JPH0244023B2 - ALNOYOKYOKUSANKAHAKUMAKUOMOCHIITASHITSUDOSENSASOSHIOYOBISONOSEIZOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a humidity sensor element using an anodic oxide thin film of Al and a method for manufacturing the same.

[Prior Art] Humidity sensors have traditionally been used in some areas for humidity observation, but recently their applications have been rapidly expanded to include home appliances and the like.

Some sensors using Al oxide thin films are already known. The representative ones are as follows.

(a) Japanese Patent Application Publication No. 53-9595 (Japanese Patent Application No. 51-83507)
"Moisture content detection element using anodized thin film of aluminum" (b) Prototype of moisture sensing element (Tokyo Metropolitan Industrial Technology Center Research Report No. 6; 1976, pp. 51-56) (c) Anodized Al Sealing treatment effect
Effects near the Barrier―Porous Layer
Interface of Anodic Aluminas；Solid State
Science, Sep, 1970) The structure and manufacturing method of a humidity sensor element using a general anodic oxidation thin film of Al will be briefly explained with reference to FIG. The figure is a plan view of this type of sensor element, in which 1 is a ceramic substrate, 2 is a ceramic substrate;
is a thin film-like comb-shaped electrode formed by vacuum evaporation or sputtering. This comb-shaped electrode 2 is made by forming a thin film over the entire surface of the substrate 1 by vapor deposition or sputtering using a valve metal such as Ti.
This thin film is formed by photoetching into a desired comb shape. Next, an aluminum thin film is formed on the electrode part of the comb-shaped electrode 2 by mask vapor deposition, and then an anodic oxidation thin film 3 of Al (anodized aluminum thin film 3) is formed by anodic oxidation using an acid such as sulfuric acid or oxalic acid. (indicated by diagonal lines). Next, in order to solder the external lead wire 5 after the sensor element is completed, a terminal portion 4 of Au is formed by a mask vapor deposition method. After that, the element was immersed in boiling pure water for about 30 minutes.
A so-called sealing process is performed, and finally the lead wire 5 is soldered to the Au terminal portion 4.

[Problem to be solved by the invention] The humidity sensor element manufactured as described above is
It has the following drawbacks.

(1) Hysteresis against humidity is large.

The conductance between the lead wires 5, 5 in FIG. 1 increases as the humidity increases. However, when the humidity decreases, the conductance value decreases through a different route (bus) than when the humidity increases, and the difference becomes large. A so-called hysteresis phenomenon occurs.

(2) In low humidity, sensitivity gradually decreases over time.

That is, the conductance value and the slope of its change with respect to humidity between the lead wires 5 decrease with time.

(3) Sensitivity increases and becomes unstable in high humidity.

Generally, in high humidity environments with relative humidity of 80% RH or higher, sensitivity gradually increases and becomes unstable.

(4) In particular, the humidity sensor element having the structure shown in FIG. 1 has a relatively high input impedance.

Although the structure is different from that shown in FIG. 1, the humidity sensor element shown in the above-mentioned Japanese Patent Laid-Open No. 53-9595 is designed to lower the input impedance. In other words, this humidity sensor element has a structure in which an anodic oxide thin film layer of Al is sandwiched between a pair of thin film electrodes, and the impedance between the two thin film electrodes is made capacitive to reduce input impedance. However, in this structure, since the impedance is capacitive, there is a problem that the sensitivity to humidity is considerably reduced.

An object of the present invention is to provide a humidity sensor element with a structure using comb-like electrodes, which has low input impedance.
An object of the present invention is to provide a humidity sensor element using an Al anodized thin film.

Another object of the present invention is to provide a method for manufacturing a humidity sensor element using an anodic oxidation thin film of Al, which can produce a humidity sensor element with low input impedance at a high yield.

[Means for Solving the Problems] The present invention includes a pair of comb-shaped electrodes made of a thin valve metal formed on an insulating substrate, and an Al anode provided on the electrode portions of the pair of comb-shaped electrodes. The present invention is directed to a humidity sensor element comprising an oxide thin film. In the present invention, the anodized thin film is coated with a conductive metal thin film having water permeability in order to lower the input impedance.

In the manufacturing method of the present invention, in order to prevent the impedance from decreasing to the extent that it cannot be used when an anodized thin film is coated with a water permeable conductive metal thin film, one of the water permeable conductive metal thin films is coated with a water permeable conductive metal thin film. An appropriate voltage is applied to the pair of comb-shaped electrodes to short-circuit the comb-shaped electrodes or to self-recover the portion where the insulation resistance between the pair of comb-shaped electrodes is reduced.

[Function] When a water-permeable conductive metal thin film is provided on an anodic oxide thin film of Al, the impedance between the opposing electrode pieces of a pair of comb-shaped electrodes is connected in parallel, and the input impedance becomes low. .

When the thickness of the anodic oxidized Al thin film becomes thin, the fine particles of the water permeable conductive metal thin film approach the comb-shaped electrode through the pores of the porous anodic oxidized Al film, lowering the impedance more than necessary. When an appropriate voltage is applied between a pair of comb-shaped electrodes, particles that approach the comb-shaped electrodes are instantly vaporized, and the insulation is restored (self-recovery).

[Example] Next, the configuration of the present invention will be explained.

FIG. 2 is a plan view of one embodiment of the present invention. In FIG. 2, the same parts as those shown in FIG. 1 are given the same reference numerals and their explanation will be omitted. 2
1 shows a part of a conductive metal thin film having water permeability, which is a feature of the present invention. In reality, the conductive metal thin film 21 having water permeability completely covers the portion of the anodic oxide thin film 3 of Al shown by rough hatching, but it is shown as shown in the figure for convenience of explanation.

The ceramic substrate 1 is made of high-purity alumina porcelain and has dimensions of 10 mm x 15 mm x 0.6 mm. Wash and dry this thoroughly. Next, this substrate 1 is placed in a high frequency sputtering bath, and a Ta film is sputtered on the surface. The film thickness is 2000 Å. Next, a comb-shaped electrode 2 is formed by chemical etching. The width of the comb teeth is 50μ
m, and the interval was 50 μm.

Next, a thin Al film 3 (thickness 5000 Å to 7000 Å) and an Au terminal portion 4 were formed by mask evaporation in a high vacuum.
form. Next, an insulating band with a width of several mm is formed between the Al thin film 3 and the terminal portion 4.

Next, put the board 1 in common with the terminal part 4, and
A portion of the thin film 3 is suspended in an electrolytic solution of dilute sulfuric acid or oxalic acid to serve as an anode. In this case, the insulator is immersed up to the vicinity of the center line of the range several mm wide. This is done in order to prevent current from concentrating near the surface during anodic oxidation and to ensure that subsequent oxidation is performed uniformly over the entire surface. Next, a piece of Ta, which is a highly pure valve metal, is suspended in the electrolyte to serve as a cathode. First, a constant current is passed between the negative and anode electrodes to sufficiently form the anodizing material, and then a constant voltage forming process is performed using a slightly higher voltage to complete the anodic forming process.

Regarding the necessity of using a valve metal during anodization and the chemical phenomena during anodization, please refer to the above patent application.
Since it was explained in detail in No.-008601 (Japanese Unexamined Patent Publication No. 57-124401), the explanation will be omitted.

After completion of chemical formation, the product is thoroughly washed and stabilized heat treated at 300°C to 350°C for about 2 hours.

Next, seal the holes thoroughly in boiling pure water. As for the sealing treatment,
This has been explained in detail in Japanese Patent Application No. 56-008601 (Japanese Unexamined Patent Publication No. 57-124401), so the explanation will be omitted.

Next, an Au water-permeable conductive metal thin film 21 is deposited on the surface of the Al anodized thin film 3 of the substrate 1 in a high vacuum. The relationship between the thickness of the deposited Au film and the surface resistivity (hereinafter abbreviated as specific resistance) ρ' (Ω/□) is shown in FIG. 3 when actually measured. Therefore, by monitoring the value of ρ', the film thickness can be determined. According to experimental results, good results are obtained when the thickness of the water-permeable conductive metal thin film of Au is in the range of 500 Å to 2000 Å.
Especially around 2000Å is good. Finally, connect lead wire 5 to Au
Solder it to the terminal section 4 of.

According to the humidity sensor element of the above embodiment, the following effects can be obtained.

(1) Since the input impedance is low, a circuit consisting of a standard resistor, an amplifier (hereinafter abbreviated as an amplifier), etc. of a humidity measuring circuit using this element is stable and inexpensive.

(2) made by the same applicant as the applicant;
The sensor element according to the invention of Japanese Patent Application No. 56-008601 (Japanese Unexamined Patent Publication No. 57-124401) showed good characteristics at an excitation frequency of around 10 Hz, but the characteristics deteriorate when the excitation frequency exceeds 50 Hz. This humidity sensor element is 10Hz~
Shows good characteristics over a wide range of 100kHz. Therefore, the range of application becomes very wide.

When measuring the insulation resistance of the products completed in this way, it was found that there were many cases in which the terminal resistance (input impedance) between 5 and 5 was lower than necessary. In particular, this tendency becomes more pronounced as the thickness of the Al anodic oxide thin film 3 becomes smaller. This phenomenon becomes an obstacle to increasing production yield. As a result of the research, the layer of Al anodized thin film 3 is
It has been found that when the thickness is thin, it is quite porous. Then, on top of the oxide film 3
When Au is deposited, the porous parts are filled with Au molecules. That is, when expressed as a model, its cross section is represented by a structure as shown in FIG. In Figure 4, 1 is the substrate, 3 is the layer of Al anodized thin film 21
is a layer of conductive metal thin film with water permeability of Au. 2a and 2b represent two adjacent pieces of a comb-shaped electrode. Then, as is clear from Figure 2, if you measure the resistance between terminals 5 and 5, you will end up measuring the resistance between the comb teeth, so if the structure is as shown in Figure 4, 2a The resistance between -2b will obviously be extremely small, and in extreme cases it will be shot by fine Au particles.

The present inventor has discovered that if an appropriate voltage is applied between 2a and 2b, the Au fine particles that approach the electrode will vaporize in an instant, and the insulation between 2a and 2b will be restored, that is, self-recovery (self-recovery). healing;
I realized that it is possible to do self-healing. According to the experimental results, it was found that when the Au film thickness is about 2000 Å or less, self-healing ends in an extremely short time and the insulation is restored.

That is, when the thickness of the Al anodized thin film 3 shown in FIG.
130V to 150V is appropriate, and the self-healing time also depends on the thickness of the Al anodic oxide thin film 3, but if the film thickness is as described above, it may take less than 1 second, so in practice it can take as long as 10 seconds. I confirmed that it was sufficient. In any case, it turned out that the yield problem could be solved in this way. Note that it is desirable that the self-healing voltage be as small as possible.
This is because if the size is too large, the anodic oxide thin film 3 of Al will be damaged and the sensor characteristics will be adversely affected. Also, if the voltage is too low, self-healing will not occur. A suitable voltage can therefore be easily determined by experiment. The self-healing voltage mentioned above was determined through experiments. By the way, self-healing technology has been used in the production of capacitors using metallized paper for a long time. However, the manner in which the self-healing technique is utilized in the present invention is different from that of metallized paper capacitors.

Finally, in order to further stabilize and improve the properties as a sensor, it may be treated with a nonionic surfactant polyoxyethylene alkyl phenyl ether. Regarding the technology, a patent application and a patent application filed in 1982 by the same applicant as the present applicant are disclosed.
128170 (Japanese Unexamined Patent Publication No. 58-30101), the detailed description is omitted.

Briefly discuss the effects obtained through self-healing techniques.

(i) By developing self-healing technology, a conductive metal thin film with water permeability is provided.
Sensor elements with low input impedance can be easily mass-produced, and therefore can be provided at low cost.

(ii) By performing self-healing under appropriate conditions, it has become possible to maintain high insulation resistance between electrodes. Therefore, sensor characteristics can be maintained safely.

(iii) If the thickness of the Al oxide layer is 5000 Å to 7000 Å, a self-healing voltage of 130 V to 150 V is sufficient, and the application time may be practically 10 seconds or less.

[Effects of the Invention] According to the humidity sensor element of the present invention, in the humidity sensor element using an anodic oxide thin film of Al on the comb-shaped electrode, a water permeable conductive metal thin film is placed on the anodic oxide thin film of Al. As a result, the impedance between the opposing electrode pieces of a pair of comb-shaped electrodes can be connected in parallel without affecting humidity detection, and as a result, the input impedance of the element can be significantly lowered. can do.

According to the manufacturing method of the present invention, when fine particles of a water-permeable conductive metal thin film approach a comb-shaped electrode through the pores of a porous Al anodized thin film and the impedance decreases more than necessary, By applying an appropriate voltage between a pair of comb-shaped electrodes to vaporize the fine particles that have come close to the comb-shaped electrodes, insulation can be easily restored and product yields can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a film type (including thin film type) sensor element, Fig. 2 is a plan view of a humidity sensor element according to the present invention, and Fig. 3 shows the relationship between the thickness of the Au deposited film and the surface resistivity. The graph shown in FIG. 4 is a schematic cross-sectional view of a portion including a substrate, a comb-shaped electrode piece, an anodic oxidation thin film layer of Al, and a conductive metal thin film having water permeability. 1... Ceramic substrate, 2... Comb-shaped electrode, 3... Al
anodized thin film, 4...terminal part, 5...lead wire, 2
1...A conductive metal thin film having water permeability.

Claims (1)

[Claims] 1. A pair of comb-shaped electrodes made of a thin-film valve metal formed on an insulating substrate, and a pair of comb-shaped electrodes provided on the electrode portions of the pair of comb-shaped electrodes.
A humidity sensor element using an anodic oxide thin film of Al, characterized in that the anodic oxide thin film is coated with a conductive metal thin film having water permeability. Humidity sensor element using 2 The conductive metal thin film is made of Au, Ag, Cr, Ni
A humidity sensor element using an anodic oxidation thin film of Al according to claim 1, characterized in that it is a non-rusting metal thin film. 3 Au is used as the conductive metal thin film,
A humidity sensor element using an anodic oxide thin film of Al according to claim 2, characterized in that the film thickness is 500 Å to 2000 Å. 4. Forming a pair of comb-shaped electrodes made of thin film valve metal on an insulating substrate, and forming an anodic oxidation thin film of Al by anodizing the Al thin film on the electrode portions of the pair of comb-shaped electrodes. a step of covering the anodic oxidation thin film of Al with a conductive metal thin film having water permeability; short-circuiting between the pair of comb-shaped electrodes of the conductive metal thin film having water permeability; Manufacturing a humidity sensor element using an anodic oxide thin film of Al, which comprises the step of applying an appropriate voltage between the pair of comb-shaped electrodes to self-recover the portion where the insulation resistance between the comb-shaped electrodes is reduced. Method.