Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1994-04-21
1996-10-01
Williams, Hezron E.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
7351436, 3612833, G01P 15125
Patent
active
055612482
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
This invention relates to an acceleration sensor which can be suitably used for detecting the degree of acceleration of a moving body, for example, of a motor vehicle or the like, and more particularly to an acceleration sensor of the type which employs a cantilever type support beam to be displaced in a horizontal direction according to the degree of acceleration.
DESCRIPTION OF THE PRIOR ART
As disclosed in Japanese Laid-Open Patent Specification 62-232171, for example, conventional cantilever type acceleration sensors generally include, in or on a silicon substrate, a support beam which is fixed at its base end and has a mass portion in its fore free end portion to be displaced together with the silicon substrate in a horizontal direction according to the degree of acceleration, a substantially U-shaped groove opened through the upper and lower sides of the silicon substrate in such a manner as to circumvent the peripheral edges of the support beam except the fixed base end thereof, a stationary section defined by the just-mentioned groove as an integral part of the silicon substrate around and with a predetermined spacing from the peripheral edges of the support beam, a movable electrode formed on the support beam by means of a p-type diffusion layer of low resistance provided on the surface of the silicon substrate, and a stationary electrode formed similarly on the stationary section in face to face relation with the support beam.
Further, Japanese Laid-Open Patent Specification 60-159658 discloses another conventional acceleration sensor which employs a support beam having its fixed base end integrally connected with the substrate and having a mass portion on its fore end portion for displacement in a horizontal direction according to the degree of acceleration, a stationary section formed on one side of the support beam by a recess substantially of U-shape, a movable electrode formed on a lateral side surface of the support beam by a vapor deposition process or the like, and a stationary electrode formed on a lateral side surface of the stationary section in face to face relation with the side surface of the support beam.
The support beam in each of the above-described conventional acceleration sensors is designed to have a smaller dimension in width than in thickness for the purpose of imparting directionability in a particular direction pertaining to the detection of acceleration. While the support beam is displaced horizontally together with the silicon substrate, a variation in electrostatic capacity which takes place between the two electrodes is detected as a signal indicative of the degree of acceleration.
In the above-described conventional acceleration sensors, the support beam and the stationary section are formed in a silicon substrate with normally high resistivity of several .OMEGA.cm or higher. Therefore, for the purpose of detecting variations in electrostatic capacity resulting from horizontal displacements of the support beam, it has been necessitated to form a layer of low resistance on the surfaces of the stationary section (i.e., on the surfaces on the opposite side walls of the recess) by diffusing phosphorus or the like, or by depositing a metal on the surfaces of the support beam and the stationary section, for example, by a vapor deposition process separately in different stages of the fabrication process to provide the movable and stationary electrodes thereon.
Therefore, in order to enhance the sensitivity of detection of the acceleration force, the above-described conventional arrangements require to narrow the width of the groove between the electrodes to a dimension of the order of several tens .mu.m and to provide low resistivity portions separately on the opposite side walls of the narrow groove for the formation of the movable and stationary electrodes, resulting in complication of the fabrication process and increases in production cost.
Especially, in the case of the conventional construction as shown in Japanese Laid-Open Patent Specification
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Moller Richard A.
Murata Manufacturing Co. Ltd.
Williams Hezron E.
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