JPH0318750A - Humidity sensor element - Google Patents

Abstract

PURPOSE:To obtain the humidity sensor element which obviates the generation of the deterioration in characteristics, is small in size and has high production efficiency by specifying the total area of an insulating substrate surface in contact with a humidity sensitive film and comb-shaped electrodes to a specific area. CONSTITUTION:The humidity sensor element is obtd. by successively forming the comb-shaped electrodes, the moisture sensitive film and a protective film on the insulating substrate. The transverse length of the substrate is designated as L1, the longitudinal length of the substrate as L2, the longitudinal length at which the moisture sensitive film sticks as L3 and the longitudinal length at which the moisture sensitive film does not stick as L4 at this time. While the surface area over the entire part of the insulating substrate is 5X7=35mm<2>, the surface area to be stuck with the moisture sensitive film is 5X5.5=27.5mm<2> if, for example, L1 is assumed to be 5mm, L2 to be 7mm and L3 to be 5mm. The total area of the comb-shaped electrodes in this area is 0.5X22.5=11.25mm<2> as the electrode width is 0.35mm and the overall length of the comb-shaped electrode is 22.5mm. The adhesive strength of the moisture sensitive film is enhanced and the stability to a long-term change in temp. is obtd. by specifying the total area of the comb-shaped electrodes to <=3cm<2> and the area ratio of the surface area of the insulating substrate in contact with the moisture sensitive film and the comb-shaped electrode to 1.3 to 10:1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a humidity sensor element that utilizes the fact that the electrical resistance characteristics of the element change in response to environmental humidity.

[Prior Art] With the rapid development of electronics, various environments are being controlled. Generally, the types of environment are temperature and humidity, but in the case of humidity, there is a lack of good humidity sensors due to problems with reliability and temperature characteristics, and there is a strong demand for them.

[Problem to be solved by the invention] It is well known that porous silica membranes have moisture-sensitive properties, and they have excellent reliability and temperature characteristics, but humidity sensor elements using this as a moisture-sensitive membrane have not been put into practical use. Not yet.

The reason for this is that the structure of a humidity sensor is generally one in which a comb-shaped electrode is fabricated on a substrate, and a moisture-sensitive film is attached on top of the comb-shaped electrode, but the only way to do this is to use the sol-gel method. However, when this sol-gel method is used, problems such as poor adhesion between the electrode material of the comb-shaped electrode and the silica film, such as the silica film peeling off from the substrate, have been a barrier to practical use. Therefore, in the present invention, the above-mentioned problems can be easily solved, and the object thereof is to provide an excellent humidity sensor cord with high reliability and good temperature characteristics using a sol-gel method silica film.

[Means for Solving the Problems] The humidity sensor element of the present invention is a humidity sensor element in which a comb-shaped electrode, a moisture-sensitive film, and a protective film are sequentially formed on an insulating substrate. It is characterized in that the total area of the contacting insulating substrate surface and the comb-shaped electrode is 3 cm2 or less.

The humidity sensor element of the present invention is characterized in that the ratio of the surface area of the insulating substrate in contact with the humidity sensitive film to the area of the comb-shaped electrode is 1.3 to 10:1.

The humidity sensor element of the present invention is characterized in that the main component of the moisture sensitive film is porous silica.

The humidity sensor element of the present invention is characterized in that the protective film is made of porous silicon.

[Example-1] Fig. 1(a) is a block diagram of an insulating substrate and a comb-shaped electrode pattern of the present invention, where L1 is the horizontal length of the substrate, L2 is the vertical length of the substrate, and L3 is the Vertical length to which the moisture sensitive film adheres, L4
is the vertical length of the moisture-sensitive film without adhesion, l1 is the electrode width of the comb-shaped electrode, 12 is the space between the electrodes, and 13 is the space around the outer periphery. The specific dimensions are 5mm for L+ and 7mm for L2.
, L3 is 5.5 mm, the total surface area of the insulating substrate is 5×7=35 mm2, but the surface area to which the moisture-sensitive film is attached is 5×5.5=27.5 mm2. Among these, the total area of the comb-shaped electrode is 0.5 x 2 2. since the electrode width is 0.5 mm and the total length of the comb-shaped electrode is 22.5 mm.
It becomes 511.25mm2. Therefore, the breakdown of the surface area (27.5 mm2) to which the moisture sensitive film adheres is that the electrode area is 11.25 mm2.
mm2, the substrate area is 16.25 mm2, and the area ratio is 1 (electrode area) to 1.44 (substrate area). In order to attach a moisture sensitive film using this electrode-equipped substrate, the substrate is immersed in a silica sol solution to a distance of L3 and then pulled up. The composition of the silica sol solution at this time was 50 m of tetraethoxysilane (Si (OCzHs)4).
Add 25 ml of ethanol and 4 ml of 0.02N hydrochloric acid to l, stir, and then add 16 g of finely powdered silica + 10 ml of glycerin.
By adding . Further, if necessary, impurities (carbon, metal powder, etc.) may be added to the silica sol solution for resistance adjustment. After being attached in this manner, it was dried at room temperature and then heat treated at 500°C to complete the process. The cross-sectional structure of the completed humidity sensor element is shown in FIG. 1(b).

1 is an insulating substrate, 2 is an electrode extraction part, 3 is a comb-shaped electrode, 4
is a moisture sensitive membrane. When we investigated the adhesion strength and moisture sensitivity characteristics of the moisture-sensitive film of this completed temperature sensor element, we found that the adhesion strength of the moisture-sensitive film was determined by cellotape peeling test (total area of substrate) and drop strength test at 2 m height (5 times). There were no problems during repeated tests, and although the impedance was somewhat high, the linearity was excellent as shown in Figure 2. Furthermore, in terms of reliability, we conducted a storage test at 100℃ for 1000 hours, but the change from the initial value was only 0.5%.
It was good.

[Example-2] A humidity sensor was prototyped using the same method as in Example-1.

At this time, the area of the comb-shaped electrode was changed to check the adhesion strength with the moisture-sensitive membrane. The results are shown in Table 1 below.

Table-1 In Table-1 above, the substrate area to which the moisture-sensitive film can be attached is 2
It is based on 7.5 mm2, and the comb-shaped electrode area is calculated by keeping the number of comb teeth constant and changing only the electrode width. To explain an example of the area ratio in Table 1, the area ratio of 13.5 mm2, which has the largest electrode area, is 27.5 mm2-13.
5 mm2:=14 mm2, 13.5 (comb-shaped electrode area) to 14 (substrate area), which is 1 to 1.03. With this area, as shown in Table 1, there was a problem with the adhesion strength, which did not reach the commercial level. On the other hand, when the comb-shaped electrode has an area of 9 mm2, the area ratio to the substrate is approximately 1:2, and at this level, there is no problem in adhesion strength.

[Effects of the Invention] The present invention, as shown in the examples above, uses porous silica for the moisture-sensitive membrane, and the relative ratio of the area of the substrate in contact with the porous silica membrane to the area of the comb-shaped electrode is 1.3 to 10:1. By doing so, it is possible to provide a highly reliable humidity sensor element that does not exceed the adhesion strength of the moisture sensitive film.

Another advantage is that by reducing the sum of the surface area of the substrate and the total area of the comb-shaped electrodes to 3 cm2 or less, it is possible to easily provide a small sensor element, and since it does not have an unnecessary size, production efficiency is high and it can be manufactured at low cost. It's also effective.

Furthermore, since porous silica is used for the temperature-sensitive film, the function of the sensor element has the effect that there is almost no deterioration in characteristics over long periods of high temperature, low temperature, high temperature, and low humidity.

In addition, in the examples, the comb-shaped electrode area is expressed by specifying the number of comb-shaped electrodes, but of course the number of comb-shaped electrodes, the length of the comb teeth, etc. are not specified, and the area of the insulating substrate is expressed. As long as the ratio of the area of the comb-shaped electrode and the area of the comb-shaped electrode is in the range of 1.3 to 10:1, the shape of the comb-shaped electrode is not restricted.

[Brief explanation of drawings]

FIG. 1(a) is an explanatory diagram of an electrode in the present invention. FIG. 1(b) is a sectional view of a humidity sensor element prototyped according to the present invention. FIG. 2 is a diagram showing the humidity sensitivity characteristics of the humidity sensor of the present invention. 1...Insulating substrate 2...Electrode extraction part 3...Comb-shaped electrode 4...Moisture sensitive membrane 1111111-1 9i or more

Claims (4)

[Claims] (1) In a humidity sensor element in which a comb-shaped electrode, a moisture-sensitive film, and a protective film are sequentially formed on an insulating substrate, the total area of the insulating substrate surface and the comb-shaped electrode in contact with the humidity-sensitive film is 3 cm^ A humidity sensor element characterized in that the humidity is 2 or less. (2) The humidity sensor element according to claim 1, wherein the ratio of the surface area of the insulating substrate in contact with the humidity sensitive film to the area of the comb-shaped electrode is 1.3 to 10:1. (3) The humidity sensor element according to claim (1), wherein the main component of the humidity sensitive film is porous silica. (4) The humidity sensor element according to claim (1), wherein the protective film is made of porous silica.