Capacitive pressure sensor and method of making it

• US 4,184,189 A
• Filed: 08/14/1978
• Issued: 01/15/1980
• Est. Priority Date: 08/14/1978
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Taylor, Scot W., Wentworth, Robert M., Hansen, Kent W., Davis, Earl K.
• Primary Examiner(s): Kellogg, Arthur D.
• Application Number:
  US05/933,318
• Time in Patent Office: 519 Days
• Field of Search: 65/42, 65/43, 65/59 A, 73/718, 361/283
• US Class Current: 361/283.4
• CPC Class Codes: C03C 27/06 Joining glass to glass by processes other than fusing fusing C03B23/20; units for use as elements for closing wall or like openings and comprising two or more parallel glass panes in spaced relationship, the panes being permanently secured together E06B3/66
• CPC Class Codes: C03C 8/245 containing more than 50% lead oxide, by weight
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: Y10T 29/43 Electric condenser making

Abstract

An inexpensive glass capacitive pressure sensor. Conductive capacitor electrodes are disposed on two flat glass plates, one serving as a diaphragm, the other as a substrate. The electrodes are positioned in a spaced apart, substantially parallel relationship to form the plates of a parallel plate capacitor. The glass plates are sealed together with a sealing glass mixture to bound a volume between the conductors. The volume is at a reference pressure, preferably a substantial vacuum. Differences between the pressure to be measured and this reference pressure cause a flexing of the glass diaphragm which is detected by measuring the capacitance between the two electrodes. A suitable sealing glass mixture which provides a hermetic seal between the glass plates is comprised of, in weight percent, 8-10 SiO₂, 1-2 Al₂ O₃, 55-60 PbO, 7-9 PbF₂, 7-10 ZnO, 4-6 CdO, and 10-15 B₂ O₃. The sealing glass mixture must be vacuum fined to permit hermetic sealing within a vacuum.

Claims

1. A method for fabricating a pressure sensor comprising vacuum fining a sealing glass mixture;

providing two substantially flat glass plates having conductive electrodes thereon, at least one of said glass plates being flexible to render it capable of deforming in response to a change in pressure;

applying said sealing glass mixture to one of said glass plates in the shape of a perimeter seal;

positioning said plates with a space between said electrodes;

evacuating the space between said electrodes to a reference pressure;

heating said glass plates and said sealing glass mixture to a temperature to cause said mixture to flow and to seal together said plates.

2. The method of claim 1 wherein said plates are spaced apart by about 0.5 to 2.0 mils.

3. The method of claim 1 wherein said space is evacuated to a substantial vacuum.

4. A method for fabricating a capacitive pressure sensor which comprises providing glass plates each having a substantially flat surface and having a conductive electrode disposed thereon;

applying a sealing glass mixture to one of said plates, said mixture having, in weight percent, 8-10 SiO₂, 1-2 Al₂ O₃, 55-65 PbO, 6-10 PbF₂, 7-11 ZnO, 4-6 CdO, and 10-14 B₂ O₃ ;

positioning said glass plates to place said conductive electrodes in a substantially parallel relationship having a space therebetween;

evacuating said space to a reference pressure;

heating said glass plates and said mixture to about 500°

-550°

C. to cause said mixture to flow and seal said glass plates together, said glass plates and said mixture bounding a volume at said reference pressure.

5. The method of claim 4 further comprising the step of vacuum fining said sealing glass mixture.

6. A capacitive sensor for measuring ambient pressure comprising:

two glass pieces, at least one of said glass pieces being capable of flexing in response to a change in pressure, each having a substantially plane surface with conductive electrodes thereon, said glass pieces being positioned to place said conductive electrodes in a spaced apart, substantially parallel relationship;

a sealing glass mixture disposed on one of said pieces to seal together said glass pieces, said mixture and said glass pieces acting together to bound a volume having a reference pressure therein whereby changes in ambient pressure cause a change in the capacitance measured between said conductive electrodes.

7. The capacitive sensor of claim 6 wherein said conductive electrodes are patterned films of indium oxide/tin oxide.

8. The capacitive sensor of claim 6 wherein said two glass pieces comprise a substantially rigid base piece and a thinner, flexible diaphragm piece.

11. The capacitive sensor of claim 6 wherein said reference pressure is a substantial vacuum.

12. The capacitive sensor of claim 6 wherein said reference pressure is less than about 100 mm Hg.

9. A capacitive sensor for measuring ambient pressure comprising:

two glass pieces, each having a substantially plane surface with conductive electrodes thereon, said glass pieces being positioned to place said conductive electrodes in a spaced apart, substantially parallel relationship;

a sealing glass mixture disposed on one of said pieces to seal together said glass pieces, said mixture having, in weight percent, about 8-10 SiO₂, 1-2 Al₂ O₃, 55-60 PbO, 7-9 PbF₂, 7-10 ZnO, 4-6 CdO, and 10-15 B₂ O₃ said mixture and said glass pieces acting together to bound a volume having a reference pressure therein whereby changes in ambient pressure cause a change in the capacitance measured between said conductive electrodes.

10. The capacitive sensor of claim 9 wherein said sealing glass mixture has, in weight percent, about 8.8 SiO₂, 1.2 Al₂ O₃, 57 PbO, 8 PbF₂, 8 ZnO, 5 CdO, and 12 B₂ O₃.

13. A method for fabricating a capacitive pressure sensor comprising the steps of:

providing two glass plates, at least one of said glass plates being flexible enough to be capable of responding to a change in pressure, and each having a substantially plane surface;

providing conductive electrodes on said substantially plane surfaces;

applying a sealing glass material to at least one of said two glass plates;

positioning said two glass plates to place said conductive electrodes in a substantially parallel relationship having a space therebetween;

evacuating the space between said spaced apart electrodes;

heating said glass plates to cause said sealing glass material to flow and to seal said glass plates together, said glass plates and said sealing glass material bounding an evacuated volume.