JP2012145384A - Capacitive humidity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitive humidity sensor capable of restraining reduction in detection accuracy over time.SOLUTION: In a capacitive humidity sensor, a gradient of change in electrostatic capacity of a reference capacity section 30 is different from the gradient of the change in the electrostatic capacity of a detection section 20 by the following arrangements: an area of an upper electrode 22 opposite to a lower electrode 21 in the detection section 20 is equal to the area of an upper electrode 32 opposite to a lower electrode 31 in a reference capacity section 30; and a distance between the lower electrode 21 and the upper electrode 22 in the detection section 20 is different from the distance between the lower electrode 31 and the upper electrode 32 in the reference capacity section 30. Thus, in the capacitive humidity sensor, because holes formed on the upper electrodes 22 and 32 are clogged in the same way, the detection section 20 and the reference capacity section 30 change over time also in the same way. Therefore, the capacitive humidity sensor can restrain reduction in detection accuracy over time.

Description

  The present invention relates to a capacitive humidity sensor for detecting humidity, and more particularly to a capacitive humidity sensor having a detection unit and a reference capacitance unit for the detection unit.

  2. Description of the Related Art Conventionally, a capacitive humidity sensor is known in which a detection unit and a reference capacitance unit that change in capacitance according to a change in ambient temperature are formed on a substrate (see, for example, Patent Document 1). Specifically, such a capacitive humidity sensor is provided with two lower electrodes on a substrate. Then, on each lower electrode, a humidity sensing member whose capacitance changes according to humidity is arranged, and on each of the moisture sensing members, an upper electrode is arranged, and a detection unit and a reference that are stacked capacitive elements A capacitor portion is formed. The detection unit and the reference capacitance unit are electrically connected.

  The upper electrodes in the detection unit and the reference capacitance unit are each formed with a hole so that moisture can be supplied to the moisture sensitive member, and the surrounding moisture is adsorbed by the moisture sensitive member through the hole. . In addition, the area of the upper electrode facing the lower electrode in the detection unit is larger than the area of the upper electrode facing the lower electrode in the reference capacitance unit, and the inclination of the change in capacitance with respect to the humidity of the detection unit and the reference capacitance unit The slope of the change with respect to humidity is made different.

  In such a capacitive humidity sensor, the moisture constant of the moisture sensitive member changes due to the adsorption and desorption of moisture on the moisture sensitive member. Specifically, the moisture sensitive member is composed of, for example, a polymer material such as a polyimide-based polymer. Since the dielectric constant of moisture (water) is higher than the dielectric constant of the moisture sensitive member, Adsorption increases the dielectric constant. Therefore, the capacitance in the detection unit and the capacitance in the reference capacitance unit change according to the humidity, and the detection unit and the reference capacitance unit have different inclinations of the change in capacitance with respect to humidity. The relative humidity of the surroundings is detected from the difference between the capacitance of the reference capacitance and the capacitance of the reference capacitance portion.

JP 2007-248065 A

  However, in such a capacitive humidity sensor, the hole of the upper electrode may be clogged with foreign matters such as dust. In this case, in the capacitive humidity sensor, since the areas of the upper electrodes facing the lower electrodes in the detection unit and the reference capacitance unit are different from each other, the clogging method differs between the detection unit and the reference capacitance unit. That is, the amount of passage of the surrounding moisture by the upper electrode differs between the detection unit and the reference capacitance unit, and the manner of change with time is different. For this reason, for example, compared with the initial state, the method of changing the amount of moisture supplied to the moisture sensitive member differs between the detection unit and the reference capacitance unit, and there is a problem that the detection accuracy decreases with time. .

  An object of this invention is to provide the capacity | capacitance type humidity sensor which can suppress that a detection accuracy falls over time in view of the said point.

  In order to achieve the above object, according to the first aspect of the present invention, each of the detection section (20) and the reference capacitance section (30) is provided with a lower electrode (see FIG. 1) that is disposed opposite to the substrate (10) in the thickness direction. 21, 31) and upper electrodes (22, 32), and a humidity sensitive member (23) whose dielectric constant changes according to the humidity between the lower electrodes (21, 31) and the upper electrodes (22, 32). , 33), and the upper electrodes (22, 32) of the detection unit (20) and the reference capacitance unit (30) receive moisture from the moisture sensitive members (23, 33). ), The area of the upper electrode (22) facing the lower electrode (21) in the detection part (20), and the upper part facing the lower electrode (31) in the reference capacitor part (30) The area of the electrode (32) is made equal. The distance between the lower electrode (21) and the upper electrode (22) in the portion (20) and the distance between the lower electrode (31) and the upper electrode (32) in the reference capacitance portion (30) are different, so that the reference capacitance It is characterized in that the slope of the change in capacitance in the section (30) is different from that in the detection section (20).

  In such a capacitive humidity sensor, the area of the upper electrode (22) facing the lower electrode (21) in the detection section (20), and the upper electrode facing the lower electrode (31) in the reference capacitance section (30) ( 32). For this reason, the holes formed in the upper electrodes (22, 32) are clogged in the same manner, and the amount of the surrounding moisture passing through is similarly changed. That is, the detection unit (20) and the reference capacitance unit (30) change with time similarly. Therefore, it can suppress that detection accuracy falls over time.

  For example, as in the invention described in claim 2, the upper electrode (22) in the detection unit (20) and the upper electrode (32) in the reference capacitance unit (30) are configured using the same material, and the detection unit The moisture sensitive member (23) in (20) and the moisture sensitive member (33) in the reference capacity portion (30) can be configured using the same material.

  In such a capacitive humidity sensor, for example, a hole is formed in the upper electrode (22, 32) due to thermal stress caused by a difference in thermal expansion coefficient between the upper electrode (22, 32) and the moisture sensitive member (23, 33). When forming, the hole formed in the detection part (20) and the reference | standard capacity | capacitance part (30) can be made into the substantially same shape.

  Further, as in the invention described in claim 3, in addition to the detection unit (20) and the reference capacitance unit (30), signals from the detection unit (20) and the reference capacitance unit (30) are applied to the substrate (10). The signal processing circuit (60) for processing the signal is electrically connected, and the detection unit (20), the reference capacitor unit (30), and the signal processing circuit (60) are electrically connected through the wiring formed on the substrate (10). be able to.

  In such a capacitive humidity sensor, for example, compared to the case where the detection unit (20), the reference capacitance unit (30), and the signal processing circuit (60) are electrically connected by wire bonding, the interval between wire bondings is reduced. Parasitic capacitance can be eliminated and detection accuracy can be improved.

  Further, as in the invention described in claim 4, a protective film can be formed between the lower electrode (21, 31) and the moisture sensitive member (23, 33). In such a capacitive humidity sensor, for example, a hole is formed in the upper electrode (22, 32) due to thermal stress caused by a difference in thermal expansion coefficient between the upper electrode (22, 32) and the moisture sensitive member (23, 33). When forming, it can suppress that a thermal stress is relieve | moderated by a protective film and a crack etc. generate | occur | produce in a lower electrode (21, 31).

  Further, as in the invention described in claim 5, the lower electrode (21) in the detection section (20) and the lower electrode (31) in the reference capacitance section (30) can be configured by a common electrode. In such a capacitive humidity sensor, the lower electrode (21) in the detection section (20) and the lower electrode (31) in the reference capacitance section (30) are compared with the case where they are configured by separate electrodes. The pattern can be simplified.

  Then, as in the invention described in claim 6, the distance between the lower electrode (21) and the upper electrode (22) in the detection unit (20) is set to the lower electrode (31) and the upper electrode ( 32).

  Furthermore, as in the invention described in claim 7, a capacitor having a constant capacitance with respect to a temperature change is provided for the lower electrode (31) and the upper electrode (32) in the reference capacitor portion (30). be able to.

  In such a capacitive humidity sensor, the initial capacitance difference between the detection unit (20) and the reference capacitance unit (30) can be reduced by appropriately setting the capacitance value of the capacitor. Noise due to the difference can be suppressed.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a top view of the capacity type humidity sensor in a 1st embodiment of the present invention. It is AA sectional drawing of the capacity type humidity sensor shown in FIG. (A) is a figure which shows the relationship between the relative humidity and electrostatic capacitance of the detection part and reference | standard capacity | capacitance part in the conventional capacitive humidity sensor, (b) is the detection part and reference | standard capacity | capacitance in the capacitive humidity sensor of 1st Embodiment. It is a figure which shows the relationship between the relative humidity of a part and an electrostatic capacitance. It is a top view of the capacity type humidity sensor in a 2nd embodiment of the present invention.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a plan view of a capacitive humidity sensor according to the present embodiment, and FIG.

  As shown in FIGS. 1 and 2, a detection unit 20 and a reference capacitance unit 30 are formed on a semiconductor substrate 10 made of silicon or the like via an oxide film (not shown). Specifically, the detection unit 20 includes a lower electrode 21 and an upper electrode 22 that are disposed to be opposed to each other in the thickness direction of the semiconductor substrate 10, and the humidity is between the lower electrode 21 and the upper electrode 22. Accordingly, the multilayer capacitive element is provided with a moisture sensitive member 23 whose dielectric constant changes accordingly. Similarly, the reference capacitor unit 30 includes a lower electrode 31 and an upper electrode 32 that are disposed to be opposed to each other in the thickness direction of the semiconductor substrate 10, and according to humidity between the lower electrode 31 and the upper electrode 32. Thus, the multilayer capacitive element is provided with a moisture sensitive member 33 whose dielectric constant varies. The detection unit 20 and the reference capacitance unit 30 are electrically connected.

  The lower electrodes 21 and 31 are formed of Al, Al-Si or the like on the semiconductor substrate 10 via an oxide film, and the surface opposite to the semiconductor substrate 10 side is a silicon nitride film corresponding to the protective film of the present invention. Covered with In the present embodiment, these lower electrodes 21 and 31 are constituted by a part of the lower layer electrode 40 formed on the semiconductor substrate 10. In other words, the lower electrodes 21 and 31 are configured by a common electrode.

  In the present embodiment, the upper electrodes 22 and 32 have a rectangular shape smaller than the lower electrodes 21 and 31, respectively, and are made of Au, Cr, or the like. The holes for supplying the surrounding moisture to the moisture sensitive members 23 and 33, in other words, the plurality of holes (not shown) for exposing the moisture sensitive members 23 and 33 from the upper electrodes 22 and 32 are formed in substantially the same amount.

  Further, the area of the upper electrode 22 facing the lower electrode 21 in the detection unit 20 is made equal to the area of the upper electrode 32 facing the lower electrode 31 in the reference capacitance unit 30. That is, the upper electrodes 22 and 32 have a rectangular shape, and the holes for supplying moisture to the moisture-sensitive members 23 and 33 are formed in almost the same amount. Therefore, the holes surrounded by the long side and the short side are included. The areas are equal to each other. In this specification, the areas of the upper electrodes 22 and 32 facing the lower electrodes 21 and 31 are equal to each other, including the case where they are almost equal in addition to the case where they are completely equal, and 5% due to manufacturing errors or the like. This includes the deviation.

  Furthermore, in the present embodiment, the interval between the lower electrode 21 and the upper electrode 22 in the detection unit 20 is narrower than the interval between the lower electrode 31 and the upper electrode 32 in the reference capacitor 30. That is, the detection unit 20 and the reference capacitance unit 30 are configured such that the slopes of the capacitance with respect to the humidity change are different from each other by making the distance between the electrodes different. In other words, the detection unit 20 and the reference capacitor unit 30 have a sensitivity difference.

  The moisture sensitive members 23 and 33 are respectively formed on the lower electrodes 21 and 31 via a silicon nitride film, and are made of the same material having a hygroscopic polymer material made of polyimide polymer or the like. Yes. That is, in this embodiment, since the moisture sensitive members 23 and 33 are made of the same material, the dielectric constant is changed in the same manner according to the ambient humidity.

  The lower layer electrode 40 and the upper electrodes 22 and 32 are electrically connected to a CV conversion circuit 60 as a signal processing circuit formed on a substrate different from the semiconductor substrate 10 through bonding wires 51 to 53. The change in capacitance in the detection unit 20 and the reference capacitance unit 30 is processed by the CV conversion circuit 60.

  In such a capacitive humidity sensor, the moisture-sensitive members 23 and 33 absorb and desorb moisture from the portions not in contact with the upper electrodes 22 and 32 and the lower electrodes 21 and 31, so The electrostatic capacitance in the capacitor unit 30 changes. And since the inclination of the change of the electrostatic capacitance with respect to humidity differs mutually from the detection part 20 and the reference | standard capacity | capacitance part 30, from the CV conversion circuit 60, the electrostatic capacitance of the detection part 20 and the electrostatic capacitance of the reference | standard capacity | capacitance part 30 The ambient relative humidity is detected by converting the difference between the two into a voltage and outputting it to an external circuit.

  Next, a method for manufacturing the capacitive humidity sensor shown in FIG. 1 will be briefly described.

  First, the semiconductor substrate 10 is prepared and an oxide film is formed on the surface. Thereafter, a lower electrode layer including the lower electrodes 21 and 31 is formed by forming and patterning a lower electrode layer on the oxide film by vapor deposition or sputtering. Then, a silicon nitride film is formed so as to cover the lower layer electrode 40 by plasma CVD or the like. Thereafter, the moisture sensitive member 23 is formed on a predetermined region of the lower layer electrode 40, that is, the lower electrode 21, and the moisture sensitive member 33 is formed on the lower electrode 31. Specifically, the moisture sensitive member 23 is formed so that the film thickness of the moisture sensitive member 23 is smaller than the film thickness of the moisture sensitive member 33 by an inkjet method or the like.

  Thereafter, an upper electrode layer is formed so as to cover the moisture sensitive members 23 and 33 by vapor deposition, sputtering, or the like. Thereafter, the upper electrode layer is patterned by photolithography or the like to form the upper electrode 22 on the moisture sensitive member 23 and to form the upper electrode 32 on the moisture sensitive member 33.

  Subsequently, the semiconductor substrate 10 is heated, and thermal stress resulting from the difference in thermal expansion coefficient between the moisture sensitive members 23 and 33 and the upper electrodes 22 and 32 is applied to the upper electrodes 22 and 32, and the upper electrodes 22 and 32 are cracked. A hole including a tear and a tear is formed. This hole becomes a portion for supplying moisture to the moisture-sensitive members 23 and 33.

  In the present embodiment, the upper electrodes 22 and 32 are made of the same material, and the moisture sensitive members 23 and 33 are made of the same material. Is formed. Further, a silicon nitride film is formed on the lower electrode 40 including the lower electrodes 21 and 31, and the thermal stress caused by the difference in thermal expansion coefficient between the lower electrode 40 and the moisture sensitive members 23 and 33 is caused by the silicon nitride film. Since it is absorbed (relaxed), cracking of the lower layer electrode 40 is suppressed.

  As described above, in the present embodiment, the area of the upper electrode 22 facing the lower electrode 21 in the detection unit 20 is equal to the area of the upper electrode 32 facing the lower electrode 31 in the reference capacitance unit 30. .

  For this reason, clogging occurs in the holes formed in the upper electrodes 22 and 32 in the same manner, and the amount of the surrounding moisture passing through changes similarly. That is, the detection unit 20 and the reference capacitance unit 30 change with time almost equally, and it is possible to suppress a decrease in detection accuracy over time.

  FIG. 3A is a diagram showing the relationship between the relative humidity and capacitance of the detection unit and the reference capacitance unit in the conventional capacitive humidity sensor, and FIG. 3B is the detection unit in the capacitive humidity sensor of the present embodiment. It is a figure which shows the relationship between the relative humidity of 20 and the reference | standard capacity | capacitance part 30, and an electrostatic capacitance. In FIG. 3, the initial capacitance is indicated by a solid line, and the capacitance after change with time is indicated by a broken line.

  In the conventional capacitive humidity sensor, for example, the area of the upper electrode facing the lower electrode in the reference capacity portion is smaller than the area of the upper electrode facing the lower electrode in the detection portion. For this reason, as shown in FIG. 3A, after the change with time, the electrostatic capacity at the relative humidity of 0% RH is the reference capacity with respect to the initial state (solid line in FIG. 3A). The portion of the reference capacitance portion is greatly reduced, and the inclination of the capacitance with respect to the humidity change is also greatly reduced.

  On the other hand, in the present embodiment, the detection unit 20 and the reference capacitance unit 30 change with time similarly. Therefore, as shown in FIG. 3 (b), after the change over time, the electrostatic capacity at the relative humidity of 0% RH is the same as that in the initial state (solid line in FIG. 3 (b)). And the slope of the capacitance with respect to the humidity change is also reduced by the same amount. That is, it can suppress that the detection accuracy after a time-dependent change falls.

(Second Embodiment)
A second embodiment of the present invention will be described. The capacitive humidity sensor according to the present embodiment includes the CV conversion circuit 60 on the semiconductor substrate 10, and the other aspects are the same as those of the first embodiment, and thus the description thereof is omitted here. FIG. 4 is a plan view of the capacitive humidity sensor in the present embodiment.

  As shown in FIG. 4, the capacitive humidity sensor in the present embodiment has a detection unit 20, a reference capacitance unit 30, and a CV conversion circuit 60 formed on a semiconductor substrate 10. The lower electrodes 21 and 31 and the upper electrodes 22 and 32 and the CV conversion circuit 60 are electrically connected by a pattern wiring or the like formed on the semiconductor substrate 10. That is, compared with 1st Embodiment, it is set as the structure which is not provided with a bonding wire.

  In such a capacitive humidity sensor, the bonding wires connecting the lower electrodes 21 and 31 and the upper electrodes 22 and 32 and the CV conversion circuit 60 are eliminated as compared with the first embodiment. Can eliminate the parasitic capacitance generated in the above, and improve the detection accuracy.

(Other embodiments)
In the first and second embodiments, the capacitance of the lower electrode 31 and the upper electrode 32 constituting the reference capacitance unit 30 is constant with respect to temperature change, and the detection unit 20 and the reference capacitance unit It is also possible to provide a capacitor having a capacity that reduces the initial capacitance difference from 30, for example, the capacitance difference at 0% RH relative humidity (preferably 0). In such a capacitive humidity sensor, noise due to an initial capacitance difference can be suppressed as compared with a case where the capacitor is not provided.

  Moreover, although the said 1st, 2nd embodiment demonstrated the example which comprised the moisture sensitive members 23 and 33 with the same material, the moisture sensitive members 23 and 33 can also be comprised with a different material. Similarly, the upper electrodes 22 and 32 can be made of different materials.

  Furthermore, in the first and second embodiments, an example in which the interval between the lower electrode 21 and the upper electrode 22 in the detection unit 20 is narrower than the interval between the lower electrode 31 and the upper electrode 32 in the reference capacitor unit 30. As described above, for example, the interval between the lower electrode 21 and the upper electrode 22 in the detection unit 20 may be wider than the interval between the lower electrode 31 and the upper electrode 32 in the reference capacitor unit 30.

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 20 Detection part 21 Lower electrode 22 Upper electrode 23 Moisture sensitive member 30 Reference capacity part 31 Lower electrode 32 Upper electrode 33 Moisture sensitive member

Claims (7)

A detection unit (20) in which the capacitance changes in accordance with a change in ambient humidity, and a change in capacitance in accordance with a change in ambient humidity and the inclination of the change in capacitance with respect to a change in humidity is the detection unit (20 In the capacitive humidity sensor, a reference capacitance unit (30) different from) is formed on the substrate (10), and relative humidity is detected from an output difference between the detection unit (20) and the reference capacitance unit (20).
Each of the detection unit (20) and the reference capacitance unit (30) includes a lower electrode (21, 31) and an upper electrode (22, 32) that are arranged to be opposed to each other in the thickness direction of the substrate (10). And having a moisture sensitive member (23, 33) whose dielectric constant changes according to humidity between the lower electrode (21, 31) and the upper electrode (22, 32). And
Holes for supplying moisture to the moisture sensitive members (23, 33) are formed in the upper electrodes (22, 32) of the detection unit (20) and the reference capacitor unit (30), respectively.
The area of the upper electrode (22) facing the lower electrode (21) in the detection unit (20) and the upper electrode (32) facing the lower electrode (31) in the reference capacitance unit (30). The area is equal,
The interval between the lower electrode (21) and the upper electrode (22) in the detection unit (20), and the interval between the lower electrode (31) and the upper electrode (32) in the reference capacitance unit (30) The capacitance humidity sensor is characterized in that the difference in the capacitance of the reference capacitance unit (30) is different from that of the detection unit (20). The upper electrode (22) in the detection unit (20) and the upper electrode (32) in the reference capacitance unit (30) are configured using the same material,
The said moisture sensitive member (23) in the said detection part (20) and the said moisture sensitive member (33) in the said reference | standard capacity | capacitance part (30) are comprised using the same material. The capacitive humidity sensor described in 1. In the substrate (10), in addition to the detection unit (20) and the reference capacitance unit (30), a signal processing circuit for processing signals from the detection unit (20) and the reference capacitance unit (30) ( 60)
The detection unit (20), the reference capacitor unit (30), and the signal processing circuit (60) are electrically connected via a wiring formed on the substrate (10). The capacitive humidity sensor according to claim 1 or 2.   The capacitance according to any one of claims 1 to 3, wherein a protective film is formed between the lower electrode (21, 31) and the moisture sensitive member (23, 33). Humidity sensor.   The said lower electrode (21) in the said detection part (20) and the said lower electrode (31) in the said reference capacity | capacitance part (30) are comprised by the common electrode, The 1 thru | or 4 characterized by the above-mentioned. The capacitive humidity sensor according to any one of the above.   The interval between the lower electrode (21) and the upper electrode (22) in the detection unit (20) is greater than the interval between the lower electrode (31) and the upper electrode (32) in the reference capacitance unit (30). 6. The capacitive humidity sensor according to claim 1, wherein the humidity sensor is narrow.   The capacitor having a constant capacitance with respect to a temperature change is provided for the lower electrode (31) and the upper electrode (32) in the reference capacitance section (30). The capacitive humidity sensor according to any one of 1 to 6.

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