Combination pressure sensor with capacitive and thermal elements

• US 6,619,131 B2
• Filed: 03/14/2002
• Issued: 09/16/2003
• Est. Priority Date: 07/16/1998
• Status: Expired due to Term

• Current Assignee: Unaxis Balzers AG (Oerlikon USA, Inc. (Florida))
• Original Assignee: Unaxis Balzers AG (Oerlikon USA, Inc. (Florida))
• Inventors: Björkman, Per, Wälchli, Urs, Stocker, Rudolf, Gantner, Marcel
• Primary Examiner(s): Oen, William
• Application Number:
  US10/099,053
• Publication Number:
  US 20020129657A1
• Time in Patent Office: 551 Days
• Field of Search: 737/08, 737/18, 737/24, 737/53, 737/55, 361/283.1, 361/283.2, 361/283.3, 361/283.4
• US Class Current: 73/718
• CPC Class Codes: G01L 21/12 measuring changes in electric resistance of measuring members, e.g. of filaments; Vacuum gauges of the Pirani type
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass

Abstract

A pressure sensor has a baseplate and a support plate with a membrane. Layers on the membrane and the support plate are connected to a circuit for capacitively measuring pressure to generate a first pressure signal. A thermal conductivity measuring element that generates a second pressure signal has a heating element connected to the baseplate adjacent the support plate at a location opposite from the membrane for protecting the membrane from thermal effects. The method uses the sensor apparatus to generate an output signal representing a measured result when the measured result is above a transition value, on the basis of the first pressure signal and, when the pressure falls below a threshold value, any offset of the first pressure signal is compensated in such a way that determination of the output signal on the basis of the first pressure signal leads to the same result as determination of the output signal on the basis of the second pressure signal.

Claims

1. A pressure sensor apparatus comprising:

a baseplate;

a support plate mounted to the baseplate;

a capacitive measuring element spaced from and gas-tightly mounted to the support plate, the capacitive measuring element comprising a ceramic membrane having a surface facing the support plate;

electrically conducting layers on the surface of the membrane facing the support plate and on a surface of the support plate facing the membrane, the layers being adapted to be connected to a circuit for capacitively measuring pressure;

a thermal conductivity measuring element with at least one heating element connected to the baseplate adjacent the support plate at a location opposite from the membrane for protecting the membrane from thermal effects of the heating element while keeping the thermal conductivity measuring element near the capacitive measuring element, the heating element being adapted to be connected to a circuit for thermally conductively measuring pressure.

2. A pressure sensor apparatus according to claim 1, wherein the support plate extends substantially perpendicularly from the baseplate.

3. A pressure sensor apparatus according to claim 1, wherein the distance between the membrane and the at least one heating element is not more than 5 mm.

4. A pressure sensor apparatus according to claim 1, wherein the membrane consists of a ceramic which contains Al₂O₃ and has a thickness of between 10 μ

m and 1000 μ

m.

5. A pressure sensor apparatus according to claim 1, wherein the diameter of the membrane is between 2 mm and 15 mm.

6. A pressure sensor apparatus according to claim 1, wherein a gettered reference vacuum is enclosed between the support plate and the membrane.

7. A pressure sensor apparatus according to claim 1, wherein each heating element is one of a measuring wire, a tape, a thin-film arrangement and a microchip.

8. A pressure sensor apparatus according to claim 1, including at least two said heating elements and means for independently heating the at least two said heating elements.

9. A pressure sensor apparatus according to claim 1, wherein the at least one heating element contains at least 1% of at least one of nickel, platinum and tungsten.

10. A pressure sensor apparatus according to claim 1, wherein the at least one heating element is parallel to the support plate.

11. A pressure sensor apparatus according to claim 1, including a pin passing through the baseplate and approximately perpendicular to the baseplate, the support plate being fastened to the pin.

12. A pressure sensor apparatus according to claim 1, including a protective tube gas-tightly connected to the baseplate and surrounding the support plate, the membrane and the thermal conductivity measuring element.

13. A pressure sensor apparatus according to claim 12, including at least one further measuring element for pressure measurement in the protective tube.

14. A pressure sensor apparatus according to claim 13, wherein the at least one further measuring element is a cold-cathode element.

15. A pressure sensor apparatus according to claim 13, wherein the at least one further measuring element is a hot-cathode element.

16. A pressure sensor apparatus according to claim 15, wherein the hot-cathode is one of a triode and a Bayard-Alpert element.

17. A method for monitoring pressure in a chamber, comprising:

providing a sensor apparatus having a capacitive measuring element connected to a first circuit for producing a first pressure signal corresponding to capacitively measured pressure, a thermal conductivity measuring element connected to a second circuit for producing a second pressure signal corresponding to thermally conductively measured pressure; and

generating an output signal representing a measured result at least when the measured result is above a transition value, on the basis of the first pressure signal and, when the pressure falls below a threshold value, in each case compensating the first pressure signal in such a way that determination of the output signal on the basis of the first pressure signal leads to the same result as determination of the output signal on the basis of the second pressure signal.

18. A method according to claim 17, wherein the compensation of the offset is repeated as long as the pressure is below the threshold value and is decreasing, but not in the case of increasing pressure.

19. A method according to claim 17, wherein the threshold value is not greater than 50 mbar.

20. A method according to claim 17, wherein the output signal is determined, at least when the measured result is below the transition value, on the basis of the second pressure signal.

21. A method according to claim 17, wherein the chamber is a lock.

22. A method for monitoring pressure in a chamber, comprising:

providing a pressure sensor apparatus containing a capacitive measuring element with a support plate and a membrane gas-tightly connected to the support plate, the support plate and the membrane each with an electrically conducting layer, the layers being connected to a first electrical circuit for producing a first pressure signal corresponding to capacitively measured pressure, the pressure apparatus further containing a thermal conductivity measuring element with at least one heating element placed in proximity of the capacitive measuring element, the heating element being connected to a second electrical circuit for producing a second pressure signal corresponding to thermally conductively measured pressure;

generating an output signal representing a measured result, at least when the measured result is above a transition value or transition interval, on the basis of the first pressure signal; and

when the pressure falls below a threshold value, compensating any offset of the first pressure signal in such a way that determination of the output signal on the basis of the first pressure signal leads to the same result as determination of the output signal on the basis of the second pressure signal.

23. A method for monitoring pressure in a chamber, comprising:

providing a pressure sensor apparatus containing a capacitive measuring element with a support plate and a ceramic membrane gas-tightly connected to the said support plate, the support plate and the ceramic membrane each carrying an electrically conducting layer, the layers being connected to a first electrical circuit for producing a first pressure signal corresponding to capacitively measured pressure, the pressure apparatus further containing a thermal conductivity measuring element with at least one heating element placed in proximity of the capacitive measuring element in such a way that the membrane is shielded from thermal effects of the same, the heating element being connected to a second electrical circuit for producing a second pressure signal corresponding to thermally conductively measured pressure;

generating an output signal representing a measured result, at least when the measured result is above a transition value or transition interval, on the basis of the first pressure signal; and

when the pressure falls below a threshold value, compensating any offset of the first pressure signal in such a way that determination of the output signal on the basis of the first pressure signal leads to the same result as determination of the output signal on the basis of the second pressure signal.