JPS63278302A - Humidity sensing element - 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 relates to a moisture-sensitive element, and particularly to a moisture-sensitive element in which a specific substance is added in advance to improve the strength and stability of the characteristics of the moisture-sensitive element. The present invention relates to a moisture sensitive element characterized by: The humidity sensing element according to the present invention exhibits stable characteristics with very little variation in the resistance-humidity characteristic curve not only in the normal humidity range but also in high-humidity and low-humidity environments.

In recent years, moisture-sensitive elements have come to be used in many fields. In household products, it is often used to control food cooking in microwave ovens, to detect dryness in clothes dryers, to control humidity in room air conditioners, to detect condensation in VTR cylinders, and in industrial applications, it is used in various electronic components. Widely used for humidity control during manufacturing. In addition, attempts are being made to use it for air conditioning in agricultural houses and for preventing dew condensation on automobile rear windows. Humidity control is essential in addition to temperature control in various automated systems for food cooking, air conditioning, drying, etc., and there is a need for the development of moisture-sensitive elements that operate with high reliability.

In order to meet these demands, electrical resistance variable moisture sensing elements have been put into practical use. This detects changes in humidity as changes in electrical resistance, and there are many types of moisture-sensitive materials used, including electrolyte materials such as lithium chloride, organic polymer materials, and ceramic materials. has been proposed.

A variable resistance humidity sensing element is basically required to have a low electrical resistance value, good linearity in resistance-humidity characteristics, an appropriate operating range, and not to deteriorate in the environment in which it is used. Recently, ceramic moisture-sensitive materials have been attracting attention as a material that comprehensively satisfies these requirements.

There have been many proposals for ceramic moisture-sensitive materials, but the important properties are (a) moderately low electrical resistance, (b) good linearity of resistance-humidity characteristics, C) good sensitivity, (d) good precision, and (e) good stability are required, and various materials have been studied as ceramic moisture-sensitive materials for forming the moisture-sensing part.

As a ceramic moisture-sensitive material that basically satisfies these characteristics, the present inventors have found (i) Y2O, (2) Y, O, + Z r 02 (0,01 to 99.
00%), (3)Y2O,+ (0801Mg0IBa
OITi02#Ta2031Nb203 and V2O5)
(7) At least one type (0.01-99.00%).

(4) Z ro2+ (CaO, MgO, BaO, T
iO,, Ta2O,, NbaO.

and Y2O,') (7) At least one type (0,01~
99.00%) etc., Y2O3+ Z r
It has been concluded that Oz-based and zrO2-based ceramics are good.

The moisture sensing element may be in the form of a bulk type in which a pair of electrodes are provided on opposing surfaces of the ceramic sintered body.
A preferred form is a thick film type in which an electrode layer is formed on at least one surface of a ceramic substrate, and a moisture sensitive layer is formed by coating a mixture of the above ceramic with a binder on the electrode layer, drying and sintering the electrode layer. It is. It is preferable to form the coating film by screen printing. More importantly, the electrode pattern in the electrode layer should be formed so that the spacing between the electrodes is as small as possible, 0.20 nm or less. For example, good results can be obtained by interlocking the comb teeth of a pair of comb-shaped electrodes with the comb teeth spacing being 0.20 nn or less.

However, such Y2O3 system, y, o, +zr○
There is still much room for improvement in the performance of ZrO2-based and ZrO2-based ceramic moisture-sensitive elements, and trials are currently being carried out. The points to be improved are the strength and stability of moisture sensitivity, and it is also desired to further reduce the resistance value.

In order to obtain this stability, a method of adding LiC◯ as a binder has been found, but there has been a need for something that provides even more stability.

As a result of intensive study, the inventors of the present invention have made the following invention.

That is, the present invention can be used as a binder for sintering in a humidity sensor in which the humidity sensing portion is made of ceramic.

The present invention relates to a moisture-sensitive element using an element and/or compound that forms an oxide of one or more of Eu, Cs, Rb, and Sb after sintering.

Moreover, as one of the embodiments, we propose the above-described moisture-sensitive element characterized in that the binder for sintering is Eu2O3 and the amount added is 2 to Lowt%. As yet another embodiment, we propose the above-mentioned moisture-sensing element, wherein the ceramic of the humidity-sensing part is made of stabilized zirconia powder in which one of yttria, calcia, and magnesia is dissolved in zirconia. .

The moisture-sensitive element used in the present invention can also be realized as a type in which a pair of electrodes are formed on opposing surfaces of a ceramic sintered body, but preferably a moisture-sensitive element is formed on the substrate. It is manufactured as a thick film type that forms a .

FIG. 1 shows an example of a thick film type moisture sensitive element. An electrode section 3 is formed on one or both surfaces of the substrate 1, and a moisture sensing section 5 is formed thereon (the moisture sensing layer is partially omitted). As the substrate, ceramics such as Al2O3, Sin□, ZrO2, etc. are used. Formation of the electrode layer on the substrate is achieved by using screen printing, vapor deposition, and photoetching methods for gold, silver, platinum, and ruthenium electrodes.

Recently, many microfabrication techniques for manufacturing printed circuit boards for electronic circuits have been put into practical use, and by applying them, it is possible to form fine electrode patterns.

For example, sputtering is also a useful method. The electrode pattern is preferably one in which a pair of comb-shaped electrodes are interlocked with comb teeth as shown in FIG. The smaller the interval between the comb teeth, the lower the resistance value, so the sensitivity of the moisture sensing element can be increased.

Good results were obtained using a comb spacing of 0.05 to 0.20 mn+.

In particular, comb-shaped gold electrodes are useful in reducing the resistance of produced moisture-sensitive elements. Formation of the gold electrode by screen printing is preferred. However, if the device is to be miniaturized, it is preferable to form the gold electrode by vapor deposition.

Next, the process of preparing a paste for a moisture-sensitive material will be described: Although the ceramic for the moisture-sensing part is not particularly defined in the present invention, for example, stabilized ZrO2 powder is used.

Stabilized Zr○2 has a composition in which at least one of Y2O, CaO, and MgO is made into a solid solution in ZrO2, and falls into the ZrO2 side solid solution region in the phase diagram. Zr02-Y.

0, system is preferred. Y2O, may be added in a range of 10 to 60% by weight. Such a Z r O2Y 203 solid solution forming powder is produced by, for example, causing a coprecipitation reaction in a mixture of ZrOCl2 and YCI at a predetermined ratio using an alkali such as NH, (ammonia) by a coprecipitation method, and then producing Y2O3 at the raw material powder stage. It is a homogeneous mixed powder dissolved in ZrO2. In addition to the coprecipitation method described above, these solid solution powders can be prepared by
It can be produced by a hydrolysis method, an alkoxide method, a melting method, etc.

After calcination at 60°C to 800°C, main firing is performed at 900°C to 110°C, and the starting powder is obtained by pulverizing to 1625 mesh using a ball mill or the like.

The powder is then preferably dissolved in KOH, 20 or 2
It is pretreated in order to react with the addition of at least one type of C○. KOH treatment is preferred.

The KOH treatment is carried out by immersing the powder in a solution containing KOH at a concentration of 5 to 20% by weight, and immersing it for 1 to 20 minutes while stirring. This gives a powder containing 1 to 10% by weight of KOH.

The powder, which has been pretreated for impregnation with KOH, etc., is filtered and dried, and then primarily calcined at a temperature of 800 to 1150°C.

In order to improve the film strength, stability, precision, and sensitivity of the humidity sensing element, Eu, Cs, Rb, and Sb are added to the ceramic powder forming the humidity sensing part at this stage as a binder for sintering according to the present invention.
Elements and/or compounds that form one or more oxides after sintering are added.

For example, Eu2O3, C520, Rb2O, 5b203
etc. are added. Further, the above-mentioned carbonates, hydroxides, etc. may also be used.

The amount added is, for example, 2 to 10 wt% for Eu2O.
Can be added before and after. This is because if it is less than 2%, the change over time after manufacture is large and the strength is weak, and if it is more than 10%, the resistance value will be too high.

More preferably, it is 3 to 10 wt%.

This is because if Eu2O is less than 3 wt%, the strength of the moisture sensitive film becomes weak.

The powder to which a binder for sintering is added is primarily fired at a temperature of 800 to 1150°C.

After mixing, secondary firing is performed at a temperature of 700 to 900°C, and the mixture is ground again.

The powder thus obtained is thoroughly kneaded with the addition of an appropriate resin coating, and the viscosity is adjusted with ethyl acetate or the like to produce a paste for moisture-sensitive materials.

The moisture-sensitive paste thus produced is applied onto the electrode layer by screen printing to a final film thickness of 5 to 200 μm, preferably 20 to 50 μm.

After drying, 500-870℃, typically 700-870℃
Firing takes place at a temperature of .degree. Baking time is 5-90 minutes.
Usually 8 to 20 minutes is sufficient. The firing process fires the ceramic particles to provide the skeletal structure of the moisture sensitive membrane and provide structural strength.

After the moisture-sensitive film is formed, solder is applied.

The device is completed through the device assembly process of aging, casing, and marking. Aging is 50-90
It is carried out at a temperature of 60 to 85 °C, preferably 60 to 85 °C. The aging process produces a stable device with less degradation under the conditions of use.

These moisture-sensing elements are exposed to the atmosphere under various usage environments and detect the water vapor contained therein. If pollen or other dust particles adhere to the moisture-sensitive portion of the device, its performance will deteriorate. In particular, adhesion of water is extremely harmful to the moisture sensitive element.

Therefore, in order to prevent water, dust, etc. from adhering to the humidity sensing part, it is preferable to use the humidity sensing element by storing it in a case in which a window with a filter membrane is formed on the part facing the humidity sensing part.

The filter membrane must have good responsiveness so that it can effectively prevent harmful substances such as water and dust from reaching the humidity sensing part, and at the same time can quickly transmit the humid atmosphere to the humidity sensing part. Polymer filter membranes made of fluororesin, silicone resin, etc. have been proposed as filter membranes that meet these conditions. In particular, the applicant has previously confirmed that chlorine-containing polymer membranes, typically chlorinated ethylene membranes, that meet the following conditions exhibit excellent properties: (1) Porosity 35-85 % (2) Pore diameter 0.01~3μm (3) Thickness 20~200
With the IT M element board, for example, 24 elements are printed on one board, so if KOH treatment is applied after forming the moisture sensitive film, the KOH treatment will be applied to the conductor pads to which the lead pins are attached. , when soldering later,
Soldering is undesirable because it deteriorates the properties, but according to the present method in which the moisture-sensitive material powder is treated with KOH before firing, soldering does not deteriorate the properties.

1"Y 85% by weight ZrO2-15% by weight Y20 by coprecipitation method
．． A solid solution powder was prepared and calcined at 800°C. after that,
A paste for moisture-sensitive materials was prepared through the following steps.

Calcination ↓ Grinding (wet) Ball mill, ethyl alcohol added ↓ Classification -625 mesh, ethyl alcohol added ↓ Drying 60℃, 5 hours ↓ KO) 1 Impregnation treatment 15% KOH aqueous solution, immersed for 10 minutes ↓ Mixing ↓ Drying ↓ Primary firing 900°C, 1 hour ↓ Addition of 1 to 1wt% Eu2O3 ↓ Mixing/drying Add ethyl acetate, mix for over 1 hour ↓ Secondary firing 800°C, 1 hour pulverization ↓ Mixed wires Resin, organic solvent, DOP (dioctyl phthalate) ), ethyl acetate was added. On the other hand, a comb-engraved electrode was formed by screen printing on an Al2O3 substrate with a length of 18 mm and a width of 911 Il.

The spacing between each comb tooth was 0.2 mm, and the electrode array was printed over a length of 12 mm+.

The moisture-sensitive paste was applied onto the electrode layer by screen printing, dried in two stages at 160°C for 50 minutes and at 330°C for 50 minutes, and then baked at 800°C for 12 minutes. Final film thickness is 30
It was μm.

After soldering, aging was performed at 80° C. and 60% relative humidity in a constant temperature and humidity chamber.

FIG. 2 shows the stability of the resistance value when the amount of Eu2O added was changed.

It is shown that when the addition amount is 2 to 10 wt%, the change in resistance value one week after aging treatment is small compared to immediately after aging.

In addition, when the strength of the moisture-sensitive film was compared with respect to the state of the film missing in the Si resin coating process, the following results were obtained.

Table 1 shows the strength of the moisture-sensitive film, that is, it is understood that addition of 3 to 10 wt% is preferable.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an example of a coated film type moisture-sensitive element, and Figure 2 is an E
The change in resistance value and the amount of u2O3 added is shown.

Claims (3)

[Claims] (1) Eu, Cs, Rb, S as a binder for sintering in a humidity sensor whose humidity sensing part is made of ceramic.
A moisture-sensitive element characterized by using an element and/or compound that forms one or more oxides after sintering. (2) The moisture-sensitive element according to claim 1, wherein the binder for sintering is Eu_2O_3, and the amount added is 2 to 10 wt%. (3) The moisture sensing element according to claim 1, wherein the ceramic of the humidity sensing portion is made from stabilized zirconia powder in which one of yttria, calcia, and magnesia is dissolved in zirconia as a solid solution. .