JPS584441B2 - Moisture content detection element using aluminum anodic oxide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a moisture content detection element using an anodic oxide film of aluminum without an active layer.

Conventionally, anodic oxide films of aluminum have been used as moisture content detection elements, but they have the disadvantage that sensitivity decreases in high humidity.

The reason for the decrease in sensitivity at high humidity is the presence of an active layer in the aluminum oxide film produced during anodic oxidation.

As a countermeasure, a method of chemically dissolving and removing the active layer and aluminum substrate is currently being considered.

However, the membrane produced by this method has low mechanical strength;
Difficult to handle.

An object of the present invention is to obtain a moisture content detection element that avoids a decrease in sensitivity at high humidity and has extremely strong mechanical strength by utilizing an anodic oxide film of aluminum without an active layer.

The present invention will be explained based on examples as follows.

Example 1 Titanium is deposited on a ceramic substrate to a thickness of about 1.0 μm by vapor deposition or sputtering.

When a vapor deposition method is used, a comb-shaped transmission mask is brought into close contact with the substrate during vapor deposition to form a comb-shaped electrode of the titanium film.

When using the sputtering method, titanium is deposited over the entire surface of the ceramic substrate, and then comb-shaped electrodes are formed by photo-etching.

A diluted hydrogen fluoride solution is used as the etching solution.

Aluminum is deposited to a thickness of about 0.5 μm on the substrate on which interdigitated electrodes are formed by any of the above methods.

At this time, both ends of the electrode are covered to prevent aluminum from adhering.

Next, both ends of the comb-shaped electrode are short-circuited, and oxidation is performed using this as an anode.

A 15% sulfuric acid aqueous solution is used as the electrolytic solution, and a current of 4 A/dm2 is supplied from a constant current source.

Oxidation of the aluminum film begins when current is started, and when the active layer reaches titanium, oxidation of the titanium electrode begins.

During the oxidation of titanium, oxidation of aluminum takes place over the entire surface.

When the electrodes are removed from the electrolytic solution after applying a voltage of about 60 V, the comb-shaped electrodes are completely separated by an oxide layer.

If a material without valve action, such as gold, is used as an electrode instead of titanium, the oxidation of the aluminum is only partially completed.

The reason is that when the oxidation of aluminum partially reaches the gold, the electrical resistance of that part is not large enough like the oxide of the valve metal, so current concentration occurs, and the current is transferred to other, not yet oxidized parts. This is because it does not pass through the aluminum part.

In this case, since the metal aluminum remains, the comb-shaped electrodes are in a short-circuited state and do not function as a moisture content detection element.

After anodizing, a sealing treatment is performed in boiling water for about 30 minutes to reduce changes in characteristics over time.

Finally, a conductive adhesive is applied to the electrode portion and lead wires are attached to form an element.

A cross-sectional view of the completed moisture content detection element is shown in FIG. 1, and its characteristics are shown in FIGS. 3 and 4.

Example 2 Aluminum is deposited to a thickness of about 0.5 μm on a titanium substrate.

Anodic oxidation of aluminum is performed using the titanium substrate as an anode, and the pores are sealed.

The conditions are the same as in Example 1.

Next, a gold water-permeable electrode is deposited onto the aluminum oxide.

Lead wires are taken out from the electrode and the titanium substrate using a conductive adhesive to form a moisture content detection element.

A cross-sectional view of the device is shown in FIG. 2, and its characteristics are shown in FIGS. 3 and 4.

Although the elements manufactured according to Example 1 and Example 2 have different shapes, their operations are similar.

The electrical resistance and capacitance of both aluminum oxide and titanium oxide change depending on the moisture content.

The electrical impedance of the entire element is that of the two connected in series.

As can be seen from FIGS. 3 and 4, the sensitivity of the moisture content detection element according to the present invention does not decrease even at high humidity.

Furthermore, since it is fabricated on a substrate, it has sufficient mechanical strength and is easy to handle.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the device manufactured according to Example 1, and FIG.
The figure is a cross-sectional view of the device according to Example 2, and FIGS. 3 and 4 are graphs showing the characteristics of the resistance value and capacitance value with respect to relative humidity of the detection element obtained in the example of the present invention. Codes in figures 1 and 2: 1; Ceramic substrate, 2
; titanium electrode; 3; titanium oxide layer; 4; aluminum oxide layer; 5; titanium substrate; 6; water-permeable electrode (gold). Symbols in FIGS. 3 and 4: I: Characteristic curve of Example 1, Ij Characteristic curve of Example 2, ■: Characteristic curve of a device having a conventional aluminum active layer.

Claims (1)

[Claims] 1. It is characterized by having no active layer, which is produced by attaching an aluminum film to a valve metal such as titanium or tantalum, and performing anodic oxidation in an electrolytic solution such as oxalic acid, sulfuric acid, or chromic acid, using the valve metal as an anode. A method for manufacturing a moisture content detection element using an anodic oxide film of aluminum.