensing tip and a counter electrode. Such a tunnel based sensor has been proposed in a paper entitled "A miniature high sensitivity broad-band accelerometer based on electron tunnelling transducers", authored by Howard K. Rockstad et al and published at the 7th International Conference on Solid State Sensors and Actuators, pages 836 to 839. Such tunnel based accelerometers have a greater sensitivity than capacitive accelerometers, but they require more than one silicon wafer for their manufacture. In the arrangement described in the preceding article by Rockstad et al, three wafers are required to make the accelerometer. Each wafer includes components of the accelerometer which must be carefully aligned when the wafers are secured together. Manufacturing costs of such accelerometers are high because of the need to produce components within three wafers and then to carefully align the wafers during construction of the accelerometer.
It is an object of the present invention to provide an accelerometer which combines high sensitivity and low cost manufacture.


SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided an accelerometer comprising: a substrate; a proof mass mounted relative to the substrate for movement in a first direction perpendicular to the plane of the substrate, the proof mass carrying a first sensing electrode; and a second sensing electrode mounted relative to the substrate, wherein the first and second sensing electrodes comprise surfaces which are respectively formed by cutting so as to extend at an angle relative to the substrate and define between them a sensing gap which is held to a predetermined width by use of an activation applied between the substrate and the structure constituting the proof mass and the second electrode, and the width of which varies with movement of the proof mass in the first direction.
It will be apparent that the second sensing electrode will generally be mounted relative to the substrate in a manner which is relatively stiff compared to the mounting of the proof mass to the substrate.
In the described embodiment, the proof mass is mounted in a cantilevered fashion, that is with one end of a cantilever fixed to the substrate and the other end of the cantilever free to move in the first direction. In one embodiment, the cantilever itself can constitute the proof mass. In another embodiment, the cantilever carries a region of larger cross-section which constitutes the proof mass. In a still further embodiment, a region of larger cross-section constituting the proof mass is mounted relative to the substrate using two cantilevers on either side of the proof mass. This arrangement is stiffer in a plane parallel to the plane of the substrate.
The accelerometer can comprise circuitry for sensing variations in the width of the sensing gap. In one arrangement, the sensing circuitry detects change

REFERENCES:
patent: 4999735 (1991-03-01), Wilner
patent: 5431051 (1995-07-01), Biebl et al.
patent: 5490422 (1996-02-01), Tabota et al.
K. Minami et al., "YAG Laser Assisted Etching for Releasing Silicon Micro Structure", IEEE Cat. No. 93CH2365-6, Ft. Lauderdale, Florida, Jul. 2, 1993, pp. 53-58.
Kaiser et al., "Tunnel Effect Displacement Sensor", NTIS Tech Notes, Springfield, Virginia, Apr. 1990.
Rockstad et al., "A Miniature High--Sensitivity Broad-Band Accelerometer Based on Electron Tunneling Transducer", Sensors and Actuators--A Physical, Lausanne, vol. A43, No. 1/3, May 1994, pp. 107-114.

Affiliated with

Also associated with

Rating

Micromechanical accelerometer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Micromechanical accelerometer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micromechanical accelerometer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-316340