JPS62118237A - Humidity sensor consisting of crystal resonator - Google Patents

Abstract

PURPOSE:To make a crystal resonator effectively usable as a humidity sensor and to facilitate the mass production of the sensor by forming a plasma- polymerized film consisting of a hydroxyl group-contg. polymer on the surface of the crystal resonator. CONSTITUTION:A piece or many pieces of the crystal resonators 24 are installed simultaneously into a plasma polymn. device and a gaseous 2-hydroxyethyl methacrylate monomer is introduced under 0.5Torr pressure conditions into the reaction vessel to generate high-frequency plasma with 120W electric powder. A crystal surface 21 and silver electrode 22 are coated with such plasma. The frequencies measured by using a piece of the crystal resonator 25 formed with the plasma-polymerized film in the above-mentioned manner are measured by a frequency counter 26. As a result, the frequency change of about -35Hz for each 10% relative humidity is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a quartz crystal humidity sensor.

More specifically, the present invention relates to a crystal resonator humidity sensor that is easy to manufacture.

[Prior Art] and [Problems to be Solved by the Invention] In the production of conventionally used quartz crystal humidity sensors, a polymer having the property of adsorbing moisture, generally a polyamide-based polymer, is mixed with a suitable solvent. The solution was applied to the surface of a crystal resonator, and the solvent was evaporated to form a moisture adsorption film on the surface of the resonator, which was then used as a humidity sensor.

However, with this manufacturing method, it is generally difficult to meet the natural requirement of forming a moisture adsorption film of uniform thickness on the surface of the vibrator.
Further, it requires a complicated operation in which a polymer solution must be applied to each point of the vibrator and dried.

As a result of various studies in search of a method for overcoming such manufacturing difficulties, the present inventor has found that such problems can be effectively solved by forming a plasma polymerized film of a hydroxyl group-containing polymer on the surface of a crystal resonator. I discovered that.

Means for Solving Problem C] and [Operation] Accordingly, the present invention relates to a quartz crystal oscillator humidity sensor, and this quartz crystal oscillator humidity sensor has a plasma polymerized film of 2-hydroxyethyl methacrylate on the surface of the quartz crystal oscillator. Consists of what caused it to form.

The plasma polymerized film is formed using, for example, an apparatus as schematically shown in FIG. That is, it is connected to the vacuum pump 1, the leak valve 2 and the main valve 3,
A crystal oscillator 6 is housed in a plasma reactor 5 equipped with a vacuum gauge 4, and the pressure inside one reactor is maintained at approximately 0.01 to 0.1 Torr.
After this, the valve was opened and 2-hydroxyethyl methacrylate was introduced from tank 8 into the reactor. While introducing this monomer, a high frequency generator (13, 56
Plasma is irradiated from the oscillation coil 11 using a high frequency power source consisting of a MHz) 9 and a matching unit 10 under conditions of an effective power of 50 to 200 W and a time of approximately 172 to 120 minutes.

As the reaction vessel, either a tubular type or a Pelger type can be used, and as the radiation electrode, in addition to a coiled type, an external or internal parallel electrode plate can also be used.

As a crystal resonator, an AT-cut crystal resonator with a frequency of 6 MHz or more is preferably used, and an example of its usage is shown in a plan view in Fig. 2. For example, a crystal resonator with a surface area of about 0.64 d
A silver electrode 22 is attached to the center of the crystal surface 21, and lead wires 23 and 23' are drawn out from each of the crystal surface and the silver electrode. The plasma polymerized film is formed to cover the crystal face and silver electrodes of such a crystal resonator 24.

A plasma-polymerized film of 2-hydroxyethyl methacrylate formed on the surface of a crystal resonator in this way can function as a humidity sensor because a good correlation is observed in the frequency change of the crystal resonator with respect to relative humidity. This was confirmed.

〔Effect of the invention〕

A crystal oscillator with a plasma polymerized film of 2-hydroxyethyl methacrylate formed on its surface can be effectively used as a humidity sensor, but the plasma polymerized film cannot be formed uniformly in a short time. Moreover, since it can be done in large quantities at the same time, it can be said that it is extremely superior in terms of productivity.

〔Example〕

Next, the present invention will be explained with reference to examples.

Example: A crystal resonator having the shape shown in Fig. 2 (manufactured by Hegu Tsushin Kogyo,
AT cut, 6M) 12) one or many at the same time,
The reactor was installed in a reaction vessel of the plasma polymerization apparatus shown in FIG. 1, and 2-hydroxyethyl methacrylate monomer gas was then introduced into the reaction vessel under a pressure condition of 0.5 Torr. In this state, high-frequency plasma was generated with a power of 120 W, and a reaction was performed for 10 minutes.

An example of a frequency measuring circuit using one crystal resonator 25 having a plasma polymerized film formed on its surface in this way is shown in the third example.
A frequency measuring device shown in the figure, in which the measured frequency was measured by a frequency counter 26, was placed in a constant temperature and humidity chamber at 25° C., and changes in frequency with respect to relative humidity were measured.

As the measurement results are shown in the graph of FIG. 4, a frequency change of about -35 Hz per 10% relative humidity is shown.
A good correlation was observed between relative humidity and frequency change, confirming that this plasma-polymerized film-formed crystal resonator can form a humidity sensor.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of a plasma polymerization apparatus used in the present invention. FIG. 2 is a plan view of one embodiment of a crystal resonator used in the present invention. FIG. 3 is an example of a frequency measuring circuit for a plasma polymerized film-formed crystal resonator according to the present invention. Moreover, FIG. 4 is a graph showing the relationship between relative humidity and frequency change (ΔF). (Explanation of symbols) 1...Vacuum pump 5...Plasma reaction vessel 6...Crystal oscillator 9...High frequency generator 10...Matching unit 11 ...Oscillation coil 21 ...Crystal surface 22 ...Silver electrode 24 ...Crystal resonator

Claims (1)

[Claims] 1. A quartz crystal oscillator humidity sensor formed by forming a plasma polymerized film of 2-hydroxyethyl methacrylate on the surface of a quartz crystal oscillator.