JPH0415413B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a humidity sensor. More specifically, it relates to a method for manufacturing a humidity sensor that uses a mixed gas of an organosilicon compound and ammonia (hereinafter abbreviated as NH ₃ ) as a monomer to form a plasma polymerized film used as a temperature-sensitive resistor on a sensor substrate. .

Conventionally, humidity sensors include electrolyte-based sensors, organic-based sensors, metal-based sensors, and metal-oxide-based sensors in terms of the materials used.
In electrolyte-based sensors, for example, polystyrene sulfate membranes, potassium metaphosphate membranes, phosphorus pentoxide membranes, etc. are used, and when water is adsorbed to these membranes, an electrolyte aqueous solution is produced, which causes a change in electrical resistance. Humidity is detected by Furthermore, organic sensors use carbon-containing cellulose, carbon-containing resin, etc., and measure humidity by detecting changes in electrical resistance due to swelling due to adsorption of moisture. For metal and metal oxide sensors, Si sintered films, tin oxide ultrafine particle films,
Coating films of Cr ₂ O ₃ , Ni ₂ O ₃ , Fe ₂ O ₃ , Al ₂ O ₃ , ZnO, etc., Ni _1-x Fe _2+x O ₄ , Fe ₂ O ₃ −K ₂ O, ZnO−Li ₂ O−
Humidity is measured using ceramics such as V ₂ O ₅ mainly by utilizing the porosity of the ceramics.

However, each of the above-mentioned sensors has the following problems.

Although it has high sensitivity, it is difficult to detect high humidity of 50% or more.

Because it uses swelling, the detection speed is slow and therefore cannot follow rapid changes in humidity.

It can withstand high temperatures, has high sensitivity, and can detect a wide range of humidity, and has extremely high performance.However, because it is porous, if water is adsorbed, it will desorb the adsorbed water unless it is heated or depressurized. I can't do it.

The present inventor has conducted extensive research with the aim of developing a manufacturing method for manufacturing a highly durable humidity sensor that can be used over and over again in response to rapid changes in high humidity. I was able to complete it.

That is, the present invention is characterized in that a plasma polymerized film is formed on a sensor substrate using a gas mixture having a molar ratio of organosilicon compound and ammonia (organosilicon compound/ammonia) of 0.1 to 1.5. A method for manufacturing a sensor is provided.

The plasma polymerization apparatus used in the present invention is not particularly limited. The plasma polymerization vessel may be a bell gear type or a tubular flow type, and the plasma discharge type may be any type, such as direct current discharge, low frequency discharge, high frequency discharge, or microwave discharge, and the shape of the electrodes and coils may be arbitrary. That's fine.

As for the plasma polymerization conditions in the present invention, the pressure inside the polymerization vessel is usually within the range of 1 mTorr to 3 Torr, and the electric power depends on the type and size of the electrode, but the It is preferable to set the temperature (Te) within the range of 10,000≦Te≦80,000. If it is less than 10,000, the plasma polymerization rate is too slow to be practical, and if it exceeds 80,000, the sensitivity of the polymerized film to humidity may decrease. Note that the electron temperature Te can be measured using a probe. For example, single probe method,
By two-probe method, three-probe method, etc. (Unexamined Japanese Patent Publication 1973-
135574) The monomer gas used in the present invention is a mixed gas of an organosilicon compound and NH ₃ . The magnitude _of the change in electrical resistance of a polymerized film due to humidity varies depending on the molar ratio of the organosilicon compound to _NH3 . ₃ ) is 0.1-1.5, more preferably 0.3-1. If it exceeds 1.5, high humidity detection sensitivity is low, and if it is less than 0.1, the plasma polymerization reaction is slow.

As the organosilicon compound used in the present invention,
A typical example is the general formula SiR ₁ R ₂ R ₃ R ₄ (however,
R ₁ , R ₂ , R ₃ and R ₄ are different or the same,
Selected from CH ₃ , C ₂ H ₅ , C ₃ H ₇ , etc. ), preferably tetramethylsilane (hereinafter abbreviated as TMS).

The feed amount of the mixed gas to the polymerization container varies depending on the size of the container and the pumping speed of the vacuum pump, but for example, in the case of 1 to 200 containers, it is 0.1 cc.
(STP)/min to 100 c.c. (STP)/min is preferable. If it is less than 0.1 cc (STP)/min, the plasma polymerization rate is too slow to be practical, and 100 c.c.
(STP)/min, it is difficult to make a uniform polymer film.

The thickness of the polymer film produced according to the present invention is 100 Å.
It is preferable to control the thickness within the range of ~1 μm, particularly preferably within the range of 500 Å to 6000 Å. 100
If it is less than 1 μm, pinholes may be formed in the polymer film that is formed, and if it exceeds 1 μm, cracks are likely to occur in the polymer film that is formed, resulting in poor durability and poor electrical resistance tracking against humidity changes. is delayed. In the range of 500Å to 6000Å, the electrical resistance follows humidity changes extremely quickly.
Within 1 second.

As the substrate of the sensor used in the present invention, any solid material that does not generate gas in vacuum can be used, and depending on the type of sensor electrode, not only an insulator but also a conductor can be used. can be used, and its shape does not matter. Usually, glass, ceramic, etc. are used.

An example of the method for manufacturing the humidity sensor of the present invention will be explained with reference to FIG.

FIG. 1 shows an example of the plasma polymerization apparatus used in this example, in which 1 is a polymerization container, 2 is a plasma generation coil, 3 is a high frequency power source for plasma excitation, and 4 is a plasma polymerization apparatus.
is a pressure gauge, 5 and 6 are cylinders, 7 is a gas flow rate adjustment valve, 8 is a vacuum exhaust port, 9 is a sensor base, 1
0 is a probe, 11 is a voltmeter, 12 is an ammeter, 13 is a variable voltage power supply, 14 is a displacement control valve, and 15 is a vacuum pump.

Monomer gas is introduced from the cylinders 5 and 6 into the polymerization container 1 at an appropriate flow rate using the gas flow rate control valve 7, plasma is generated by the plasma generation coil 2, a polymerization reaction is performed, and the substrate 9 is heated. A polymeric film was formed on the surface. The pressure gauge 4 is used to confirm that the degree of vacuum within the polymerization container is at a predetermined value. Note that the electron temperature Te can be determined by measuring the current-voltage characteristics of the two probes 10.

After forming a polymer film on the surface of the substrate in this way,
A pair of electrodes with a certain pattern is deposited on the surface of the polymer film to create a product.

A humidity sensor using the plasma polymerized film obtained by the present invention as a resistor has the following features compared to conventional products.

Extremely quick response to humidity.

It has no hysteresis and has good followability to changes in humidity.

Excellent mechanical strength.

It can be used even under high humidity conditions.

It is possible to make it lighter and smaller.

Examples of the present invention are shown below, but the present invention is not limited to the examples unless the gist of the invention is exceeded.

Example 1 Using the apparatus shown in Fig. 1, the molar ratio of TMS and NH ₃ was adjusted to be (TMS/NH ₃ ) 1/2, and the flow rate of the mixed gas was 0.44 cc (STP)/min. The degree of vacuum was maintained at 10 mm Torr by adjusting the exhaust volume from the exhaust port. 13.56 MHz high frequency power was applied to the plasma generation coil 2, giving 25 W of power, and the electron temperature was increased to 30,000 m Torr near the substrate 9. And so. A glass plate was used as the substrate 9, and a polymer film was formed on the surface thereof. Polymerization was carried out for 60 minutes. After the polymerization was completed, the substrate was taken out, a mask for producing electrodes was fixed on the polymer film, and electrodes in the pattern shown in FIG. 2 were provided on the polymer film by vacuum evaporation. The relationship between the resistance value between both ends T ₁ and T ₂ of the electrode and humidity was determined. The results are shown in FIG. A test regarding the humidity responsiveness of the sensor was conducted using the method described later, and the results are shown in FIG. From the same figure, it can be seen that the response time is within 1 second, and the response time of the commercially available ceramic sensor (approximately 5
It is clear that the time has been significantly shortened compared to the actual time (minutes). Furthermore, the error in the measured value due to the hysteresis of the sensor was within 1% of the measured relative humidity value.

The response time of the humidity sensor was measured using the apparatus shown in FIG.

In the figure, 16 and 17 are glass containers with a volume of 4;
8 to 20 are electromagnetic valves, 21 is a humidity sensor of the present invention, and 22 is a measurement chamber with a volume of 10 c.c. 23 is an electrical resistance meter, and the lead wire from the sensor is guided from the measurement chamber in a sealed state.

First, keep the container 16 with a volume of 4 at a humidity of 82%,
Keeping container 17 of the same volume at 61% humidity, valve 1
8, 19, and 20 are all closed. The volume of the room 22 in which the sensor was installed was 10 c.c., and the humidity was initially maintained at 63%.

Valve 18 is opened at time _t1 and closed after 2 seconds.
Valve 19 is opened at time t ₂ and closed after 2 seconds. FIG. 4 shows changes in the electrical resistance of the sensor manufactured according to the present invention measured during this period. In this example the response time was 0.4-0.7 seconds.

Example 2 Example 1 except that the mixing molar ratio of TMS and NH ₃ (TMS/NH ₃ ) in Example 1 was changed to 1/1.
A humidity sensor was created under the same conditions. The relationship between the resistance value of the polymer film of the sensor and the humidity is as shown in FIG. 3, and the sensor exhibited almost the same characteristics as that of Example 1.

In addition, in Examples 1 and 2 above, a polymer film was formed on the surface of the substrate and an electrode was formed on the surface of the film, but it is also possible to form an electrode on the surface of the substrate and form a polymer film thereon. . In addition, a polymer film is formed on the surface of the base particles, and a large number of base particles with these polymer films are
A sensor may be constructed by filling an air-permeable container under pressure and providing electrodes at both ends of the container. In addition, the present invention can be applied to manufacture a humidity sensor having a structure similar to that conventionally used.

Comparative Example 1 Example 1 except that the mixing molar ratio of TMS and NH ₃ (TMS/NH ₃ ) in Example 1 was changed to 2/1.
A humidity sensor was created under the same conditions. The relationship between the resistance value of the polymer film of the sensor and the humidity is as shown in FIG. 3, and it can be seen that the humidity detection sensitivity is low.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a plasma polymerized film forming apparatus used for manufacturing a humidity sensor according to the present invention, FIG. 2 is a diagram showing an example of an electrode pattern, and FIG. 3 is a diagram showing an example of an electrode pattern. A chart showing the change in electrical resistance value with respect to humidity of the manufactured humidity sensor,
FIG. 4 is a chart showing the response characteristics of the humidity sensor manufactured according to Example 1, and FIG. 5 is a schematic diagram of an apparatus for measuring the response time of the humidity sensor. 1... Polymerization container, 2... Coil for plasma generation, 3... High frequency power source for plasma excitation, 4... Pressure gauge, 5, 6... Cylinder, 7... Gas flow rate adjustment valve, 8... Vacuum exhaust port , 9...sensor base,
10... Probe, 11... Voltmeter, 12... Ammeter, 13... Variable voltage power supply, 14... Displacement adjustment valve, 15... Vacuum pump.

Claims (1)

[Claims] 1. A method for producing a humidity sensor, which comprises forming a plasma polymerized film on a sensor substrate using a gas mixture of an organosilicon compound and ammonia in a molar ratio (organosilicon compound/ammonia) of 0.1 to 1.5.