Humidity sensor

Abstract

To provide a humidity sensor which comprehends a deterioration state of moisture sensitive films as a change of an output value of the humidity sensor.SOLUTION: A humidity sensor includes a first element 121 and a second element 122. The first element 121 includes: a first electrode 101; a first moisture sensitive film 102 formed on the first electrode 101; and a second electrode 103a formed on the first moisture sensitive film 102. The second element 122 includes: a third electrode 103b; a second moisture sensitive film 104 formed on the third electrode 103b; and a fourth electrode 105 formed on the second moisture sensitive film 104. The second moisture sensitive film 104 is formed thinner than the first moisture sensitive film 102.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a humidity sensor using a humidity-sensitive film. [Background technology]

[0002] For example, in air conditioning control, humidity control is important in addition to temperature control. Humidity control uses a humidity sensor. For example, a humidity sensor in which a humidity-sensitive film is sandwiched between two electrodes is known (Patent Document 1). Since the capacitance value of the humidity-sensitive film changes with changes in humidity, the humidity can be calculated from the measured capacitance value based on the corresponding relationship between the humidity and the capacitance value between the two electrodes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-019964 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the moisture-sensitive film deteriorates under high temperature and humidity conditions or in a chemical atmosphere. However, there is a problem in that it is not easy to detect the deterioration of the moisture-sensitive film as a change in the output value of the humidity sensor.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to make it possible to detect the deterioration of a humidity-sensitive film as a change in the output value of a humidity sensor. [Means for solving the problem]

[0006] The humidity sensor of the present invention comprises a first element having a first electrode, a first humidity-sensitive film formed on the first electrode, and a second electrode formed on the first humidity-sensitive film; a second element having a third electrode, a second humidity-sensitive film formed on the third electrode and thinner than the first humidity-sensitive film, and a fourth electrode formed on the second humidity-sensitive film; an arithmetic circuit configured to determine the difference between a first output value of the first element and a second output value of the second element; and a degradation determination circuit configured to determine degradation when it detects that the absolute value of the difference between the first output value and the second output value exceeds a reference value.

[0007] In one configuration example of the humidity sensor, the second element is laminated on the first element, and the second electrode and the third electrode are common.

[0008] In one configuration example of the humidity sensor described above, the area of ​​the second element in a planar view is smaller than the area of ​​the first element in a planar view.

[0009] In one configuration example of the humidity sensor, the first electrode is formed in an area where the fourth electrode is not formed.

[0010] In one configuration example of the humidity sensor, the first moisture-sensitive film and the second moisture-sensitive film are made of the same material. Effect of the Invention

[0011] As described above, according to the present invention, the first element and the second element having moisture-sensitive films with different thicknesses are used, so that the deterioration of the moisture-sensitive film can be detected as a change in the output value of the humidity sensor. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the structure of a humidity sensor according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view showing a partial configuration of another humidity sensor according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a cross-sectional view showing a partial configuration of another humidity sensor according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a partial configuration of another humidity sensor according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a cross-sectional view showing a partial configuration of another humidity sensor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A humidity sensor according to an embodiment of the present invention will now be described with reference to Fig. 1. This humidity sensor includes a first element 121 and a second element 122. In this example, the second element 122 is layered on the first element 121.

[0014] The first element 121 includes a first electrode 101, a first humidity-sensitive film 102 formed on the first electrode 101, and a second electrode 103a formed on the first humidity-sensitive film 102. The second element 122 includes a third electrode 103b, a second humidity-sensitive film 104 formed on the third electrode 103b, and a fourth electrode 105 formed on the second humidity-sensitive film 104. The second humidity-sensitive film 104 is formed thinner than the first humidity-sensitive film 102. Therefore, the second humidity-sensitive film 104 has a lower strength than the first humidity-sensitive film 102. The first humidity-sensitive film 102 and the second humidity-sensitive film 104 can be made of the same material.

[0015] The first moisture-sensitive film 102 and the second moisture-sensitive film 104 can be made of an organic polymer resin material such as polymethyl methacrylate resin (PMMA), crosslinked PMMA, polyimide, polysulfone, polyethersulfone, etc. The first moisture-sensitive film 102 and the second moisture-sensitive film 104 can have a thickness of, for example, 1 to 10 μm.

[0016] This humidity sensor also includes an arithmetic circuit 106 and a deterioration determination circuit 107. The arithmetic circuit 106 determines the difference between the first output value of the first element 121 and the second output value of the second element 122. Incidentally, the second moisture-sensitive film 104 is thinner than the first moisture-sensitive film 102, and therefore the response time of the second element 122 to changes in ambient humidity is faster than that of the first element 121. For this reason, the difference between the first output value and the second output value is determined in a state in which the output values ​​(relative humidity) of the first element 121 and the second element 122 are determined to be stable.

[0017] For example, the difference between the first output value and the second output value is obtained when the temperature and humidity of the measurement space are stable, such as in the middle of the night when there are few people in and out. In addition, measurements are made, for example, every five minutes for two hours, and a state in which the deviation between the first output value and the second output value is equal to or less than a certain value is defined as a stable state, and in this state, the difference between the first output value and the second output value is obtained.

[0018] Each element is equipped with a table showing the correlation between the capacitance value of the humidity-sensitive film measured by the two electrodes and the relative humidity, and can output the relative humidity obtained from this correlation corrected by a temperature correction coefficient as an output value.

[0019] The deterioration determination circuit 107 determines that deterioration has occurred when it detects that the absolute value of the difference between the first output value and the second output value obtained by the arithmetic circuit 106 exceeds a set reference value. For example, the deterioration determination circuit 107 can perform the deterioration determination by comparing the difference between the first output value and the second output value obtained by the arithmetic circuit 106 in the stable state as described above with the difference between the first output value and the second output value recorded at the time of shipment and confirming whether the compared data is within a threshold value or exceeds the threshold value.

[0020] The deterioration determination circuit 107 outputs the determination result. The second moisture-sensitive film 104, which is thinner than the first moisture-sensitive film 102, deteriorates faster than the first moisture-sensitive film 102. Therefore, when the second moisture-sensitive film 104 deteriorates, the first moisture-sensitive film 102 has not deteriorated, and the first output value and the second output value are different. Therefore, when it is detected that the first output value and the second output value are different, deterioration of the second moisture-sensitive film 104 can be determined. In this way, when deterioration of the second moisture-sensitive film 104 is determined, measures such as the timing to replace the humidity sensor can be taken.

[0021] For example, the relative humidity value used for humidity control can be either the first output value or the second output value. As described above, the response time of the second element 122 to changes in ambient humidity is faster than that of the first element 121. Therefore, by using the second output value for humidity control, it is possible to speed up the response of the control. The second output value can be used for humidity control until the deterioration determination circuit 107 determines that the second humidity-sensitive film 104 has deteriorated.

[0022] In the configuration in which the second element 122 is stacked on the first element 121, a common electrode 103 can be used that serves as the second electrode and the third electrode, as shown in Fig. 2. In this configuration, the common electrode 103 is formed on the first moisture-sensitive film 102, and the second moisture-sensitive film 104 is formed on the common electrode 103. Note that the arithmetic circuit and the deterioration determination circuit are omitted in Fig. 2. The first output value is calculated from the capacitance value between the first electrode 101 and the common electrode 103, and the second output value is calculated from the capacitance value between the common electrode 103 and the fourth electrode 105.

[0023] Furthermore, as described above, when the second moisture-sensitive film 104 is thinner than the first moisture-sensitive film 102, the base capacitance of the second element 122 is higher than that of the first element 121. The base capacitance indicates the electrostatic capacitance value (pF) of the moisture-sensitive film at a relative humidity of 0% RH. In order to make the base capacitance value the same for the first moisture-sensitive film 102 and the second moisture-sensitive film 104, the area of ​​the second element 122' (fourth electrode 105) in a plan view can be made smaller than that of the first element 121, as shown in FIG. 3. The arithmetic circuit and the deterioration determination circuit are omitted in FIG. 3.

[0024] 4, by forming the first electrode 101a in a region where the fourth electrode 105 is not formed (a region where the fourth electrode 105 is not formed) in a plan view, it is possible to suppress the generation of parasitic capacitance caused by the fourth electrode 105 and the first electrode 101a. Note that the arithmetic circuit and the deterioration determination circuit are omitted in FIG.

[0025] Also, as shown in Fig. 5, first element 121 and second element 122' can be arranged in parallel on substrate 110. The arithmetic circuit and deterioration determination circuit are omitted in Fig. 5. Note that, in order to avoid the thermal influence from the surroundings of the element such as peripheral circuits and to reduce size, it is desirable to have a structure in which first element 121 and second element 122 are stacked as described above.

[0026] The above-mentioned arithmetic circuit 106 and deterioration determination circuit 107 can be computer devices equipped with a CPU (Central Processing Unit), a main storage device, an external storage device, a network connection device, etc., and the above-mentioned functions can be realized by the CPU operating (executing) a program deployed in the main storage device. The above-mentioned program is a program for causing a computer to execute the above-mentioned functions. The network connection device connects to a network. Also, each function can be distributed to multiple computer devices. Also, the arithmetic circuit 106 and deterioration determination circuit 107 can be configured by a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0027] As described above, according to the present invention, a first element and a second element having moisture-sensitive films with different thicknesses are used, so that a deterioration state of the moisture-sensitive film can be detected as a change in the output value of the humidity sensor.

[0028] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0029] 101...first electrode, 102...first moisture-sensitive film, 103...common electrode, 103a...second electrode, 103b...third electrode, 104...second moisture-sensitive film, 105...fourth electrode, 106...arithmetic circuit, 107...deterioration determination circuit, 121...first element, 122...second element.

Claims

1. A first element including a first electrode, a first moisture-sensitive film formed on the first electrode, and a second electrode formed on the first moisture-sensitive film; a second element including a third electrode, a second humidity-sensitive film formed on the third electrode and thinner than the first humidity-sensitive film, and a fourth electrode formed on the second humidity-sensitive film; an arithmetic circuit configured to determine a difference between a first output value of the first element and a second output value of the second element; a deterioration determination circuit configured to determine deterioration when it is detected that an absolute value of a difference between the first output value and the second output value exceeds a reference value; A humidity sensor comprising:

2. 2. The humidity sensor according to claim 1, A humidity sensor in which the second element is stacked on the first element, and the second electrode and the third electrode are common to each other.

3. 3. The humidity sensor according to claim 2, A humidity sensor in which the area of ​​the first element in a plan view is smaller than the area of ​​the second element in a plan view.

4. 4. The humidity sensor according to claim 3, The humidity sensor is configured such that the first electrode is formed in an area where the fourth electrode is not formed.

5. The humidity sensor according to any one of claims 1 to 4, The first and second moisture-sensitive films are made of the same material.

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