JPH02151753A - Laminated structure type humidity sensor element - Google Patents

Abstract

PURPOSE:To simplify a measuring circuit and to impart excellent water resistance to said circuit by laminating an inner electrode layer and a humidity- sensitive layer and further providing an outer electrode. CONSTITUTION:Inner electrode layers 1 and humidity-sensitive layers 3 are alternately laminated to form a multilayer structure and external electrode layers 2 are provided to one sets of the opposed surfaces crossing the laminated surfaces of the formed laminate and the electrode layers 1 are alternately connected to the electrode layers 2. By this constitution, detection sensitivity is enhanced and humidity-to-electrostatic capacity shows excellent linearity. Further, since a temp.-to-humidity coefficient is constant in a usual total temp.- humidity region, a measuring circuit is simplified and reduced in its change with the elapse of time, and stability and excellent water resistance can be imparted to said circuit.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a moisture sensitive layer containing (Pb, La) (Zr, Ti).
) The present invention relates to a laminated structure humidity sensor element that uses an Os sintered body and whose capacitance changes according to changes in humidity.

[Conventional technology]

Conventionally, there are temperature sensor elements whose electrical resistance changes in response to atmospheric humidity and temperature sensor elements whose capacitance changes in response to atmospheric humidity. As capacitive humidity sensor elements, organic polymers include cellulose acetate, cellulose acetate butyrate, polyimide, etc., and inorganic types include thin film A 1 z03,
There are TazOs-MnOz and the like.

[Problem to be solved by the invention]

In conventional capacitive humidity sensor elements, the measurement range in which capacitance changes in response to humidity is around 1 to 90 pF, and the range of change in capacitance is small, making it difficult to measure with high precision in many cases. On the other hand, if we try to solve the range of change in capacitance, we have to complicate the structure and shape of the humidity sensor element.
There are some that require considerable ingenuity in manufacturing methods, etc., and that pose problems in terms of strength. Furthermore, conventional humidity sensor elements generally suffer from large changes over time and have poor salt resistance.

The present invention aims to solve these problems, and also utilizes a single layer type (Pb, La) (Zr
, Ti)Oz-based sintered body (Japanese Unexamined Patent Publication No. 62-216963) is further developed, and the objective is to provide a humidity sensor element that is stronger and has better detection sensitivity. That is.

[Means for solving the problems] For this purpose, the laminated structure type humidity sensor element of the present invention has a multilayer structure in which internal electrode layers and moisture sensitive layers are alternately laminated, and a layer that is perpendicular to the laminated surface of the laminated body is provided. It is characterized in that external electrode layers are provided on a pair of opposing surfaces, and the internal electrode layers are alternately connected to the opposing external electrode layers, and the moisture sensitive layer is made of an organic polymer. For molecular systems, cellulose acetate, cellulose acetate butyrate, polyimide, etc. can be used, and for inorganic systems, thin films Al z03, TazOs-MnOz, etc. can be used, but from the viewpoint of moisture sensitivity, the basic composition (Pb1-XLax) ( Zr, Tt+-y)
l-X/40sO<x≦0.25 Q<y
< 1 is preferably used.

Further, the ferroelectric metal oxide sintered body having the above basic composition may contain re, Si, Na, etc.
It is desirable to contain at least 98% or more of the metal oxide having the above basic composition.

There is no particular limitation on the number of laminated humidity sensor layers, but if the humidity sensor element has a small number of laminated layers and a large laminated surface area as shown in Figure 1, ruthenium oxide paste may be used as the electrode layer forming material. For baking, it is best to use a conductive material with moisture permeability as the electrode material when forming the electrode, such as a film or a vapor deposited film of gold, platinum, etc., and create a shape that has moisture permeability from the laminated surface. As shown in the figure, when the number of laminated layers is increased, the laminated surface is formed into a narrow shape, and moisture permeability is imparted to the side surface of the laminated body where no external electrode is provided, there is no particular restriction on the electrode layer forming material. The shape of the humidity sensor element is preferably cubic, but any shape can be adopted as long as it does not change the gist of the present invention, and the shape, number of laminated layers, area of the laminated surface, etc. The material for forming the electrode layer can be selected appropriately.

The method for laminating the humidity sensitive body layer and electrode layer is to coat a molded humidity sensitive body with a paste-like electrode material and then layer the humidity sensitive body, or to stack the humidity sensitive body layer by coating the pasted electrode material on the molded humidity sensitive body, and then stacking the humidity sensitive body layer by coating the pasted electrode material on the molded humidity sensitive body and then laminating the humidity sensitive body layer. It can be made into a paste with a binder and laminated by alternately coating it with a paste electrode material.

The thus formed laminate is pressed in the direction of the laminated surfaces, and external electrodes are formed on a pair of opposing sides of the laminate by coating with a conductive material that may be the same as or different from the internal electrode material. The humidity sensor element of the present invention can be obtained by alternately connecting internal electrode layers to opposing external electrode layers and firing as shown in FIG.

The thinner the thickness of the moisture sensitive layer is, the better, but it is preferable to set the thickness to such a level that there is no electrical conduction between the electrodes.

[Effect]

The capacitance of the laminated structure type humidity sensor element of the present invention is expressed by the following formula.

C = ε Therefore, in order to obtain high capacitance with a constant volume and thereby increase the range of change in response to humidity changes, the number of laminated layers n should be increased.
It is better to increase the temperature, reduce the thickness d of the moisture sensitive layer, and use a material with a high dielectric constant.

The present invention has a multilayer structure as a humidity sensor element, and uses metal oxides (Pb, L
a) It has been found that a humidity sensor element that satisfies the above formula can be obtained by specifically using a (Zr, Ti)03-based sintered body.

If the moisture sensitive layer is a single layer, the firing temperature must be lowered in order to increase the surface area so that it can take in more moisture, and as a result, the strength is insufficient.However, the present invention By creating a multilayer structure like this, it is possible to ensure strength even at low firing temperatures, and even if the surface area is slightly smaller due to higher firing temperatures, the actual electrode area is large, so the sensitivity range is wide. There are advantages. Therefore, the humidity sensor element of the present invention has high detection sensitivity, is easy to manufacture, has strength, has little change over time, and has excellent water resistance.

Examples will be described below with reference to the drawings.

[Example 1] FIG. 1 is a perspective view of a laminated structure type humidity sensor element of the present invention,
FIG. 2 is a perspective view showing another form of the laminated structure type humidity sensor element of the present invention, and FIG. 3 shows the humidity sensitivity characteristics of the laminated structure type humidity sensor element of the present invention at each frequency at 30°C. The figure shown,
Figures 4 and 5 show the capacitance C at each relative humidity at 20''C, 130''C and 40'C, and the capacitance C at 0% relative humidity.
It is a diagram showing the relationship between the logarithm value of the difference from 0 and relative humidity,
In the figure, 1 is an internal electrode, 2 is an external electrode, 3 is a moisture sensitive layer, and 4 is a lead wire.

As starting materials, PbO, (, at03, Zr0z, ,
After mixing Ti0z in a molar ratio of 0.91:0.45:0.64:0.34, kneading and drying using a vibration mill, calcining at 700°C, first, the calcined product raw material Obtained. This calcined product raw material was further compression molded at 1000 kg/cm2, and then heated at 1150'C for 20 to 20 minutes in an oxygen and PBO atmosphere.
It was sintered under normal pressure for 40 hours. Incidentally, the pbo atmosphere can be formed by adding 0.06 mol more to the above starting materials.

This baked crystal is crushed using a crusher and dried to obtain a raw material for a humidity sensitive body, and then this raw material for a humidity sensitive body is shaped into a shape of 6×6nu++ square and 0.5III+ thick using a binder.
A molded body was formed by pressure molding at 200 kg/cm'', and then baked at 1000'C for 2 hours to form a flat plate-shaped wet and dry body.

The specific surface area of this fired product was measured by the nitrogen adsorption method using the BET method, and the pore volume was measured by the mercury intrusion method.
The results are shown below.

Specific surface area 0.50 m”/g pore volume
0.04ml/g Note that once the fired product is pulverized and then re-fired, a uniform composition can be obtained, and it is possible to maintain stable moisture sensitivity characteristics for a long period of time.

Next, as shown in FIG. 1, RuO2 paste was applied to the surface of the moisture sensitive body, and further moisture sensitive bodies were laminated on the coated surface, which was repeated to assemble a laminate consisting of five moisture sensitive body layers. Internal electrodes 1 are applied to both the upper and lower surfaces of the laminate at a 4×4+w+++ angle. In forming the electrode layer, as shown in FIG. 1, the electrode layer is not coated on the entire surface of the moisture sensitive element layer, but is applied alternately up to the ends of the opposing sides of the moisture sensitive element. Next, external electrode layers 2 are formed by applying RuO□ paste to both sides of this laminate. In this way, the external electrode layers and the internal electrode layers can be alternately connected to opposing external electrode layers.

The obtained laminate was crimped from the laminate surface and heated to 850'C11.
After baking for 5 minutes, a lead wire is finally attached to the external electrode layer 2 to produce a laminated structure type humidity sensor element of the present invention.

The measurement results regarding the moisture sensitivity characteristics of this element are shown in Section 3.4.5.
Figure 3 shows 100Hz at 30°C, IKIIz,
10Kllz.

This is a diagram showing the humidity sensitivity characteristics for each frequency of 100 Hz, and it can be seen that the humidity sensor element of the present invention has a large variation range at low frequencies such as IKIIz, which is commonly used, and is suitable for practical use. , and its capacitance is also 0% relative humidity.
The initial value of capacitance is as high as about 1 nF or more, making it easy to measure changes in capacitance.

Also, Fig. 4 shows the frequency of I KHz, and Fig. 5 shows the frequency of 10 KHz.
20°C and 130°C respectively at a frequency of KHz
Relationship between relative humidity at 140°C and the logarithm of the difference between the capacitance C at each relative humidity and the capacitance C (capacitance of the humidity sensitive body) at 0% relative humidity This is a diagram showing
The humidity sensor element of the present invention can obtain good linearity at 30% RH or higher when measured at a frequency of 1 MHz, and
It can be seen that when measured at 0KIIz, good linearity can be obtained at 1O%RH or higher. In addition, especially as a moisture-sensitive material (
When a Pb, La) (Zr, Ti) 03-based sintered body is used, the range of change (gradient) in capacitance for each relative humidity at each measurement temperature is the same, making it possible to create a humidity sensor that is stable at each temperature. Moreover, this allows the hygrometer to be configured with a fixed circuit configuration such as an hour wheel. The temperature characteristics were 0°6% RH/'C for both IKHz and 10KIIz.

In addition, the humidity sensor element of the present invention responds to humidity changes from 30 to 90% RH1 and from 90 to 30% RH within 2 minutes, and even when immersed in water for 60 minutes, the humidity sensitivity characteristics change. It was also found that it is an excellent humidity sensor element that does not.

As shown in FIG. 2, when the number of laminated layers was set to 20, a humidity sensor element was manufactured using a co-stamp in the same manner as in the above example, and it exhibited similar moisture sensitivity characteristics.

[Comparative example]

A moisture-sensitive body (6 x 611
I11 corner, thickness 0. 5+wm) A Ru0z paste was fired at 4Xb on both the upper and lower surfaces of one sheet for 15 minutes to form a porous RuO□ electrode.

Next, after attaching lead wires to the external electrodes, the moisture sensitivity characteristics were measured under the same conditions as shown in FIG. The results are shown in FIG.

As can be seen from FIG. 6, the single-layer humidity sensor element has a lower capacitance than the laminated humidity sensor element of the present invention, and the range of change with respect to changes in humidity is also smaller.

Further, when the relationship between relative humidity and capacitance corresponding to FIG. 4.5 was determined, it was found that good linearity could only be obtained at 60% R0 or more.

(Effects of the Invention) The present invention provides a capacitive humidity sensor element in which internal electrode layers and moisture sensitive layers are alternately laminated to form a multilayer structure, and a set of opposing surfaces perpendicular to the laminated surface of the laminated body. By providing a laminated structure humidity sensor element in which an external electrode layer is provided and the internal electrode layers are alternately connected to the opposing external electrode layers, the detection sensitivity is high and the humidity versus capacitance is shows excellent linearity over a wide range, and the temperature vs. humidity coefficient is constant over the entire normal temperature-humidity range, making it possible to simplify the measurement circuit, and to ensure that the change over time is small (and stable). This allows a humidity sensor element with excellent water resistance.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a laminated structure type humidity sensor element of the present invention, FIG. 2 is a partially cutaway perspective view showing another form of the laminated structure type humidity sensor element of the present invention, and FIG. Figures 4 and 5 are diagrams showing the humidity sensitivity characteristics for each frequency at 30°C of the laminated structure humidity sensor element of the present invention, and Figures 4 and 5 are at 20°C.
Capacitance C and relative humidity O at 30'C and 140°C
FIG. 6 is a diagram showing the relationship between the logarithm of the difference from the capacitance C0 in % and the relative humidity, and FIG. 6 is a diagram showing the humidity sensitivity characteristics of a conventional single-layer humidity sensor element. In the figure, 1 is an internal electrode, 2 is an external electrode, 3 is a moisture sensitive layer, and 4 is a lead wire. Figure 1 Figure 2 Applicant Shinagawa White Brick Co., Ltd. Agent Patent Attorney (1) Nobuhiko (5 others) Figure 3 Relative Humidity'/, RH Figure 5 Relative Temperature'/, RH Figure 4 Relative Temperature '/, RH off size 5JL &'/-RH

Claims (2)

[Claims] (1) Internal electrode layers and moisture sensitive body layers are alternately laminated to form a multilayer structure, and external electrode layers are provided on a set of opposing surfaces perpendicular to the laminated surfaces of the laminate, and the opposing external electrode layers are provided. A humidity sensor element with a laminated structure, characterized in that the internal electrode layers are alternately connected to the inner electrode layers. (2) The moisture sensitive layer has a basic composition (Pb_1_-_xLa_x) (Zr_yTi_1_-
_y)_1_-_x_/_4O_30<x≦0.25,
The laminated structure type humidity sensor element according to claim 1, comprising a ferroelectric metal oxide sintered body in which 0<y<1.