Capacitive pressure sensor and reference with stress isolating pedestal

• US 5,515,732 A
• Filed: 06/06/1995
• Issued: 05/14/1996
• Est. Priority Date: 09/01/1992
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Ley, Kevin R., Petersen, Eric P., Willcox, Charles R., Peitersen, Larry A.
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US08/471,608
• Time in Patent Office: 343 Days
• Field of Search: 73/718, 73/724, 73/756, 73/431, 29/25.41, 29/621.1, 361/283.3, 361/283.4
• US Class Current: 73/724
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

A pedestal mount capacitive pressure sensor (10) is supported in a housing (11) and used to sense fluid pressures to provide air pressure data relating to the performance of air vehicles. The capacitive sensor uses a thick base plate (40) on which a diaphragm (48) is mounted. A capacitive electrode (52) is mounted to the diaphragm and pressure deflects the diaphragm to provide an output. The pressure sensor (10) is mounted in an outer housing (11) using a stress isolating pedestal (20).

Claims

1. A pressure sensor comprising:

a backing plate;

a semiconductor material diaphragm having a peripheral rim mounted on the backing plate with portions of the diaphragm within the peripheral rim being deflectable relative to the backing plate under fluid pressure;

an electrode plate for forming a capacitive pressure sensor in combination with the diaphragm mounted to the diaphragm around the peripheral rim of the diaphragm;

a support for mounting the pressure sensor relative to a housing for said sensor, the support comprising a glass tube directly supporting the backing plate for stress isolation of the backing plate and the electrode plate relative to the housing; and

a fluid pressure inlet passing through the support and the backing plate to permit fluid pressure to act on the diaphragm to deflect the diaphragm relative to the electrode plate, to cause a change in spacing between the diaphragm and the electrode plate.

2. The pressure sensor of claim 1 wherein said electrode plate comprises a glass plate having a metalizing layer thereon, said metalizing layer having a first portion on a surface of the electrode plate facing the diaphragm and a second portion on an opposite surface of the electrode plate substantially the same size and thickness, and in registry with the first portion.

3. The pressure sensor of claim 2 wherein said metalizing layer comprises thin film deposited layers of metal adhering to the glass plate.

4. The pressure sensor of claim 1 wherein said backing plate comprises a silicon plate that is substantially thicker than the peripheral rim, said diaphragm comprising a silicon diaphragm and the peripheral rim being fused to a surface of the backing plate.

5. The sensor as specified in claim 4 wherein the backing plate is substantially in the range of four times as thick as the diaphragm peripheral rim, the diaphragm having a deflecting portion substantially thinner than the peripheral rim.

6. The sensor as specified in claim 1 wherein the diaphragm is made of silicon and the backing plate is made of silicon and is at least two and one half times as thick as the peripheral rim of the diaphragm.

7. The pressure sensor of claim 1 wherein said diaphragm is a plate and generally defines a plane, the diaphragm having a thin center web the peripheral rim having a thickness measured perpendicular to the plane of the diaphragm substantially equal to the thickness of the center web, plus twice the spacing from a surface of the center web facing the electrode plate to the electrode plate.

8. The pressure sensor of claim 1 and a housing for supporting the support, said housing comprising a radial fitting of stainless steel having a center through bore, said support being made of a borosilicate glass, and an intermediate pedestal between said support and said fitting comprising a machined shoulder surface surrounding a portion of the center through bore in the fitting, a pilot boss on the pedestal formed by a second shoulder surface and fitting into a portion of said through bore in the fitting, and said second shoulder surface resting on the first shoulder surface on the fitting for positioning the support, said shoulder surfaces being bonded together.

9. The pressure sensor of claim 8 wherein pedestal is made of a nickel-iron alloy.

10. The pressure sensor of claim 9 wherein the nickel-iron alloy pedestal is nickel-plated.

11. The pressure sensor of claim 8 wherein said glass tube is supported on said pedestal, and has an end surface having a metalization of zirconium in contact with the glass tube and facing the pedestal, and a further layer of nickel bonded to the zirconium and soldered to the pedestal.

12. The pressure sensor of claim 1 wherein the backing plate is made of glass.

13. The pressure sensor of claim 12 and a glass to glass anodic bond joining the support means to the backing plate.

14. A pressure sensor assembly comprising:

an outer housing having a substantially rectangular configuration with a base wall, upstanding sidewalls extending from said base wall, and a cover plate overlying said base wall;

a pressure sensing die having a pressure fitting formed to extend to the exterior of the housing sealingly mounted on said base wall;

a reference pressure die constructed substantially identically to the pressure sensing die and sealingly mounted on said base wall and oriented substantially parallel to said pressure sensing die;

electrical connector means sealingly passing through one sidewall; and

a pair of mounting studs mounted on said one sidewall adjacent opposite ends thereof, with the electrical connector means therebetween, said studs being welded to the one sidewall for supporting the housing in a usable position.

15. The pressure sensor assembly of claim 14 wherein the pressure sensing die has a pressure fitting portion protruding from the base wall of the housing and said reference pressure die has a portion also protruding from the base wall of the housing to provide a reference pressure sensor that reacts to thermal, mechanical and acceleration forces and stresses substantially identically to the pressure sensing die.

16. The pressure sensor assembly of claim 15 wherein the pressure sensing die and the reference pressure die are each supported relative to the base wall through a separate first metal fitting, a second metal fitting bonded to a bore in each first metal fitting, and a separate glass tube fixedly supported on each second metal fitting and directly supporting the pressure sensing die and reference pressure die, respectively, said second metal fitting having a thermal coefficient of expansion that is intermediate the thermal coefficients of expansion of the first metal fittings, and of the glass tubes.

17. A pressure sensor comprising:

a backing plate made of a rigid material;

a semiconductor material diaphragm mounted on the backing plate, the diaphragm having a support rim around a periphery of the diaphragm, the diaphragm having portions within the support rim which are deflectable relative to the backing plate when under fluid pressure, the backing plate being at least two and one half times as thick as the rim;

an electrode plate forming a capacitive pressure sensor in combination with the diaphragm and mounted to the diaphragm support rim;

a housing for enclosing the pressure sensor;

a glass tube secured to a wall of the housing and directly supporting the backing plate for stress isolation of the backing plate and electrode plate relative to the housing; and

a fluid pressure inlet passing through the wall of the housing, the glass tube and the backing plate to permit fluid pressure to act on center portions of the diaphragm to deflect the center portions of the diaphragm relative to the electrode plate, and to cause a change in spacing between the center portions of the diaphragm and the electrode plate.