Capped sensor

• US 20050205959A1
• Filed: 01/20/2005
• Published: 09/22/2005
• Est. Priority Date: 02/05/2004
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Geen, John A., Judy, Michael W., Martin, John R., Felton, Lawrence E., Chau, Kevin H.-L.
• Granted Patent: US 7,795,723 B2
• Time in Patent Office: Days
• US Class Current: 257/467
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 7/0041 maintaining a controlled atmosphere with techniques not provided for in B81B7/0038
• CPC Class Codes: B81C 2203/0109 Bonding an individual cap on the substrate
• CPC Class Codes: B81C 2203/0136 Growing or depositing of a covering layer
• CPC Class Codes: B81C 2203/019 characterised by the material or arrangement of seals between parts
• CPC Class Codes: G01K 1/08 Protective devices, e.g. casings
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/008 by using thermal pick-up
• CPC Class Codes: G01P 15/0802 Details

Abstract

A sensor element is capped by bonding or otherwise forming a cap on a sensor element. The sensor may be hermetically sealed by using a hermetic cap and hermetic bonding material or by applying a hermetic coating. The sensor may be filled with a gas at an elevated pressure. The sensor may alternatively or additionally be filled with a special gas, such as a gas having a density-to-viscosity ratio above approximately 0.2.

Claims

1. Apparatus comprising:

a substrate having at least one heating element and at least one temperature-sensing element; and

a hermetic cap disposed on the substrate over the at least one heating element and the at least one temperature-sensing element, wherein the substrate and the hermetic cap form a hermetically sealed cavity around the at least one heating element and the at least one temperature-sensing element.

2. Apparatus according to claim 1, wherein the hermetic cap is bonded to the substrate using a hermetic bonding material.

3. Apparatus according to claim 1, wherein the hermetic cap is formed on the substrate in-situ as part of a wafer fabrication process.

4. Apparatus according to claim 1, wherein the cavity is filled with gas other than air.

5. Apparatus according to claim 4, wherein the ratio of density (in grams per liter) to viscosity (in micropascal-seconds) of the gas, when measured at a temperature of approximately 25 degrees Celsius and pressure of approximately one atmosphere, is above approximately 0.2.

6. Apparatus according to claim 1, wherein the cavity is filled with gas at a pressure greater than atmospheric pressure.

7. Apparatus according to claim 1, wherein at least one of the substrate and the cap includes a thermal insulating layer about the cavity so as to reduce loss of heat from the cavity.

8. Apparatus comprising:

a substrate having at least one sensing element;

a cap bonded to the substrate over the at least one sensing element using a bonding material, wherein the substrate and the cap form a cavity around the at least one sensing element, and wherein at least one of the cap and the bonding material is porous; and

a hermetic coating disposed over the cap and the bonding material so as to hermetically seal the cavity.

9. Apparatus according to claim 8, wherein the cavity is filled with gas other than air.

10. Apparatus according to claim 9, wherein the ratio of density (in grams per liter) to viscosity (in micropascal-seconds) of the gas, when measured at a temperature of approximately 25 degrees Celsius and pressure of approximately one atmosphere, is above approximately 0.2.

11. Apparatus according to claim 8, wherein the cavity is filled with gas at a pressure greater than atmospheric pressure.

12. Apparatus according to claim 8, wherein at least one of the substrate and the cap includes a thermal insulating layer about the cavity so as to reduce loss of heat from the cavity.

13. Apparatus according to claim 8, wherein the cap is porous, and wherein the porous cap provides thermal insulation for reducing loss of heat from the cavity.

14. Apparatus according to claim 8, wherein the at least one sensing element comprises:

at least one heating element; and

at least one temperature-sensing element.

15. Apparatus comprising:

a substrate having at least one sensing element; and

a cap bonded to the substrate over the at least one sensing element, wherein the substrate and the cap form a cavity around the at least one sensing element, and wherein at least one of the substrate and the cap includes a thermal insulating layer about the cavity so as to reduce loss of heat from the cavity.

16. Apparatus according to claim 15, wherein the cap is a hermetic cap, and wherein the hermetic cap is bonded to the substrate using a hermetic bonding material so as to hermetically seal the cavity.

17. Apparatus according to claim 15, wherein the cap is bonded to the substrate using a bonding material, at least one of the cap and the bonding material being porous, and wherein the capped sensor further comprises a hermetic coating disposed over the cap and the bonding material so as to hermetically seal the cavity.

18. Apparatus according to claim 15, wherein the cavity is filled with gas other than air.

19. Apparatus according to claim 18, wherein the ratio of density (in grams per liter) to viscosity (in micropascal-seconds) of the gas, when measured at a temperature of approximately 25 degrees Celsius and pressure of approximately one atmosphere, is above approximately 0.2.

20. Apparatus according to claim 15, wherein the cavity is filled with gas at a pressure greater than atmospheric pressure.

21. Apparatus according to claim 15, wherein the at least one sensing element comprises:

at least one heating element; and

at least one temperature-sensing element.

22. Apparatus comprising:

a substrate having at least one sensing element; and

a cap bonded to the substrate over the at least one sensing element, wherein the substrate and the cap form a gas-filled cavity around the at least one sensing element, wherein the ratio of density (in grams per liter) to viscosity (in micropascal-seconds) of the gas, when measured at a temperature of approximately 25 degrees Celsius and pressure of approximately one atmosphere, is above approximately 0.2.

23. Apparatus according to claim 22, wherein the gas is introduced into the cavity at a pressure greater than atmospheric pressure.

24. Apparatus according to claim 22, wherein the at least one sensing element comprises:

at least one heating element; and

at least one temperature-sensing element.