JP2005201872A - Capacitive type humidity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitive type humidity sensor of reduced sensitivity dispersion and enhanced responsiveness. <P>SOLUTION: A moisture sensitive membrane 50 is formed to make 3μm or more to 8μm or less of a membrane thickness, in this capacitive type humidity sensor 100 constituted of a semiconductor substrate 10, a pair of electrodes 31, 32 arranged opposedly with a space on the same plane on the semiconductor substrate 10, and the moisture sensitive membrane 50 formed on the semiconductor substrate 10 to cover the both electrodes 31, 32 and a space between the semiconductor substrate 10, and comprising a polyimide polymer with a dielectric constant varied in response to humidity. The dispersion of the sensitivity thereby comes within ±5%, and the responsiveness is brought into 30s or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  The capacitive humidity sensor disclosed in Patent Document 1 is a so-called comb-type capacitive humidity sensor in which a pair of electrodes formed in a comb shape are arranged on the same plane of a substrate so as to mesh with each other.

In such a capacitive humidity sensor having a comb-tooth structure, for example, by forming a polyimide-based moisture sensitive film so as to cover a pair of comb-shaped electrodes, a polyimide-based moisture sensitive film is interposed between the pair of electrodes, A change in dielectric constant accompanying a change in humidity in the moisture sensitive film is detected as a change in capacitance between the pair of electrodes.
JP 2003-156464 A

  The capacitive humidity sensor described above can be formed by an existing semiconductor process. However, since the film thickness of a polyimide-based moisture sensitive film varies within the processing error range of the semiconductor process, the film thickness variation varies with the film thickness. Sensitivity will vary. In the case of a configuration in which output correction is performed by a correction circuit, if the variation in sensitivity is large, the correction circuit may be complicated.

  In general, a capacitive humidity sensor is required to have a predetermined response performance (the time required for the absorbed water molecules to diffuse through the polyimide moisture-sensitive film and reach equilibrium). It varies depending on the thickness of the moisture sensitive film.

  In view of the above problems, an object of the present invention is to provide a capacitive humidity sensor in which variation in sensitivity is reduced and responsiveness is improved.

  In order to achieve the above object, a capacitive humidity sensor according to claim 1 includes a substrate, a pair of electrodes that are spaced apart from each other on the same plane on the substrate, a pair of electrodes, and a pair of electrodes. A polyimide-based moisture-sensitive film that is formed on the substrate so as to cover and whose dielectric constant changes according to humidity is provided. And the film thickness of a polyimide type moisture sensitive film is 3 micrometers or more and 8 micrometers or less, It is characterized by the above-mentioned.

  The present inventor paid attention to the variation in sensitivity due to the film thickness of the polyimide-based moisture sensitive film and studied to reduce the variation in sensitivity by optimally designing the film thickness of the polyimide-based moisture sensitive film. At that time, the sensitivity variation target was set to ± 5% or less, which can simplify the correction circuit. As a result, it has been found that the variation in sensitivity is reduced as the thickness of the polyimide moisture sensitive film is increased. In particular, when the film thickness is 3 μm or more, the variation in sensitivity can be reduced to 5% or less.

  However, it became clear that if the thickness of the polyimide-based moisture sensitive film is increased, the response of the sensor deteriorates. Therefore, the present inventor assumed a case where a response performance (responsiveness 30 s) equal to or higher than that of a known resistance change type humidity sensor is required, and examined the film thickness of a polyimide-based moisture sensitive film that satisfies the request. . As a result, it was found that a response of 30 s can be secured by setting the film thickness to 8 μm or less.

  In the capacitive humidity sensor of the present invention, the film thickness of the polyimide moisture sensitive film is in the range of 3 μm to 8 μm. Therefore, variations in sensitivity are reduced and responsiveness is improved.

  In addition, since the variation in sensitivity is suppressed to 5% or less, the correction circuit is simplified. In particular, in the case of a configuration in which the correction circuit is integrally formed, the size of the sensor is reduced.

  Note that the sensitivity variation refers to the sensitivity of the moisture sensitive film whose film thickness is shifted by ± 20% (a processing error of a general semiconductor process) with respect to the target value A, and the sensitivity of the moisture sensitive film having the target film thickness. When the sensitivity is B, (AB) / B × 100 (%) is shown.

  More preferably, as described in claim 2, the thickness of the polyimide moisture sensitive film is in the range of 4 μm or more and 6 μm or less.

  Thereby, variation in sensitivity can be reduced to ± 2.5% or less, and responsiveness can be improved by 20% or more than a known resistance change type humidity sensor.

  According to a third aspect of the present invention, it is preferable that a protective film formed on the substrate is provided so as to cover the pair of electrodes and the pair of electrodes, and the polyimide moisture sensitive film is formed on the protective film.

  In this case, the electrodes can be reliably protected from moisture, and the corrosion resistance of each electrode to moisture is improved.

  As described in claim 4, the polyimide moisture sensitive film preferably has a minute groove.

  As described above, when the polyimide moisture sensitive film has a minute groove, the surface area of the polyimide moisture sensitive film that comes into contact with moisture increases, so that the responsiveness is improved as compared with the case without the groove. Can do.

  In particular, as described in claim 5, when the groove is a through-hole, the surface area of the polyimide moisture sensitive film in contact with moisture is increased, which is suitable for improving the response.

  According to a sixth aspect of the present invention, the pair of electrodes are comb-shaped and may be 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.

  Preferably, a semiconductor substrate is used as the substrate, and the electrode is preferably provided on the substrate via an insulating film.

  As the substrate, an insulating substrate such as a glass substrate can be used. By using a semiconductor substrate including an insulating film, a sensor can be formed by a semiconductor process. Therefore, the manufacturing cost can be reduced.

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. 1 (a), for the sake of convenience, a pair of electrodes under the moisture sensitive film and the protective film are shown through.

  In FIGS. 1A and 1B, reference numeral 10 denotes a semiconductor substrate as a substrate, which is formed of silicon in this embodiment. A silicon oxide film 20 is formed as an insulating film on the upper surface of the semiconductor substrate 10. In addition, the pair of electrodes 31 and 32 are disposed opposite to each other on the same plane on the silicon oxide film 20.

  Although the shape of the electrodes 31 and 32 is not particularly limited, in the present embodiment, as shown in FIG. 1A, each of the electrodes 31 and 32 includes the common electrode portions 31A and 32A. It is composed of a plurality of comb electrode portions 31B and 32B extending in one direction from the common electrode portions 31A and 32A. And a pair of electrodes 31 and 32 are arrange | positioned so that each comb-tooth electrode part 31B and 32B of a pair of electrodes 31 and 32 may be arranged alternately. Thus, by adopting a comb-teeth shape as the pair of electrodes 31 and 32, the area where the comb-teeth electrode portions 31B and 32B face each other is increased while the arrangement area of the electrodes 31 and 32 is reduced. Can do. As a result, the amount of change in capacitance between the electrodes 31 and 32 that changes with changes in the surrounding humidity increases, and the sensitivity of the capacitive humidity sensor 100 improves.

  For the electrodes 31 and 32, a low-resistance metal material such as aluminum, copper, gold, or platinum is attached to the semiconductor substrate 10 by a technique such as vapor deposition or sputtering, and then patterned into a comb-like pattern by photolithography. Formed by. In the present embodiment, the electrodes 31 and 32 are formed using aluminum.

  A silicon nitride film 40 is formed as a protective film on the semiconductor substrate 10 so as to cover the pair of electrodes 31 and 32. The silicon nitride film 40 is deposited and formed so as to have the same thickness in each part on the semiconductor substrate 10 by, for example, a plasma CVD method or the like. However, when the electrodes 31 and 32 have corrosion resistance against moisture, the protective film (silicon nitride film 40) may not be formed.

  As shown in FIG. 1 (a), pads 31C and 32C as external connection terminals are formed at the ends of the electrodes 31 and 32, and the output is corrected via the pads 31C and 32C. And a signal processing circuit for detecting the amount of change in capacitance and the like. The pads 31C and 32C need to be exposed for connection to a correction circuit or the like, and are not covered with the silicon nitride film 40. In the present embodiment, since the semiconductor substrate 10 is employed as the substrate constituting the capacitive humidity sensor 100, the above-described correction circuit and the like can be formed on the same substrate.

  On the silicon nitride film 40, a moisture sensitive film 50 having a hygroscopic property made of a polyimide-based polymer is formed so as to cover the pair of electrodes 31, 32 and the electrodes 31, 32. The moisture sensitive film 50 can be formed by applying a polyimide polymer by spin coating or printing and then curing. In FIG. 1A, a rectangular region surrounded by a broken line indicates a region where the moisture sensitive film 50 is formed.

  In the capacitive humidity sensor 100 configured as described above, when moisture penetrates into the moisture sensitive film 50, the moisture has a large dielectric constant, so that the dielectric constant of the moisture sensitive film 50 changes according to the amount of moisture penetrated. To do. As a result, the capacitance of the capacitor constituted by the pair of electrodes 31 and 32 with the moisture sensitive film 50 as a part of the dielectric changes. Since the amount of moisture contained in the moisture sensitive film 50 corresponds to the humidity around the capacitive humidity sensor 100, the humidity can be detected from the capacitance between the pair of electrodes 31 and 32.

  Here, since the capacitive humidity sensor 100 shown in the present embodiment can be formed by an existing semiconductor process, the manufacturing cost can be reduced. However, since the film thickness of the moisture-sensitive film 50 varies within the processing error range of the semiconductor process, the moisture-sensitive characteristics of the sensor 100, that is, the output (sensitivity) of the sensor 100 at a certain humidity, due to the variation in the film thickness. It will also vary.

  In particular, as shown in the present embodiment, when the capacitive humidity sensor 100 has a so-called comb-teeth structure, the initial capacity compared to that of a so-called parallel plate structure as shown in Japanese Patent No. 3084735, for example. Therefore, the sensitivity of the moisture sensitive film 50 is strongly affected by the film thickness variation.

  Further, in the case of a configuration in which output correction is performed by a correction circuit, if the variation in sensitivity is large, the correction circuit may be complicated.

  Accordingly, the present inventor has focused on sensitivity variations due to the film thickness of the moisture sensitive film 50. Then, by designing the film thickness of the moisture sensitive film 50 optimally, a simulation study was conducted to reduce the variation in sensitivity.

  In the present embodiment, the capacity of the sensor 100 at a humidity of 0% RH is defined as an initial capacity, and the capacity difference between the initial capacity and the capacity value of the sensor 100 at a humidity of 100% RH is defined as sensitivity. At that time, the dielectric constant of the moisture-sensitive film 50 made of a polyimide-based polymer was 2.9 at a humidity of 0% RH and 3.3 at a humidity of 100% RH. In addition, the variation in film thickness with respect to the target value is within ± 20% (with respect to the target value), which is a processing error of a general semiconductor process, and the film is shifted by ± 20% with respect to the target value. Assuming that the sensitivity of 50 is A and the sensitivity of the moisture sensitive film 50 having the target film thickness is B, (AB) / B × 100 is defined as the sensitivity variation (%). And the change of the dispersion | variation in the sensitivity by a film thickness was confirmed. The result is shown in FIG. In FIG. 2, circles are plots of sensitivity variations.

  As shown in FIG. 2, when the film thickness of the moisture sensitive film 50 is thin, the influence of processing variations on the target value is large, so the sensitivity varies greatly. As the film thickness of the moisture sensitive film 50 increases, the processing variation with respect to the target value increases. It was found that the effect was reduced and the sensitivity variation was reduced. In particular, it was found that by setting the film thickness of the moisture sensitive film 50 to 3 μm or more, it is possible to reduce the sensitivity variation to ± 5% or less with respect to the sensitivity of the sensor 100 having a target film thickness.

  Thus, if the film thickness of the moisture sensitive film 50 is 3 μm or more, the variation in sensitivity can be suppressed to ± 5% or less, and the correction circuit can be simplified. In particular, when the correction circuit is formed integrally with the semiconductor substrate 10, the size of the sensor 100 can be reduced.

  However, if the thickness of the moisture sensitive film 50 is increased, the variation in sensitivity is reduced, but at the same time, the response of the sensor 100 (until the absorbed water molecules diffuse in the moisture sensitive film 50 and reach equilibrium). It is conceivable that the time) will deteriorate. Therefore, the present inventor assumes a case where a response performance (responsiveness 30 s) equal to or higher than that of a known resistance change type humidity sensor is required, and examines the film thickness of the moisture sensitive film 50 that satisfies the request. went.

  Specifically, when the capacitive humidity sensor 100 disposed in an atmosphere with a humidity of 0% RH is instantaneously exposed to an atmosphere with a humidity of 100% RH, the output of the capacitive humidity sensor 100 is 63.2% RH. Was measured, and the time was taken as the response (s) of the capacitive sensor 100. Then, the thickness of the moisture sensitive film 50 of the capacitive humidity sensor 100 was changed, and the relationship between the film thickness and the responsiveness was confirmed by experiments. The result is shown in FIG. In FIG. 2, a triangle mark is a plot of responsiveness.

  As shown in FIG. 2, it has been found that the responsiveness is improved as the thickness of the moisture sensitive film 50 is reduced. In particular, it was found that if the thickness of the moisture sensitive film 50 is 8 μm or less, a response performance (responsiveness 30 s) equal to or higher than that of a known resistance change type humidity sensor can be secured.

  From the above, in the so-called comb-shaped capacitive humidity sensor 100 including the moisture-sensitive film 50 made of a polyimide-based polymer, the target value of the film thickness is set in the range of 3 μm to 8 μm, and the moisture-sensitive film 50 is formed. It has been clarified that by forming the sensor 100, the sensitivity variation is small and the sensor 100 is excellent in responsiveness.

  As shown in FIG. 2, by setting the target value of the film thickness of the moisture sensitive film 50 in the range of 4 μm or more and 6 μm or less, and forming the moisture sensitive film 50, variation in sensitivity can be further reduced, and A capacitive humidity sensor 100 having excellent responsiveness can be obtained. In fact, if the film thickness (target value) of the moisture sensitive film 50 is 4 μm or more, the variation in sensitivity can be halved (± 2.5% or less) compared to the case where the film thickness target value is 3 μm or more. Further, when the film thickness (target value) of the moisture sensitive film 50 is 6 μm, the response can be improved by 20% with respect to the case of 8 μm. In the capacitive humidity sensor 100 of the present embodiment, the moisture sensitive film 50 is formed so as to have a film thickness of 5 μm.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is an enlarged cross-sectional view of a part of the capacitive humidity sensor 100 in the present embodiment.

  Since the capacitive humidity sensor 100 according to the second embodiment is common in common with that according to the first embodiment, a detailed description of the common parts will be omitted, and different parts will be described mainly.

  The second embodiment is different from the first embodiment in that a groove is provided in the moisture sensitive film 50 in order to improve responsiveness.

  As shown in FIG. 3, the capacitive humidity sensor 100 of this embodiment has a minute groove 60 in a moisture sensitive film 50 made of a polyimide polymer. Thus, when the groove part 60 is provided in the moisture sensitive film 50, the surface area of the moisture sensitive film 50 in contact with moisture increases, so that the groove part 60 with the same film thickness (target value) is not provided. The responsiveness of the sensor 100 is improved.

  Further, as shown in FIG. 3, the groove portion 60 in the present embodiment is a through-hole having a small-diameter opening cross section penetrating from the upper surface of the moisture-sensitive film 50 to the lower surface in contact with the protective film 40. 50 is provided with a plurality. Accordingly, the surface area of the moisture sensitive film 50 that comes into contact with moisture is further increased, so that the responsiveness is further improved. Note that the area, the formation position, and the number of formation of the opening cross section of the groove 60 affect the initial capacitance (capacitance at a humidity of 0% RH or humidity of 100% RH) formed between the pair of electrodes 31 and 32. It is preferable that the setting is not made. Also in the present embodiment, the protective film 40 is formed on the electrodes 31 and 32, and the electrodes 31 and 32 are configured to be protected from moisture even if the groove 60 is a through hole. .

  In the present embodiment, an example in which the groove 60 is a through hole is shown. However, the groove 60 is a recess with respect to the surface of the moisture-sensitive film 50, and if the surface area of the moisture-sensitive film 50 in contact with moisture increases due to the formation of the recess, the shape and depth from the surface of the moisture-sensitive film 50 are increased. The size is not limited to the above example. For example, a non-through hole that does not penetrate to the lower surface side in contact with the protective film 40 may be used. The groove 60 is a recess formed on the region between the electrodes 31 and 32 when the protective film 40 and the moisture sensitive film 50 are formed on the substrate 10 so that the film thickness is uniform. Also good.

  Moreover, the formation method of the groove part 60 is not specifically limited. For example, the groove part 60 may be formed by etching after forming the moisture sensitive film 50, or the groove part 60 may be formed by processing the moisture sensitive film 50 with a laser or a drill after the film formation. In addition, the constituent material or film forming conditions of the moisture sensitive film 50 may be adjusted to intentionally generate a crack in the moisture sensitive film 50 during the film forming process of the moisture sensitive film 50, and the crack may be used as the groove 60. .

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  In the present embodiment, an example in which the semiconductor substrate 10 made of silicon is employed as the substrate and the electrodes 31 and 32 are formed on the semiconductor substrate 10 via the insulating film 20 has been shown. When the semiconductor substrate 10 is used as the substrate in this manner, the capacitive humidity sensor 100 can be formed by a general semiconductor process, so that the manufacturing cost can be reduced. However, an insulating substrate such as a glass substrate can also be applied as the substrate.

It is a figure which shows schematic structure of the capacitive humidity sensor in the 1st Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the AA cross section of (a). It is the graph which showed the influence of the film thickness with respect to sensitivity variation and responsiveness. It is sectional drawing to which a part of capacity type humidity sensor in a 2nd embodiment was expanded.

Explanation of symbols

10 ... Semiconductor substrate (substrate)
20 ... Silicon oxide film (insulating film)
31, 32 ... Electrode 40 ... Silicon nitride film (protective film)
50 ... moisture sensitive film (polyimide moisture sensitive film)
60 ... groove 100 ... capacitive humidity sensor

Claims (7)

A substrate,
A pair of electrodes arranged opposite to each other on the same plane on the substrate;
In the capacitive humidity sensor, which is formed on the substrate so as to cover between the pair of electrodes and the pair of electrodes, and a polyimide moisture sensitive film whose dielectric constant changes according to humidity,
2. The capacitive humidity sensor according to claim 1, wherein the polyimide moisture sensitive film has a thickness of 3 μm to 8 μm.   2. The capacitive humidity sensor according to claim 1, wherein the polyimide moisture-sensitive film has a thickness in a range of 4 μm to 6 μm. A protective film formed on the substrate so as to cover the pair of electrodes and the pair of electrodes;
The capacitive humidity sensor according to claim 1, wherein the polyimide moisture sensitive film is formed on the protective film.   The capacitive humidity sensor according to claim 1, wherein the polyimide-based moisture sensitive film has a minute groove.   The capacitive humidity sensor according to claim 4, wherein the groove is a through hole.   6. The capacitive humidity sensor according to claim 1, wherein the pair of electrodes have a comb-teeth shape and are arranged so as to mesh with each other.   The capacitive humidity sensor according to claim 1, wherein a semiconductor substrate is used as the substrate, and the electrode is provided on the substrate via an insulating film.

Images