I/o Sensors, Inc.

Raymond K Erickson

Matthew W Ip

W S Henrion

Franklin W Mayo

Burton A Devolk

Hubert R Plumlee

Bing F Fung

Apparatus for measuring a characteristic of motion and methods for its manufacture are disclosed in which a sensor structure includes a support structure, and a mass suspended from such support structure by a spring connecting arrangement and electrical devices for measuring displacement of the mass which results from a force applied to the support structure. An apparatus is provided where the mechanical spring constant of the connecting arrangement of the sensor structure is provided to be a high value representative of a strong, stiff spring which resists breaking due to high forces applied to it, and where an electric spring constant is provided to yield a small effective sensor spring constant K.sub.eff =K.sub.m -K.sub.e. Methods are also provided to manufacturing the apparatus by specifying the mechanical spring constant and providing an electric spring constant which will yield a desired effective spring constant which produces a desired characteristic of the sensor structure. Alternatively, the apparatus may be manufactured by specifying the electric spring constant which, with a mechanical spring constant, provides a certain sensor structure characteristic, e.g., natural frequency, and then providing a connecting arrangement characterized by a mechanical spring constant which yields such sensor characteristic. According to another aspect of the invention, the sensing force applied to the mass is adjusted in coordination with the mechanical spring constant and damping factor of the apparatus so that a desired characteristic of the apparatus is achieved.

Apparatus with mechanical and electric springs and method for its

A sensor structure (10) has a central mass (16) mounted within a support structure comprising an outer support frame (18), and upper and lower plates or covers (12, 14). Eight L-shaped ribbon springs (32, 34) fit about the corners (28) of the mass (16) to mount mass (16) for movement from a reference position with respect to the support structure. One leg (38) of each spring (32, 34) is connected to an associated side (26A) of the mass (16) centrally of the length of the associated side (26A). The other leg (40) is connected to the outer support frame (18). The sensor structure is designed for use as a sensing mechanism in an electrostatic accelerometer arrangement.

Sensor structure with L-shaped spring legs

A method for fabricating a connecting spring member (24) of an arbitrary shape extending between a central mass (21) and an outer support frame (23) of a sensor as shown in FIG. 7 is disclosed. Each of a pair of generally identical silicon wafers (10, 12) has an inner etch stop layer (16) applied to one face with an outer epitaxial layer (18) formed over such etch stop layer (16). A photosensitive oxide layer (30) is applied to the other face of each of the wafers (10, 12). Next, a pattern of the central mass (21) and outer support frame (23) as shown in FIG. 2 is photographically imposed on the photosensitive oxide layers (18) of each wafer (10, 12). After wet chemical etching of the wafers (10, 12) removes silicon material to the etch stop layer, and the etch stop layer is itself removed in the space between the mass and the frame, the two wafers (10, 12) are bonded to each other as shown in FIG. 5 . Next, the spring shape, of any arbitrary shape is formed by plasma etching from the outer surfaces of the bonded wafers (10, 12) in the area between the mass and the frame. Accordingly the spring members (24) extend between the central mass (21 ) and the outer support frame (23).

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Taylor, TX, United States of America

Raymond K Erickson