Rapid humidity sensor and method for calibrating a rapid humidity sensor

Abstract

According to an example aspect of the invention, there is provided a sensor structure (19) formed on a substrate (12) comprising a sensor frame (21), the sensor frame (21) comprising electrical contacts (1-6) for the sensor, the active sensor (22) within the sensor frame (21) comprising at least a capacitive humidity sensor (9). According to the invention, the active sensor (22) is connected to the sensor frame (23) only by a thin thermal insulation layer (14) supporting the active sensor (22), the thermal insulation layer (14) comprising the electrical contacts from the sensor frame (21).

Description

Technical Field

[0001] This invention relates to a humidity sensor and a method for calibrating the humidity sensor. Background Technology

[0002] Capacitive humidity sensors have been used in existing technology for decades. These sensors have been calibrated using heated elements (such as resistors) to obtain zero-point humidity measurements for calibration purposes. However, due to the slow response time of humidity sensors, these known methods have not yet achieved true zero-point humidity calibration. Summary of the Invention

[0003] This invention is defined by the features of the independent claims. Specific embodiments are defined in the dependent claims.

[0004] According to a first aspect of the invention, a heatable humidity sensor is provided, wherein the humidity measuring capacitor and the resistance heating and measuring element are thermally insulated from the rest of the sensor structure.

[0005] According to a second aspect of the invention, a sensor structure is provided in which the sensor frame and the active sensor are concentric with each other.

[0006] According to a third aspect of the invention, a sensor structure is provided, wherein the total width of the support bridge is approximately 0.5-75% of the perimeter of the active sensor.

[0007] According to a fourth aspect of the invention, a sensor structure is provided, wherein the total thickness of the active sensor is in the range of 1-100 μm, typically about 2 μm.

[0008] According to a fifth aspect of the invention, a sensor structure is provided, wherein the thickness of the layer supporting the active sensor is 100-1000 nm, typically 350 nm.

[0009] According to a sixth aspect of the invention, a sensor structure is provided, wherein the heating power of the active sensor is in the range of 0.1 mW / ℃ to 5 mW / ℃.

[0010] According to a seventh aspect of the invention, a sensor structure is provided in which the temperature change rate of the active sensor (22) during heating is typically greater than 200°C / s.

[0011] According to an eighth aspect of the invention, a sensor structure is provided in which the ratio of the length of each support bridge to the width of the active sensor is typically in the range of 1:6 to 1:2, preferably about 1:4.

[0012] According to a ninth aspect of the present invention, a sensor structure is provided in which the thermal response time of an active sensor is at least 10 times shorter, preferably at least 20 times shorter, than the humidity response time of an active sensor. According to a tenth aspect of the present application, a calibration method for a sensor structure is provided in which the minimum value of the capacitance is determined at least at a relative humidity (RH) point of 0%. Attached Figure Description

[0013] Figure 1 The cross-sectional sensor structure according to at least some embodiments of the present invention has been explained;

[0014] Figure 2 A top view of another sensor structure according to at least some embodiments of the present invention is described;

[0015] Figure 3 The explanation was based on Figure 3 Cross-section of the sensor structure along pads 3 and 4;

[0016] Figure 4 A diagram illustrating a calibration method according to at least some embodiments of the present invention is provided; Detailed Implementation

[0017] By utilizing the sensor structure according to the invention, low thermal mass of the active sensing region is achieved, resulting in a rapid thermal response. Consequently, the required heating power is also lower. Therefore, heating-based calibration methods are also possible in ATEX classification environments where explosion risks exist.

[0018] Rapid thermal response enables the development and use of enhanced automated calibration methods. For the same sensor structure, accurate temperature measurement is also possible using the same sensor element if sensor heating is employed. In existing solutions, temperature measurement requires a separate temperature measuring element because high heating power can lead to self-heating issues within the integrated system.

[0019] Figure 1 A cross-section of the humidity sensor structure 19 according to the present invention is shown. An LPCVD nitride layer 14 is formed on a silicon substrate 12, which also serves as a support layer for the actual capacitor 9 formed by the niobium electrode 13, the active polymer layer 10, and the upper porous chromium electrode 11. The substrate may also be germanium. In a preferred embodiment of the invention, the heat insulation layer 14 has a uniform structure. A heating resistor 7 (or alternatively, a temperature sensor 8) is located within the LPCVD nitride layer 14. The humidity measuring capacitor 9 is protected by a top protective polymer layer 15.

[0020] according to Figure 2 and Figure 3The sensor structure comprises two main components: an active sensor 22 surrounded by a sensor frame 21. The sensor frame 21 is formed on a silicon substrate 12. The active sensor 22 is mechanically connected to the sensor frame 23 only through a thin thermal insulation layer 14 supporting the active sensor 22, which includes electrical contacts from the sensor frame 21. In one embodiment of the invention, the layer 14 includes isolation gaps 18 such that the active sensor 22 contacts the sensor frame through thin support bridges 16 and 17 of the thermal insulation layer 14, which is covered with niobium for electrical contact. Each support bridge is approximately 0.5 mm long, typically in the range of 0.1–1 mm, and the ratio of the length of each support bridge 16, 17 to the width of the active sensor 22 is approximately 1:4, typically in the range of 1:6–1:2. These isolation gaps 18 create additional thermal insulation between the active sensor 22 and the sensor frame 21. The active sensor 22 typically includes a planar humidity measuring capacitor 9 and at least one or both of a heating resistor 7 and a temperature sensor 8. The sensor frame 21 includes contact pads 1 and 2 for the heating resistor 7, contact pads 3 and 4 for the humidity measuring capacitor 9, and contact pads 5 and 6 for the temperature sensor 8. The total width of the support bridges 16 and 17 represents approximately 0.5-75% of the perimeter of the active sensor 22, and through this structure, the active sensor is efficiently thermally isolated from the sensor frame 21. The active sensor 22 is also very thin, approximately 2 μm, typically in the range of 1-100 μm, while the supporting LPCVD nitride layer 14 is approximately 350 nm thick, typically in the range of 100-1000 nm. The thermal insulation layer 14 may also be formed from several sublayers; however, the total thermal insulation of layer 14 must be sufficient.

[0021] The key difference from existing solutions lies in the fact that this invention allows for the measurement of actual dry capacitance. In existing solutions, dry capacitance is never actually measured but is merely assumed through extrapolation. This method is inaccurate because temperature dependence changes with aging, and is therefore one of the biggest sources of error in current humidity sensors.

[0022] The invention described above achieves a significant difference in response time between humidity and temperature measurements required for dry capacitance measurement. Typically, the response time for humidity measurement is more than 10 times longer than that for temperature measurement. Figure 4 The graph graphically displays the capacitance of the humidity sensor 9 as a function of the duration of the heating pulse and the temperature of the same element as measured by the temperature sensor. The temperature rise in the curve represents the heating pulse. The minimum capacitance 20 represents dry capacitance because at this point, due to the very fast (short) response time of the temperature measurement, the temperature of the active sensor 22 is at ambient temperature (or another desired temperature for dry calibration), but the humidity sensor 9 has not yet absorbed moisture. In other words, at point 20, the humidity sensor is at 0% relative humidity and the measured temperature.

[0023] The typical characteristics of the active sensor structure 22 are as follows:

[0024] – The heating power may be in the range of 0.1mW / ℃ to 5mW / ℃.

[0025] – The rate of temperature change is typically greater than 200℃ / s.

[0026] – The temperature range used is typically between 5 and 300°C.

[0027] The structure according to the invention makes it possible to use an additional method with rapid temperature changes. In the capacitance curve, 23 represents the point where water has not yet been removed from the sensor 9 due to heating, but the temperature has reached a stable value. The temperature dependence of the humidity sensor 9 can be determined through this calibration point.

[0028] As examples, some features of the present invention are listed below:

[0029] The capacitance of capacitor 9 changes as molecules are absorbed into the dielectric material, and the measured capacitance is related to the concentration of the substance.

[0030] The temperature of capacitor 9 is measured by temperature-dependent resistor 8.

[0031] Capacitor 9 can be heated by a separate heater resistor 7, or alternatively by periodically energizing or measuring temperature resistor 8.

[0032] The dielectric material 10 of capacitor 9 may be an organic polymer, ceramic, or any other dielectric material that can absorb molecules.

[0033] The self-sustaining thin film 14 can be SiN.

[0034] The materials for resistors 7 and 8 can be platinum, molybdenum, or other monotonic temperature-response materials.

[0035] The capacitor 9, temperature measuring device 8, and heating element 7 are placed so that they are considered as islands 22 with low thermal conductivity from the maintaining film 14. Figure 2 (Central region). The purpose is to fabricate very thin metal wires for the electrical contacts, so that they have no substantial impact on thermal conductivity. Electrical contact pads 1-6 are located on the surrounding sensor frame 21 formed from the silicon substrate 12.

[0036] By heating only the low-thermal-mass region 22 where capacitor 9 is housed, the sensor structure described above, combined with rapid temperature changes, makes it possible to use a novel drift compensation method. With this method, dry capacitance can be measured at the actual measurement temperature. Existing methods can only predict dry capacitance by using calculations and assumptions about its thermal dependence. It is now possible to measure dry capacitance because the thermal response time is approximately 20 times faster than the humidity response time. At elevated temperatures, virtually all water desorbs from the sensor, and during rapid cooling, water has no time to be absorbed into the sensor; therefore, the measured capacitance only indicates the dry capacitance of sensor 9. Dry capacitance drift can then be compensated for. Other advantages include a very fast automatic calibration cycle and short readout lock-in time.

[0037] It should be understood that the embodiments of the disclosed invention are not limited to the specific structures, process steps, or materials disclosed herein, but extend to their equivalents as would be recognized by one of ordinary skill in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0038] Throughout this specification, references to "an embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the appearance of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification does not necessarily refer to the same embodiment.

[0039] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be understood as each component in the list being individually identified as a separate and unique component. Therefore, any single component on such a list should not be considered a de facto equivalent of any other component on the same list solely based on its presentation in a common group, without the contrary indication. Furthermore, various embodiments and examples of the invention, as well as alternatives to its various components, are mentioned herein. It should be understood that these embodiments, examples, and alternatives should not be construed as actual equivalents of each other, but rather as separate and independent representations of the invention.

[0040] Furthermore, in one or more embodiments, the described features, structures, or characteristics can be combined in any suitable manner. Numerous specific details, such as examples of length, width, shape, etc., are provided in the following description to provide a thorough understanding of embodiments of the invention. However, those skilled in the art will recognize that the invention can be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the invention.

[0041] While the foregoing examples illustrate the principles of the invention in one or more specific applications, it will be apparent to those skilled in the art that various modifications can be made to the form, use, and details of implementation without departing from the principles and concepts of the invention and without the use of inventiveness. Therefore, the invention is not intended to be limited except as limited by the following claims.

[0042] The verbs “comprising” and “including” are used in this document as open-ended restrictions, neither excluding nor requiring the presence of any undescribed features. Unless otherwise expressly stated, the features described in the dependent claims are freely combined with each other. Furthermore, it should be understood that the use of “a” or “an” throughout this document, i.e., the singular form, does not exclude the plural.

[0043] Industrial applicability

[0044] This invention is industrially applicable.

[0045] List of acronyms

[0046] RH (Relative Humidity)

[0047] LPCVD (Low Pressure Chemical Vapor Deposition)

[0048] PECVD (Plasma Enhanced Chemical Vapor Deposition)

[0049] Figure Labels

[0050] 1. First heating resistor contact pad

[0051] 2 Second heating resistor contact pad

[0052] 3. First humidity measurement capacitor contact pad

[0053] 4. Second humidity measurement capacitor contact pad

[0054] 5. First temperature sensor contact pad

[0055] 6 Second temperature sensor contact pad

[0056] 7 Heating Resistance

[0057] 8 temperature sensors

[0058] 9. Humidity measuring capacitor, capacitive humidity sensor

[0059] 10 Active polymer for humidity measurement capacitor

[0060] 11. Porous electrodes at the top of the humidity measuring capacitor

[0061] 12 Silicon or Germanium substrate

[0062] 13. Lower electrode of the humidity measuring capacitor

[0063] 14LPCVD nitride layer (support), thermal insulation layer

[0064] 15 Protective Polymers

[0065] 16 Resistor Conductor Support Bridge

[0066] 17 Capacitor Conductor Support Bridge

[0067] 18 isolation gaps

[0068] 19 Sensor Structure

[0069] 20RH 0% point

[0070] 21 Sensor Frame

[0071] 22 active sensors

[0072] 23 RH maximum point

Claims

1. A calibration method using a sensor structure (19) formed on a substrate (12), the sensor structure comprising: The sensor frame (21) includes electrical contacts (1-6) for the sensor. The active sensor (22) within the sensor frame (21) includes at least one capacitive humidity sensor (9). in, The active sensor (22) is connected to the sensor frame (21) only through a heat insulation layer (14) supporting the active sensor (22), the heat insulation layer (14) including electrical contacts from the sensor frame (21). The substrate (12) is removed from the region of the active sensor (22), and The active sensor (22) includes a heating resistor (7) and a temperature sensor (8); The method is characterized by comprising: The active sensor (22) is heated by heating pulses through a heating resistor (7). During the application of the heating pulse, the capacitance of the capacitive humidity sensor (9) is determined, and the temperature of the active sensor (22) is determined by the temperature sensor (8), wherein... The minimum value (20) of the capacitance representing the dry capacitance is determined to be the point of 0% relative humidity, at which the capacitive humidity sensor (9) is located at 0% relative humidity and in the measured temperature; The maximum value of the capacitance is determined as the maximum point of relative humidity, which represents the point where the temperature has reached a stable value before the moisture has been removed from the humidity sensor (9) due to heating. The sensor structure is configured to generate the difference between the thermal response time and the humidity response time of the active sensor (22), and the difference is used for the determination of the dry capacitance.

2. The calibration method as described in claim 1, characterized in that, The duration of the heating pulse is in the range of 0.05 to 5 seconds.

3. The calibration method as described in claim 2, characterized in that, The duration of the heating pulse is 2.5 seconds.

4. The calibration method as described in claim 1, characterized in that, The heating power of the active sensor (22) is in the range of 0.1 mW / °C to 5 mW / °C.

5. The calibration method as described in claim 1, characterized in that, The temperature change rate during the heating of the active sensor (22) is greater than 200 °C / s.

6. The calibration method as described in claim 1, characterized in that, The thickness of the heat insulation layer (14) supporting the active sensor (22) is 100-1000 nm.

7. The calibration method as described in claim 6, characterized in that, The thickness of the heat insulation layer (14) supporting the active sensor (22) is 350 nm.

8. The calibration method as described in claim 1, characterized in that, The total thickness of the active sensor (22) is 1-100 mm. Within the range of m.

9. The calibration method as described in claim 8, characterized in that, The total thickness of the active sensor (22) is 2. m.

10. The calibration method as described in claim 1, characterized in that, The ratio of the width of the heat insulation layer (14) between the sensor frame (21) and the active sensor (22) to the width of the active sensor (22) is in the range of 1:6–1:

2.

11. The calibration method as described in claim 10, characterized in that, The width of the heat insulation layer (14) between the sensor frame (21) and the active sensor (22) is in the ratio of 1:4 to the width of the active sensor (22).

12. The calibration method as described in claim 1, characterized in that, The sensor frame (21) and the active sensor (22) are concentric.

13. The calibration method as described in claim 1, characterized in that, The heat insulation layer (14) between the active sensor (22) and the sensor frame (21) includes an isolation gap (18) such that the total width of the first support bridge (16) and the second support bridge (17) is 0.5-75% of the perimeter of the active sensor (22).

14. The calibration method as described in claim 1, characterized in that, The active sensor (22) includes the heating resistor (7) and the temperature sensor (8), and the thermal response time of the active sensor (22) is more than 10 times faster than the humidity response time of the active sensor (22).

15. The calibration method as described in claim 14, characterized in that, The active sensor (22) includes the heating resistor (7) and the temperature sensor (8), and the thermal response time of the active sensor (22) is more than 20 times faster than the humidity response time of the active sensor (22).

16. The calibration method as described in claim 1, characterized in that, The heat insulation layer (14) is SiN.

17. The calibration method as described in claim 1, characterized in that, The substrate (12) is silicon.

18. The calibration method as described in claim 1, characterized in that, The substrate (12) is germanium.

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