JPH02296140A - Humidity sensor - Google Patents

Abstract

PURPOSE:To improve water repellancy, oil repellancy and chemical resistance by providing a pair of electrodes on a substrate, and forming an evaporated film of pitch fluoride on the electrodes. CONSTITUTION:A pair of electrodes 3 and 3' comprising conductive material such as gold and silver are formed on a substrate 1 comprising insulating material such as glass and ceramics. A thin film 5 of pitch fluoride is formed on the electrodes 3 and 3' in tight contact manner by a vacuum evaporation method and the like. It is desirable that the evaporation temperature of the pitch fluoride is about 100-600 deg.C in consideration of the decomposition temperature of the pitch. It is desirable that the thickness of a thin film 5 is about 10 Angstrom -10mum. By such constitution, water repellancy, oil repellancy and chemical resistance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a humidity sensor with excellent water resistance and heat resistance.

Prior Art and Its Problems A typical humidity sensor includes a humidity-sensitive material as a humidity-sensing part, the electrical resistance of which changes in response to changes in atmospheric humidity.

Although a wide variety of such moisture-sensitive materials have been proposed in the past, it is difficult to say that any of them are satisfactory from a practical standpoint.

For example, a sensor using a hydrocarbon-based polymer electrolyte as a moisture-sensitive material generally has poor heat resistance, and therefore cannot be used if the ambient temperature exceeds 60°C.

In addition, sensors that use an organic film as a moisture-sensing part have the disadvantage that the electrolyte will dissolve in an environment where dew condensation occurs over a long period of time.

Furthermore, in the case of a humidity sensor that uses a metal oxide ceramic as a humidity sensing part, there is a problem in that energy consumption is high because the mechanical strength is increased by sintering at a high temperature. Furthermore, since the sintering temperature of the metal oxide ceramic is high, the raw material powder particles are likely to sinter, resulting in a decrease in the effective moisture sensing area and a decrease in sensitivity.

Means for Solving the Problems As a result of repeated research in view of the problems of the prior art as described above, the present inventor discovered that a thin film of fluorinated pitch having a specific composition can be used as a moisture-sensitive sensor. It was discovered that the present invention has extremely excellent performance as a part of the invention, leading to the completion of the present invention.

That is, the present invention provides a deposited film of pitch fluoride, a pair of electrodes connected to the deposited film for measuring the electrical resistance of the deposited film, and a substrate to which the deposited film and/or the electrodes are fixed. It pertains to a humidity sensor consisting of:

The fluorinated pitch used in the present invention has the composition formula CFx (
0.5≦X≦1.8), in which 1 to 3 fluorine atoms are firmly bonded to each carbon atom through fT bonds. A typical example of such a fluorinated pitch is that disclosed in Japanese Patent Application Laid-Open No. 62-275190.

JP-A No. 62-275190 discloses a film having a layered structure formed in the pitch used as a raw material (isotropic pitch, mesophase pitch, hydrogenated mesophase pitch, mesocarbon microbeads, etc.) and having the following characteristics. ``consisting essentially of carbon atoms and fluorine atoms, *:/C
The atomic ratio is 0.5 to 1.8, and the following (a) and (b)
A fluorinated pitch characterized by exhibiting the characteristics of , (c) and (d).

(a) In powder X-ray diffraction, a peak with maximum intensity is shown near 2θ=13°, and a peak with lower intensity than the peak near 2θ=13° is shown near 2θ-40°.

(b) In X-ray photoelectron spectroscopy, 290.0±1,
A peak corresponding to the CF group and 292.5±0.
A peak corresponding to CF2 group was shown near 9cV, and CF2
The intensity ratio of the peak corresponding to the group to the peak corresponding to the CF group is 0.15 to 1.5.

(c) A thin film can be formed by vacuum evaporation. ” The present invention will be described in more detail below with reference to the drawings.

FIG. 1 is a perspective view schematically showing the manufacturing process of the humidity sensor of the present invention. Substrate of humidity sensor according to the present invention (
1) is the same as the substrate in known humidity sensors, and is made of an insulating material such as a glass plate or ceramics.

On such a substrate (1), a pair of electrodes (3) made of a conductive material such as gold, silver, or aluminum is placed according to a conventional method.
, (3°) are formed.

Then, a fluoride pitch thin film (5) is closely formed on the pair of electrodes (3) and (3°) provided on the above-mentioned insulating substrate by a known vacuum evaporation method, sputtering method, etc. Ru. The vapor deposition temperature of the fluorinated pitch is preferably about 100 to 600°C in consideration of its decomposition temperature. The substrate temperature during normal vapor deposition may be lower than the vapor deposition temperature of fluorinated pitch. However, if the operating temperature of the obtained moisture sensitive sensor becomes high, it is necessary to set the substrate temperature in the operating temperature tool.

This is because if the substrate temperature is set lower than the operating temperature of the sensor, there is a risk that the fluorinated pitch thin film will be destroyed when the sensor is used.

FIG. 2 is a plan view showing an outline of the humidity sensor of the present invention formed as described above.

FIG. 3 shows an example of a vacuum evaporation apparatus used for forming the humidity sensing part of the humidity sensor of the present invention.

The inside of the Pel jar (11) is evacuated by a vacuum pump (not shown) connected to the exhaust path (13).

A substrate (15) on which a pair of electrodes are formed in advance, ... (
15) is attached to the rotating dome (17),
The fluorinated pitch (19), which is a vapor deposition material, is deposited on a boat (21).
) is housed in. The vapor deposition operation is performed using a heater (23),
This is carried out by opening and closing the shutter (25) as appropriate while heating the substrate (15) to a predetermined temperature using (23). The vacuum evaporation method itself is a well-known technique, and it goes without saying that equipment other than the type shown in the drawings may be used.

Note that in the structure shown in FIG. 1, an electrode (
3) and (3') are provided, and the fluoride pitch vapor deposited film (5) is further placed thereon, but this order may be changed. That is, the fluoride pitch vapor deposited film (5) may be provided on the bottom of the substrate (1), and the electrodes (3) (3°) may be further arranged thereon.

Alternatively, one electrode (3) is provided on the substrate (1), a fluoride pitch vapor deposited film (5) is formed on it, and the other electrode (3°) is placed on it to form a sandwich structure. It's good as well. Further, the pair of electrodes (3) and (3°) are not limited to the comb-shaped ones shown in FIG.

The thickness of the fluorinated pitch thin film serving as the moisture sensitive part in the present invention is preferably about 10 to 10 μm, and about 100 μm to 10 μm.
More preferably, the thickness is about 1 μm. If the thickness is less than 10, it will be difficult to control the film thickness, resulting in variations in quality.

On the other hand, if it exceeds 10 μm, the sensitivity of the sensor decreases.

Effect of the invention According to the present invention, the following remarkable effects are achieved.

(a) Fluorinated pitch used as a raw material contains a large amount of fluorine, so it has excellent water and oil repellency and chemical resistance, and thin films obtained from such fluorinated pitch also have similar properties. It has a characteristic.

Therefore, unlike existing moisture-sensitive sensors equipped with organic film, the humidity-sensitive sensor of the present invention does not deteriorate in performance due to component elution even when used in a dew-condensed state for a long time.

(b) Furthermore, the fluorinated pitch thin film of the present invention is poorly soluble in nail machine solvents and has excellent oil resistance, so it can be used even in oily environments.

(C) The heat resistance of the thin film can be improved by adjusting the substrate heating temperature during the formation of the fluorinated pitch thin film, which is different from the known moisture-sensitive sensor that uses a white-organic film. , there are very few restrictions on the operating temperature.

(d) Energy consumption is relatively low.

(e) Maintain high sensitivity from the beginning for a long time.

EXAMPLES Examples will be shown below to further clarify the features of the present invention.

Example 1 Thickness 0. After forming a fluorinated pitch thin film on one surface of a 5 mm x 14 mm x 17 mm glass substrate by a known vacuum evaporation method, a pair of comb-shaped aluminum electrodes were formed on the surface of the fluorinated pitch thin film by a vacuum evaporation method,
A moisture-sensitive sensor of the present invention was manufactured.

The vacuum deposition conditions for forming the fluorinated pitch thin film are as follows.

*Vacuum level: -2, OX 10-” Torr or less *Substrate heating temperature: 50°C *Final heating temperature for fluorinated pitch: 500°C *Temperature increase rate for fluorinated pitch: 5°C/min *Membrane Thickness...Q, 31
℃m When the humidity sensor obtained as described in 1- above was placed in a constant temperature room at 500C and the humidity was varied in the range of 10% to 85%, the output resistance value (measured voltage 10V) was 1. 25
It varied in the range from x1012Ω to 5.76x109Ω.

In addition, the humidity sensor obtained as described in - is placed in a constant temperature room at 50℃, and the resistance value when the humidity is increased from 10% to 85% and the resistance value when it is decreased from 85% to 10%. When contrasted, they showed similar changes as in Habo, and no hysteresis was observed.

Furthermore, changes in resistance values were measured under the same humidity conditions as in item 1-, using measurement voltages of 20 V and 30 V, and the resistance values showed similar changes.

In addition, the moisture-sensitive portion of the obtained sensor had water and oil repellency of H, similar to the raw material fluorinated pitch.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing the process of manufacturing a humidity sensor according to the present invention. FIG. 2 is a W-side view of the humidity sensor according to the present invention. FIG. 3 is a sectional view showing an example of a vacuum evaporation apparatus used in manufacturing the humidity sensor of the present invention. (1)... Substrate (3) (3°)... Electrode, (5)... Moisture sensing part (11) made of fluoride pitch thin film
...Pelger (13) ...Exhaust path (I5) ...Substrate with electrodes ...Rotating dome ...Fluoride pitch ...Boat ...Heater ...Shutter (and above) Chapter 1 Figure 5--F type Z' No. 3-l Goo 3 Meeting diagram Figure 2

Claims (1)

[Claims] (1) Humidity consisting of a deposited film of fluoride pitch, a pair of electrodes connected to the deposited film for measuring the electrical resistance of the deposited film, and a substrate to which the deposited film and/or the electrodes are fixed. sensor.