JPH0727733A - Capacitance type humidity sensor - Google Patents

Abstract

PURPOSE:To obtain a humidity sensor which shows superior safety in an environment of a high temperature and high humidities by using an aromatic polyamide thin film as a polymer humidity-sensitive film. CONSTITUTION:After Mo, Au films are continuously formed on an insulated substrate 31 having a terminal part 32 by sputtering, a resist pattern is formed by photolithography. Then, the resist pattern is etched to form a lower electrode 34. A humidity-sensitive film 35 is formed on the electrode 34 by vapor deposition by using aromatic polyamide over the metal-masked substrate 31. An upper electrode 36 of a specific thickness is further formed out of Au on the humidity- sensitive film 35 by vapor deposition. The change of the capacitance to the relative humidity of the humidity sensor holds a favorable correlation. Moreover, the relative humidity deviation is 4%RH in 1000 hours in an environment of such high temperature and high humidity as 60 deg.C and 90%RH.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type humidity sensor. More specifically, it relates to a capacitance type humidity sensor in which a lower electrode, a polymer moisture sensitive film and an upper electrode are sequentially formed on an insulating substrate.

[0002]

2. Description of the Related Art In a capacitance type humidity sensor in which a lower electrode, a polymer moisture sensitive film and an upper electrode are sequentially formed on an insulating substrate, one using a polyimide thin film as the polymer moisture sensitive film is first known. Proposed by the applicant (Japanese Patent Laid-Open No.
-19553 publication).

In this humidity sensor, the moisture-sensitive film is formed of a polyimide resin, which enables quick response due to thinning (less than several μm) and adjustment of film thickness. Although the objective of the period was achieved, further improvement was required in terms of stability under high temperature and high humidity environmental conditions such as 60 ° C-90% RH and 1000 hours.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitance type humidity sensor having excellent stability under high temperature and high humidity environmental conditions such as 60 ° C.-90% RH and 1000 hours. is there.

[0005]

The object of the present invention is as follows.
In a humidity sensor in which a lower electrode, a polymer moisture sensitive film and an upper electrode are sequentially formed on an insulating substrate, this is achieved by using an aromatic polyamide thin film as the polymer moisture sensitive film, more preferably the lower electrode-aromatic An oriented polyimide thin film is formed between the polyamide thin films.

In a capacitance type humidity sensor, the surface of a conductive electrode formed on an insulating substrate is covered with a polymer thin film, and a moisture permeable upper electrode is formed on the polymer moisture sensitive film. And a lower electrode composed of a conductive electrode sandwiching a polymer moisture sensitive film. The function of the capacitance-type humidity sensor is based on the principle that the change amount of the dielectric constant due to the change of the water content in the moisture sensitive film due to the humidity is detected as the change amount of the electrostatic capacitance.

Conventionally, the following two types of capacitance type humidity sensors have generally been generally adopted, and the same applies to the present invention. (1) As shown in FIGS. 2 (a) to 2 (c), a pair of opposed shapes having terminal portions 22 and 22 'on an insulating substrate 21 by applying a sputtering method or a vapor deposition method and a photolithography method. After the lower electrodes 23, 23 'are formed, the moisture-sensitive film 24 and the upper electrode 25 made of a vapor deposition film are successively formed in layers (2) As shown in (a) to (c) of FIG. A lower electrode 34 having a terminal portion 32 on an insulating substrate 31 and a large electrode portion 33
After forming the above, a moisture sensitive film 35 is formed on the electrode portion, and the upper electrode 36 having a shape symmetrical with the lower electrode is formed.
(Or a comb-shaped upper electrode) formed so that its electrode portion 37 is located on the moisture sensitive film and the terminal portion 38 is symmetrical to the terminal portion of the lower electrode.

As the insulating substrate, glass, alumina,
Quartz, a silicon wafer whose surface has been subjected to an insulation treatment, or the like is used.As the electrode material of the upper electrode and the lower electrode having the above-described structure, a conductor that can be thinned such as Au, Pt, or Al is used. It is performed by a vapor deposition method, a sputtering method, or the like. The patterning is performed by forming a resist pattern by photolithography and etching.

The aromatic polyamide moisture-sensitive film is obtained by subjecting an aromatic polyamide resin such as Kevlar 49 manufactured by DuPont or Technora manufactured by Teijin Co., Ltd. to an insulating substrate on which a lower electrode is formed, after performing a necessary masking with a metal mask. It is formed with a film thickness of about 1 to several μm by a method such as vapor deposition.

Although such an aromatic polyamide moisture sensitive film can be formed directly on the lower electrode, it is preferable to interpose an oriented polyimide thin film therebetween. The polyimide thin film to be oriented is formed by using a polyimide resin coating agent (which may be a commercially available product as it is), pre-baking it after spin coating,
The positive photoresist is spin-coated, pre-baked, exposed, and developed, and then the resist is removed and heat treatment is performed.

The orientation treatment of the polyimide thin film is carried out by applying a rubbing operation of rubbing in a certain direction with gauze, felt or the like to the polyimide thin film several times to ten times. When an aromatic polyamide thin film is formed on the oriented polyimide thin film by a vapor deposition method or the like, the aromatic polyamide thin film is naturally oriented.

[0012]

By using an aromatic polyamide thin film as the polymer moisture sensitive film of the capacitance type humidity sensor, the stability under high temperature and high humidity environmental conditions is improved. Such an improving effect is further enhanced by interposing a oriented polyimide thin film between the lower electrode and the aromatic polyamide thin film, and thereby orienting the aromatic polyamide thin film.

[0013]

EXAMPLES The present invention will now be described with reference to examples.

Example 1 On a glass substrate, 500 Å Mo and
After continuously forming u with a film thickness of 2000Å, a resist pattern was formed by photolithography, and then etching was performed to form a lower electrode having a shape shown in FIG. On the electrode, a moisture-sensitive film having a thickness of 2.2 μm was formed by vapor deposition on a metal-masked substrate using aromatic polyamide (Kevlar 49 manufactured by DuPont). Further, an upper electrode having a film thickness of 100 Å was formed of Au on the moisture sensitive film by a vapor deposition method.

Example 2 A lower electrode was formed on a glass substrate in the same manner as in Example 1, and a polyimide coating agent (Pyrarin SP P1-2570-D manufactured by DuPont Co., Ltd.) was spin-coated on this electrode for 10 seconds, and the temperature was raised to 100 ° C. Prebaking was performed for 3 minutes at -140 ° C for 3 minutes, and positive photoresist (Tokyo Ohka Products OFPR-
800) by spin coating, pre-baking at 85 ° C for 30 minutes, exposure, development and resist removal, followed by heat treatment at 200 ° C in air for 30 minutes and 350 ° C in nitrogen gas atmosphere for 30 minutes. A polyimide thin film (film thickness 0.5 μm) having the shape shown in FIG. 3B was formed.

The rubbing operation of rubbing the polyimide thin film in a certain direction with gauze was applied 10 times, masking was performed with a metal mask, and aromatic polyamide (Kevlar 49) was vapor-deposited to have the same shape as the polyimide thin film. The aromatic polyamide thin film (thickness: 1.7 μm) was formed.

Further, Au was vapor-deposited to form an upper electrode having a film thickness of 100 Å in the shape shown in FIG. 3 (c).

With respect to the capacitance type humidity sensor obtained in each of the above examples, when the change in capacitance with respect to relative humidity was measured under the following conditions, the results shown in the graph of FIG. 1 were obtained, A good correlation was confirmed there. Constant humidity chamber: Divergent precision humidity generator made by Shinei Measuring instrument: LCR meter made by YHP Condition: 30 ° C, 1V, 1KHz applied

With respect to these capacitance type humidity sensors, the stability in the high temperature and high humidity environment of 60 ° C.-90% RH and 1000 hours was measured as relative humidity deviation (when the capacitance drift amount is converted to relative humidity). Deviation; the smaller the drift amount, the better the stability), and the change amount was 4% RH in Example 1 and within 3% RH in Example 2.

On the other hand, in Example 2, after forming the polyimide thin film of 2.5 μm, the polyimide thin film was used as the moisture sensitive film without the alignment treatment and the formation of the aromatic polyamide thin film. The humidity sensor had a relative humidity deviation of 5% RH.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the relative humidity and the capacitance of a capacitance type humidity sensor in Examples 1 and 2.

FIG. 2 is a perspective view showing a manufacturing sequence of a conventional capacitance type humidity sensor.

FIG. 3 is a perspective view showing a manufacturing sequence of another conventional capacitance type humidity sensor.

[Explanation of symbols]

21, 31 Insulating substrate 23, 34 Lower electrode 24, 35 Aromatic polyamide thin film (and polyimide thin film) 25, 36 Upper electrode

Claims (2)

[Claims] 1. A humidity sensor in which a lower electrode, a polymer moisture sensitive film and an upper electrode are sequentially formed on an insulating substrate,
A capacitance type humidity sensor that uses an aromatic polyamide thin film as a polymer moisture sensitive film. 2. Between the lower electrode and the aromatic polyamide thin film,
The capacitance type humidity sensor according to claim 1, wherein a polyimide thin film subjected to orientation treatment is formed.