Capacitive pressure sensor with low parasitic capacitance

• US 4,530,029 A
• Filed: 03/12/1984
• Issued: 07/16/1985
• Est. Priority Date: 03/12/1984
• Status: Expired due to Term

• Current Assignee: VTI Holding Oy
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Beristain, Charles D.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US06/588,584
• Time in Patent Office: 491 Days
• Field of Search: 361/283, 73/718, 29/25.42
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: H01G 5/18 due to change in inclination, e.g. by flexing, by spiral wrapping
• CPC Class Codes: Y10T 29/435 Solid dielectric type

Abstract

A plurality of two-plate capacitive pressure sensors with low parasitic capacitance and easily accessible plates are made with microcircuit and thin film technology by depositing a thin layer of glass over a plurality of thin, rigid plates and thin, narrow electrodes previously deposited on a thick glass dielectric substrate, by etching cavities in the thin layer of glass over the plates, and by anodically bonding, in vacuum, thin, doped silicon diaphragms to the thin layer of glass to form variable capacitors each of whose capacitance varies with the pressure outside the sensor.

Claims

1. A capacitive pressure sensor, comprising:

a thick glass dielectric substrate having a conductive surface formed on a central region thereof with a narrow electrode extending radially outward therefrom;

a thin, doped silicon diaphragm; and

a wall of glass joining said glass dielectric substrate to said silicon diaphragm and providing a chamber between said substrate, said diaphragm, and said wall;

the central conductive surface on said substrate being spaced at a distance from said diaphragm, forming the plates of a capacitor, said distance and therefore the capacitance of said capacitor varying in response to changes in fluid pressure external to said sensor.

2. The method of fabricating a pressure sensor of the type providing a capacitive indication of pressure, comprising the steps of:

forming an electrically conductive surface and an associated electrode on a surface of a glass dielectric substrate;

forming a layer of glass dielectric on said glass dielectric substrate, said conductive surface and said electrode;

creating a cavity in said glass dielectric layer over said conductive surface;

anodically sealing said cavity with an electrically conductive doped semiconductor diaphragm having a flexing portion which covers said cavity in opposition to said conductive surface and which flexes in response to differences in pressure between the pressure in the cavity and the environment outside the sensor for providing a variable capacitance between said diaphragm and said conductive surface in response to said differences in pressure.