ENVIRONMENT SENSOR SYSTEM

Abstract

We disclose herein an environmental sensor system comprising an environmental sensor comprising a first heater and a second heater in which the first heater is configured to consume a lower power compared to the second heater. The system also comprises a controller coupled with the environmental sensor. The controller is configured to detect if a measured value of a targeted environmental parameter is present. The controller is configured to switch on at least one of the first and second heaters based on the presence and/or result of the measured value of the targeted environmental parameter.

Claims

1. An environmental sensor system comprising: an environmental sensor comprising at least a first heater and a second heater, wherein the first heater is configured to consume a lower power compared to the second heater; a controller coupled with the environmental sensor, wherein the controller is configured to switch on at least one of the first and second heaters based on a predetermined technique.

2. A sensor system according to claim 1, wherein the controller is configured to apply the predetermined technique to detect if a measured value of a targeted environmental parameter is present, and wherein the controller is configured to switch on at least one of the first and second heaters based on the presence and/or result of the measured value of the targeted environmental parameter.

3. A sensor system according to claim 1, wherein the controller is configured to apply the predetermined technique to switch on at least one of the first and second heaters based on a time based event or based on a power change detection in the sensor system.

4. A sensor system according to claim 1, wherein the first heater has a smaller size compared to the second heater.

5. A sensor system according to claim 1, wherein the controller is configured to detect if there is no measured value of the targeted environmental parameter.

6. A sensor system according to claim 5, wherein the controller is configured to switch on the first heater.

7. A sensor system according to claim 1, wherein the controller is configured to analyse the measured value and if the measured value exceeds a predetermined threshold limit the controller is configured to switch on the second heater.

8. A sensor system according to claim 7, wherein the controller is configured to switch on both the first and second heaters if the measured value exceeds the predetermined threshold limit.

9. A sensor system according to claim 1, wherein the controller is configured to: store a set of measured values; analyse a predetermined number of recent measured values from the set of measured values; and determine which of the first and second heaters to be switched on based on the analysed results of the predetermined number of recent measured values.

10. A sensor system according to claim 9, wherein the controller is configured to switch on the first heater if the controller determines from the analysed results that there are no measured values or the measured values are less than a pre-determined threshold limit.

11. A sensor system according to claim 9, wherein the controller is configured to switch on the second heater or both the first and second heaters if the controller determines from the analysed results that the measured values are more than a pre-determined threshold limit.

12. A sensor system according to claim 1, wherein the environmental sensor comprises: a substrate comprising an etched portion; a dielectric region on the substrate, the dielectric region being formed such that a dielectric membrane is formed adjacent the etched portion; wherein the first and second heaters are formed in or on the dielectric membrane.

13. A sensor system according to claim 1, wherein the environmental sensor comprises: a substrate comprising a first etched portion and a second etched portion; a dielectric region on the substrate, the dielectric region being formed such that a first dielectric membrane is formed adjacent the first etched portion and a second dielectric membrane is formed adjacent the second etched portion; wherein the first heater is formed in or on the first dielectric membrane, and the second heater is formed in or on the second dielectric membrane.

14. A sensor system according to claim 12, wherein the dielectric membrane is formed by any one of: back-etching using Deep Reactive Ion Etching (DRIE) of the substrate, and using anisotropic etching such as Potassium Hydroxide (KOH) or TetraMethyl Ammonium Hydroxide (TMAH).

15. A sensor system according to claim 12, wherein the dielectric membrane comprises: 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.

16. A sensor system according to claim 12, wherein the sensor further comprises: a sensing material in one side of the dielectric membrane; and an electrode between the sensing material and the dielectric membrane.

17. A sensor system according to claim 16, wherein the sensor is a resistive gas sensor.

18. A sensor system according to claim 12, wherein the sensor is a calorimetric gas sensor, wherein a catalyst material is provided which is configured to increase a heater temperature when a targeted gas is present.

19. A sensor system according to claim 1, wherein the sensor is a Non-Dispersive Infrared (NDIR) sensor, wherein the first and second heaters are configured to operate as Infrared (IR) sources.

20. A sensor system according to claim 1, wherein the environmental sensor is a humidity sensor.

21. A sensor system according to claim 1, wherein the first and second heaters are configured to operate in one or more of the following modes: direct current (DC) mode; pulsed mode comprising pulse width modulation (PWM) mode.

22. A sensor system according to claim 21, wherein the heaters are configured to operate using a series of pulses at a different temperature.

23. A sensor system according to claim 21, wherein the controller is configured to: vary pulse frequency, vary duty cycle or the amplitude of the voltage applied to the heaters; and vary the temperature of the heaters.

24. A sensor system according to claim 1, wherein the first and second heaters are configured to operate in an alternative current (AC) mode or a dynamic mode.

25. A sensor system according to claim 24, wherein the controller is configured to detect different species of gases which have different chemical reaction rates.

26. A sensor system according to claim 25, wherein the controller is configured to operate the heaters such that two different gases are distinguished by analysing the chemical reaction rates.

27. A sensor system according to claim 12, wherein the first and second heaters are formed in one or more of the following configurations: concentrically to one another; on top of one another; and laterally spaced to one another.

28. A method for controlling an environmental sensor, the sensor comprising at least a first heater and a second heater, wherein the first heater consumes a lower power compared to the second heater; the method comprising: switching on at least one of the first and second heaters based on a predetermined technique.

29. A method according to claim 28, further comprising: detecting if a measured value of a targeted environmental parameter is present, and switching on at least one of the first and second heaters based on the presence and/or result of the measured value of the targeted environmental parameter.

30. A method according to claim 29, further comprising detecting if there is no measured value of the targeted environmental parameter; and switching on the first heater.

31. A method according to claim 29, further comprising analysing the measured value and if the measured value exceeds a predetermined threshold limit switching on the second heater.

32. A method according to claim 31, further comprising switching on both the first and second heaters.

33. A method according to claim 29, further comprising: storing a set of measured values; analysing a predetermined number of recent measured values from the set of measured values; and determining which of the first and second heaters to be switched on based on the analysed results of the recent measured values.

34. A method according to claim 33, further comprising switching on the first heater if it is determined from the analysed results that there are no measured values or the measured values are less than a pre-determined threshold limit.

35. A method according to claim 33, further comprising switch on the second heater or both the first and second heaters if it is determined from the analysed results that the measured values are more than a pre-determined threshold limit.

Description

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] FIG. 1 shows the schematic cross-section of a resistive gas sensor with two micro-hotplates, one having a large heater, and one having a small heater.

[0060] FIG. 2 shows the schematic cross-section of a calorimetric gas sensor with two micro-hotplates, one having a large heater, and one having a small heater.

[0061] FIG. 3 shows the top-view of a calorimetric gas sensor with two micro-hotplates, one having a large heater, and one having a small heater.

[0062] FIG. 4 shows the top-view of a resistive gas sensor with two micro-hotplates, one having a large heater, and one having a small heater.

[0063] FIG. 5 shows the top-view of a calorimetric gas sensor with two hotplates having different heater and membrane sizes.

[0064] FIG. 6-8 show the top-view of a hotplate for calorimetric gas sensing, where there is a large and small heater on the same membrane.

[0065] FIG. 9 shows the top-view of a hotplate for resistive gas sensing where there is a large and small heater on the same membrane

[0066] FIG. 10 shows the top-view of electrodes, meant for a hotplate with large and small heater on the same membrane.

[0067] FIGS. 11 and 12 show example flow chart of operating the large and small heaters depending on results of gas sensing.

[0068] FIGS. 13-15 show the schematic cross-section of different designs of gas sensors with two heaters in the same membrane.

[0069] FIG. 16 shows different design of electrodes for resistive gas sensors.

[0070] FIG. 17 is a schematic block diagram illustrating an environmental sensor and a controller coupled with the sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] FIG. 1 shows the schematic cross-section of a resistive gas sensor comprising two micro-hotplates, supported on a silicon substrate 1. One micro-hotplates has a large heater 2 (the second heater) embedded within the membrane, and electrodes 7 on top of the membrane. A sensing material 9 is deposited on top of the electrodes 7. The other micro-hotplate has a small heater 4 (the first heater) embedded within the membrane, and electrodes 8 on top of the membrane. A sensing material 10 is deposited on top of the electrodes 8.

[0072] When gas is not present, then the small heater 4 will be powered, and the resistance of the sensing material 10 will be measured. If the measured resistance of the material 10 indicates a presence of gas, then heater 2 will be powered instead and the resistance of sensing material 9 measured.

[0073] FIG. 2 shows the schematic cross-section of a calorimetric gas sensor comprising two micro-hotplates. One hotplate has a large heater 2 embedded within the membrane, and a catalyst 11 on top of the membrane. The other hotplate has a small heater 4 embedded within the membrane and a catalyst 12 on top of the membrane.

[0074] FIG. 3 shows the top view of a calorimetric gas sensor comprising two micro-hotplates. Each hotplate comprises a heater and a membrane 13. The heaters and membranes are shown as circular, however they can also be square, or rectangular, or rectangular with rounded corners. The heaters can be of any shape such as meander, spiral, ring or multi-ring.

[0075] FIG. 4 shows the top view of a resistive gas sensor comprising two micro-hotplates. Each hotplate comprises a membrane, and a heater embedded within the membrane, and electrodes on top of the membrane. The electrodes are shown as interdigitated, but they can be of many different shapes, including just to electrodes side by side.

[0076] FIG. 5 shows the top view of a calorimetric gas sensor comprising two micro-hotplates. Each hotplate comprises a heater and a membrane. In this case the size of the membranes is different too as well as the heaters. One of the hotplates comprises a small heater 4 embedded within a small membrane 16, while the other hotplate comprises a larger heater 2 embedded within a large membrane 15.

[0077] FIG. 6 shows the top-view of a micro-hotplate for a calorimetric gas sensor with two heaters on the same membrane 13. One heater is large 2, and the other is small 4. The device can have a catalyst deposited on the membrane. When gas is not present, the small heater 4 (the first heater) maybe operated. When gas presence is detected, then either just the large heater 2 (the second heater) may be operated, or both the large 2 and small 4 heaters maybe operated.

[0078] FIG. 7 shows the top view of a micro-hotplate for a calorimetric gas sensor with two heaters on the same membrane, having different sizes of the heaters. The large outer heater 2 comprises two parallel heaters.

[0079] FIG. 8 shows the top view of a micro-hotplate for a calorimetric gas sensor with three heaters on the same membrane, having a different design of the heaters. The inner heater 4 is the smallest one, a larger ring heater 2 is outside, and a still larger heater 14 is also present (made on a different layer).

[0080] It should be noted that during operation when the larger heaters are operated, the smaller heaters may also be operated to improve the temperature uniformity within the heater region. Alternately the larger heaters can be on a different layer than the smaller heater allowing a more complicated design than just a ring to be made. Besides this many number and combination of heaters and heater designs are possible.

[0081] FIG. 9 shows the top view of a micro-hotplate for resistive gas sensors with two heaters on the same membrane. The design is the same as in FIG. 5, but has an addition of electrodes 7 on top of the membrane to measure the resistance and/or capacitance of the sensing material. There is only one set of electrodes 7 for both the large and small heater and can be used in all three heater operating configurations: (1) small heater 4 on, (2) large heater 2 on, (3) or both small 4 and large 2 heaters on.

[0082] FIG. 10 shows an example design of heater electrodes where the electrodes can be configured to either measure the resistance of the entire sensing material, or to just measure the resistance of the sensing material within the heater area.

[0083] FIG. 11 shows the flow diagram of an example algorithm to control a gas sensor with a large and small heater. The gas sensor makes a measurement, and depending on the system, if gas is measured to be present, or above a certain concentration threshold, then the large heater is powered, then the next measurement made. Otherwise the small heater is powered (with the large one turned off), and the next measurement made.

[0084] FIG. 12 shows the flow diagram of an example algorithm to control a gas sensor with a large and small heater. The gas sensor makes a measurement, and stores the value. Then it analyses the stored values from the last few measurements (the number can be defined in software) to determine whether the large or small heater should be on. Based on this decision either the large or small heater is powered, and the next measurement taken.

[0085] FIG. 13 shows the schematic cross-section of a gas sensor with a micro-hotplate where there is a large and small heater within the same membrane. In this case the membrane cavity has sloping sidewalls. This can be caused by wet anisotropic etching, for example using potassium hydroxide (KOH) or Tetramethylammonium hydroxide (TMAH).

[0086] FIG. 14 shows the schematic cross-section of a gas sensor with a micro-hotplate where there is a large and small heater within the same membrane. In this case the membrane is a suspended membrane, and only supported by two or more beams, usually formed by a front side etch process.

[0087] FIG. 15 shows the schematic cross-section of a gas sensor with a micro-hotplate where there is a large and small heater within the same membrane, with each heater on a separate layer.

[0088] FIG. 16 shows different designs of electrodes on top of the membrane that are used to measure the resistance and/or capacitance of the sensing material in resistive gas sensors.

[0089] FIG. 17 is a schematic block diagram illustrating an environmental sensor 1701 and a controller 1702 coupled with the sensor. The controller 1702 may be integrated with the sensor 1701, or the controller 1702 may be a discrete device coupled with the sensor 1701.

[0090] The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘below’, ‘front’, ‘back’, ‘vertical’, ‘underneath’ etc. are made with reference to conceptual illustrations of a semiconductor device, such as those showing standard cross-sectional perspectives and those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to a semiconductor device when in an orientation as shown in the accompanying drawings.

[0091] 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.