Gas-sensing semiconductor devices

• US 20060154401A1
• Filed: 03/30/2005
• Published: 07/13/2006
• Est. Priority Date: 01/10/2005
• Status: Active Grant

• Current Assignee: ScioSense B.V. (Ams-Osram AG)
• Original Assignee: University of Warwick
• Inventors: Udrea, Florin, Gardner, Julian William, Covington, James Anthony
• Granted Patent: US 7,495,300 B2
• Time in Patent Office: Days
• US Class Current: 438/53
• CPC Class Codes: G01N 27/128 Microapparatus

Abstract

A gas-sensing semiconductor device is fabricated on a silicon substrate having a thin silicon oxide insulating layer in which a resistive heater made of a CMOS compatible high temperature metal is embedded. The high temperature metal is tungsten. The device includes at least one sensing area provided with a gas-sensitive layer separated from the heater by an insulating layer. As one of the final fabrication steps, the substrate is back-etched so as to form a thin membrane in the sensing area. Except for the back-etch and the gas-sensitive layer formation, that are carried out post-CMOS, all other layers, including the tungsten resistive heater, are made using a CMOS process employing tungsten metallisation. The device can be monolithically integrated with the drive, control and transducing circuitry using low cost CMOS processing. The heater, the insulating layer and other layers are made within the CMOS sequence and they do not require extra masks or processing.

Claims

9. A gas-sensing semiconductor device comprising a semiconductor substrate, at least one sensing area provided with a gas-sensitive layer and a heater for heating the gas-sensitive layer to promote gas reaction with the gas-sensitive layer, and a sensor for providing an electrical output indicative of gas reaction with the gas-sensitive layer, wherein the heater has in its composition at least one layer of tungsten and comprises two or more heating layers.

10. A device according to claim 9, wherein the heating layers are offset laterally relative to one another.

11. A device according to claim 9, wherein the heating layers are interlaced relative to one another.

14. A gas-sensing semiconductor device comprising a semiconductor substrate, at least one sensing area provided with a gas-sensitive layer and a heater for heating the gas-sensitive layer to promote gas reaction with the gas-sensitive layer, and a sensor for providing an electrical output indicative of gas reaction with the gas-sensitive layer, wherein the heater has in its composition at least one layer of tungsten, and wherein the sensor incorporates laterally spaced tungsten electrodes in the vicinity of the gas-sensitive layer.

15. A device according to claim 14, wherein the gas-sensitive layer is located between the electrodes.

16. A device according to claim 14, wherein the electrodes incorporate two or more electrodes spaced vertically one above the other.

26. (canceled)

27. A smart sensor comprising a gas-sensing device monolithically integrated with an electronic circuit for drive, control and transducing functions, wherein tungsten is used both as a metallisation layer for contacts and interconnects in the electronic circuit and to form a heater of the gas-sensing device.

1. A smart sensor according to claim 27, comprising a semiconductor substrate, wherein the gas-sensing device has at least one sensing area provided with a gas-sensitive layer to be heated by the heater to promote gas, and sensing means for providing an electrical output indicative of gas reaction with the gas-sensitive layer.

2. A smart sensor according to claim 1, wherein an insulating layer is provided on one side of the substrate.

3. A smart sensor according to claim 2, wherein a passivation layer is provided on the insulating layer on one side of the substrate.

4. A smart sensor according to claim 3, wherein the gas-sensitive layer is formed on the passivation layer.

5. A smart sensor according to claim 2, wherein the heater is embedded in the insulating layer.

6. A smart sensor according to claim 2, wherein the insulating layer is a silicon oxide layer.

7. A smart sensor according to claim 3, wherein a conductive polymer layer is provided which acts as the gas-sensitive layer.

8. A smart sensor according to claim 27, wherein the heater is a meander-shaped tungsten heater.

12. A smart sensor according to claim 27, wherein the heater incorporates a spreading plate.

13. A smart sensor according to claim 1, wherein the sensing means incorporates laterally spaced electrodes in the vicinity of the gas-sensitive layer.

17. A smart sensor according to claim 1, wherein the gas-sensitive layer is provided around the periphery of an air gap extending through the membrane.

18. A smart sensor according to claim 27, which has been produced utilising CMOS, Bi-CMOS or SOI CMOS processing steps, or Bi-CMOS processing steps followed by a post-CMOS back-etch.

19. A smart sensor according to claim 1, wherein the gas-sensitive layer is of tin oxide.

20. A smart sensor according to claim 1, wherein the said at least one sensing area incorporates temperature sensing means.

21. A smart sensor according to claim 1, wherein the material of the substrate has been removed in at least one sensing area to leave a membrane incorporating the sensing area.

22. A smart sensor according to claim 1, wherein the material of the substrate has been removed in at least one sensing area by back etching.

23. A smart sensor according to claim 1, wherein said at least sensing area is integrated with at least one electronic circuit area incorporating associated circuitry.

24. A smart sensor according to claim 27, which is a resistive gas-sensing device.

25. A smart sensor according to claim 27, which is a calorimetric gas-sensing device.

28. A smart sensor according to claim 27, which has been fabricated using CMOS, Bi-CMOS or SOI technology.

29. A smart sensor according to claim 27, wherein the material of the substrate has been removed in at least one area in a post-CMOS process to leave a membrane.

30. A smart sensor according to claim 29, wherein the removal of the material of the substrate to define the membrane has been carried out by deep reactive ion etching

31. A smart sensor according to claim 29, wherein the removal of the material of the substrate has been carried out by anisotropic wet etching.