Pressure sensor with improved capacitive pressure transducer

• US 4,716,492 A
• Filed: 05/05/1986
• Issued: 12/29/1987
• Est. Priority Date: 05/05/1986
• Status: Expired due to Term

• Current Assignee: Sensata Technologies Incorporated (Sensata Technologies Holding Plc)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kawate, Keith W., Charboneau, Thomas J.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US06/859,566
• Time in Patent Office: 603 Days
• Field of Search: 361/283, 73/718, 73/724
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass

Abstract

A pressure sensor comprises an improved capacitive pressure transducer having a first capacitor plate secured to a limited portion of a first surface of a relatively rigid ceramic substrate and having a diaphragm with an electrically conductive surface forming a second capacitor plate, the diaphragm being secured to the ceramic substrate at a location spaced inwardly from the periphery of that first substrate surface for disposing the second capacitor plate in spaced, overlying relation to the first capacitor plate to be movable in response to applied pressure for varying the capacitor formed by the plates. Support means bear against opposite surfaces of the ceramic substrate at the periphery of the substrate for mounting the transducer with the diaphragm thereof substantially free of mounting stresses to be exposed to a pressure force in a pressure zone to be monitored.

Claims

1. A transducer comprising a substantially flat ceramic substrate having a flat surface on one side and having an opposite side, a first electrically conductive capacitor plate mounted on a central part of the flat surface on said one side of the flat, ceramic substrate, movable means mounted on said substrate surface at a location spaced to leave a peripheral portion of the flat ceramic substrate free to be engaged from each of two opposite sides of the flat ceramic substrate and having an electrically conductive surface portion of the movable means forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectivly movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored while leaving the peripheral portion of said substrate accessible to be gripped at said two opposite sides of said peripheral portion of the flat ceramic substrate for mounting the transducer while leaving the movable means substantially free of stresses assciated with such mounting.

2. A transducer comprising a substantially flat ceramic substrate, a first electrically conductive capacitor plate mounted on a central part of a flat surface of the flat, ceramic substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of said substrate surface to leave a peripheral portion of the flat ceramic substrate free to be engaged from each of two opposite sides of the flat ceramic substrate and having an electrically conductive surface portion of the movable means forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored while leaving said peripheral portion of said substrate accessible to be gripped at said two opposite sides of said peripheral portion of the flat ceramic substrate for mounting the transducer while leaving the movable means substantially free of stresses associated with such mounting, the movable means comprising a cup-shaped member having a flexible bottom with an inner and outer bottom surface, a side wall, and a rim and having said bottom provided with a selected thickness for forming both the second capacitor plate and a pressure responsive diaphragm, the cup-shaped member having its rim mounted and sealed to the said ceramic substrate surface at said location spaced inwardly from said peripheral portion of the flat ceramic substrate surface and at a location spaced around the first capacitor plate for excluding extraneous materials from between the first and second capacitor plates and disposing the second capacitor plate in precisely selected spaced relation to the first capacitor plate to be movable in response to application of pressure to an outer surface of the flexible bottom of the cup-shaped member while leaving said peripheral portion of the substrate free to be engaged from each of said two opposite substrate sides in mounting the transducer.

3. A pressure transducer according to claim 2 wherein the cup-member has a resiliently flexible bottom formed of a selected thickness to adapt the bottom for movement in response to application of pressures within a selected range and has a relatively thicker, relatively rigid side wall for securing and mounting the bottom of the cup-shaped member for flexing movement proportional to the pressures applied within said selected range.

4. A pressure transducer according to claim 2 wherein the cup-shaped member is formed of a metal material having a coefficient of thermal expansion substantially corresponding to the coefficient of thermal expansion of the ceramic substrate.

5. A pressure transducer comprising a ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored, and said peripheral portion of said substrate surface being accessible to be engaged for mounting the transducer while leaving the movable means substantially free of stresses associated with such mounting, the movable means comprising a cup-shaped member formed of a metal material having a coefficient of thermal expansion substantially corresponding to the coefficient of thermal expansion of the ceramic substrate having a flexible bottom with an inner and outer bottom surface, a side wall, and a rim and having said bottom forming the second capacitor plate and a pressure responsive diaphragm, the cup-shaped member having its rim sealed to the said substrate surface at a location spaced around the first capacitor plate for excluding extraneous materials from between the first and second capacitor plates and disposing the second capacitor plate in precisely selected spaced relation to the first capacitor plate to be movable in response to application of pressure to the outer surface of the flexible bottom of the cup-shaped member, the cup-shaped metal member being formed of a cupped composite metal laminate material comprising at least one layer of a copper material of selected coefficient of thermal expansion having relatively high electrical conductivity and at least one layer of an iron alloy of selected electrical conductivity having a relatively low coefficient of thermal expansion, the relative thicknesses of the layers in the composite metal laminate material being selected for providing the laminate material with a coefficient of thermal expansion corresponding to the substrate.

6. A pressure transducer according to claim 5 wherein the first capacitor plate is formed of said composite metal laminate material secured to the substrate.

7. A pressure transducer comprising a ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored, and said peripheral portion of said substrate surface being accessible to be engaged for mounting the transducer while leaving the movable means substantially free of stresses associated with such mounting, the movable means comprising a cup-shaped member having a flexible bottom with an inner and outer bottom surface, a side wall, and a rim and having said bottom forming the second capacitor plate and a pressure responsive diaphragm, the cup-shaped member having its rim sealed to the said substrate surface at a location spaced around the first capacitor plate for excluding extraneous materials from between the first and second capacitor plates and disposing the second capacitor plate in precisely selected spaced relation to the first capacitor plate to be movable in response to application of pressure to the outer surface of the flexible bottom of the cup-shaped member, the cup-shaped member being formed of a ceramic material and having a layer of a metal material secured to the inner surface of the flexible bottom of the cup-shaped member for forming said second capacitor plate.

8. A pressure transducer according to claim 7 wherein the metal material forming at least one of the first and second capacitor plates is formed of a material having a coefficient of thermal expansion corresponding to the substrate.

9. A pressure transducer according to claim 8 wherein the metal material in the first and second capacitor plates comprises a composite metal laminate material having a layer of a copper material of selected coefficient of thermal expansion having relatively high electrical conductivity and a layer of an iron alloy of selected electrical conductivity having a relatively lower coefficient of thermal expansion, the relative thickness of the layers in the composite metal laminate material being selected for providing the laminate material with a coefficient of thermal expansion corresponding to the substrate.

10. A pressure transducer comprising a ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of the said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored, and said peripheral portion of said substrate surface being accessible to be engaged for mounting the transducer while leaving the movable means substantially free of stresses associated with such mounting, the movable means comprising a flexible sheet member having the second capacitor plate portion of the diaphragm means disposed at one side of the sheet member, and a mixture of a glass frit fusible at one temperature and a plurality of balls of a selected diameter of a material which retains its shape at said one temperature arranged between said one sheet member side and the substrate surface at said location spaced inwardly from the peripheral portion of the substrate surface for disposing the first and second capacitor plates in precisely spaced relation to each other as determined by the diameter of said balls, the glass frit being fused at said one temperature for securing the first and second capacitor plates in said precisely spaced relation to each other.

11. A pressure transducer according to claim 10 wherein the sheet member is formed of an electrical conductive metal material having a coefficient of thermal expansion corresponding to the substrate.

12. A pressure transducer according to claim 11 wherein the sheet member is formed of a composite metal laminate material having a layer of a copper material of selected coefficient of thermal expansion having relatively high electively high electrical conductivity and a layer of an iron alloy of selected electrical conductivity having a relatively lower coefficient of thermal expansion, the relative thickness of the layers in the composite metal laminate material being selected for providing the laminate material with a coefficient of thermal expansion corresponding to the substrate.

13. A pressure transducer according to claim 10 wherein the sheet member is formed of ceramic material and has a layer of electrically conductive metal material secured to said one side of the sheet member for forming said second capacitor plate.

14. A pressure transducer comprising a ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored, and said peripheral portion of said substrate surface being accessible to be engaged for mounting the transducer while leaving the movable means substantially free of stresses associated with such mounting, said first and second capacitor plates comprising metal materials of coefficient of thermal expansion substantially corresponding to the coefficient of thermal expansion of the substrate material and the metal materials being formed of a composite metal laminate material having a layer of a copper material of selected coefficient of thermal expansion having relatively high electrical conductivity and a layer of an iron alloy of selected electrical conductivity having a relatively lower coefficient of thermal expansion, the relative thickness of the layers in the composite metal laminate material being selected for providing the laminate material with a coefficient of thermal expansion corresponding to the substrate.

15. A transducer comprising a ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate with selected space between the second capacitor plate and the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate into said space for varying the capacitance of the capacitor in accordance with a selected change in condition being monitored, characterized in that dielectrically stable film means are secured over one of said capacitor plates in a selected part of said space between said plates for preventing shorting between the capacitor plates due to inadvertent presence of conductive particles between the capacitor plates.

16. A condition sensor comprising a transducer having a flat ceramic substrate, a first electrically conductive capacitor plate mounted on a surface of the substrate, movable means mounted on said substrate surface at a location spaced inwardly from a peripheral portion of said substrate surface and having an electrically conductive surface portion forming a second capacitor plate disposed over the first capacitor plate in selected spaced relation to the first capacitor plate to form a capacitor, and means for electrically connecting the first and second capacitor plates in an electrical circuit, the movable means being selectively movable relative to the first capacitor plate for varying the capacitance of the capacitor in accordance with a selected change in a condition being monitored, electrical circuit means disposed at an opposite substrate surface and electrically connected to the first and second capacitor plates for providing an electrical signal corresponding to changes in said capacitance, the substrate having at least one opening in said peripheral portion thereof and at least one additional means extends through said opening in said peripheral portion of the substrate for electrically connecting one of said first and second capacitor plates to said circuit means, and support means bearing against at least part of said peripheral portion of the substrate surface and of said opposite substrate surface for mounting the transducer in the sensor to be exposed to a condition to be monitored while retaining the movable means of the transducer substantially free of mounting stresses.

17. A sensor according to claim 16 wherein the electrical circuit means comprise an integrated circuit, circuit path means are provided on said opposite substrate surface electrically connected to the integrated circuit unit, and said additional means electrically connect the first and second capacitor plates of the transducer to said circuit path means.

18. A pressure sensor comprising a capacitive pressure transducer having a ceramic substrate, a first electrically conductive capacitor plate secured to one surface of the substrate, a flexible ceramic sheet forming a diaphragm, a second electrically conductive capacitor plate secured to one surface of the flexible ceramic sheet, a mixture of a glass frit fusible at one temperature and of a plurality of balls of a selected diameter of a material which retains its shape at said one temperature being disposed between portions of said one surfaces of the ceramic substrate and the flexible ceramic sheet member at a location spaced inwardly from a peripheral portion of said substrate surface for disposing the first and second capacitor plates in precisely spaced relation to each other as determined by the diameter of said balls to form a capacitor, the glass frit being fused at said one temperature for securing the first and second capacitor plates in said precisely spaced relation to permit the second capacitor plate to be movable in response to application of pressure to an opposite surface of the flexible ceramic sheet for varying the capacitance of the capacitor in response to changes in pressures applied to the flexible ceramic sheet, and connector means for electrically connecting the first and second capacitor plates in an an electrical circuit;

support means bearing against said peripheral portion of the substrate surface and an opposite substrate surface for mounting the transducer in the sensor to be exposed to a pressure in a zone to be monitored while retaining the flexible ceramic sheet substantially free of mounting stress; and

electrical circuit means comprising an integrated circuit mounted on an opposite surface of the ceramic substrate and electrically connected to said connector means for providing an electrical signal corresponding to said pressure changes.

19. A pressure sensor according to claim 18 further characterized in that the ceramic substrate has a pair of concentric annular grooves formed therein around said first capacitor plate, and said mixture of glass frit and balls is arranged between the ceramic substrate and flexible ceramic sheet member at a location extending around the first capacitor plate between said grooves for precisely positioning the capacitor plates relative to each other.

20. A pressure sensor according to claim 19 further characterized in that said fused mixture seals the space between the capacitor plates for excluding extraneous materials therefrom.

21. A pressure sensor according to claim 19 further characterized in that said first and second capacitor plates are formed of a composite metal laminate material having a layer of copper material or selected coefficient thermal expansion having relatively high electrical conductivity and a layer of an iron alloy of selected electrical conductivity having a relatively lower coefficient of thermal expansion, the relative thickness of the layers in the composite metal laminate material being selected for providing the laminate material with a coefficient of thermal expansion corresponding to the substrate.

22. A pressure sensor according to claim 18 further characterized in that dielectric film means are secured over one of said capacitor plates for preventing shorting between the capacitor plates due to inadvertent presence of conductive particles between the capacitor plates.

23. A pressure sensor according to claim 18 further characterized in that sealing means are clamped between the support means and said peripheral portion of the substrate surface for sealing the electrical circuit means in the sensor from said fluid pressure.

24. A pressure sensor according to claim 23 further characterized in that said sealing means comprise a pliable film of organic material disposed in overlying relation to the periphery of the substrate and to said flexible ceramic sheet, and an O-ring gasket clamped between the support means and the portion of the film overlying the periphery of the substrate in sealing relation to the transducer.