JPH0656372B2 - Ceramic humidity sensor - Google Patents

Description

The present invention relates to a ceramic humidity sensor.

(Prior art and its problems) Conventionally, Ru has been applied to both sides of a bulk metal oxide ceramic.
A humidity sensor in which a porous electrode material such as O ₂ is applied and baked is widely used.

This sensor is configured to detect a change in humidity based on an electric resistance value by utilizing a change in conductivity due to moisture adsorbed by ceramics.

However, since the sensor is made of a ceramic of 2 to 4 mm square and has a large wall thickness, it takes a long time for moisture adsorption / desorption to reach an equilibrium state, and there is an inconvenience in that it cannot cope with a rapid humidity change.

Also, the conduction of protons during energization is slow, and it takes about 10 seconds to respond.

This sensor is mainly used for controlling humidity by measuring the humidity in the microwave oven, but the absolute time of cooking in the microwave oven is short, so the time difference of 10 seconds required for response is extremely long. However, there was also a problem that the accuracy of cooking control could not be expected.

In order to reduce the accuracy and response time of the sensor, the electrodes are made porous to absorb and desorb moisture, but the humidity cannot be measured unless the entire sensor is exposed at all times. There is also a disadvantage that the use of the sensor is limited because it is necessary to secure the installation place of the sensor.

(Technical problem) An object of the present invention is to increase the rate of adsorption / desorption of moisture and the conductivity of protons in a ceramic humidity sensor.

(Technical Means) Technical means for solving this technical problem are (a)
Forming a thin film layer of predelite-K ₂ O ceramic on the surface of the conductive layer by a sputtering method, and (b) forming a moisture-permeable conductive thin film layer on the outer side thereof.

(Operation of Technical Means) Since Priderite-K ₂ O ceramic has high hygroscopicity, it is possible to quickly adsorb and desorb moisture.

In addition, since the crystal structure of this ceramic is amorphous and is coarser than other amorphous ceramics, it has a high degree of freedom in the conduction of protons and can be rapidly moved.

The ceramic film layer formed on the surface of the conductive layer by the sputtering method is extremely thin, and adsorption and desorption of moisture are performed in a short time to form an equilibrium state, and the migration distance of protons is made extremely small. be able to.

Therefore, when voltages having different polarities are applied to the conductive layers on both sides of the ceramic layer, the protons can move quickly in a narrow range.

(Effects of the Present Invention) As a result of increasing the rate of adsorption and desorption of moisture in ceramics and the conductivity of protons, the response time of the sensor can be dramatically shortened, and moisture between ceramics and the atmosphere is equilibrated in almost real time. Therefore, there is an advantage that it can cope with a sudden change in humidity.

Further, since the shape and thickness of the sensor itself can be freely designed, there is an advantage that a desired resistance value and response speed can be selected.

In the conventional sensor, the humidity cannot be measured without exposing the whole and using an AC power supply, but in the sensor of the present invention, since moisture is absorbed and desorbed quickly, only the moisture-permeable conductive film side is exposed to the atmosphere. By exposing it, the humidity can be measured, and it can be used in any place, for example, when it is installed inside a densely integrated analytical instrument or the like to perform humidity compensation.

Moreover, since the sensor of the present invention can use a DC power source,
There is also an advantage that the humidity measuring device itself can be made compact.

(Embodiment) The conductive layer provided with the ceramic film layer has good workability when a good conductive metal material or a conductive resin molded body is used, but a conductive resin is applied to the surface of a base material made of a non-conductive material such as glass. Alternatively, a metal such as gold or aluminum may be formed into a film by a method such as a vacuum deposition method, a sputtering method, or an ion plating method.

As the moisture-permeable conductive thin film layer formed on the outer side of the ceramic layer, a metal film formed by a vacuum deposition method, a sputtering method, or an ion plating method is used.

In particular, a film formed of a metal such as gold or aluminum by a vacuum vapor deposition method is preferable because it has a high moisture permeability, but like a conventional sensor, a film of a metal or a conductive resin formed in a porous form. The electrodes may be formed of layers.

(Example) Priderite is represented by the general formula: Ax (B _{x / 2} Ti _{8-x / 2} ) O ₁₆ or Ax (B x Ti _8-x ) O ₁₆ (A is an alkali metal or alkaline earth metal, and B is It is a divalent or trivalent metal, and X is an artificial ore represented by 1.5 <X <2.0.

Priderite and potassium oxide or potassium hydroxide are mixed at an appropriate weight ratio, and heated and melted at 800 ° to 1400 ° C to react prederite and potassium oxide (K ₂ O), and naturally cooled and dissolved in pure water. The resulting precipitate gives an amorphous Priderite-K ₂ O ceramic. In this case, since excess K, H ₂ O, CO _{2 and the} like dissolve in pure water or escape into the air, the mixing ratio of predelite and potassium oxide or potassium hydroxide need not be strict.

Next, a specific example of a sensor using this ceramic will be described.

i) Preparation of target K-Mg predelite represented by Kx (Mg _{x / 2} Ti _{8-x / 2} ) O ₁₆ (X = 1.6) was mixed with K ₂ CO ₃ in a weight ratio of 4: 3, and then at 900 ° C. When melted, the crystal structure of predelite is broken, becoming amorphous, and dangling bonds increase. When this is naturally cooled and dissolved in pure water, a white precipitate is obtained.
This precipitate was an amorphous ceramic containing 14 potassium, 36 titanium, and 84 oxygen with respect to 1 magnesium.

The ceramic itself has hygroscopicity due to the hygroscopicity of potassium, but the excess potassium contained during melting dissolves in water when dissolved in pure water, so the ceramic itself may deliquesce when it absorbs moisture. Nonetheless, the amorphous ceramic was an extremely stable substance.

A pressure-molded product of the precipitate is used as a sputtering target.

ii) Preparation of sensor A vacuum deposition film (2) of aluminum is formed on the glass substrate (1) in advance, and the discharge power is 100 W, Ar flow rate is 300 to 400 sccm, and pressure is 2X10 ^-3 Torr. Sputtering was performed for 5 hours to form an amorphous ceramic layer (3) having a film thickness of 600 nm, and gold was vacuum-deposited on the amorphous ceramic layer (3) to form an electrode (4) (see FIGS. 1 and 2).

iii) Sensor characteristics Resistance-humidity characteristics As shown in Fig. 3, the logarithmic resistance value in resistance-absolute humidity characteristics changes linearly over a wide range, and the resistance value changes 1000 times. It is clear that the sensitivity of the sensor is good and it is in a range that is practically easy to handle.

Response characteristics 90% response time during direct current operation against sudden humidity changes between 95% RH and 55% RH is 10 seconds or less, and response time between 60% RH and 10% RH is 20 seconds or less. It was

iv) Use as absolute humidity sensor Since the resistance value of the sensor of the present invention is a function of water vapor and temperature, it is not possible to detect absolute humidity as it is, but two sensors are used, one for temperature compensation. When used for, it is possible to detect absolute humidity.

That is, by sealing the temperature compensating element Z ₁ by the bridge circuit shown in FIG. 4, only temperature information can be obtained from the resistance value of the element, and the other non-sealing element Z ₂ can be obtained.
Provides temperature and water vapor information.

Therefore, these differences appear in the bridging output voltage V, and the amount of water vapor at the absolute temperature can be measured.

In the current-absolute humidity property at each temperature, the measured value is linear at any temperature (see FIG. 3).

The empirical formula with temperature as a parameter is R = exp (C (T)) ・ (AH)
It is represented by ^{B (T)} .

However, AH: absolute humidity (mg / m ³ ), R: resistance value (Ω) of element, B (T): inclination of graph, C (T): vertical axis intercept of graph.

Further, B (T) = a ₁ · T + b ₁ and C (T) = a ₂ · T + b ₂ and a ₁ to −0.03, b ₁ to −2, a _{2 to} 0.2, b ₂ to Twenty.

The absolute humidity can be easily calculated using this formula. This means that the sensor of the present invention is sensitive to changes in temperature and absolute humidity, indicating that the sensor can also be an absolute humidity sensor.

Therefore, the absolute humidity can be easily detected by using the sensor in combination with the closed type, and the closed type alone can be used as a temperature sensor.

[Brief description of drawings]

The drawings are for explaining an embodiment of the present invention.
Fig. 2 is a plan view of the sensor, Fig. 2 is a sectional view of II-II in Fig. 1, Fig. 3 is a graph showing resistance-absolute humidity characteristics of the sensor, and Fig. 4 is a bridge circuit diagram for detecting absolute humidity. is there. (1) Substrate, (2) Aluminum vacuum deposition film, (3) Amorphous ceramic layer, (4) Gold deposition film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshige Yamamoto 6-17, Eggashisaku Kitamachi, Hirakata-shi, Osaka (72) Inventor Ichiro Taniguchi, Kuromon-dori Shijo-Kami Fujioka-cho, Nakagyo-ku, Kyoto, Kyoto 497 (56) References JP-A 61-292545 (JP, A) JP-A 60-141623 (JP, A)

Claims (4)

[Claims] 1. A ceramic humidity sensor in which a thin film layer of predelite-K ₂ O ceramic is formed on the surface of a conductive layer by a sputtering method, and a moisture-permeable conductive thin film layer is formed on the outside thereof. 2. The sensor according to claim 1, wherein the conductive layer is made of metal or conductive resin. 3. The sensor according to claim 1 or 2, wherein the moisture-permeable conductive layer is a metal film formed by a vacuum deposition method, a sputtering method, or an ion plating method. 4. The sensor according to claim 1, wherein the moisture-permeable conductive layer is a porous conductive film.