Sensor Device and Method for Operating A Sensor Device

Abstract

In an embodiment a sensor device include a first sensor including a heating element configured to heat up the first sensor in a controllable manner and a second sensor thermally coupled to the heating element of the first sensor such that the heating element is further configured to heat up the second sensor in a controllable manner.

Claims

1.-15. (canceled)

16. A sensor device comprising: a first sensor comprising a heating element configured to heat up the first sensor in a controllable manner; and a second sensor thermally coupled to the heating element of the first sensor such that the heating element is further configured to heat up the second sensor in a controllable manner.

17. The sensor device according to claim 16, wherein the first sensor is a gas sensor, and wherein the second sensor is an environmental sensor configured to measure a relative humidity of a gas surrounding the sensor device.

18. The sensor device according to claim 16, wherein the first sensor is configured to heated up within a time of less than 2 seconds to an operating temperature that is between 300° C. and 500° C., inclusive, when in a sensing mode.

19. The sensor device according to claim 16, wherein the heating element is configured to heat up the second sensor to a maximum set point that is above an ambient temperature of an environment of the sensor device.

20. The sensor device according to claim 16, wherein the heating element is configured to heat up the second sensor at a lower rate than the first sensor.

21. The sensor device according to claim 16, further comprising a temperature sensor configured to measure a momentary temperature of the second sensor.

22. The sensor device according to claim 16, wherein the first sensor is arranged on a first die, wherein the second sensor is arranged on a second die, and wherein the first die and the second die are arranged in a single sensor package.

23. The sensor device according to claim 16, wherein the first sensor is arranged on a surface of a substrate body of the second sensor.

24. The sensor device according to claim 16, wherein the heating element is operatable in a duty cycle when operated in a regular mode of operation, and wherein, within an active time of the duty cycle, the first sensor is operatable in a sensing mode and the second sensor is operatable in an idle mode and vice versa, within a passive time of the duty cycle.

25. A method for operating a sensor device comprising a first and a second sensor, wherein the first sensor comprises a heating element, and wherein the second sensor is thermally coupled to the heating element of the first sensor, the method comprising: controllably heating up the second sensor to a set point using the heating element of the first sensor.

26. The method according to claim 25, further comprising heating up, in a calibration mode, the second sensor to a number of calibration set points; recording, at each of the number of calibration set points, a temperature-dependent measurement value with the second sensor; and recording each measurement value with a corresponding one of the number of calibration set points in a calibration table and/or determining from the measurement values and calibration set points calibration coefficients.

27. The method according to claim 25, further comprising: recording, in a self-diagnosis mode, a first measurement value of a temperature-dependent quantity when the second sensor is at a first test set point; recording, in the self-diagnosis mode, a second measurement value of the temperature-dependent quantity when the second sensor is at a second test set point; comparing the first measurement value to the second measurement value via a conserved quantity; and based on a result of a comparison determining whether an error condition of the second sensor exists.

28. The method according to claim 25, further comprising: detecting, in an aging-prevention mode, whether the second sensor is in a regime outside its specification; and based on a result of a detection, heating the second sensor to a temperature set point that is higher than an ambient temperature of the sensor device.

29. The method according to claim 28, further comprising recording, in the aging-prevention mode, an uncorrected measurement value at the temperature set point; and calculating from the uncorrected measurement value and the temperature set point a corrected measurement value at the ambient temperature.

30. The method according to claim 25, further comprising: heating, in a reconditioning mode, the second sensor to a reconditioning set point that depends on a boiling point of a contaminating compound; and maintaining the second sensor at the reconditioning set point for an extended period such that the contaminating compound evaporates from the second sensor.

31. A sensor device comprising: a first sensor comprising a heating element configured to heat up the first sensor in a controllable manner; and a second sensor thermally coupled to the heating element of the first sensor such that the heating element is further configured to heat up the second sensor in a controllable manner, wherein the first sensor is arranged on a surface of a substrate body of the second sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The following description of figures of exemplary embodiments may further illustrate and explain aspects of the improved concept. Components and parts of the sensor device with the same structure and the same effect, respectively, appear with equivalent reference symbols. Insofar as components and parts of the sensor device correspond to one another in terms of their function in different figures, the description thereof is not repeated for each of the following figures.

[0044] FIG. 1 shows a schematic top view of an exemplary embodiment of a sensor device according to the improved concept;

[0045] FIGS. 2, 3A, and 3B show schematic cross-sectional views of further exemplary embodiments of a sensor device; and

[0046] FIGS. 4 and 5 show exemplary data indicating the temperature behavior of the second sensor of an exemplary embodiment of a sensor device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0047] FIG. 1 shows a schematic top view of an exemplary embodiment of a sensor device 1 according to the improved concept. In this embodiment, the sensor device 1 comprises a substrate body 9 with a surface, on which the second sensor 3 and a temperature sensor 6 are arranged in close vicinity of each other. Close vicinity in this context means that a temperature measured at the location of the temperature sensor 6 corresponds to a temperature at the location of the second sensor.

[0048] The second sensor 3 is an environmental sensor such as a relative humidity sensor configured to measure a quantity of a gas 5 surrounding the sensor device 1. For example, the second sensor 3 is a capacitive humidity sensor comprising electrodes arranged as a capacitor and a sensitive material arranged between and/or around the electrodes. The temperature sensor 6 is for example a thermistor or a thermocouple or a PTAT circuit.

[0049] Furthermore, the heating element 4 and the first sensor 2 are arranged on the surface of the substrate body 9. For example, the heating element 4 is a hotplate such as a micro-hotplate and the first sensor 2 is arranged on the heating element 4. The second sensor 3 is for example a gas sensor such as a metal-oxide, MOX, gas sensor comprising one or more MEMS transducers. MOX gas sensors typically operate at 300° C. to 500° C. in a sensing mode of operation and therefore require a respective powerful heating element 4.

[0050] The substrate body 9 may also comprise an integrated circuit, which may be a CMOS circuit with active and/or passive circuitry such as an application-specific integrated circuit configured for reading out and evaluating values from the first sensor 2 and the second sensor 3. Such integrated circuits are known per se, and are not shown in the figures. The substrate body 9 may be a semiconductor substrate chip diced from a wafer, for instance. The surface of the substrate body 9 is, for example, a surface parallel to the main extension plane of the substrate body 9 and may be referred to as a top surface without loss of generality.

[0051] The substrate body 9 may be of a material with significant thermal conductivity such that the heating element 4 also increases the temperature of the second sensor 3. Alternatively, the substrate body may comprise heat conducting paths connecting the heating element 4 to the second sensor 3. The heat conductivity between the heating element 4 and the second sensor 3 may be dimensioned such that a maximum temperature increase of the second sensor 3 induced by the heating element 4 is in the order of several tens degrees Celsius.

[0052] The substrate body 9 may further comprise a control circuit for heating up the first sensor 2 and the second sensor 3 in a controllable manner. Alternatively, the substrate body 9 may comprise control connections for connecting an external control circuit. The control circuit may be a servo loop or a feedback control system and may use sensor readings from the temperature sensor 6 for controlling the temperature of the second sensor 3. The control circuit may further use sensor readings from a further temperature sensor that measures a temperature that corresponds to that of the first sensor 2.

[0053] The first sensor 2 and the heating element 4 may be arranged on a first die 7, such as a further substrate body, that is arranged on the substrate body 9. Alternatively or in addition, the second sensor 3 and the temperature sensor 6 may be arranged on a second die 8 that is arranged on the substrate body 9. Alternatively, the second die 8 can act as a substrate body for the first die 7.

[0054] FIG. 2 shows a cross-sectional view of the exemplary embodiment of the sensor device 1 shown in FIG. 1.

[0055] The exemplary embodiment according to FIG. 3A essentially corresponds to that of FIGS. 1 and 2. As shown in the cross-sectional view of FIG. 3A, the second die 8 may form a substrate body of the second sensor 3, wherein the first sensor 2 is arranged on a surface 30 of the substrate body, namely the second die 8. Thus, the first sensor 2 and the second sensor 3 are arranged on top of each other.

[0056] In this arrangement, the second sensor 3 is thermally coupled to the heating element 4 of the first sensor 2. The substrate body 9 underneath the second die 8 of the second sensor 3 may also be dispensed with.

[0057] FIG. 3B shows a cross-sectional view of a further exemplary embodiment of the sensor device 1. In this embodiment, the heating element 4 and the first sensor 2 are arranged on a first die 7. The second sensor 3 together with the temperature sensor 6 are arranged on a second die 8. The first die 7 and the second die 8 are arranged on the surface of the substrate body 9. The second die 8 may comprise circuitry, such as a control circuit, to read out sensor values of the second sensor 3 and/or of the temperature sensor 6, for instance. Likewise, the first die 7 may comprise circuitry to control the heating element 4 and/or to read out sensor values of the first sensor 2.

[0058] In some cases, fabrication processes of the first sensor 2 and the second sensor 3 are not or only partially compatible with each other such that a separate fabrication is necessary. Also aspects like cost-effectiveness, yield, fabrication time and complexity of the overall process may be reasons for a separate fabrication process. For example, the first sensor 2 comprises MEMS structures such as MEMS transducers. Such MEMS structures may not be compatible with a purely CMOS compliant fabrication method of the second sensor 3, for instance.

[0059] The common substrate 9 enables the co-packaging of the first and the second sensors 2, 3 despite the separate dies. The substrate body 9 may act as a mediator for heat such that the second sensor 3 is heated by means of the heating element 4. Alternatively, heat conducting paths such as thermally conductive wire may be employed to thermally couple the heating element 4 and the second sensor 3.

[0060] FIGS. 4 and 5 show exemplary data indicating the temperature behavior of the second sensor 3 of an exemplary embodiment of a sensor device 1.

[0061] FIG. 4 shows the temperature of the second sensor 3, for example measured via the temperature sensor 6 shown in the previous Figures, versus time. The sensor device 1 in this embodiment is engineered such that the heating element 4 of the first sensor 2 is capable of heating up the second sensor 3 and achieving a temperature of in this case 20° C. above the ambient temperature of the sensor device 1, which here is about 27° C. as can be seen from the minimum of the shown curve when the gas sensor, i.e. the heating element 4 of the first sensor 2, is switched off. By adjusting the distance between the two sensors 2, 3 and/or the thermal conductivity in between the two sensors 2, 3 the maximum temperature increase of the second sensor 3 may be adjusted according to requirements of the specific application.

[0062] A maximum temperature of the second sensor 3 that is several tens of degrees Celsius above the ambient temperature is desirable for different modes of operation of the second sensor 3, such as a calibration mode, a self-diagnosis mode, an aging-prevention mode and a reconditioning mode of operation.

[0063] FIG. 5 shows similar measurement data as shown in FIG. 4. In contrast to the previous measurement data, in this embodiment, the heating element 4 is operated in a duty cycle with a period of around 20 seconds and an active time of the heating element 4 of about 1.5 seconds within the duty cycle.

[0064] In this case, the maximum temperature increase of the second sensor 3 is merely in the order of 3° C. to 5° C. The aforementioned duty cycle represents a typical duty cycle of a MOX gas sensor, which is heated to its operating temperature within 1.5 seconds during a sensing mode of operation of the MOX sensor. As the temperature increase of the second sensor 3, whose operating temperature typically is at the ambient temperature of the sensor device 1, is relatively small accurate readings of the second sensor 3 can still be obtained. For example, the second sensor 3 operates in a sensing mode of operation during a passive time of the duty cycle, in which the second sensor 3 thermalizes close to the ambient temperature of in this case 25° C. During the active time, a self-diagnosis is still possible.

[0065] The embodiments shown in the FIGS. 1 to 5 as stated represent exemplary embodiments of the sensor device 1 and the temperature behavior of the second sensor 3. Therefore, they do not constitute a complete list of all embodiments according to the improved concept. Actual sensor device configurations may vary from the embodiments shown in terms of shape, size and materials, for example.

[0066] Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention.