GAS SENSOR WITH A GAS PERMEABLE REGION

Abstract

Disclosed herein is a gas sensing device comprising a dielectric membrane formed on a semiconductor substrate comprising a bulk-etched cavity portion, a heater located within or over the dielectric membrane, a material for sensing a gas which is located on one side of the membrane, a support structure located near the material, and a gas permeable region coupled to the support structure so as to protect the material.

Claims

1. A gas sensing device comprising: a dielectric membrane formed on a semiconductor substrate comprising a bulk-etched cavity portion; a heater located within or over the dielectric membrane; a material for sensing a gas, wherein the material is located on one side of the membrane; a support structure located near the material; a gas permeable region coupled to the support structure so as to protect the material, and wherein the support structure comprises an inorganic material.

2. A device according to claim 1, wherein the support structure comprises a semiconductor material.

3. A device according to claim 1 wherein the support structure comprises a material comprising any of glass and ceramic.

4. (canceled)

5. A device according to claim 1, wherein the material is located on a first side of the dielectric membrane, the first side being an opposite side of the bulk-etched substrate, optionally wherein the support structure is located on the first side of the device and the permeable region is formed on the support structure, and/or the gas permeable region is configured to allow air and gas flow to the device and configured to block liquid and/or particles from getting to the material.

6. (canceled)

7. A device according claim 5, wherein the support structure is formed surrounding the material.

8. A device according to claim 3, wherein the material is located on a second side of the device, the second side being the same side where the bulk-etched substrate is formed, optionally wherein: the material is formed in the back-etched cavity of the device; and/or the semiconductor substrate forms the support structure; and/or the gas permeable region is coupled with the semiconductor substrate supporting the dielectric membrane.

9-11. (canceled)

12. A device according to claim 1, wherein the membrane is supported along its entire perimeter by the semiconductor substrate.

13. A device according to claim 1, wherein the membrane is only supported by one or more dielectric beams to connect the membrane to the substrate.

14. A device according to claim 1, wherein the gas permeable region is a polymer film, optionally wherein the polymer film is gore-tex; or the gas permeable region comprises a film of metal, dielectric or semiconductor with several holes; and/or the support structure is formed on a top-side or back-side of a chip in which the device is included.

15-17. (canceled)

18. A device according to claim 1, wherein the material is a gas sensing material optionally further comprising an electrode underneath the gas sensing material, optionally wherein the electrode is configured to measure resistance and/or capacitance of the gas sensing material.

19-20. (canceled)

21. A device according to claim 20, wherein the gas sensing material comprises a metal oxide material or a combination of metal oxides: optionally wherein the gas sensing material comprises a metal oxide material selected from a group comprising tin oxide, tungsten oxide, zinc oxide, chromium oxide, or the sensing layer comprises a combination of said metal oxides.

22. (canceled)

23. A device according to claim 1, wherein the material is a catalytic material; or the material is deposited as a gate electrode, or is electrically connected to the gate electrode of a field effect transistor (FET).

24. (canceled)

25. A device according to claim 1, wherein either: the dielectric membrane is formed using an etching technique for back-etching the substrate, the etching technique being selected from a group comprising deep reactive ion etching (DRIE), anisotropic or crystallographic wet etching, potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH); or the dielectric membrane is formed by a front side etch of the substrate.

26. (canceled)

27. A device according to claim 1, wherein the dielectric membrane comprises: a membrane cavity comprising vertical side walls or sloping side walls or a cavity formed by a front side etch that does not extend all the way through the substrate; one or more dielectric layers comprising silicon dioxide and/or silicon nitride; one or more layers of spin on glass, and a passivation layer over the one or more dielectric layers; optionally wherein the material for sensing a gas is formed on the passivation layer of the dielectric membrane or in the membrane cavity of the device.

28. (canceled)

29. A device according to claim 1, wherein the heater is a resistive heater comprising a CMOS usable material comprising aluminium, copper, titanium, molybdenum, polysilicon, single crystal silicon tungsten, or titanium nitride.

30. A device according to claim 1, wherein: the device is a CMOS based micro-hotplate in which the heater comprises a CMOS interconnect metal, and the dielectric membrane comprises CMOS dielectric layers; and/or the semiconductor substrate is a bulk silicon substrate or an SOI substrate; and/or the device is packaged in a flip chip on a printed circuit board (PCB); and/or the device comprises through silicon vias (TSVs); and/or the support structure covers the dielectric membrane area, leaving a bond pad area open to allow wire bonding.

31-34. (canceled)

35. An array of gas sensing devices incorporating a gas sensing device according to claim 1, wherein: the array of gas sensing devices are arranged on the same chip, optionally wherein either: each sensing device comprises a separate gas permeable region; or the sensing devices comprise a common gas permeable region; and/or the distance between the gas permeable layer and the material for sensing is between about 150 m and about 200 m.

36-38. (canceled)

39. A method of manufacturing a gas sensing device, the method comprising: forming a dielectric membrane formed on a semiconductor substrate comprising a bulk-etched cavity portion; forming a heater within or over the dielectric membrane; forming a material for sensing a gas on one side of the membrane; forming a support structure near the material, wherein the support structure comprises an inorganic material; and forming a gas permeable region coupled to the support structure so as to protect the material.

40. A method according to claim 39 wherein: the support structure is attached by wafer bonding; and/or the gas permeable layer is attached to the support structure, before the support structure is attached to the gas sensing device.

41. (canceled)

42. A method according to claim 39, wherein forming the dielectric membrane comprises: forming the dielectric membrane such that it is supported along its entire perimeter by the semiconductor substrate: and/or using an etching technique to back-etch the semiconductor substrate to form the back-etched portion, optionally wherein the etching technique is selected from a group comprising deep reactive ion etching (DRIE), anisotropic or crystallographic wet etching, potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH).

43-44. (canceled)

Description

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Some preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0065] FIG. 1 shows a gas sensor with a gas permeable layer;

[0066] FIG. 2 shows an alternative gas sensor in which through silicon vias (TSVs) are used;

[0067] FIG. 3 shows an alternative gas sensor;

[0068] FIG. 4 shows an alternative gas sensor in which the gas permeable layer has holes;

[0069] FIG. 5 shows an alternative gas sensor in which the sensing material is below the membrane, and the gas permeable layer is on the back side, supported by the silicon substrate itself,

[0070] FIG. 6 shows an alternative gas sensor which is bonded by a flip chip; and

[0071] FIG. 7 shows an alternative gas sensor where the membrane is formed by a front side etch

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0072] FIG. 1 shows a gas sensor with a sensing material 6, a silicon substrate 1 with a gas permeable layer 8 attached on top. The heater 2 and heater tracks or metallization 3 are embedded within the dielectric membrane 4 supported on the substrate 1. Electrodes 5 on top of the membrane connect to a sensing material 6 which has been grown or deposited on the membrane. An additional patterned semiconductor 7 (or the support structure) is attached at the top by wafer bonding and the gas permeable layer 8 is on top of this support structure 7. The dielectric membrane 4 and the passivation can include one or more combinations of silicon dioxide and silicon nitride, or other dielectric layers. In one example, the gas permeable layer or region is a metal, dielectric and/or semiconductor layer with multiple holes. This can be formed for example, by depositing a dielectric or metal layer on a substrate. Then making holes within the metal or dielectric layer. And then back etching a selected part of the substrate and joining this structure to the gas sensing hotplate by wafer bonding.

[0073] FIG. 2 shows an alternative gas sensor in which through silicon vias (TSVs) 9 are used to connect electrically to the device. The TSVs are generally connected to metallization or pads (not shown). The remaining features of the gas sensor are the same as those described in respect of FIG. 1 above and thus carry the same reference numbers.

[0074] FIG. 3 shows an alternative gas sensor in which the support structure 7 (or the additional semiconductor substrate) is smaller, so that the bond pads 11 are exposed and can be electrically connected by wire bonding to either a package or a printed circuit board (not shown in the figure). Furthermore, this figure also shows a passivation layer 10which may or may not be present on the device. The remaining features of the gas sensor are the same as those described in respect of FIGS. 1 and 2 above and thus carry the same reference numbers.

[0075] FIG. 4 shows an alternative gas sensor in which the gas permeable layer 8 has holes, or is gas permeable even in regions which connect to the semiconductor support structure 7. The gas permeable layer can be for example a film such as gore-tex. It can also be a film of metal, dielectric and/or semiconductor with holes. The remaining features of the gas sensor are the same as those described in respect of FIGS. 1 to 3 above and thus carry the same reference numbers.

[0076] FIG. 5 shows an alternative gas sensor in which the sensing material 6 is below the dielectric membrane 4, and the gas permeable layer 8 is on the back side, supported by the silicon back-etched substrate 1 itself. In this example, no additional support structure is needed as the back-etched substrate 1 acts as the support structure. The remaining features of the gas sensor are the same as those described in respect of FIGS. 1 to 4 above and thus carry the same reference numbers.

[0077] FIG. 6 shows an alternative gas sensor with the sensing material 6 below the dielectric membrane 4, and a gas permeable layer 5 on the backside, bonded by flip chip with the bonds 13 connected to a printed circuit board (PCB) 12. The bond 13 can be generally connected to metallization or pads (not shown). In this example the chip is bonded on the front or top side of the chip. The remaining features of the gas sensor are the same as those described in respect of FIGS. 1 to 5 above and thus carry the same reference numbers.

[0078] FIG. 7 shows an alternative gas sensor, where the membrane 14 is a suspended membrane, formed by a front side etching of the substrate, and is supported by one or more beams (not shown). The membrane 14 includes dielectric material, for example, silicon oxide. The substrate 1 includes a triangle region 10 which is generally empty and is formed due to the front-side etching of the substrate. The remaining features of FIG. 7 are the same as those described above and thus carry the same reference numbers.

[0079] In the above mentioned embodiments, a gas sensing material 6 is disposed on an electrode 5. The electrode 5 is configured to measure resistance and/or capacitance of the gas sensing material 6. In an alternative embodiment, a catalytic material can be used instead of the gas sensing material. When the catalytic material is used, no electrode underneath it is generally necessary, since the detection is done by measuring the change in temperature of the membrane rather than the resistance or capacitance of the material. Alternately, the gas sensing material could be deposited as part of a gate, or an extended gate of a gas sensing FET.

[0080] In summary, the present invention provides a micro-hotplate based gas sensor chip that attaches the gas permeable layer onto the chip itself. The prior art reports typically have the gas permeable layer on the package, whereas the present invention provides the gas permeable layer in the chip level. The prior art devices are not for a membrane based device, whereas the present invention uses membrane based devices. The prior art devices generally have relatively larger holes for the purpose of allowing air flow, but do not stop water or particles. The prior art devices generally have a single hole (for example EP1775259). Alternately, the method of the present invention can allow a smaller package (or even a chip level package), easier handling during assembly, and lower cost. Furthermore, in the prior art device, the gas permeable layer can be formed on the sensing material itself which can affect the properties of the sensing material. This problem does not exist in the present invention as there is a support structure provided to create a gap between the sensing material and the gas permeable layer. Further, in some prior art devices, a plastic moulded cap is provided on which it is difficult to have the gas permeable layer. This problem does not exist in the present invention.

[0081] Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.