Overpressure-protected, differential pressure sensor and method of making the same

• US 5,220,838 A
• Filed: 03/28/1991
• Issued: 06/22/1993
• Est. Priority Date: 03/28/1991
• Status: Expired due to Fees

• Current Assignee: Invensys Systems Incorporated (Invensys PLC)
• Original Assignee: The Foxboro Company (Schneider Electric SE)
• Inventors: Chau, Kevin H.-L., Fung, Clifford D., Harris, P. Rowe, Panagou, John G., Dahrooge, Gary A.
• Primary Examiner(s): WOODIEL, DONALD
• Application Number:
  US07/676,914
• Time in Patent Office: 817 Days
• Field of Search: 73/721, 73/727, 73/754, 73/756, 73/DIG. 4, 73/706, 73/708, 338/4, 338/42, 29/621.1
• US Class Current: 73/721
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: Y10T 29/49103 Strain gauge making
• CPC Class Codes: Y10T 29/49812 Temporary protective coating, impregnation, or cast layer
• CPC Class Codes: Y10T 29/49996 Successive distinct removal operations

Abstract

An overpressure-protected, differential pressure sensor (37) is formed by depositing diaphragm material (24) over a cavity (23) formed and filled with sacrificial material (22) into a front surface of a substrate. The sacrificial material (22) is then removed to create a free diaphragm. The floor of the cavity (23) defines a first pressure stop to limit the deflection of the diaphragm in response to pressure applied to the top of the diaphragm. A port (33) is created to allow pressure to be applied to the bottom side of the diaphragm (24). An optional second pressure stop, which limits the deflection of the diaphragm in response to pressure applied to the bottom side of the diaphragm, is formed by bonding a cap (35) to standoffs (34) placed around the top of the diaphragm. The standoffs are spaced to allow pressure to be applied to the top of the diaphragm.

Claims

1. A differential pressure sensor comprising:

a silicon substrate having a cavity formed into a top surface of said substrate, wherein the floor of the cavity defines a forward pressure stop;

a deformable diaphragm formed of polysilicon material deposited over and spanning the cavity, wherein the deflection of the diaphragm in response to pressure applied to the top side of the diaphragm is limited by the forward pressure stop;

means for applying a first fluid pressure to the underside of the diaphragm; and

means for applying a second fluid pressure to the top side of the diaphragm; and

electrical means for detecting the relative deflection of the diaphragm due to a pressure differential between said first and said second fluid pressure exerted across the diaphragm.

3. The differential pressure sensor of claim 1 wherein said means for applying pressure includes a port formed by etching the back surface of the substrate.

4. The differential pressure sensor of claim 1 wherein the floor of the cavity is coated with material that prevents said diaphragm from sticking to the floor of the cavity during overpressure conditions.

5. The differential pressure sensor of claim 4 wherein said coating material is a nitride coating.

2. The differential pressure sensor of claim further comprising:

standoffs placed about the diaphragm to support a back pressure stop;

a cap placed on said standoffs and over the diaphragm to define the back pressure stop for limiting the deflection of the diaphragm in response to pressure applied to the underside of the diaphragm.

6. A differential pressure sensor comprising:

a silicon substrate having a cavity formed into a top surface of said substrate, wherein the floor of the cavity defines a first pressure stop;

a deformable diaphragm deposited over the cavity, wherein the deflection of the diaphragm in response to pressure applied to the top side of the diaphragm is limited by the first pressure stop;

standoffs placed about the diaphragm to support a second pressure stop;

a cap placed on said standoffs and over the diaphragm to define the second pressure stop for limiting the deflection of the diaphragm in response to pressure applied to the underside of the diaphragm;

means for applying pressure to the top surface of the diaphragm;

means for applying pressure to the underside of the diaphragm; and

electrical means for detecting the relative deflection of the diaphragm due to a pressure differential across the diaphragm.

7. The differential pressure sensor of claim 6 wherein said means for applying pressure includes a port formed by etching the back surface of the substrate.

8. The differential pressure sensor of claim 6 wherein the floor of the cavity is coated with material that prevents said diaphragm from sticking to the floor of the cavity during overpressure conditions.

9. The differential pressure sensor of claim 8 wherein said coating material is an oxide coating.

10. The differential pressure sensor of claim 8 wherein said coating material is a nitride coating.

11. The differential pressure sensor of claim 6 wherein the cap is coated with material that prevents the diaphragm from, sticking to the cap during overpressure conditions.

12. The differential pressure sensor of claim 6 wherein the cap is bonded against said standoffs using boron-doped oxide as a bonding agent.

13. The differential pressure sensor of claim 6 wherein the cap is bonded against said standoffs using spin-on-glass as a bonding agent.

14. The differential pressure sensor of claim 6 wherein the cap is bonded against said standoffs using metal to silicon bonds.

15. A method of producing an overpressure-protected differential sensor comprising the steps of:

forming a cavity in a top surface of a substrate, wherein said cavity has a preselected depth and shape to define a forward pressure stop;

filing the cavity with s acarificial spacer material;

depositing a layer of deformable diaphragm material over the top surface of the substrate and sacrificial material;

removing substrate material to provide a port for removing said sacrificial spacer material and for applying back pressure to the underside of said diaphragm material; and

removing said sacrificial spacer material from the cavity so that the cavity forms said forward pressure stop for limiting deflection of said diaphragm material when pressure applied to the top surface thereof greatly exceeds pressure applied to said port.

16. The method of producing an overpressure-protected, differential sensor as claimed in claim 15 further including the step of depositing material in the cavity to prevent the diaphragm from sticking to the floor of the cavity during overpressure conditions.

17. The method of producing an overpressure-protected, differential sensor as claimed in claim 15 further comprising the steps of:

depositing standoffs on the top surface of the substrate about the cavity for supporting a back pressure stop;

bonding a cap against the standoffs, wherein the cap defines the back pressure stop;

18. A method of producing a bi-directional, overpressure-protected differential sensor comprising the steps of:

forming a cavity in a top surface of a substrate, wherein the cavity has preselected depth and shape to define a forward pressure stop;

filling the cavity with a sacrificial spacer material;

depositing a layer of deformable diaphragm material over the top surface of the substrate and sacrificial material;

depositing standoffs on the top surface of the substrate about the cavity for supporting a back pressure stop;

bonding a cap against the standoffs, wherein the cap extends over the diaphragm material and defines the back pressure stop;

removing substrate material to provide a port for removing said sacrificial spacer material; and

removing said sacrificial spacer material from the cavity leaving the diaphragm material suspended over the cavity to bidirectionally deflect in response to differences between pressure applied to said cavity and pressure applied between said cap and the diaphragm material....

19. The method of producing a bi-directional, overpressure-protected, differential sensor as claimed in claim 18 wherein the cap is bonded against the standoffs using spin-on-glass as a bonding agent.

20. The method of producing a bi-directional, overpressure-protected, differential sensor as claimed in claim 18 wherein the cap is bonded against the standoffs using boron-doped oxide as a bonding agent.

21. The method of producing a bi-directional, overpressure-protected, differential sensor as claimed in claim 18 wherein the cap is bonded against the standoffs using silicon to metal bonding.

22. The method of producing a bi-directional, overpressure-protected, differential sensor as claimed in claim 18 wherein the cap is coated with material to prevent the diaphragm from sticking to the cap during overpressure conditions.

23. The method of producing a bi-directional, overpressure-protected, differential sensor as claimed in claim 44 further including the step of depositing material in the cavity to prevent the diaphragm from sticking to the floor of the cavity during overpressure conditions.