Multiple-cavity variable capacitance pressure transducer

• US 4,390,925 A
• Filed: 08/26/1981
• Issued: 06/28/1983
• Est. Priority Date: 08/26/1981
• Status: Expired due to Term

• Current Assignee: Leeds & Northrup Co.
• Original Assignee: Leeds & Northrup Co.
• Inventors: Freud, Paul J.
• Primary Examiner(s): Reynolds, B. A.
• Assistant Examiner(s): Keve, Alfred S.
• Application Number:
  US06/296,290
• Time in Patent Office: 671 Days
• Field of Search: 361/283, 361/328, 73/718, 73/724, 29/25.41, 357/26, 324/71 SN
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: Y10T 29/43 Electric condenser making

Abstract

A plurality of recesses and interconnecting paths are etched into the surface of a silicon wafer. A plate of borosilicate glass carrying thin-film metal deposits in a corresponding pattern is electrostatically bonded to the silicon to form a multiple-cavity variable capacitance pressure transducer.

Claims

1. A method for manufacturing a variable capacitance pressure transducer comprising the steps of:

removing from spaced areas and interconnecting paths therebetween on a surface of a conductive wafer of semiconductor material a portion of the semiconductor material to form a plurality of connected recesses in the surface of the material;

forming on the surface of a dielectric material spaced areas of electrically conductive material;

forming an aperture through said dielectric material at one of said areas;

coating the circumference of said aperture with an electrically conductive material; and

electrostatically bonding the surface of the semiconductor material to the surface of the dielectric material so that the recesses of the semiconductor material are in adjacent spaced and substantially parallel alignment with the areas of electrically conductive material on the dielectric material, thereby to form in the resulting cavities electrical capacitors which have the semiconductor material as one plate thereof spaced from another plate comprising at least one of the electrically conductive areas so that the capacitance of the capacitor formed thereby is variable as a function of changes in the pressure difference acting on opposite sides of said wafer of semiconductor material.

2. A manufacturing method according to claim 1 wherein the removal of the semiconductor material in the spaced area is accomplished by etching.

3. A manufacturing method according to claim 2 wherein the semiconductor material is silicon, the dielectric material is borosilicate glass, and wherein the spaced areas of electrically conductive material are formed by application of thin films of metal to a surface of the glass dielectric material.

4. A method for manufacturing a variable capacitance differential pressure transducer comprising the steps of:

etching a plurality of shallow recesses and interconnecting grooves therebetween in opposing areas on each of the opposing sides of a conductive plate of silicon;

depositing on two plates of borosilicate glass an electrically conductive thin-film in areas and along interconnecting paths spaced to match the spacing of said recesses on said diaphragm surfaces;

forming in each of said plates in at least one of said areas, an aperture to provide a pressure transmitting passage through said wafers to all of said recesses;

coating said aperture with an electrically conductive film to provide electric contact to all of said deposits; and

electrostatically bonding said plates to opposite sides of said diaphragm so that conductive areas are opposite the recesses of said diaphragm and in registration therewith, and so that all areas on each side of the diaphragm are exposed to the same fluid pressure.

5. A differential pressure transducer of the capacitor type comprising:

a pair of plates of inorganic electrically insulating material with a plurality of electrically conducting surfaces deposited over spaced areas on one surface of each of said plates;

a wafer of electrically conductive semiconductor material electrostatically bonded between said plates, said semiconductor material having a plurality of recesses in both of its faces in opposing relationship and in registration with said conductive surfaces so as to form with said plates a plurality of fluid tight cavities on opposing sides of the diaphragm;

means providing fluid communication with all of the cavities on each side of said semiconductor material so that the opposing sides of said semiconductor material may be exposed to different fluid pressures; and

means providing electrical communication between all of the conducting surfaces on each of said plates so that the capacitors formed in each of the cavities between the semiconductor material and the conducting surfaces on any one side of the semiconductor material are all connected in parallel.

6. A pressure transducer as set forth in claim 5 in which:

the inorganic electrically insulating material is borosilicate glass;

the semiconductor material is a doped silicon;

the means providing fluid communication between the cavities on each side of the semiconductive material is a series of paths interconnecting those of said cavities on one side of the semiconductor material and an aperture through each of said plate to connect said cavities on each side to a different fluid pressure;

said electrically conductive surfaces are a thin-film deposit of metal; and

said means providing electrical communication includes a thin-film deposit of metal along paths interconnecting said conducting surfaces.

7. A pressure transducer of the capacitor type comprising:

a wafer of inorganic electrically insulating material having a plurality of interconnected electrically conductive surfaces deposited over spaced portions of one surface of said wafer to form a capacitor plate thereon;

a semiconductor diaphragm structure having a plurality of spaced recesses, said structure being electrostatically bonded to said wafer so as to form with said wafer a plurality of cavities with the conductive surfaces of said wafer facing said diaphragm structure; and

means providing fluid communication between said cavities so that the diaphragm structure acts as an opposing capacitor plate responsive to the application of changes in the fluid pressure in the cavities so as to change the capacitance between the diaphragm structure and the conductive area as an indication of the magnitude of the pressure change.

8. A pressure transducer as set forth in claim 7 in which the wafer of inorganic electrically insulating material is borosilicate glass and the semiconductor material of the diaphragm structure is a doped silicon.

9. A pressure transducer as set forth in claims 7 or 8 in which said means for providing fluid communication between said cavities includes a series of paths interconnecting said recesses.

10. A pressure transducer as set forth in claims 7 or 8 in which said recesses are produced by etching and in which said electrically conductive surfaces are produced by depositing a thin film of metal on the surface of said insulating material.

11. A pressure transducer as set fort in claim 9 in which there is included means for providing a fluid connection through said insulating material and connecting with said cavities.