MEDIA-COMPATIBLE ELECTRICALLY ISOLATED PRESSURE SENSOR FOR HIGH TEMPERATURE APPLICATIONS

• US 20100224004A1
• Filed: 03/03/2009
• Published: 09/09/2010
• Est. Priority Date: 03/03/2009
• Status: Active Grant

• Current Assignee: Nagano Keiki Company Limited
• Original Assignee: S3C Inc. (Nagano Keiki Company Limited)
• Inventors: Suminto, James Tjanmeng, Yunus, Mohammad
• Granted Patent: US 7,775,119 B1
• Time in Patent Office: Days
• US Class Current: 73/727
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: G01L 19/147 Details about the mounting of the sensor to support or covering means
• 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 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49007 Indicating transducer
• CPC Class Codes: Y10T 29/49126 Assembling bases
• CPC Class Codes: Y10T 29/49165 by forming conductive walled aperture in base

Abstract

A pressure sensor is described with sensing elements electrically and physically isolated from a pressurized medium. An absolute pressure sensor has a reference cavity, which can be at a vacuum or zero pressure, enclosing the sensing elements. The reference cavity is formed by bonding a recessed cap wafer with a gauge wafer having a micromachined diaphragm. Sensing elements are disposed on a first side of the diaphragm. The pressurized medium accesses a second side of the diaphragm opposite to the first side where the sensing elements are disposed. A spacer wafer may be used for structural support and stress relief of the gauge wafer. In one embodiment, vertical through-wafer conductive vias are used to bring out electrical connections from the sensing elements to outside the reference cavity. In an alternative embodiment, peripheral bond pads on the gauge wafer are used to bring out electrical connections from the sensing elements to outside the reference cavity. In various embodiments, a regular silicon-on-insulator wafer or a double silicon-on-insulator wafer may be used as the gauge wafer, and appropriate micromachining steps are adopted to define the diaphragm. A layer of corrosion resistant material is deposited on the surface of the diaphragm that is accessed by the pressurized medium.

Claims

1. A Micro-Electro-Mechanical System (MEMS) pressure sensor, comprising:

a gauge wafer, comprising;

a micromachined structure comprising a diaphragm region and a pedestal region, wherein a first surface of the diaphragm region is configured to be accessed by a pressurized medium that exerts a pressure resulting in a deflection of the diaphragm region;

an electrical insulation layer disposed on a second surface of the diaphragm region opposite to the first surface; and

a plurality of sensing elements patterned on the electrical insulation layer disposed on the second surface of the diaphragm region, wherein a thermal expansion coefficient of the material of the sensing elements substantially matches with a thermal expansion coefficient of the material of the gauge wafer;

a cap wafer coupled to the gauge wafer, comprising;

a recess on an inner surface of the cap wafer facing the gauge wafer that defines a sealed reference cavity that encloses the sensing elements and prevents exposure of the sensing elements to external environment;

a plurality of through-wafer embedded vias made of an electrically conductive material to bring out electrical connections from the sensing elements to an outer surface of the cap wafer opposite to the inner recessed surface; and

a spacer wafer with a central aperture aligned to the diaphragm region, bonded to the pedestal region of the micromachined structure.

2. The MEMS pressure sensor of claim 1, wherein the micromachined structure is made of silicon, and a layer containing the sensing elements is made of silicon doped to achieve a desired sheet resistance.

3. The MEMS pressure sensor of claim 1, wherein the cap wafer is made of an electrically conductive material, wherein portions of the cap wafer are used as the embedded vias, and the embedded vias have electrically insulating sidewalls.

4. The MEMS pressure sensor of claim 1, wherein the layer containing the sensing elements is a polycrystalline silicon layer, a single-crystalline silicon layer, or a layer formed by fusion bonding a sacrificial wafer on top of the electrical insulation layer followed by removing a substantial portion of the sacrificial wafer.

5. The MEMS pressure sensor of claim 1, wherein the spacer wafer is made of Pyrex or silicon.

6. The MEMS pressure sensor of claim 1, wherein the spacer wafer and the micromachined structure are bonded by using one of the following processes:

anodic bonding, fusion bonding, glass frit bonding, eutectic bonding, solder preform bonding, and thermo-compressive bonding.

7. The MEMS pressure sensor of claim 1, wherein the cap wafer is coupled to gauge wafer using glass frit bonding, eutectic bonding, solder preform bonding, flip-chip bonding, fusion bonding, or thermo-compressive bonding.

8. The MEMS pressure sensor of claim 1, wherein a layer of corrosion resistant material is deposited on the first surface of the diaphragm region accessed by the pressurized medium.

9. The MEMS pressure sensor of claim 8, wherein the corrosion resistant material is aluminum oxide.

10. A method for manufacturing a Micro-Electro-Mechanical System (MEMS) pressure sensor, the method comprising:

forming a micromachined structure comprising a diaphragm region and a pedestal region, wherein a first surface of the diaphragm region is configured to be accessed by a pressurized medium that exerts a pressure resulting in a deflection of the diaphragm region;

forming an electrical insulation layer disposed on a second surface of the diaphragm region opposite to the first surface;

forming a plurality of sensing elements patterned on the electrical insulation layer disposed on the second surface in the diaphragm region, wherein a thermal expansion coefficient of the material of the sensing elements substantially matches with a thermal expansion coefficient of the material of the gauge wafer;

forming a cap wafer with a central recess in an inner surface;

forming a plurality of through-wafer embedded vias made of an electrically conductive material in the cap wafer;

creating a sealed cavity by coupling the inner recessed surface of the cap wafer to the gauge wafer, such that the sensing elements are enclosed in the recess, and electrical connections from the sensing elements come out to an outer surface of the cap wafer opposite to the inner recessed surface through the electrically conductive through-wafer embedded vias;

forming a spacer wafer with a central aperture; and

attaching the spacer wafer to the pedestal region of the micromachined structure with the central aperture aligned to the diaphragm region.

11. The method of claim 10, wherein the micromachined structure is made of silicon, and a layer containing the sensing elements is made of silicon doped to achieve a desired sheet resistance.

12. The method of claim 10, wherein the step of forming the plurality of through-wafer via comprises:

selecting a cap wafer material that is electrically conductive;

making trenches surrounding portions of the cap wafer defined to be via regions; and

filling up the trenches with an electrically insulating material.

13. The method of claim 10, wherein the layer containing the sensing elements is a polycrystalline silicon layer, a single-crystalline silicon layer, or a layer formed by fusion bonding a sacrificial wafer on top of the electrical insulation layer followed by removing a substantial portion of the sacrificial wafer.

14. The method of claim 10, wherein the spacer wafer is made of Pyrex or silicon.

15. The method of claim 10, wherein the step of attaching the spacer wafer comprises using one of the following processes:

anodic bonding, fusion bonding, glass frit bonding, eutectic bonding, solder preform bonding, and thermo-compressive bonding.

16. The method of claim 10, wherein the cap wafer is coupled to the gauge wafer using glass frit bonding, eutectic bonding, fusion bonding, solder preform bonding, flip-chip bonding, or thermo-compressive bonding.

17. The method of claim 10, wherein the method further comprises:

depositing a layer of corrosion resistant material on the first surface of the diaphragm region accessed by the pressurized medium.

18. The method of claim 17, wherein the corrosion resistant material is aluminum oxide.

19. The method of claim 10, further comprising:

planarizing portions of an outer surface of the gauge wafer to be mated with the cap wafer.

20. A Micro-Electro-Mechanical System (MEMS) pressure sensor, comprising:

a gauge wafer, comprising;

a micromachined structure comprising a diaphragm region and a pedestal region, wherein a first surface of the micromachined structure is configured to be accessed by a pressurized medium that exerts a pressure resulting in a deflection of the diaphragm region;

an electrical insulation layer on a second surface of the diaphragm region opposite to the first surface; and

a plurality of sensing elements patterned on the electrical insulation layer on the second surface in the diaphragm region, wherein a thermal expansion coefficient of the material of the sensing elements substantially matches with a thermal expansion coefficient of the material of the gauge wafer;

a cap wafer coupled to the gauge wafer, comprising;

a recess on an inner surface of the cap wafer facing the gauge wafer that defines a sealed reference cavity that encloses the sensing elements and prevents exposure of the sensing elements to an external environment;

peripheral bond pads defined on the gauge wafer to bring out electrical connections from the sensing elements to outside the sealed reference cavity; and

a spacer wafer with a central aperture aligned to the diaphragm region, bonded to the pedestal region of the micromachined silicon structure.

21. The MEMS pressure sensor of claim 20, wherein the micromachined structure is made of silicon, and a layer containing the sensing elements is made of silicon doped to achieve a desired sheet resistance.

22. The MEMS pressure sensor of claim 20, wherein the layer containing the sensing elements is a polycrystalline silicon layer, a single-crystalline silicon layer, or a layer formed by fusion bonding a sacrificial wafer on top of the electrical insulation layer followed by removing a substantial portion of the sacrificial wafer.

23. The MEMS pressure sensor of claim 20, wherein the spacer wafer is made of Pyrex or silicon.

24. The MEMS pressure sensor of claim 20, wherein the spacer wafer and the micromachined structure are bonded by using one of the following processes:

anodic bonding, fusion bonding, glass frit bonding, eutectic bonding, solder preform bonding, and thermo-compressive bonding.

25. The MEMS pressure sensor of claim 20, wherein the cap wafer is coupled to the gauge wafer using glass frit bonding, fusion bonding, eutectic bonding, solder preform bonding, flip-chip bonding, or thermo-compressive bonding.

26. The MEMS pressure sensor of claim 20, wherein a layer of corrosion resistant material is deposited on the first surface of the micromachined structure accessed by the pressurized medium.

27. The MEMS pressure sensor of claim 26, wherein the corrosion resistant material is aluminum oxide.