JPH0114536B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity sensing element using a valve metal oxide layer, and particularly to a humidity sensing element comprising a valve metal oxide layer and conductive electrodes located at different locations on the oxide layer. The present invention relates to a capacitance variable humidity sensing element.

Conventionally, as a method for detecting humidity, an Assmann psychrometer, a hair type, an optical type, an electronic type humidity sensor, etc. have been used. Each method has the following advantages and disadvantages. That is, although the Assmann psychrometer is capable of highly accurate measurement, it requires labor to handle and maintain, and continuous recording using electrical output is difficult. Although the hair formula is easy to use, it does not provide accurate humidity values. Since the optical humidity measurement method measures the dew point, it is easy to perform highly accurate measurements and can be output as continuous electrical output, but it is expensive.

In response to these, many so-called "electronic humidity sensors" have recently been developed, with a wide variety of methods and demand in various fields. Typical of these are moisture-sensitive materials such as lithium chloride, ceramic mixtures of magnesium pinel and titanium oxide, zinc oxide, organic resins with conductive metal particles dispersed in them, and porous Aluminum oxide film (dielectric valve metal oxide film)
One example is a capacitance changing type that consists of a semiconductor layer and a counter electrode (dielectric organic polymer).
These "electronic humidity sensors" are the dry-wet type mentioned above,
Compared to hair type, optical type, etc., it is simple and inexpensive.
It has features such as continuous humidity output, and meets the needs of various current electronic devices.

However, in terms of measurement accuracy and reliability,
There is still room for improvement, and the current situation is that it is desired to develop an "electronic humidity sensor" with even higher performance and reliability.

In view of these circumstances, the present invention provides a humidity sensing element that is smaller, cheaper, has higher performance, is highly reliable, and has excellent mass productivity. The valve metal oxide layer is basically composed of a valve metal oxide layer such as a conductive oxide film, and conductive electrodes located at a plurality of spaced apart positions on the oxide layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific content of the present invention will be described below with reference to the drawings, taking as an example a case where a dielectric oxide film on a valve metal substrate is used as a valve metal oxide layer.

FIG. 1 is a schematic cross-sectional view of the humidity sensing element of the present invention, showing a dielectric anodic oxide film 2 on a valve metal base 1.
and conductive electrodes 3a and 3b present on the dielectric anodic oxide film 2. The conductive electrodes 3a, 3b are present at a plurality of spaced apart locations on the dielectric anodic oxide film 2.

Here, the interaction between atmospheric humidity and the tantalum oxide film will be described.

FIG. 2 shows the correlation between the degree of hydration of tantalum oxide and the relative pressure p/p ₀ (corresponding to relative humidity) of water vapor in the atmosphere in which tantalum oxide is placed.

As shown in FIG. 2, in tantalum oxide, the number of hydrated water molecules per molecule of tantalum oxide changes in proportion to the relative humidity. That is, the value of n in Ta ₂ O ₅ ·nH ₂ O is proportional to the relative humidity. This hydration reaction is
This is thought to occur due to reversible adsorption and desorption of H ₂ O molecules on the tantalum oxide film in proportion to the relative humidity, and the adsorption/desorption response speed is also very fast.

As a result of such a reversible hydration reaction of the tantalum oxide film, the structure of the dielectric anodic oxide film existing between the two electrodes changes as shown in FIG.
In addition, in Fig. 3, 1' is tantalum base, 2
a' is a tantalum oxide film, 2b' is a hydrated tantalum oxide film, and 3a' and 3b' are conductive electrodes.

That is, the thickness of the tantalum oxide film 2a' is A ₂ ,
The thickness of the hydrated tantalum oxide film 2b' is A ₁ , the thickness of both is A ₁ +A ₂ = A, the distance between both electrodes 3a' and 3b' is l, the length of the opposing electrode is B, tantalum oxide Let the dielectric constant of the film 2a′ be ε ₂ =
28. If the dielectric constant of the hydrated tantalum oxide film 2b' is ε ₁ (however, 28<ε ₁ <82) and the dielectric constant of water is 82, then the capacitance detected between the electrodes 3a' and 3b' is C is as follows: C=C ₁ +C ₂ =ε ₁ A ₁ ×B/l+ε ₂ A ₂ ×B/l =B/l (ε ₁ A ₁ +ε ₂ A ₂ ) (1). FIG. 4 is an equivalent circuit of this part.

As can be seen from equation (1), the degree of hydration is low at a humidity of 0% RH, and A ₁ O (in Figure 2, 0
%RH, n = 1.6, but here there is no problem even if it is A ₁ O), and C ₀ = B/lε ₂ A ₂ ...(2), and the tantalum oxide film 2a' The capacitance caused only by this is detected from both electrodes 3a' and 3b'.

In a high humidity atmosphere, the tantalum oxide on the surface
It _is hydrated in proportion _to the relative _humidity Since ε ₂ =28 and 28<ε ₁ <82, Cx>Co.

In the end, from A ₁ ∝XRH%, A ₂ ∝1/XRH%, and ε ₁ > ε ₂ , Cx=B/l(ε ₁ A ₁ +ε ₂ A ₂ )∝x, and the electrodes 3a' and 3b' The capacitance value Cx detected during this period is proportional to the relative humidity.

Here, a water vapor permeable semiconductive metal oxide layer may be formed between the tantalum oxide layer and the electrode. This layer contains, for example, manganese, nickel, lead,
Since it is formed from an oxide of a metal such as ruthenium and has semiconductivity, it not only maintains ohmic contact with the valve metal oxide layer, but also the aforementioned valve metal oxide layer. Mediates hydration at the layer surface. That is, a valve metal oxide layer,
By existing in the detected atmosphere, moisture is adsorbed to a uniform metal oxide layer, such as a manganese dioxide layer, and through the process of adsorption of this moisture to the valve metal oxide layer, the moisture absorption and desorption buffer is reduced. play a role.

In addition to tantalum as mentioned above, titanium, aluminum, germanium, silicon, or an alloy thereof may be used as a valve metal as a material for a humidity sensing element having such a structure and principle.
In addition, as for the shape of the conductive electrodes 3a and 3b, if they are formed at separate locations on the dielectric anodic oxide film 2, the basic conditions will be satisfied, but when considering the area efficiency per unit area, , a comb-like shape as shown in FIG. 5 is desirable. This conductive electrode can be formed by metal evaporation spraying, thick film firing, coating of conductive paint, etc. As the conductive paint, an organic resin which itself has conductivity, so-called "silver paint", and a material in which conductive metal powder is dispersed in the organic resin can be considered.

In addition, in the above explanation, the dielectric anodic oxide film 2 on the valve metal base 1 was used as an example of the valve metal oxide layer, but for example, a vapor deposited film, a sputtering film, a thick film fired body, etc. of the valve metal oxide may be used. It can also be used and has a humidity detection function based on the same principle as the dielectric anodic oxide film 2 described above.

Next, examples of the present invention will be described.

Example 1 A tantalum film measuring 10 mm x 10 mm and having a thickness of 1 μm was deposited on a ceramic substrate. On this tantalum film,
At room temperature, 0.01 mole/oxalic acid, current density 1A/ ^cm2
Form a tantalum oxide film of 500 Å. A pair of comb-shaped electrodes are formed on this tantalum oxide film as a deposited gold layer.

FIG. 6 shows the appearance of the humidity sensing element according to this example, and FIG. 7 shows the relative humidity dependence of the capacitance detected between the two electrodes of this element. In FIG. 6, 4 is a ceramic substrate, 5 is a tantalum vapor deposited film, and a tantalum oxide film 6 is present on the surface of this tantalum vapor deposited film 5. 7a and 7b are a pair of conductive electrodes, and the capacitance between these electrodes changes depending on the humidity. 8 is the lead.

Example 2 A tantalum oxide layer (thickness: 1 μm) is formed on a ceramic substrate by a reactive sputtering method. A pair of comb-shaped electrodes are formed on this tantalum oxide layer by vapor deposition of gold. FIG. 8 shows the characteristics of a humidity sensing element using this method.

Example 3 A pair of comb-shaped electrodes are formed on a ceramic substrate by vapor deposition of gold. A tantalum oxide layer with a thickness of 0.3 μm is formed by reactive sputtering so as to cover the entire surface of the electrode. A pair of leads are taken out from the electrode between the ceramic substrate and the tantalum oxide layer. FIG. 9 shows the external appearance of a humidity sensing element produced by this method, and the humidity characteristics of this element are also shown in FIGS. 7 and 8. In addition, in FIG. 9, 9a, 9
b is a deposited gold current, and 10 is a tantalum oxide layer.

Example 4 A tantalum oxide layer (thickness: 1 μm) is formed on a ceramic substrate by a reactive sputtering method.
A manganese dioxide layer (thickness: 10μ) is formed on the tantalum oxide layer by thermally decomposing manganese nitrate with a specific gravity of 1.5 at 300°C. A pair of comb-shaped electrodes are formed on this manganese dioxide layer by vapor deposition of gold. FIG. 10 is an external view thereof, and in the figure, 11 is a tantalum oxide layer, 12 is a manganese dioxide layer, and 13a and 13b are a pair of comb-shaped electrodes.

As described above, the humidity sensing element of the present invention has a simple structure, is inexpensive, has excellent mass production, has a capacitance value that changes linearly according to relative humidity, and is easy to use from a circuit. be.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the humidity sensing element of the present invention, and FIG.
The figure shows the relationship between the hydration of tantalum oxide and relative humidity. 4 is an equivalent circuit diagram of the tantalum oxide part in FIG. 3, FIG. 5 is a plan view showing an example of a comb-shaped electrode, FIG. 6 is a perspective view showing a humidity sensing element according to an embodiment of the present invention, and FIG. FIG. 8 is a characteristic diagram of a humidity sensing element according to another embodiment of the present invention, and FIGS. 9 and 10 are characteristic diagrams of a humidity sensing element according to still another embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1... Valve metal base, 2... Dielectric anodic oxide film, 3a, 3b, 7a, 7b... Conductive electrode, 5
...Tantalum vapor deposited film, 6...Tantalum oxide film, 9
a, 9b... Vapor deposited gold electrode, 11, 11... Tantalum oxide layer, 12... Manganese dioxide layer, 13a,
13b...Comb-shaped electrode.

Claims (1)

[Scope of Claims] 1. A base body, a valve metal oxide layer provided on the base body, and pairs of valve metal oxide layers present at a plurality of spaced apart locations on the surface of the valve metal oxide layer opposite to the base body. A humidity sensing element comprising a conductive electrode. 2. The humidity sensing element according to claim 1, characterized in that a semiconductive metal oxide layer is formed on the valve metal oxide layer. 3. The humidity sensing element according to claim 2, wherein the semiconductive metal oxide layer is composed of at least one of oxides of manganese, lead, nickel, and ruthenium. 4. The humidity sensing element according to claim 1 or 2, wherein the valve metal oxide layer is a dielectric anodic oxide film on a valve metal substrate. 5. Claim 1, characterized in that the valve metal base is tantalum, aluminum, titanium, silicon, germanium alone or an alloy thereof.
The humidity sensing element according to item 1 or 2. 6. Humidity detection according to claim 1 or 2, wherein the valve metal base is any one of a vapor deposited film, a plate, a wire, a sprayed film, and a thick film fired body of valve metal. element. 7. Humidity detection according to claim 1 or 2, wherein the conductive electrode is at least one of a thermally sprayed metal film, a vapor deposited film, a thick fired layer, and a conductive paint. element. 8. The humidity sensing element according to claim 1 or 2, wherein the conductive electrodes are two comb-shaped electrodes separated from each other.