Electromechanical pressure transducer

• US 4,178,621 A
• Filed: 01/23/1978
• Issued: 12/11/1979
• Est. Priority Date: 01/23/1978
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Ho, Roland K., Simonelic, Joseph J.
• Primary Examiner(s): Goldberg, E. A.
• Application Number:
  US05/871,274
• Time in Patent Office: 687 Days
• Field of Search: 361/283, 73/718, 73/724, 179/111 R
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass

Abstract

An improved ceramic capacitive pressure sensor adaptable for use in automobiles is disclosed. The pressure sensor comprises a thin flexible diaphragm disc having a capacitor electrode deposited on it. A thick cylindrical base substrate has a top surface with a second capacitor electrode deposited thereon and the diaphragm is bonded to the top surface of the base substrate by an annular glass ring such that the first and second electrodes are separated from each other and face each other directly across an air gap. The diaphragm, the top surface of the base substrate and the annular glass ring form an internal cavity in which a reference vacuum is stored. In response to pressure changes outside of this cavity, the diaphragm will flex and thereby change the capacitance created by the first and second electrodes. At least one channel portion is provided in the base substrate top surface which opens into the cavity storing the reference vacuum. This improves the electrical and mechanical characteristics of the pressure sensor. The diaphragm electrode is substantially larger than the base electrode and extends substantially over all of the central portion of the diaphragm within the glass annular ring and in this manner the electrode acts as a shield against conductive elements which are exterior to the internal cavity and are adjacent to the thin diaphragm.

Claims

1. A pressure transducer in which pressure changes displace a diaphragm whose position determines electrical characteristics of said transducer, comprising:

base substrate means having top and bottom substantially planar end surfaces;

flexible diaphragm means, relatively thin with respect to the distance between said top and bottom end surfaces, having a planar central portion and a peripheral portion; and

mounting means for mounting said peripheral portion of said diaphragm means to said base substrate top surface, said mounting means, said diaphragm planar central portion and said substrate top surface generally forming a sealed internal, substantially air tight cavity, a predetermined reference pressure being stored in said cavity, said base substantially thicker than said diaphragm means, said diaphragm central portion being displaceable with respect to said top surface in response to pressure changes, said base substrate means having at least one channel in the form of a surface groove in said substrate top surface opening into said internal cavity, wherein said channel substantially increases the volume of said cavity and thereby permits said cavity to more readily maintain a predetermined reference pressure in said cavity for increasing the lifetime of the transducer despite any leakage of said reference pressure from said cavity;

said transducer including,

a first planar capacitor electrode mounted on said diaphragm central portion and a second planar electrode substantially mounted on a central planar portion of said substrate top surface, said electrodes being separated from each other by just a gap included in said internal cavity which contains a fixed predetermined reference pressure, the distance between said electrodes being determined by said mounting means, said electrodes forming a parallel plate capacitor with the capacitance created by said electrodes being altered in response to flexing said diaphragm means in response to pressure changes.

2. A pressure transducer according to claim 1 wherein said base substrate means has a sealed entryway extending through said base substrate and opening into said internal cavity, whereby a predetermined reference pressure can be initially applied to said cavity through said entryway and whereby said channel aids in maintaining said predetermined reference pressure in said internal cavity.

3. A pressure transducer according to claim 2 wherein said mounting means comprises an annular glass ring located between said top surface of said base substrate means and the peripheral portion of said diaphragm means.

4. A pressure transducer according to claim 3 wherein said diaphragm means comprises a disc shaped ceramic plate.

5. A pressure transducer according to claim 4 wherein said base substrate means comprises a generally cylindrically shaped ceramic substrate.

6. A pressure transducer according to claim 5 wherein said electrode on said top surface of said base substrate means and said annular glass ring are deposited on substantially coplanar portions of said base substrate top surface.

7. A pressure transducer according to claim 1 wherein said channel is substantially C-shaped and substantially surrounds said second electrode, and wherein said channel has an opening portion across which a radial projection of said second electrode passes.

8. A pressure transducer according to claim 7 wherein said second electrode on said central planar portion of said top surface of said base substrate means and said annular glass ring are deposited on substantially coplanar portions of said base substrate top surface.