JPS5830101A - Method of producing humidity sensor element using aluminum anode oxide thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention is based on AI! The present invention relates to a method of manufacturing a humidity sensor element using a thin oxide film. Humidity 1 sensors have traditionally been used in some areas for humidity observation, but recently their use has rapidly expanded to include home appliances and the like.

Some sensors using Al films are already known. A typical example is the following.

(a) Patent Application No. 51-83507 (Moisture content detection element using anodized aluminum film) (b) Prototype production of moisture sensing element (Tokyo Metropolitan Industrial Technology Center Research Report No. 6;
1976, pp. 51-56) eU Anodization A/
Sealing Effects
ar the fiarier - Porous L
ayer 1interface of AnodicA
luminas; 5solidSate 5ienc
E, Sep., 1970) The manufacturing method will be explained very simply with reference to FIG. The figure is a plan view of this type of sensor element. In the figure, 1 is a ceramic substrate, 2 is a comb formed by vacuum evaporation or sputtering.
It is a thin film electrode shaped like <C>. That is, a thin film is formed using a valve metal such as Ti over the front surface of the substrate 1 by vapor deposition or sputtering, and then a desired comb-shaped electrode is formed by photoetching. Next, a thin aluminum film is formed on the entire surface of the comb-shaped electrode part by mask vapor deposition, and then a thin film 6 of oxidized AJ (indicated by loosely hatched lines) is formed by anodizing using an acid such as sulfuric acid or oxalic acid. do. Next, after the sensor element is completed, an Au terminal portion 4 is provided by a mask vapor deposition method in order to solder the external lead wire 5. After that, immerse the reading element 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 All terminal portion 4.

Although the sensor made as described above has many features, it also has some drawbacks.

(1) Hysteresis with respect to humidity is large.

That is, the conductance between the lead wires 5 and 5 in FIG. 1 increases as the humidity increases, but when the humidity decreases, the conductance value changes through a different path than when the humidity increases. The difference is huge.

A so-called hysteresis phenomenon occurs.

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

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

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

That is, in high humidity environments where the relative humidity is 80% R, H or higher, the sensitivity gradually increases and becomes unstable.

An object of the present invention is to provide a method for manufacturing an Al oxide thin film sensor element with excellent characteristics, which can be put to practical use by eliminating or significantly improving the above-mentioned drawbacks.

In order to achieve the above object, the method for manufacturing a humidity sensor element using an anodic oxide thin film of AJ according to the present invention provides a method for manufacturing a humidity sensor element using an anodic oxide thin film of AJ according to the present invention. Oxidized At produced by anodizing the Al thin film
! A temperature sensor element whose surface is coated with a surfactant is characterized in that it is subjected to high-temperature heat treatment in a vacuum immediately before coating with the surfactant. .

Next, the configuration of the present invention will be explained.

The present invention relates to an application filed by the same applicant, that is, Japanese Patent Application No. 56-008601 (hereinafter referred to as "previous application"), that is, an invention of a humidity sensor element, and a method of manufacturing the sensor element disclosed as an embodiment of the manufacturing method. This invention relates to improvements in manufacturing methods.

Therefore, we will first discuss the previous application very briefly.

The humidity level sensor element of the previous application uses the surface of oxidized AA' produced by anodizing an Al thin film provided over the entire surface of a thin pulp metal electrode formed on an insulating substrate.
It is characterized by being coated with a surfactant,
Ru.

In your invention, you have investigated in detail the reasons for the above-mentioned drawbacks (1) to (3), and have therefore clarified a method for improving them.As a result, you have provided the sensor element according to the invention of the previous application, and An example of the manufacturing method was described, and the effects of the sensor element were also described.

Since it would be complicated to repeat the above explanation over and over again, it will be omitted, and the manufacturing method according to the present invention will be described in detail immediately.

As described above, this manufacturing method belongs to an improvement of the manufacturing method detailed as an example of the manufacturing method of the humidity sensor according to the previous application, so there are many points that are essentially similar. That is, there are many points that overlap with the manufacturing method of the previous application, and therefore it indirectly shows the structure of the sensor of the previous application.

Next, the present invention will be explained using the following examples.

Referring to FIG. 1, high-purity alumina porcelain is used as the ceramic-free substrate 1, and the dimensions are 101101111X15.
×Q, 61111. Wash and dry this thoroughly.

Next, the substrate is placed in a high frequency sputtering bath, and a Ta film is sputtered on the surface. The film thickness is 2.0OOA. Next, a comb-shaped electrode 2 is formed by chemical etching.

The width of the comb teeth was 50'μm2 and the interval was 50μm.

Next, in a high vacuum, a thin diagonal line 6 is suspended in an electrolyte of dilute sulfuric acid or oxalic acid using a mask vapor deposition method to form an anode.

In this case, the resin layer is immersed up to the vicinity of the center line. This is done to prevent current concentration near the surface during anodic oxidation and to ensure that subsequent oxidation is performed uniformly over the entire surface. It is suspended inside and serves as a cathode. First, a constant current is passed between the positive and negative electrodes to sufficiently form the anode, and then constant voltage formation is performed using a slightly higher voltage to complete the anodic formation process.

In this case, Ta was used as the pulp metal. Although the definition of a metal is not clear today, it is said to be a metal that produces an insulator through anodization.

For example, Se, Ti, Ta, Nb, Hf, etc.

The necessity of using pulp metal in the anodizing process will be briefly explained with reference to FIG. 2. The figure is an enlarged sectional view of the comb-shaped electrode portion of FIG. 1. In the figure, the same parts as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted. The anodic oxidation starts from the surface of the A4 layer, then reaches the comb-like teeth of Ta, and the surface becomes an insulating layer of oxidized 'fa', and the oxidation of this part ends, thus gradually reacting to the deep part of the A1 layer. extends. Reference numeral 6 indicates an oxidized A1 layer, and reference numeral 21 indicates a metal Ta portion 22 indicating oxidized Ta. That is, the scattered electrode 2 is not made of pulp metal, but for example A.
When u, the oxide film 22 is not formed, so the chemical formation current is 2.
Therefore, the deep part of the A4 layer is not easily oxidized. Therefore, the circuit between 2 and 2 in FIG. 2 remains short-circuited.

Next, the reason for using Ta as the pulp metal is that the thickness of the oxide film 22 is extremely thin and dense compared to other pulp metals, and that oxidation will not progress further after it is made into a finished product. Due to the benefits. Therefore, if it is later used as a sensor element, it will be stable.

Shows excellent characteristics such as sensitivity.

After completion of chemical formation, the product is thoroughly washed and subjected to stabilization heat treatment at 30°C to 550°C for about 2 hours.

Next, the pores are thoroughly sealed in boiling pure water.

Finally, the nonionic surfactant polyoxyethylene alkyl phenylethe
AlkylPhenyl Ether; R00(
The process is completed by treating with 1 to 1 volume % liquid of CH2CH20)n H) and drying to form an active layer with a thickness of around α5 μm (previous application). The inventor's research has revealed that the following steps are added before treatment with the activator to significantly improve the Sentsu properties.

Next, this point will be explained in detail.

Conventionally, it has been said that the best heat treatment conditions for AJ oxide films are in the air at a temperature of 100 to 200 degrees Celsius for several hours to about 20 hours. (See Document 1 below) O Document 11 Magazine name: Humidity and Molture magazine 1965, 1. p, 572 Author: A, C, Jason Publisher: Re1nhold Publishing
Co.

U, S, A.

However, in our experiments, almost no stabilizing effect was observed in the sensor element according to the previously filed invention (its manufacturing method is as described above).

Next, when the processing conditions are set to 250° C. to 350° C. for 1 to 2 hours, the sensitivity increases somewhat, but returns to the original value with the passage of time. If the temperature is further increased to 400° C. or higher, the Ta electrode etc. will be oxidized and the characteristics will be significantly deteriorated.

However, the processing conditions were set to a degree of vacuum (101 to 10').

Treatment temperature (1gO~300℃), treatment time (1-2
) - ψ, and it was confirmed that immediately after the treatment, the sensor characteristics were significantly improved by immersing the sensor in the surfactant. Especially as the voltage applied to the sensor element (
5-10) Excellent characteristics can be obtained by using Herz's low frequency.

Next, I will briefly explain reason 1.

An Al film obtained by vacuum evaporation is generally a collection of microcrystals, and some of them react with water to form oxides during the anodic oxidation process, so they contain impurities. Therefore, even if the detailed pore sealing treatment described in the previous application is performed, it cannot be said that a dense alumite layer is necessarily formed on the surface.

The film formed on the surface in this way has (1.4 to 2.0) moles of crystal water, whereas axial frame boehmite has crystal water of 1 mole of Hzo per 1 mole of Altos. This is so-called pseudo-boehmite.

Furthermore, during anodic oxidation, a large amount of 804- ions or C2O4-
Ions remain. These factors contribute to adsorption with water and ionic conductivity, which becomes a factor that makes the sensor properties unstable.

Therefore, if we perform vacuum treatment at high temperature, the dehydration reaction and the aforementioned ions and gasified impurities will be removed.Therefore, after the treatment, the surface will be activated and will easily adsorb moisture, gas, etc. in the air. Immediately immersing in a surfactant for treatment allows the surfactant to penetrate evenly into the oxide film surface, pores, etc.

It is thought that the characteristics of the oxide film surface were significantly improved in this manner, resulting in a dramatic improvement in the characteristics.

The processing conditions are a temperature of 400℃ or higher and a vacuum level of 10".
-' ) - When the temperature exceeds 100 mm, evaporation and agglomeration of thin films such as Al and Ta occur (agglomeration).
ration), resulting in severe deterioration. The processing time may be 6 hours or more, but if the processing time is too long, the characteristics will deteriorate. In practice, the shorter the treatment time, the better; one to two hours is sufficient in most cases.

Furthermore, as it was explained in the previous application that a nonionic surfactant is desirable, the description will be omitted for the sake of brevity.

Next, the effect will be briefly described.

(The resensor characteristics, that is, the temperature characteristics, are greatly improved. Especially when excited at an extremely low frequency of 1OH2 or less, the improvements are remarkable.

The straight line (1) in FIGS. 6 to 6 is the characteristic of the sensor element of the present invention, and the curves (II) and (to) are the characteristics of the sensor element according to the previous application and the conventional sensor element. The measuring circuit is as shown in FIG. Resistance R shown as 1D in the figure
8 is a standard resistance, Rx resistance 11 is a sensor resistance, 1
2 is an amplifier, 1! 1 and 14 are negative feedback resistors.

Now, when an AC voltage of input voltage Vi is applied between input AB, and if the amplification degree of amplifier 12 is A, output terminal CD
The output voltage V between is clearly as follows.

Rx Vo = (□) Vi-A (1)
Rx 10Rs In the above measurement, Rs = 1.000MΩ.

A = 100 (select resistance 15.14 appropriately) Vi
= [L8V (frequency 6H7) was selected.

In other words, it is clear that the sensor produced by the manufacturing method of the present application has excellent characteristics.

Next, since the present application relates to an improvement of the invention of the previous application,
The sensor element produced by the manufacturing method of the present application has the following effects compared to conventional elements. That is, (2) the increase in conductor 7 with respect to humidity is large, especially when the relative humidity is 60% or more.

(3) The hysteresis phenomenon in the characteristic curve showing the relationship between humidity and conductance is small.

(4) If the thickness of the layer coated with surfactant is 1 μm or less, the response speed is fast.

(5) If the thickness of the activator layer is 1 μm or less, the activator layer will not peel off even after strong washing, and will not easily dissolve even at high temperatures.

[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 partially enlarged cross-sectional view of the comb-shaped electrode in Fig. 1, and Fig. 6 is a sensor element according to the present invention and the previous application. 4 is a graph showing the humidity characteristics with respect to a conventional sensor element. FIG. 4 is a circuit diagram for measuring the humidity characteristics. In the figure, 1... ceramic substrate 2... comb-shaped thin film electrode 3... oxidized AI thin film 4... terminal 5 of the comb-shaped electrode... lead wire. Agent Patent Attorney Oka 1) Goki Part Figure 1 Relative 1 degree (%) □ Procedural amendment (IT-kai) Date of December 1987 Commissioner of the Japan Patent Office Kazuo Wakasugi 1, Indication of the case 1988 Patent Application No. 128170 No. 2, invention. Name: Method for manufacturing a humidity sensor element using anodized thin film with AI 3, Relationship with the amended person case Patent applicant address: 615 Shimo-Okubo, Osawano-machi, Kamishinyo-gun, Toyama Prefecture
No. 8 Name) Hokuriku Electric Industry Co., Ltd. representative Masao Nakamura 4 Agent r-4ss (1)
460-60726, Number of inventions increased by amendment
None 7. Subject of amendment Contents of amendment In the detailed description of the invention in Book BAm, the following amendments are made. (1) Page 5 11100 1. Where it says "...Temperature sensor..."
・Humidity sensor..." I corrected it. (2) 1st line from the bottom of page 17 to 1st line of page 12. F. The phrase "impurities are removed and..." is corrected to "...impurities are mostly removed and...". (3) Page 14, line 12. The statement "The activator layer does not peel off even after vigorous washing" is deleted. (4) On page 15, in the 8th line, "4...Terminal of comb-shaped electrode" is replaced with "4...A".
s electrode terminal”.

Claims (1)

[Scope of Claims] 1.' A thin film formed on an insulating substrate (an AJ thin film provided over the entire surface of a loop metal electrode); , a method for manufacturing a humidity sensor element coated with a surfactant. 2. Claim 1, characterized in that a nonionic surfactant is used as the surfactant described in claim 1. 3. A method for producing a humidity sensor element using the anodized thin film of AJ as described in Item 3. 3. A method of manufacturing a humidity sensor element using an anodized thin film of AJ as described in Item 3. A method for manufacturing a humidity sensor element using the AI! anodized thin film as described in Scope 2. 4. Conditions for the high temperature heat treatment in vacuum as described in Paragraph 1: degree of vacuum (10-2 to 10') . Temperature (100-300)℃. Processing time (1-3) hours. A method for manufacturing a humidity sensor element using an anodic oxide thin film (AIC) according to claims 1 to 3, characterized in that: