Vacuum sealed surface acoustic wave pressure sensor

• US 20060086188A1
• Filed: 10/21/2004
• Published: 04/27/2006
• Est. Priority Date: 10/21/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Cobianu, Cornel P., Pavelescu, Ioan, Avramescu, Viorel V.
• Granted Patent: US 7,198,981 B2
• Time in Patent Office: Days
• US Class Current: 73/700
• CPC Class Codes: G01L 9/0025 with acoustic surface waves
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/15151 the die mounting substrate comprising an aperture, e.g. for underfilling, outgassing, window type wire connections
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/1815 Shape
• CPC Class Codes: Y10T 29/49 Method of mechanical manufacture
• CPC Class Codes: Y10T 29/49007 Indicating transducer

Abstract

A vacuum sealed SAW pressure sensor is disclosed herein, which includes a sensing element configured as a SAW device (e.g., SAW resonator or SAW delay line) supported by a thin diaphragm. The substrate material can be implemented as a quartz wafer (i.e., a “base” wafer). The SAW device can be configured on one side of the wafer and the diaphragm etched on the opposite side. A quartz micromachined pressure sensor can thus be realized, which operates based on a variation of the surface wave velocity of a SAW device situated on the thin diaphragm. The SAW sensor is generally sealed in a vacuum and diaphragm sustains the sensor, thereby implementing a sensor on a wafer scale while allowing for a cost reduction per chip.

Claims

1. A pressure sensor method, comprising the steps of:

micro-machining a base from a first wafer;

micro-machining a cover from a second wafer, wherein said base and said cover form a vacuum seal therebetween; and

disposing a pressure sensing element within said vacuum between said base and said cover within said vacuum seal to form a vacuum sealed pressure sensor thereof.

2. The method of claim 1 further comprising the step of configuring said pressure sensing element to comprise at least one surface acoustic wave resonator.

3. The method of claim 2 wherein further comprising the step of configuring said base to support said at least one surface acoustic wave resonator.

4. The method of claim 1 further comprising the step of configuring said pressure sensing element to comprise at least one surface acoustic wave delay line device.

5. The method of claim 4 wherein further comprising the step of configuring said base to support said at least one surface acoustic wave delay line device.

6. The method of claim 1 wherein the step of micro-machining said cover from said second wafer, further comprises the step of:

micro-machining said cover from said second wafer by dry etching said wafer in order to form a plurality of grooves thereof, which are adaptable for use with at least one of the following;

a reference chamber, at least one over-pressure stop, and at least one trench subsequently formed upon said wafer.

7. The method of claim 1 further comprising the step of bonding said first wafer to said second wafer.

8. The method of claim 7 further comprising the step of micro-machining a mechanical support from a third wafer to support said base and said cover, wherein said third wafer is bonded to said first and second wafers.

9. The method of claim 8 wherein said first, second and third wafers form a stack when bonded together.

10. The method of claim 9 further comprising the step of forming said base from said first wafer of said stack by lapping and mirror polishing said first wafer by chemical mechanical polishing (CMP).

11. The method of claim 8 further comprising the step of forming a diaphragm by micro-machining said first wafer to form said base upon which said diaphragm is located.

12. The method of claim 11 wherein the step of forming said diaphragm further comprises the step of wet etching said first wafer in order to form said diaphragm.

13. The method of claim 11 further comprising the step of forming said diaphragm further comprises the step of dry etching said first wafer in order to form said diaphragm.

14. The method of claim 9 further comprising the step of micro-machining said mechanical support from said third wafer by sand blasting in order to obtain holes thereof.

15. The method of claim 14 further comprising the step of bonding said mechanical support to said base by bonding through an intermediate layer of at least one of the following:

a glass frit, SOG, or a polymer.

16. The method of claim 1 further comprising the steps of

performing a fist dicing operation in which all of a plurality of traces are processed in an X direction;

performing a second dicing operation in which at least one trace among said plurality of traces is processed in said X direction and at least one other trace is processed in a Y-direction such that at least three traces among said plurality of traces are required for dicing a stack of wafers, including said first wafer, said second wafer and at least one other wafer

17. The method of claim 1 further comprising the step of:

configuring said vacuum sealed pressure sensor as a package that comprises an embossed lead frame having an opening centrally located therein during a molding of said package, wherein said vacuum sealed pressure sensor is mounted into said embossed frame; and

attaching a cylinder to said embossed lead frame in order to avoid contact with a resin with a diaphragm thereof during molding thereof.

18. A pressure sensor method, comprising the steps of:

micro-machining a base from a first wafer;

micro-machining a cover from a second wafer, by dry etching said wafer in order to form a plurality of grooves thereof, which are adaptable for use with at least one of the following;

a reference chamber, at least one over-pressure stop, and at least one trench subsequently formed upon said wafer, wherein said base and said cover form a vacuum seal between said base and said cover;

micro-machining a mechanical support from a third wafer to support said base and said cover, wherein said third wafer is bonded to said first and second wafers;

forming a diaphragm by micro-machining said first wafer to form said base upon which said diaphragm is located.

configuring a pressure sensing element to comprise at least one surface acoustic wave device;

configuring said base to support said at least one surface acoustic wave device; and

disposing said pressure sensing element within said vacuum between said base and said cover within said vacuum seal to form a vacuum sealed pressure sensor thereof.

19. A pressure sensor system, comprising:

a base micro-machined from a first wafer;

a cover micro-machined from a second wafer, wherein said base and said cover form a vacuum seal therebetween; and

a pressure sensing element disposed within said vacuum between said base and said cover within said vacuum seal to form a vacuum sealed pressure sensor thereof.

20. The system of claim 19 further comprising:

a mechanical support micro-machined from a third wafer to support said base and said cover, wherein said third wafer is bonded to said first and second wafers, wherein said first, second and third wafers form a stack when bonded together; and

a diaphragm micro-machining from said first wafer to form said base upon which said diaphragm is located.

21. The system of claim 20 wherein said vacuum sealed pressure sensor is configured as a package that comprises an embossed lead frame having an opening centrally located therein during a molding of said package, wherein said vacuum sealed pressure sensor is mounted into said embossed frame;

and wherein a cylinder is attached to said embossed lead frame in order to avoid contact with a resin with a diaphragm thereof during molding thereof.