JPH04184130A - Pressure gauge - Google Patents

Abstract

PURPOSE:To measure pressure with high precision in a simple manner by utilizing a piezoelectric resonator using a piezoelectric thin film. CONSTITUTION:The peripheral edge of a constant elasticity metal thin plate 1 having a rectangular form is formed as a frame 2, and a rectangular shaped vibration part 4 is formed, separated from a U-shaped groove 3. The frame 2 and the vibration part 4 are connected by a connection part 5 having a narrow width, and the node of the vibration generated in the vibration part 4 is supported. The shape of the connection part 5 is made narrower toward the center from the peripheral edge. Continuous piezoelectric thin films 6a-6c are vapor-deposited on one connection part 5 on the vibration part 4 and a part of the frame 2. The material is ZnO, etc. The vibration part 4 of the constant elasticity metal plate 1, piezoelectric thin film 6a, and a vibration electrode 7a form a piezoelectric resonator A, and high frequency signals are inputted between an electrode 7c and the frame 2, and then the high frequency signal propagates to the vibration part 4, and vibration is generated. The impedance of the piezoelectric resonator A changes in linear form according to the degree of vacuum. Since the resonance frequency of the resonator A does not vary according to the degree of vacuum, the resonance resistance or the counter-resonance resistance can be measured directly as the function of the degree of vacuum, by inputting the signal having a certain frequency, and the degree of vacuum can be measured in simple manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure gauge, and particularly to a pressure gauge that can accurately measure the degree of vacuum from atmospheric pressure to I Torr.

[Conventional technology]

Conventionally, there are various types of pressure gauges, such as capacitance type pressure gauges and Bourdon tubes.

Among these, capacitance pressure gauges have the disadvantage of being expensive.
Bourdon tubes have the disadvantage that they are cheap or large and cannot be used in high vacuum areas.

A tuning fork type quartz resonator pressure gauge has been proposed as a solution to these drawbacks. A tuning fork type crystal oscillator pressure gauge determines the degree of vacuum by measuring the resonance resistance or anti-resonance resistance of the crystal oscillator, which changes depending on the degree of vacuum, and has the advantage of being compact and capable of highly accurate measurement. be.

[Problem to be solved by the invention]

However, the problem with the tuning fork type crystal resonator is that the resonant frequency changes depending on the degree of vacuum. Therefore, in order to use a tuning fork type crystal resonator as a pressure gauge, the following steps are required: - Incorporate the tuning fork type crystal resonator into the oscillation circuit and actually oscillate it, and determine the degree of vacuum by changing the oscillation characteristics. ■ Depending on the degree of vacuum. A method must be adopted in which a signal of the same frequency as the changing resonant frequency is input and the change in resonant resistance is measured. Therefore, the problem with (2) is that the vibrator itself is required to have low static impedance and high sensitivity, and the problem with (2) is that measurement is complicated and requires a separate device to change the frequency.

By the way, the present applicant has already used the peripheral edge of a constant elastic metal plate as a frame, integrally provided a vibrating part inside the frame via a narrow connecting part, and formed a piezoelectric thin film on the upper surface of this vibrating part. proposed a piezoelectric resonator in which electrodes are formed on a piezoelectric thin film (for example, Japanese Patent Publication No. 1-19650). After various studies on the impedance characteristics of this piezoelectric resonator, we discovered that the resonant resistance and anti-resonant resistance of the piezoelectric resonator change almost linearly depending on the atmospheric pressure, and that the resonant frequency and anti-resonant frequency do not change at all at this time. did.

Therefore, an object of the present invention is to obtain a pressure gauge that can easily and accurately measure pressure by using a piezoelectric resonator using a piezoelectric thin film.

[Means to solve the problem]

In order to achieve the above object, the pressure gauge of the present invention uses the peripheral edge of a constant elastic metal plate as a frame, and a vibrating part is integrally provided inside the frame through a narrow connection part, and the vibration A piezoelectric resonator is formed by forming a piezoelectric thin film on the upper surface of the piezoelectric resonator and forming an electrode on the piezoelectric thin film, and a constant frequency corresponding to the resonant frequency or anti-resonant frequency between the electrode of the piezoelectric resonator and the constant elastic metal plate. The apparatus is equipped with a measuring device that measures the resonant resistance or anti-resonant resistance of the piezoelectric resonator, which changes depending on the degree of vacuum, by inputting a frequency signal.

[Effect]

When a piezoelectric resonator is placed exposed to atmospheric pressure and a high frequency signal is input to it, the impedance characteristic of the piezoelectric resonator becomes as shown by the solid line in FIG. On the other hand, as the atmospheric pressure is lowered, the impedance characteristics change as indicated by the broken line in FIG. 1 as the degree of vacuum increases. In other words, the resonant resistance R1
As the resistance decreases, the anti-resonance resistance R1 increases. However, the resonant frequency f and the anti-resonant frequency f do not change at all.

In the case of a piezoelectric resonator using a piezoelectric thin film, this is the resonant resistance.

Since the anti-resonance resistance changes linearly depending on the degree of vacuum,
If you have determined the relationship between the resonant resistance or anti-resonant resistance and the degree of vacuum in advance, you can install this piezoelectric resonator in the environment where the degree of vacuum is to be measured, input the resonant frequency or anti-resonant frequency signal, and then The degree of vacuum can be easily determined by simply measuring the resonant resistance or anti-resonant resistance. Therefore, unlike a tuning fork type crystal resonator, there is no need to actually incorporate it into an oscillation circuit to generate oscillation, there is no requirement for the resonator itself to be highly sensitive, and it can generate a constant frequency signal regardless of the degree of vacuum. Measurement is easy because all you have to do is input it.

〔Example〕

2 to 4 show an example of a piezoelectric resonator used in the present invention.

In the figure, l is a rectangular constant-elastic metal thin plate, its peripheral portion is a frame portion 2, and two U-shaped grooves 3, 3 are formed inside the frame portion 2.
A rectangular vibrating section 4 is formed between the two. The frame portion 2 and the vibrating portion 4 are connected via a narrow connecting portion 5, and the connecting portion 5 supports the nodes of the spreading vibration generated in the vibrating portion 4.

In this embodiment, the connecting portion 5 has a tapered shape that gradually becomes narrower from the peripheral edge toward the center.

Constant modulus metals are alloys whose elastic modulus hardly changes with changes in temperature, and Elinvar (trade name) is a typical constant modulus metal (Fe-Ni-Cr series). Above frame part 2. The vibrating section 4 and the connecting section 5 are integrally formed from a single elastic metal plate 1 by a method such as photolithography.

Piezoelectric thin films 6a, 6b, and 6c are continuously deposited on the vibrating part 4, on one of the connecting parts 5, and on the upper surface of a part of the frame part 2 by sputtering, vacuum deposition, ion blating, or vapor phase deposition. It is formed by a known method such as the method. Piezoelectric thin film materials include zinc oxide, barium titanate,
In addition to lead zirconate titanate and lead titanate, any one selected from cadmium sulfide, cadmium selenide, beryllium oxide, wurtzite zinc sulfide, or a solid solution thereof (including zinc oxide), Furthermore, Al1N (
Aluminum nitride) etc. can also be used.

Electrodes 7 are formed on the piezoelectric thin films 6a to 6C by sputtering,
It is formed by a known method such as a vacuum evaporation method.

Examples of electrode materials include Ni, Ai! , An, etc. are used. The electrode 7 is composed of a vibrating electrode 7a on the piezoelectric thin film 6a on the vibrating part 4, a terminal electrode 7c on the piezoelectric thin film 6c on the frame part 2, and an extraction electrode 7b on the piezoelectric thin film 6b on the connecting part 5. The vibrating electrode 7a and the terminal electrode 7c are connected by an extraction electrode 7b. Note that the piezoelectric thin films 6b and 6c interposed between the extraction electrode 7b and the terminal electrode 7c, and the connecting portion 5 and frame portion 2 function as insulators.

As described above, the piezoelectric resonator A is constituted by the vibrating part 4 of the constant elastic metal plate l, the piezoelectric thin film 6a formed thereon, and the vibrating electrode 7a formed on the piezoelectric thin film 6a.

This piezoelectric resonator A is configured such that by inputting a high frequency signal between the terminal electrode 7c and the frame portion 2 of the constant elastic metal plate 1, vibration spreads to the vibrating portion 4 of the constant elastic metal plate l due to the action of the piezoelectric thin film 6a. is excited. The impedance of the piezoelectric resonator A varies linearly depending on the degree of vacuum.

Figure 5 shows the resonance resistance (Ω) and degree of vacuum (Torr) obtained using piezoelectric resonator A having the shape and dimensions shown in Figure 3.
). In addition, constant elastic metal plate (Elinbar)
), the thicknesses of piezoelectric thin 1 (ZnO) and electrode (Ni) were set to 0.1 mm, 20 μm, and 1 am. As is clear from the figure, l Torr ~ atmospheric pressure (760T
It can be seen that the resonance resistance increases almost linearly up to (orr).

! FIG. 6 shows a characteristic diagram of the degree of vacuum and anti-resonance resistance obtained using the piezoelectric resonator A having the above shape. In this case, contrary to the resonance resistance, the anti-resonance resistance tends to decrease as the degree of vacuum approaches atmospheric pressure. Incidentally, the variation in anti-resonance resistance in the region where 100 Torr is not applied is due to measurement error.

A method of actually measuring the degree of vacuum using the piezoelectric resonator A will be explained.

First, as shown in Figure 7, the air chamber is sealed to the piezoelectric resonator! Install it in an exposed state within θ. Air chamber IO exhaust pipe 11
is connected to a vacuum pump (not shown). Then, one end of the lead wire 12.13 is connected to the terminal electrode 7c of the piezoelectric resonator A and a part of the frame portion 2, and the other end of the lead wire 12.13 is provided outside the air chamber IO. Connect to.

Now, from the impedance analyzer 14, the piezoelectric resonator A
has a resonant frequency f, or an anti-resonant frequency f.

When a constant frequency signal corresponding to is input, the piezoelectric resonator A
The resonance resistance R1 or anti-resonance resistance R6 changes depending on the degree of vacuum. By measuring this resonance resistance R7 or anti-resonance resistance R1, the degree of vacuum can be easily determined from FIG. 5 or FIG. 6.

Note that the measuring device in the present invention is not limited to the impedance analyzer as in the embodiment, but also includes, for example, a high frequency power source that outputs a constant frequency signal corresponding to the resonant frequency or anti-resonant frequency, and a device that measures the resonant resistance or anti-resonant resistance. It may also be configured with an impedance meter or the like.

Further, the shape and structure of the piezoelectric resonator A are not limited to those in the embodiment.

Furthermore, the pressure gauge of the present invention can be used not only to measure the degree of vacuum but also to measure positive pressure.

〔Effect of the invention〕

As is clear from the above explanation, since the resonant frequency of the piezoelectric thin film piezoelectric resonator of the present invention does not change depending on the degree of vacuum, by inputting a constant frequency signal, the resonant resistance or resonant resistance can be changed as a function of the degree of vacuum. Resonant resistance can be measured directly. At this time, there is no problem even if the sensitivity of the piezoelectric resonator is somewhat low, and there is no need for a device to change the frequency during measurement, making it possible to measure the degree of vacuum extremely easily.

[Brief explanation of the drawing]

Fig. 1 is an impedance characteristic diagram of the piezoelectric thin film type piezoelectric resonator according to the present invention, Fig. 2 is a perspective view of the piezoelectric resonator, Fig. 3 is a plan view of the piezoelectric resonator, and Fig. 4v1 is an IV- of Fig. 3. 5 is a vacuum degree dependent characteristic diagram of the resonant resistance, FIG. 6 is a vacuum degree dependent characteristic diagram of the antiresonant resistance, and FIG. 7 is a configuration diagram of a pressure gauge. A...Piezoelectric resonator, l...constant elastic metal plate, 2...
Frame part, 4... Vibrating part, 5... Connecting part, 6a to 6C.
...Piezoelectric thin film, 7°7a~7C...electrode, 14...
impedance analyzer. Patent Applicant: Murata Manufacturing Co., Ltd. Representative: Hidetaka Tsutsui, Patent Attorney Figure 1 Figure 2 Figure 7 5...Connection Analyzer No. 3r! ! 1 Figure 4 Figure 5 Figure 6 Vacuum degree (TORR)

Claims (1)

[Claims] (1) The peripheral edge of one constant elastic metal plate is used as a frame, a vibrating part is integrally provided inside the frame via a narrow connecting part, a piezoelectric thin film is formed on the upper surface of this vibrating part, and a piezoelectric By inputting a constant frequency signal corresponding to the resonant frequency or anti-resonant frequency between the piezoelectric resonator, which has electrodes formed on a thin film, and the electrodes of the piezoelectric resonator and a constant elastic metal plate, the A pressure gauge characterized by comprising: a measuring device for measuring the resonant resistance or anti-resonant resistance of a piezoelectric resonator that changes as the piezoelectric resonator changes;