Sensor having direct-mounted sensing element

• US 5,535,626 A
• Filed: 12/21/1994
• Issued: 07/16/1996
• Est. Priority Date: 12/21/1994
• Status: Expired due to Term

• Current Assignee: Murata Electronics OY (Murata Manufacturing Co Limited)
• Original Assignee: Breed Technologies, Inc.
• Inventors: Bullis, Robert H., Swindal, James L., Wiegand, Walter J., Winston, Charles R. Jr.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US08/361,277
• Time in Patent Office: 573 Days
• Field of Search: 73/517 R, 73/517 AV, 73/651, 73/650, 73/649, 73/652, 73/493, 73/718, 73/724, 73/DIG. 1, 361/280, 361/283.3
• US Class Current: 73/514.32
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A silicon capacitive microsensor which is sensitive to acceleration forces includes a silicon capacitive sensing element 10 comprising three silicon layers 12,16,26 having glass dielectric layers 14,24 between each pair of silicon layers with the middle silicon layer 16 consisting of a proof mass 18 suspended between the two glass dielectric layers 14,24 by a silicon hinge 20 which is connected to a slightly thicker silicon support layer 17 around the periphery (FIG. 3 ) between the glass layers 14,24 (FIG. 1 ). Three metallic bond pads 40,42,44 on the surface 45 of the silicon layers 26,16,12, respectively, are soldered to circuit trace pads 108 on a circuit board 100 which has a glass upper layer 104 and a silicon support layer 102. The thermal expansion coefficient between the glass layer 104 and the sensing element 10 are substantially the same, thereby minimizing thermally induced stresses on the sensing element 10 and minimizing inaccuracies associated therewith. Such direct mounting greatly simplifies the manufacturing process for such sensors. Also, such direct mounting eliminates flying leads thereby allowing the sensing element 10 to be fabricated to much smaller dimensions than that of the prior art.

Claims

1. A capacitive sensor for sensing acceleration forces comprising a mounting board to operatively receive and support a sensing means to sense acceleration forces and generate at least one signal in response to the acceleration forces, said sensing means comprising a plurality of silicon layers having a dielectric insulator disposed between adjacent silicon layers to cooperatively form a sensing element including a sensing element mounting surface and a plurality of electrically conductive contacts formed on said element mounting surface, each of said plurality of electrically conductive contacts being disposed in operative relationship to one of said plurality of silicon layers to receive a corresponding signal therefrom when the accelerator forces are sensed by said capacitance sensor, said mounting board including a board mounting surface and a plurality of electrically conductive traces mounted to said board mounting surface and corresponding to one of said plurality of electrically conductive contacts, each of said electrically conductive traces comprising an electrically conductive pad and a corresponding electrically conductive path each of said conductive traces having a substantially fixed capacitance, said element mounting surface being disposed relative to said board mounting surface such that each of said electrically conductive contacts operatively engages said electrically conductive pad to electrically connect each of said silicon layers through said corresponding electrically conductive contacts and corresponding said electrically conductive traces to an external circuit to feed said signal corresponding to each of said silicon layers to the external circuit over a corresponding circuit comprising said corresponding plurality of electrically conductive contacts and said electrically conductive traces, said corresponding circuit having a predetermined substantially fixed capacitance to reduce stray capacitance.

2. The capacitive sensor of claim 1 wherein said board mounting surface and said element mounting surface are each constructed of material having substantially the same coefficient of thermal expansion thereby minimizing thermally-induced stresses exerted on said sensing means by said mounting board over a predetermined operational temperature range.

3. The capacitive sensor of claim 2 wherein said board mounting surface adjacent each of said plurality of electrically conductive contacts and said element mounting surface adjacent each of said plurality of electrically conductive tracers are each constructed of material having substantially the same coefficient of thermal expansion thereby minimizing thermally-induced stresses exerted on said sensing means by said mounting board over a predetermined operational temperature range.

4. The capacitive sensor of claim 2 further including a mounting means disposed between said element mounting surface and said board mounting surface, said mounting means comprising a dielectric layer to further reduce stray capacitance.

5. The capacitive sensor of claim 3 further including a mounting means disposed between said element mounting surface and said board mounting surface, said mounting means comprising a dielectric layer to further reduce stray capacitance.

6. The capacitive sensor of claim 1 further including a mounting means disposed between said element mounting surface and said board mounting surface, said mounting means comprising a dielectric layer to further reduce stray capacitance.

7. The capacitive sensor of claim 6 wherein said board mounting surface adjacent each of said, plurality of electrically conductive contacts and each of said element mounting surface adjacent each said plurality of electrically conductive tracers are constructed of material having substantially the same coefficient of thermal expansion thereby minimizing thermally-induced stresses exerted on said sensing means by said mounting board over a predetermined operational temperature range.

8. The capacitive sensor of claim 7 wherein said board mounting surface and said element mounting surface are constructed of material having substantially the same coefficient of thermal expansion thereby minimizing thermally-induced stresses exerted on said sensing means by said mounting board over a predetermined operational temperature range.