JP2006078280A - Capacitive humidity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitive humidity sensor disposed along a curved face. <P>SOLUTION: The capacitive humidity sensor 100 is provided with a substrate 10, a pair of electrodes 21, 22 coplanarly and oppositely disposed and spaced on the substrate 10, and a humidity sensing membrane 30 disposed on the substrate 10, covering the electrodes 21, 22 and a space between them and changing a relative permittivity in response to a humidity. The substrate 10 is flexible, and is deformed and fitted to the curved face of an attachment 200 when a back side of an electrode forming face of the substrate 10 is oppositely disposed to the attachment 200. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitive humidity sensor in which a humidity sensitive film whose relative dielectric constant changes according to humidity is interposed between a pair of electrodes.

  Conventionally, the present applicant has previously disclosed Patent Document 1 as an example of a capacitive humidity sensor in which a humidity sensitive film whose relative dielectric constant changes according to humidity is interposed between a pair of electrodes.

The capacitive humidity sensor disclosed in Patent Document 1 is opposed to a semiconductor substrate, a first insulating film formed on the semiconductor substrate, and a first insulating film spaced apart on the same plane. A pair of electrodes formed on the second insulating film, a second insulating film formed so as to cover the pair of electrodes, and a feeling formed on the second insulating film so as to cover the pair of electrodes and the pair of electrodes. It is composed of a wet film. Accordingly, a moisture sensitive film whose relative dielectric constant changes according to the humidity is interposed between the pair of electrodes, and the humidity can be detected based on the change in the relative dielectric constant of the moisture sensitive film.
JP 2002-243690 A

  However, the conventional capacitive humidity sensor has a configuration in which a detection unit including an electrode and a moisture-sensitive film is formed on a rigid substrate, such as a semiconductor substrate or a glass substrate described in Patent Document 1.

  Therefore, when placing directly on a mounting part having a curved surface (for example, placing it on a windshield for application to automatic control of an auto air-conditioning system for the purpose of preventing fogging of a windshield of a vehicle) Since the contact is partial, the sensor may be destroyed when an external force is applied.

  Moreover, although the structure which arrange | positions a sensor in an attachment part via the buffer member which has a curved surface according to the curved surface of an attachment part is also considered, the physique of a sensor including a buffer member becomes large. Therefore, especially in the case of a windshield, the view of the passenger is obstructed, which is not preferable.

  Therefore, conventionally, the sensor is arranged on a flat portion (for example, on the dash panel) that is separated from the mounting portion having a curved surface. Therefore, some errors have occurred with respect to the part to be actually measured.

  In view of the above problems, an object of the present invention is to provide a capacitive humidity sensor that can be arranged along a curved surface.

  In order to achieve the above object, the invention according to any one of claims 1 to 4 covers a substrate, a pair of electrodes that are spaced apart from each other on the same plane on the substrate, and a space between the pair of electrodes and the pair of electrodes. As described above, the present invention relates to a capacitive humidity sensor including a moisture sensitive film provided on a substrate and having a relative dielectric constant that changes according to humidity.

  First, as described in claim 1, when the substrate has flexibility and is disposed so that the back surface of the electrode forming surface of the substrate faces the mounting portion, the substrate deforms in accordance with the curved surface of the mounting portion. It is characterized by that.

  As described above, the capacitive humidity sensor of the present invention can be directly arranged on the mounting portion having a curved surface. That is, the humidity can be detected with higher accuracy. The capacitive humidity sensor is fixed to the surface of the mounting portion in a state of being deformed according to the curved surface of the mounting portion. Therefore, even if an external force is applied to the capacitive humidity sensor, the stress is dispersed. Therefore, the configuration is stronger against the external force than the conventional capacitive humidity sensor is directly disposed on the mounting portion having a curved surface.

  The capacitive humidity sensor of the present invention can be deformed according to an arbitrary curved surface, not deformed according to a predetermined curved surface. Moreover, it is possible to arrange not only a curved surface but also a plane.

  According to a second aspect of the present invention, it is preferable that the pair of electrodes have a comb-teeth shape and are arranged so as to mesh with each other. In this case, since the facing area between the pair of electrodes can be increased, the amount of change in capacitance between the electrodes can be increased.

  According to a third aspect of the present invention, a circuit unit that performs signal processing on capacitance change between a pair of electrodes may be provided on a substrate on which an electrode and a moisture sensitive film are provided. In addition, as described in claim 4, the circuit unit for signal processing of the capacitance change between the pair of electrodes is provided on a substrate different from the substrate on which the electrodes are formed, and the electrode and the circuit unit are connected to each other. It can also be set as the structure electrically connected through this.

  In addition, although it does not specifically limit as an attaching part, The capacitive humidity sensor in any one of Claims 1-4 prevents fogging of the windshield of a vehicle as described in, for example, Claim 5. As one object, it can be suitably attached to a windshield of a vehicle in order to be applied to automatic control of an automatic air conditioner system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
1A and 1B are diagrams illustrating a schematic configuration of a capacitive humidity sensor 100 according to the present embodiment, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. In FIG. 1A, for the sake of convenience, a pair of electrodes under the moisture sensitive film is shown by broken lines.

  In FIGS. 1A and 1B, reference numeral 10 denotes a substrate, and a flexible substrate having flexibility is applied in the present embodiment. The constituent material of the substrate 10 is not particularly limited as long as it has flexibility. In the present embodiment, a thermoplastic resin film made of a liquid crystal polymer (LCP) having a thickness of 25 μm is applied. Yes.

  In the same plane on the substrate 10, the pair of electrodes 21 and 22 are spaced apart from each other. Although the shape of the electrodes 21 and 22 is not particularly limited, in the present embodiment, as shown in FIG. 1A, each of the electrodes 21 and 22 includes the common electrode portions 21a and 22a, A plurality of comb electrode portions 21b and 22b extending in one direction from the common electrode portions 21a and 22a. The pair of electrodes 21 and 22 are arranged so that the comb-tooth electrode portions 21b and 22b of the pair of electrodes 21 and 22 are alternately arranged. Thus, by adopting a comb-teeth shape as the shape of the pair of electrodes 21 and 22, the area where the comb-teeth electrode portions 21 b and 22 b face each other is increased while the arrangement area of the electrodes 21 and 22 is reduced. Can do. As a result, the amount of change in capacitance between the electrodes 21 and 22 that changes with changes in the surrounding humidity increases, and the sensitivity of the capacitive humidity sensor 100 improves.

  The electrodes 21 and 22 are formed, for example, by etching a conductive foil stuck on one side of the substrate 10 into a desired pattern. As the conductor foil, for example, a low resistance metal foil such as Au, Ag, Cu, and Al can be used. In the present embodiment, an Au foil is used. In addition, formation of the electrodes 21 and 22 can also be implemented using the printing method, for example besides the etching of conductor foil.

  In addition, when the electrodes 21 and 22 do not have corrosion resistance against moisture, a protective film is formed on the substrate 10 so as to cover the pair of electrodes 21 and 22, thereby suppressing corrosion of the electrodes 21 and 22 due to moisture. It ’s fine.

  Further, as shown in FIG. 1A, the electrodes 21 and 22 have pad portions 21c and 22c as external connection terminals at their ends, and are connected to the pad portions 21c and 22c using solder or the like. The lead 110 is electrically connected to a circuit portion (circuit board) on which a signal processing circuit for correcting an output and detecting an amount of change in capacitance is formed. The pad portions 21c and 22c need to be exposed for connection with the lead 110, and are not covered with a moisture sensitive film described later.

  Further, a moisture sensitive film 30 made of a hygroscopic polymer material is formed on the substrate 10 so as to cover between the pair of electrodes 21 and 22 and the electrodes 21 and 22. As the polymer material, polyimide, cellulose acetate butyrate, or the like can be applied. In the present embodiment, polyimide is used. Various methods are conceivable as the forming method. In the present embodiment, a screen printing method that can eliminate the need for patterning by a photo process is applied.

  In the capacitive humidity sensor 100 configured as described above, when moisture permeates into the moisture sensitive film 30, the moisture has a large relative dielectric constant, so that the relative dielectric constant of the moisture sensitive film 30 depends on the amount of the penetrated moisture. Changes. As a result, the capacitance of the capacitor constituted by the pair of electrodes 21 and 22 with the moisture sensitive film 30 as a part of the dielectric changes. Since the amount of water contained in the moisture sensitive film 30 corresponds to the humidity around the capacitive humidity sensor 100, the humidity can be detected from the capacitance between the pair of electrodes 21 and 22.

  Next, the characteristic part of the capacitive humidity sensor 100 shown in this embodiment will be described with reference to FIGS. FIG. 2 is a view showing an example of attachment of the attachment portion of the capacitive humidity sensor 100 shown in the present embodiment to a curved surface, (a) is a configuration diagram when attached to the windshield as the attachment portion, (B) is an expanded sectional view of the sensor periphery in (a).

  For the purpose of preventing fogging of a windshield of a vehicle and applying it to automatic control of an auto air conditioner system, it is desired to accurately detect the humidity in the vicinity of the windshield. However, when a capacitive humidity sensor using a conventional rigid substrate is directly placed on the curved surface of the windshield (the windshield 200 in FIG. 2A), an external force is applied because of partial contact. When this is done, the capacitive humidity sensor may be destroyed.

  In addition, a configuration in which the capacitive humidity sensor is arranged on the mounting portion through a buffer member having a curved surface corresponding to the curved surface of the windshield is also conceivable, but the size of the capacitive humidity sensor including the buffer member is increased. That is, it is not preferable because a range that hinders the field of view of the occupant (in particular, the driver in the case of the windshield 200) becomes large.

  Therefore, conventionally, a capacitive humidity sensor has been arranged on a flat portion (for example, on the dash panel 210) away from the windshield having a curved surface. Therefore, some errors have actually occurred with respect to the part to be actually measured.

  On the other hand, in the capacitive humidity sensor 100 according to the present embodiment, the substrate 10 has flexibility, and the substrate 10 with respect to the inner surface of the windshield 200 as shown in FIGS. When the electrodes are formed so that the back surfaces of the electrode forming surfaces face each other, they can be deformed according to the curved surface of the windshield 200. As described above, the capacitive humidity sensor 100 according to the present embodiment can be directly arranged on a mounting portion having a curved surface like the windshield 200. That is, the humidity can be detected with higher accuracy. In FIG. 2A, a lead 110 having one end connected to the capacitive humidity sensor 100 is electrically connected to a circuit unit (not shown) disposed under the dash panel 210 at the other end. Yes. In FIG. 2B, reference numeral 300 denotes an adhesive layer, and a double-sided tape is employed in this embodiment.

  The capacitive humidity sensor 100 is fixed to the inner surface of the windshield 200 in a state of being deformed according to the curved surface of the windshield 200. Therefore, even if an external force is applied to the capacitive humidity sensor 100, the stress is dispersed, so that the configuration is stronger than the conventional capacitive humidity sensor 100 directly on the windshield 200.

  In addition, the capacitive humidity sensor 100 according to the present embodiment is not deformed corresponding to a curved surface having a predetermined R, but can be deformed according to a curved surface having an arbitrary R. Therefore, for example, the windshield 200 has a curved R shape depending on the type of vehicle, but can be handled by the same capacitive humidity sensor 100. Needless to say, it can be arranged not only on a curved surface but also on a flat surface. Furthermore, it is also possible to arrange at a corner such as a prism.

  Further, in the present embodiment, an example in which the detection unit and the circuit unit including the electrodes 21 and 22 and the moisture sensitive film 30 are separately provided and electrically connected via the lead 110 is shown. With such a configuration, the physique of the capacitive humidity sensor 100 disposed on the windshield 200 can be reduced in size. That is, the hindrance to the occupant's field of view can be reduced. However, the circuit unit may be provided on the substrate 10 on which the electrodes 21 and 22 and the moisture sensitive film 30 are provided. In this case, since the formation of the electrodes 21 and 22 and the wiring constituting the circuit portion can be formed at the same time, the manufacturing process can be simplified.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented with various modifications.

  In this embodiment, the example which arrange | positions the capacitive humidity sensor 100 on the surface of the windshield (front glass 200) of a vehicle as an attaching part was shown. However, the capacitive humidity sensor 100 shown in the present embodiment can also be disposed on a mounting portion having a curved surface other than the above example.

It is a figure which shows schematic structure of the capacitive humidity sensor of this invention, (a) is a top view, (b) is sectional drawing in the AA cross section of (a). It is a figure which shows the example of attachment of the capacity | capacitance type humidity sensor with respect to the curved surface of an attachment part, (a) is a block diagram at the time of attaching to the windshield as an attachment part, (b) is a sensor periphery in (a). It is an expanded sectional view.

Explanation of symbols

10 ... Substrate 21, 22 ... Electrode 30 ... Humidity sensitive film 100 ... Capacitive humidity sensor 110 ... Lead 200 ... Windshield (mounting part)
300: Adhesive layer

Claims (5)

A substrate,
A pair of electrodes arranged opposite to each other on the same plane on the substrate;
A capacitive humidity sensor provided on the substrate so as to cover between the pair of electrodes and the pair of electrodes, and a moisture sensitive film whose relative dielectric constant changes according to humidity,
The substrate is flexible, and is deformed in accordance with the curved surface of the mounting portion when the mounting portion is arranged so that the back surface of the electrode forming surface of the substrate faces the mounting portion. Humidity sensor.   2. The capacitive humidity sensor according to claim 1, wherein the pair of electrodes have a comb shape and are arranged so as to mesh with each other.   3. The capacitive humidity sensor according to claim 1, wherein the substrate is also provided with a circuit unit that performs signal processing on a change in capacitance between the pair of electrodes. 4.   The circuit unit that performs signal processing of capacitance change between the pair of electrodes is provided on a substrate different from the substrate, and the electrodes and the circuit unit are electrically connected via leads. The capacitive humidity sensor according to claim 1 or 2. The capacitive humidity sensor according to any one of claims 1 to 4, wherein the attachment portion is a windshield of a vehicle.

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