JPS5931278B2 - Piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric element and an ultra-small piezoelectric element that can simplify the manufacture of piezoelectric elements for pickups used for reproducing records, etc., and improve mass productivity accordingly. and the pickup performance associated with it (
For example, the purpose is to improve the mechanical impedance of the needle tip in the high range (high range limit).

As shown in FIG. 1, a piezoelectric element used in a conventional record playback pickup cartridge is made of a low-grade material such as Cu, Al, etc. A relatively thick metal plate 3 having a ceramic piezoelectric body 1 is bonded to
0 silver paste on the other side or e.g. Cu, AI
This piezoelectric element has an electrode 4 made of a metal vapor deposited film, etc., applied to it, and in this piezoelectric element, a mechanical signal or an acoustic signal transmitted to the element bends the element to convert it into an electric signal and take it out. An electromotive force is generated between the electrodes 3 and 4 (the metal plate 3 also serves as an electrode).

In addition, the piezoelectric output is in principle zero if the stress-neutral plane in the thickness direction of the piezoelectric element itself, including the electrodes and piezoelectric body, is on the - plane (center) when the element is bent. ,
It is impossible to deposit metal vapor deposited films of the same material and the same thickness on both sides of the ceramic piezoelectric body 10.

Therefore, in order to obtain a large piezoelectric output against bending vibration of a pickup, etc., it is necessary to deviate the stress-neutral plane by a large amount from the negative plane of the thickness of the piezoelectric element itself. It is necessary to apply on one side a metal plate 3 having a thickness that is relatively thicker than the thickness of the electrode applied on the other side.

Therefore, with such a structure, the frequency characteristics of the piezoelectric output and the mechanical Q depend on the materials of the metal plate 3 and the adhesive layer 2.
, and have the disadvantage of being limited in temperature characteristics and the accompanying temperature range in which they can be used.

For example, when epoxy resin is used as the material for the adhesive layer 2, the mechanical Q suddenly decreases at about 40 to 80°C.
Additionally, it generally takes several days for the adhesive to harden and provide stable vibration characteristics.

Furthermore, the piezoelectric element of a record pickup cartridge is desired to be small, lightweight, and have high piezoelectric sensitivity, but the Young's modulus of a ceramic piezoelectric material is usually 1 to 5.
In order to maximize the piezoelectric sensitivity of the piezoelectric element to bending vibration, a relatively thick metal plate 3 is required according to the above-mentioned principle. It has the disadvantage of being heavy.

Furthermore, in the production of conventional piezoelectric elements, there is a drawback that troubles such as uneven adhesion or defective shapes are likely to occur when the ceramic piezoelectric body 1 and the metal plate 3 are bonded together.

The present invention provides a piezoelectric element that eliminates these conventional drawbacks, and will be described below with reference to embodiments shown in FIGS. 2 and 3.

In the present invention, a T film having a Young's modulus higher than that of the piezoelectric material 5 is provided on one surface of a thin plate-like piezoelectric material 5 such as a rectangular ceramic material.
A conductive hard inorganic material 6 such as iC is deposited by reactive vapor deposition or ion blating means to a thickness of at least 10 μm.
The thin piezoelectric material 5 is placed on a predetermined mask, and is characterized in that it is deposited to a thickness of
A thick conductive film of 10μ or more is deposited on one surface of the Ti
A conductive hard inorganic material 6 such as carbon is deposited thereon, thereby making it possible to eliminate the influence of a conventional adhesive layer and the processes associated therewith.

By the way, if it is a light conductive hard inorganic material that has a Young's modulus higher than that of a ceramic piezoelectric material such as TiC, the desired purpose can be sufficiently achieved with a thin adhesion layer. Although this is very advantageous, the conventional method of forming a thin film using a highly hard and poorly soluble inorganic material has a slow film formation rate, and it has been extremely difficult to obtain a thickness sufficient to form a piezoelectric element.

However, recently, it has become easy to obtain a thickness of several tens of microns or more using the above-mentioned reactive vapor deposition or ion grating method.
In order to obtain a thick film of C, Ti is evaporated using an electron beam or the like in a high vacuum chamber of about 10-6 Torr, and then a hydrocarbon gas such as acetylene is introduced.
Adjust the gas flow rate so that the pressure inside the vacuum chamber is maintained at 1 to 5xlO'Torr, and apply 100
A voltage of around 100 volts is applied to generate a glow discharge and activate the hydrocarbon gas.

The Ti particles evaporated in such an active gas react with this activated hydrocarbon gas, and are deposited as a TiC film on the surface of a ceramic piezoelectric body, that is, a thin piezoelectric body placed at a certain distance from the Ti evaporation source. do.

Figure 2 is a cross-sectional view of the piezoelectric element obtained in this way.
Reference numeral 7 denotes an electrode made of a metal vapor-deposited film obtained by a conventional method.

The formation rate of the TiC film obtained by the above method is 1
μ/i or more is possible, resulting in a significantly higher production rate than conventional sputtering methods.

Moreover, the Young's modulus of the TiC film obtained in this way is 3
0x101ON/m2 or more, density 4.5-4.9X
It was 103 kg/m2.

The table below compares the minimum resonance frequency and weight of piezoelectric elements for pickup cartridges made by the above method as cantilever beams.The dimensions of the ceramic piezoelectric body used in the piezoelectric bimorph are as follows: thickness 0. 2mm, width 1m
7+! The length of the vibrating part is 10 mm.

As is clear from the table above, the piezoelectric element coated with a TiC film is lighter than the conventional one, and therefore, when used in a pickup cartridge, it Since the mechanical impedance can be reduced and the resonant frequency of the piezoelectric element can be increased with the same weight, it can contribute to increasing the high frequency limit.

Due to processing, the ceramic piezoelectric body has a limit of about 200μ,
Furthermore, if the TiC film is less than 10 μm, cracks may occur in the film or accidental damage to the device may occur during handling. Furthermore, it is advantageous for miniaturization.

The one shown in Fig. 3 is one in which a conductive hard inorganic material 6' serving as an electrode part and an electrode 7 of a metal vapor deposition film similar to the above are locally formed for use up to higher frequencies.
For forming such a pattern, the above-mentioned vapor deposition means are extremely advantageous.

The above describes the deposition of TiC film etc. by reactive vapor deposition, but similar deposition is also possible by other ion blating methods, and TiC
In addition to this, similar effects can be obtained with TiN, NbC, etc.

As described above, the piezoelectric element of the present invention has a film of a conductive hard inorganic material such as TiC, which has a higher Young's modulus than the piezoelectric material, on one surface of a thin piezoelectric material made of ceramic. Since it is deposited to a thickness of at least 10μ by reactive vapor deposition or ion blating means, it is lighter than conventional products and can provide a large piezoelectric output.For example, when used as a pickup cartridge. Since it can reduce mechanical impedance at high frequencies, it has the advantage of increasing the high frequency limit.Also, because it does not require the conventional bonding process, there are no problems that occur during bonding, and it is easy to mass-produce. It has many sexual advantages.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional piezoelectric element, FIG. 2 is a sectional view of a piezoelectric element according to the present invention, and FIG. 3 is a sectional view of a bimorph showing another embodiment of the present invention. 5...Thin plate-like piezoelectric material, 6,6'...--Electroconductive hard inorganic material, 7. γ... Electrode.

Claims (1)

[Claims] 1. A film of a conductive hard inorganic material such as TiC, which has a Young's modulus higher than that of the piezoelectric material, is coated on one surface of a thin plate-shaped piezoelectric material made of ceramic by reactive vapor deposition or ion blating means, at least 10 μm or more. A piezoelectric element characterized by being coated with a thickness of .