JPS6239597B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sonic probe, particularly a sonic probe suitable for use in a microscope that utilizes high frequency sonic energy.

In recent years, it has become possible to generate and detect high-frequency sound waves up to 1 GHZ, resulting in a sound wave wavelength of about 1 micron underwater, and therefore, a microscope that uses sound wave energy has been considered. Regarding this type of ultrasonic microscope, please refer to Japanese Patent Application Laid-Open No. 1986-
It is described in Publication No. 16058.

In such devices, it is important to create a narrow focused acoustic beam, and it is strongly desired to improve the performance of the acoustic probe. first,
A conventional sonic probe will be explained with reference to FIG. Regarding this conventional sonic probe,
Proceedings of the IE PRCEEDINGS OF THE IEEE) No.
Volume 67, No. 8, pp. 1092-1114 (August 1979)
The paper published in May), especially on page 1094.

That is, the sonic probe consists of a cylindrical crystal (sound wave propagation medium) 1 made of a sound wave propagation medium such as sapphire, which has one end surface polished to a flat surface and a concave hole bored in the other end surface, and this crystal 1. A lower electrode 2 made of titanium, gold, chrome, aluminum, etc. is provided on the polished end surface by vapor deposition or the like, a piezoelectric material 3 such as zinc oxide is provided on it by sputtering or the like, and an upper electrode 4 is further placed on top of it. It consists of a piezoelectric element provided by vapor deposition or the like. When an RF electric signal is applied between the upper electrode 4 and the lower electrode 2 of such a probe, the piezoelectric material 3 emits a plane wave RF sound wave within the crystal 1. This plane wave is focused at a predetermined focal point S by a positive spherical lens formed at the interface between the crystal 1 and the medium 5 formed in the concave portion.

As is well known, if the ratio of the focal length to the aperture, ie, the F-number of the lens, is sufficiently small, it is possible to create an extremely narrow acoustic beam with the above-described configuration.

The focused sound waves are subject to disturbances such as reflection, scattering, and transmission attenuation by the sample 6 placed near the focal point. This means that it is possible to obtain electrical signals that reflect the properties.

Note that for the detection of the sound wave energy, the above-described sound wave probe may be used again, or a similar sound wave probe placed facing the confocal area may be used.

As is clear from the above explanation, the conventional example uses a positive spherical lens as its focusing principle, which utilizes the difference in sound speed between the crystal and the medium. Therefore, in order to form a spherical lens with good focusing properties, it is important to form a concave hole with excellent specularity and sphericity in the crystal. Moreover, since the attenuation of sound waves in the medium from the lens surface to the focal point S is extremely large, it is necessary to create a lens with a low F number by forming a concave hole with a minute diameter, for example, 0.2 mm, and from the lens surface to the focal point S. It is necessary to reduce the distance to avoid sound wave attenuation.

On the other hand, it is desirable that the area of the piezoelectric element portion that emits RF sound waves becomes smaller as the spherical surface of the lens becomes smaller. That is, as shown in FIG. 1, it is desirable that the diameter d of the concave hole and the diameter D of the upper electrode 4 be equal. This is due to the following reasons. That is, for example, as shown in FIG.
When RF sound waves are emitted under conditions D, plane waves propagate within the crystal along the path shown by the dotted line. Therefore, the plane wave transmitted to the outside of the concave hole is diffusely reflected within the crystal and enters the piezoelectric material 3, causing unnecessary signals (noise).

Moreover, when d>D, contrary to the above-mentioned condition, the F number of the lens becomes large, resulting in poor focusing performance and high resolution cannot be obtained.

Here, the relationship between the F number of the lens and the resolution will be described based on FIG. 3. In the figure, when the wavelength of the plane plate is λ and the F number of the lens is Sinθm, the resolution Δρ can be found by the following equation.

Δρ=λ/4Sin θm Here, θm is the opening angle of the acoustic beam. Therefore, the resolution Δρ is the aperture angle θm of the acoustic beam
The larger the value, the better.

As explained above, in order to obtain high-resolution images in microscope devices that utilize sound wave energy, it is necessary to reduce the lens aperture of the focusing spherical lens in the sound wave probe and to use a piezoelectric element that emits sound waves. It is also necessary to reduce the area.

The inventors of the present invention have discovered that when creating glasses such as quartz glass, or when using natural quartz, crystal, etc., air bubbles that exist or occur inside the glass are extremely useful as spherical lenses. After polishing quartz containing bubbles up to the equatorial plane of the bubbles, we created quartz with the hemisphere of the bubbles as a spherical lens, resulting in a micro diameter (0.2 mm) and specularity that is impossible with conventional polishing methods. , it became possible to obtain a spherical lens with a degree of vacuum. However, as mentioned above, as the diameter of the concave hole becomes as small as about 0.2 mm, it becomes extremely difficult to attach an upper electrode with the same diameter on the axis of the concave hole by vapor deposition as in the past. It was hot. Moreover, even if the upper electrode is attached so as to align with the geometrical axis of the concave hole, the acoustic axes of the two do not necessarily coincide in some cases.
Furthermore, it was extremely difficult to connect a lead wire for applying an RF electric signal to the upper electrode.

The present invention has been made in view of the above points, and the upper electrode is completely made of piezoelectric material with a predetermined cross-sectional area.
Another object of the present invention is to provide a sonic probe that can be mounted accurately.

In order to achieve this object, the sonic probe of the present invention includes a sound wave propagation medium having a concave hole formed at one end thereof, and a first electrode (lower electrode) at the other end of the sound wave propagation medium. and a piezoelectric element in which a piezoelectric material and a second electrode (upper electrode) are formed in this order, the acoustic probe comprising means for rotatably supporting one end of the second electrode. , the other end of the second electrode has a flat part that contacts the piezoelectric material with a predetermined cross-sectional area, and a flexible conductor layer is provided on the flat part.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 4 is a diagram showing an embodiment of the present invention.
In the figure, a crystal 1, which is a sound wave propagation medium having a concave hole formed at one end, is supported by a case 7, and is maintained at a predetermined gap from a sample 6. At the top of case 7 is an RF oscillator (not shown).
A connector 8 is attached for connecting to. Furthermore, this connector 8 can be moved on the XY plane using four knobs 9.

A flexible bellows 10 is attached to the tip of the connector 8, and an RF signal is transmitted to the piezoelectric material 2 via a ball receiver 11 and a ball (metal ball) 12. That is, in the probe of this embodiment, the ball 12 acts as an upper electrode.

According to this configuration, the ball 12 can be arbitrarily moved on the piezoelectric material 3 by adjusting the knob 9. Therefore, by applying an electric signal between the ball 12 and the lower electrode 2, emitting a plane wave from the piezoelectric material 3 into the crystal 1, and adjusting the knob 9 while detecting the reflected wave, the ball 12 Acoustic axis alignment between the concave hole of the crystal 1 and the concave hole of the crystal 1 can be easily performed.

FIG. 5 is an enlarged view of the vicinity of the ball receiver 11.
The upper part of the ball 12 is rotatably supported by a ball receiver 11 having a concave hole that substantially matches the spherical surface of the ball. The lower part of the ball 12 is flattened to have a diameter D equal to the diameter d of the concave hole (lens spherical surface) of the crystal 1, and this flat surface is coated with a flexible conductive layer 13, such as an amalgam of gold and mercury. There are layers.

Therefore, when assembling the device, as shown in FIG. Even when the conductive layer 13 is supported by
When a portion of the piezoelectric material 3 contacts a portion of the piezoelectric material 3 (FIG. 6b), the ball 12 rotates and the conductive layer 13
completely contacts the surface of the piezoelectric material 3 (FIG. 6c).

Furthermore, even if there are minute irregularities or undulations on the flat surface of the ball 12 or the upper surface of the piezoelectric material 3, the ball 1
A flexible conductive layer 1 is provided on the contact surface between 2 and the piezoelectric material 3.
3 intervenes, and the ball 12 and the piezoelectric material 3 are in extremely light and electrically reliable contact.

Note that the ball 12 as described above can be easily manufactured by the following method. As shown in FIG. 7a, the notch length L of the ball 12 is appropriately selected, and the ball 12 is notched so that the diameter D of the notch portion of the ball 12 is equal to the diameter d of the concave hole of the crystal 1. Polish this notch. Next, gold 14 is deposited on the polished surface by plating or vapor deposition. Furthermore, when mercury 15 is applied to the surface of the gold 14, the gold 14 and mercury 15 combine to form an amalgam layer on the polished surface.

The above has described the case where a ball with a cutout part is used as the upper electrode, but instead of using the ball, the apex part of the cone is cut with length L as shown in FIG. A similar effect can be obtained by polishing so that the diameter D of the cut surface is equal to the diameter d of the concave hole, and forming an amalgam layer of gold and mercury on the polished surface in the same manner as described above. However, in this case, if the support of the cone is not flexible, and the parallelism with the top surface of the piezoelectric material 3 is not maintained as shown in FIG. Therefore, complete contact is impossible.

In the above embodiment, a sonic probe having two electrodes was explained, but the sound wave propagation medium can be made of an electrically conductive material (for example, glassy carbon such as glassy carbon). There are also sonic probes that use the medium itself as the lower electrode.
It goes without saying that the present invention can be applied.

As described above, according to the present invention, it is possible to omit the upper electrode deposition process and the lead wire connection process, which were extremely difficult in the past, and at the same time, it is possible to easily equalize the area of the sound wave focusing part and the area of the sound wave emission part. can do. Furthermore, it has the advantage of perfecting electrical contact, and is expected to have great effects in the creation of devices that use high-frequency focused sound waves, such as sonic microscopes, micro-nondestructive testing, and ultrasonic spectroscopy. I can do it.

[Brief explanation of the drawing]

Figure 1 is a diagram to explain the structure of a conventional sonic probe, Figure 2 is a diagram to explain the drawbacks of a conventional sonic probe, and Figure 3 is a diagram to explain the relationship between the F number of the lens and the resolution. FIG. 4 is a diagram showing the configuration of an embodiment of the present invention, FIG. 5 is a diagram showing the configuration of the main part of the embodiment shown in FIG. 4, and FIG.
A diagram for explaining the state of contact between the upper electrode and the piezoelectric material in one embodiment shown in the figure, FIG. 7 is a diagram showing the above-mentioned upper electrode, and FIG. 8 is a diagram showing the upper electrode of another embodiment of the present invention. It is a diagram.

Claims (1)

[Claims] 1. A sound wave propagation medium having a concave hole formed at one end, a first electrode, a piezoelectric material, and a second electrode formed at the other end of the sound wave propagation medium in this order. A sonic probe comprising a piezoelectric element made of a metal oxide, comprising means for rotatably supporting one end of the second electrode, the other end of the second electrode being connected to the piezoelectric material in a predetermined cross-sectional area. What is claimed is: 1. A sonic probe characterized in that the probe has a flat part in contact with the flat part, and a flexible conductive layer is provided on the flat part. 2. The sonic probe according to claim 1, wherein the second electrode is a metal ball whose flat portion is a cutout portion with a predetermined cross-sectional area. 3. The sonic probe according to claim 1 or 2, wherein the flexible conductive layer is an amalgam layer of gold and mercury.