Pressure sensor cavity etched with hot POCL.sub.3 gas

• US 6,082,199 A
• Filed: 03/26/1999
• Issued: 07/04/2000
• Est. Priority Date: 02/28/1995
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Toy, Adrian C., Louwagie, Bennett L., Frick, Roger L.
• Primary Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US09/277,249
• Time in Patent Office: 466 Days
• Field of Search: 29/839, 29/840, 264/248, 403/270, 73/718, 73/724, 361/283.4
• US Class Current: 73/724
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: G01L 9/125 with temperature compensating means non electric temperature compensating means G01L19/04
• CPC Class Codes: Y10T 29/49142 including metal fusion

Abstract

A transmitter in a process control system transmits a pressure over a process control loop. The transmitter includes I/O circuitry, compensation circuitry and an absolute pressure sensor. The I/O circuitry transmits information over the process control loop. Compensation circuitry receives a pressure related signal and responsively controls the I/O circuitry to transmit pressure information on the loop. The absolute pressure sensor includes a cavity which deforms as the sensor deflects in response to an applied pressure. A sensor in the cavity provides the pressure related signal to the compensation circuitry in response to the deformation.

Claims

1. A method of manufacturing a capacitance pressure sensor, comprising:

forming a first pressure sensor substrate of sapphire with a first flat polished mating surface;

etching the first pressure sensor substrate to form a cavity;

providing a first capacitor plate on the first pressure sensor substrate;

forming a second pressure sensor substrate of sapphire with a second capacitor plate and with a second flat polished mating surface;

heating the first and second pressure sensor substrates; and

mating the flat polished mating surfaces of the first and second pressure sensor substrates to form a fusion bond,

wherein the etching is done with hot POCl₃ gas.

2. The method of claim 1 where the capacitor plates are implanted.

3. The method of claim 1 wherein the heating of the first and second pressure sensor substrates is between 68% and 95% of the melting point absolute temperature of sapphire.

4. The method of claim 1 further comprising:

masking the first pressure sensor substrate with SiO₂.

5. The method of claim 1 wherein the first and second pressure sensor substrates are single crystal sapphire.

6. A capacitance pressure sensor, comprising:

a first pressure sensor substrate of sapphire with a first flat polished surface having a first cavity etched therein and a first capacitor plate in the cavity; and

a second pressure sensor substrate of sapphire with a second capacitor plate and with a second flat polished surface fusion bonded to the first flat polished surface;

wherein the first cavity is etched with hot POCl₃ gas and the first flat polished surface is fusion bonded to the second flat polished surface by heating between 68% and 95% of the melting point absolute temperature of sapphire.

7. The capacitance pressure sensor of claim 6 where the capacitor plates are implanted.

8. The capacitance pressure sensor of claim 7 wherein the first and second pressure sensor substrates are single crystal sapphire.

9. The capacitance pressure sensor of claim 8 wherein the first pressure sensor substrate is masked with SiO₂.