Integrated dual-range pressure transducer

• US 4,574,640 A
• Filed: 11/29/1984
• Issued: 03/11/1986
• Est. Priority Date: 11/29/1984
• Status: Expired due to Fees

• Current Assignee: Bourns Instruments, Inc.
• Original Assignee: Bourns Instruments, Inc.
• Inventors: Krechmery, Roger L.
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US06/676,037
• Time in Patent Office: 467 Days
• Field of Search: 73/721, 73/727, 73/720, 73/726, 73/DIG. 4, 338/4, 338/42, 338/3
• US Class Current: 73/721
• CPC Class Codes: G01L 9/0052 of piezoresistive elements circuits therefor G01L9/06

Abstract

A pressure transducing device in the form of a beam includes a monolithic chip of silicon or similar material which is mechanically supported at and near its two opposed ends and unsupported in a flexible region between the two ends. The flexible, unsupported region is one of maximized sensitivity to stresses produced by deflection or flexing of the beam due to, e.g., a differential pressure applied across it. An integral, pressure-responsive diaphragm is formed in the supported area of the chip near one of its mechanically-supported ends. This area of the chip is relatively insensitive to stresses produced by beam flexing or deflection; rather, it responds to stresses produced by a pressure (e.g., a static pressure) applied directly to its surface. A first set of strain gauges is provided in the flexible chip region, and a second set on the surface of the integral diaphragm. Thus, a single transducing element is formed which provides separate output signals simultaneously indicative of both differential and static pressures experienced by, respectively, the unsupported chip region and the surface of the integral diaphragm.

Claims

1. A pressure transducing device, comprising:

a beam element having a first region which is sensitive to stresses produced by flexing of the beam element and a second region which is relatively insensitive to such stresses;

a pressure-responsive diaphragm formed in said second region of said beam element;

first sensing means, disposed on said first region of said beam element, for sensing the stresses induced therein by the flexing of said beam element; and

second sensing means, disposed on said diaphragm, for sensing the stresses induced in said diaphragm in response to a pressure applied thereto.

2. The device of claim 1, wherein said beam element has first and second opposed surfaces, and wherein said diaphragm has an outer surface integral with said first surface of said beam element and an inner surface defined by a recess in said second surface of said beam element.

3. The device of claim 2, further comprising:

a support element attached to said second surface of said beam element in said second region thereof and defining, with said recess, an enclosed chamber underlying said diaphragm.

4. The device of claim 3, wherein said enclosed chamber is substantially evacuated so that said diaphragm is responsive to the absolute pressure applied to its outer surface.

5. The device of claim 1, wherein said beam element has first and second ends respectively supported against flexing by first and second support elements, and wherein said first region is an unsupported portion of said beam element disposed between said first and second ends.

6. The device of claim 5, wherein said unsupported portion of said beam element includes a reduced-thickness area wherein sensitivity to flexing-induced stresses is maximized.

7. The device of claim 1, wherein said first sensing means includes a first plurality of strain gauges responsive to the flexing-induced stresses in said first region of said beam element and producing a first output signal proportional to said flexing, and wherein said second sensing means includes a second plurality of strain gauges responsive to the pressure-induced stresses in said diaphragm and producing a second output signal proportional to said pressure.

8. The device of claim 7, wherein said diaphragm is responsive to a pressure differential applied across it, and wherein said second output signal is proportional to said pressure differential.

9. The device of claim 7, wherein said beam element is formed of silicon, said strain gauges are piezoresistive elements diffused into said beam element, and said diaphragm is formed by etching a recess into one side of said beam element within said second region.

10. The device of claim 7, wherein said beam element is formed of monocrystalline sapphire, said strain gauges are silicon piezoresistive elements epitaxially deposited on a first surface of said beam element, and said diaphragm is formed by an ultrasonically machined recess in a second side of said beam element opposed to said first side and within said second region.

11. The device of claim 1, wherein said beam element is flexed by the application thereto of pressures within a first pressure range, and wherein said diaphragm is responsive to pressures within a second pressure range different from said first pressure range.

12. A pressure transducing device, comprising:

a beam element having a supported region and an unsupported region, said unsupported region being relatively sensitive to stresses induced by the flexing of said beam element in response to pressure applied thereto;

a pressure-responsive diaphragm formed integrally with said beam element in said supported region;

a first plurality of strain gauges, disposed on said unsupported region of said beam element, responsive to the stresses induced in said unsupported region by the flexing of said beam element, and producing a first output signal proportional to the flexing of said beam element; and

a second plurality of strain gauges, disposed on said diaphragm, responsive to the pressure-induced stresses in said diaphragm and producing a second output signal proportional to the pressure applied to said diaphragm.

13. The device of claim 12, wherein said beam element is flexed by the application thereto of pressures within a first pressure range, and wherein said diaphragm is responsive to pressures within a second pressure range different from said first pressure range.

14. The device of claim 12, wherein said beam element has a first side and a second side, and wherein said diaphragm has an outer surface integral with said first side, and an inner surface defined by a recess in said second side of said beam element within said supported region.

15. The device of claim 14, further comprising:

a support member attached to said second side of said beam element in said supported region, said support member and said recess defining an enclosed chamber underlying said diaphragm.

16. The device of claim 15, wherein said chamber is substantially evacuated, so that said diaphragm is responsive to the absolute pressure applied to its outer surface.

17. The device of claim 12, wherein said supported region is a first supported region, said device further comprising:

a second supported region separated from said first supported region by said unsupported region.

18. The device of claim 17, further comprising:

first and second support elements respectively attached to said first and second supported regions to minimize the flexing of said beam element in said first and second supported regions.

19. The device of claim 18, wherein said beam element is formed of silicon, said first and second support elements are formed of glass, and said beam element is attached to said support elements by anodic bonding.

20. The device of claim 17, wherein said unsupported region of said beam element includes a reduced-thickness region wherein sensitivity to flexing-induced stresses is maximized.

21. A pressure transducing device of the type including a beam having a monolithic, pressure-responsive beam element, said beam element having a flexible, pressure-responsive region and a plurality of strain-sensitive elements in said flexible region, said strain-sensitive elements being responsive to the pressure-induced stresses in said flexible region and producing an output signal proportional to the pressure inducing such stresses, wherein the improvement comprises:

a second pressure-responsive region in said monolithic beam element; and

a second plurality of strain-sensitive elements in said second pressure-responsive region responsive to the pressure-induced stresses in said second pressure-responsive region and producing a second output signal proportional to the pressure which is inducing the stresses in said second pressure-responsive region;

wherein said flexible pressure-responsive region is responsive to pressures within a first pressure range and said second pressure-responsive region is responsive to pressures within a second pressure range different from said first pressure range.

22. The device of claim 21, wherein said flexible pressure-responsive region is a region of relatively high sensitivity to pressure-induced flexing of said beam element, and wherein said second pressure-responsive region is a region of relative insensitivity to such flexing.

23. The device of claim 22, wherein said plurality of strain-sensitive elements in said flexible region is a first plurality which is responsive substantially only to stresses in said flexible region resulting from said pressure-induced flexing, and wherein said second plurality of strain-sensitive elements is responsive substantially only to the pressure-induced stresses in said second pressure-responsive region.

24. The device of claim 23, wherein said second pressure-responsive region comprises a diaphragm formed integrally with said monolithic beam element and having a pressure-responsive surface which is integral with a major surface of said monolithic beam element.

25. The device of claim 24, wherein said monolithic beam element has first and second opposed major surfaces, and wherein said diaphragm is defined by a recess in said second major surface.

26. The device of claim 25, further comprising:

a support element attached to said monolithic beam element so as to underly said diaphragm, thereby defining, with said recess, an enclosed chamber.

27. The device of claim 26, wherein said chamber is substantially evacuated, so that said diaphragm is responsive to the absolute pressure applied to its pressure-responsive surface.

28. The device of claim 26, wherein said support element is a first support element, and wherein said device further comprises:

a second support element attached to said monolithic beam element at an area separated from the attachment area of said first support element by said flexible region of said monolithic beam element.