JPH0720080A - Humidity sensor - Google Patents

Abstract

PURPOSE:To obtain a humidity sensor which can be mass-produced easily, has a high reliability, and has low-power heater by using a process which is simple and is suited for mass-production. CONSTITUTION:An oxide film is formed on the surface of a silicon substrate 3 whose one surface is partially etched, a comb-shaped electrode 2 is formed on the oxide film on the other non-etched surface, and a moisture-sensing film 1 is formed so that it covers the part of the comb-shaped electrode 2. A heater electrode 5 is formed on the etching surface of the rear, the conduction part of the heater electrode 5 is left, and the etching surface is sealed by anode joint to achieve the title humidity sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor for detecting humidity by changing electric characteristics of an element in response to humidity.

[0002]

2. Description of the Related Art In recent years, the number of fields requiring humidity measurement and humidity control has increased, and the importance of humidity sensors has come to be recognized.

Humidity sensors that detect humidity by changing the electrical characteristics of the element in response to humidity include electrolyte-based, metal-based, polymer-based, and ceramic-based humidity sensors, and various systems have been studied. However, polymer and ceramic humidity sensors are currently in practical use. All of them utilize the property that the resistance value or capacitance of the element changes due to the adsorption and desorption of water with respect to the element.

An insulator such as alumina or glass is used for the substrate, and a comb-shaped electrode or a moisture sensitive film is formed on this substrate.
A sandwich type structure in which a lower electrode, a moisture sensitive film and an upper electrode are formed on a substrate is generally used.

When cleaning is required, most humidity sensors have a coil around the entire humidity sensor.
This is done by heating with the coil.

[0006]

The conventional humidity sensor has the following problems.
When cleaning is performed, a coil is wound around the entire humidity sensor to heat the entire humidity sensor, resulting in poor thermal efficiency and high power consumption.

Further, there is a problem that the structure of the humidity sensor is limited due to the structure for heating the entire humidity sensor.

Therefore, the present invention solves such a problem, and an object thereof is to provide a humidity sensor having good mass productivity, good heat resistance, high reliability, and unlimited structure. is there.

[0009]

The humidity sensor of the present invention comprises:
It is characterized in that a pair of electrodes and a moisture-sensitive film in the shape of an electrode are formed on a substrate with insulation on the outermost surface, and a heater electrode is formed on the back surface of the substrate on which the electrodes and the moisture-sensitive film are formed. .

The substrate may be a non-conductive substrate such as glass or alumina. It is preferable to use a conductive metal plate having a surface on which an insulating film is formed as a substrate because the thermal conductivity is good and the humidity sensor can be efficiently cleaned. further,
When silicon is used as the substrate, a silicon process suitable for mass production can be used, which is preferable in terms of mass productivity and reliability.

By using anodic bonding as a method of covering the heater electrode portion, a bonding strength higher than that of a normal bonding method can be obtained, and the dimensional accuracy in the thickness direction is high, which is preferable in terms of reliability. Further, by etching the heater portion, the heat generated by the heater can be efficiently transmitted to the moisture sensitive portion.

The use of comb-teeth electrodes as the pair of electrodes is preferable in that the contact area between the electrodes and the moisture sensitive film can be increased and the resistance value can be reduced.

Further, it is preferable to use nickel chromium for the heater electrode because the amount of heat generated is high and the humidity sensor can be efficiently cleaned.

When the fluorine-containing polymer film is formed so as to cover at least the moisture sensitive film portion, a more reliable humidity sensor can be obtained.

[0015]

【Example】

(Example 1) 100 ml of water, 100 ml of ethanol,
Manganese acetate 80 g, lead acetate 20 g, potassium acetate 10
g was added and the mixture was stirred for 1 hour to prepare a coating liquid for a moisture-sensitive film.

A part of one side of the silicon substrate was etched, a heater electrode was formed of nickel-chrome alloy on the etched surface where insulation was secured, and a comb-teeth electrode was formed on the back surface of the etched surface using gold. A moisture-sensitive film coating liquid was screen-printed on the comb-teeth electrode of the substrate thus formed so that the comb-teeth electrode was covered and heat-treated at 700 ° C. for 1 hour to form a moisture-sensitive film. A cross-sectional view of the humidity sensor thus produced is shown in FIG. 1, and a plan view thereof is shown in FIG. Figure 1,
In FIG. 2, 1 is a moisture sensitive film, 2 is a comb electrode, 3 is a substrate,
Reference numeral 4 is an insulating film, and 5 is a heater electrode.

FIG. 3 shows the humidity-sensitive characteristics of this humidity sensor. It can be seen from FIG. 3 that the humidity sensor of the present invention is easy to use because it has a low resistance value, an appropriate change range of the resistance value, and the characteristics do not change with temperature. The humidity sensor was left to stand in a constant temperature and humidity chamber at 60 ° C. and 90% for 1000 hours, and the characteristics were measured. The results were the same as those in FIG. 3 within the measurement error range. Therefore, it can be seen that this humidity sensor has high durability and reliability. Also, the response to temperature change is 1.
Within 0 seconds, the response to changes in humidity was sufficiently fast, within 5 seconds. Further, since the humidity sensor has a simple manufacturing process, it can be easily mass-produced and can be manufactured at low cost.

Example 2 The humidity sensor prepared in Example 1 is covered with a solution (7% by weight) of a solvent-soluble fluorine-containing polymer dissolved in a perfluoro solvent, at least all electrodes on the moisture-sensitive film are covered. Screen-print, 180
It heat-processed at 1 degreeC for 1 hour, and formed the fluorine-containing polymer film. A cross-sectional view of the humidity sensor thus produced is shown in FIG. In FIG. 4, 1 is a moisture sensitive film, 2 is an electrode, 3 is a substrate,
Reference numeral 4 is an insulating film, 5 is a heater electrode, and 6 is a fluorine-containing polymer film. The characteristics of this humidity sensor were similar to those of the humidity sensor created in Example 1. After the humidity sensor was immersed in water for 100 hours, the characteristics were measured and found to be the same as in FIG. 3 within the measurement error range. Therefore, it can be seen that this humidity sensor has high durability and reliability.

(Embodiment 3) Pyrex glass is anodically bonded so as to cover the etching surface prepared in Embodiment 1 while leaving the conductive portion of the heater electrode, and at least all of the humidity sensitive film of this humidity sensor is covered. A solution (7% by weight) of a solvent-soluble fluoropolymer dissolved in a perfluoro solvent was coated and heat-treated at 180 ° C. for 1 hour to form a fluoropolymer film. A cross-sectional view of the humidity sensor thus produced is shown in FIG. In FIG. 5, 1 is a moisture sensitive film,
2 is an electrode, 3 is a substrate, 4 is an insulating film, 5 is a heater electrode,
Reference numeral 6 is a fluorine-containing polymer film, and 7 is an anode-bonded Pyrex glass. The characteristics of this humidity sensor were similar to those of the humidity sensor created in Example 1. This humidity sensor is 60 ℃
When the characteristics were measured after being immersed in the saturated saline solution for 100 hours, the results were the same as those in FIG. 3 within the measurement error range. Therefore, it can be seen that this humidity sensor is extremely durable and highly reliable.

Although the ceramic moisture sensitive film is used in this embodiment, a ceramic moisture sensitive film of another component or a polymer moisture sensitive film may be used. Further, in this embodiment, the humidity is detected by the resistance value, but it may be detected by the capacitance.

[0021]

As described above, in the humidity sensor of the present invention, by forming the heater electrode on the back surface of the thin film humidity sensor substrate, the surface of the humidity sensor can be efficiently cleaned with low power. Further, if silicon having high thermal efficiency is used for the substrate, the surface of the humidity sensor can be cleaned with lower power, and a humidity sensor with high mass productivity and high reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a humidity sensor of the present invention.

FIG. 2 is a plan view of the humidity sensor of the present invention.

FIG. 3 is a humidity sensitive characteristic diagram of the humidity sensor of the present invention.

FIG. 4 is a sectional view of the humidity sensor of the present invention.

FIG. 5 is a sectional view of the humidity sensor of the present invention.

[Explanation of symbols]

 1 Moisture Sensitive Film 2 Electrode 3 Substrate 4 Insulating Film 5 Heater Electrode 6 Fluorine-Containing Polymer Film 7 Anodically Bonded Pyrex Glass

Claims (9)

[Claims] 1. A pair of electrodes and a humidity sensitive film having an electrode shape are formed on a substrate having insulation on the outermost surface, and a heater electrode is formed on the back surface of the substrate on which the electrodes and the moisture sensitive film are formed. A humidity sensor characterized in that 2. The humidity sensor according to claim 1, wherein a heater electrode is formed on the etched surface of the back surface. 3. The humidity sensor according to claim 1, which has a structure for sealing a heater electrode formed on the back surface. 4. The humidity sensor according to claim 1, wherein a comb-teeth electrode is used as the electrode. 5. The humidity sensor according to claim 1, wherein silicon is used as the substrate. 6. The humidity sensor according to claim 1, wherein gold is used as the comb-teeth electrode. 7. The humidity sensor according to claim 1, wherein the fluorine-containing polymer film is formed so that at least the moisture-sensitive film portion is entirely covered. 8. The humidity sensor according to claim 1, wherein anodic bonding is used as a method for sealing the heater electrode. 9. The humidity sensor according to claim 1, wherein nickel chromium is used as a heater electrode material.