JPH0381662A - Acoustic lens and its production, and acoustic microscope device - Google Patents

Abstract

PURPOSE:To obtain an acoustic image with high resolution and to measure the anisotropy of a sample at a specific position by using acoustic lens bodies formed on plural planes by applying the anisotropic etching of single crystal. CONSTITUTION:A lens body 1 has a concave lens surface 2 in a quadrangular pyramid shape at one end and also has piezoelectric elements 31 - 34 formed at the other end independently corresponding to the four pyramid surfaces. The piezoelectric elements 31 and 32 are constituted by stacking piezoelectric bodies 51 and 52 and further upper electrodes 61 and 62 on a common electrode 4. Those piezoelectric elements can be connected to a plane wave generating circuit 5 or receiving circuit 6 selectively with an electric switch 7. The lens body 1 is formed of single crystal silicon and worked by applying the anisotropic etching of the single crystal. Thus, the acoustic wave with high resolution is obtained and the anisotropy of the sample is measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device that uses high frequency sound wave energy,
In particular, the present invention relates to an acoustic lens suitable for use in a sonic microscope, a method for manufacturing the same, and a sonic microscope device applying the same.

[Conventional technology]

Conventionally, a spherical lens is commonly used in sound wave microscopes.The spherical lens is used to focus sound waves on a single point in the sample, scan this point over a certain area within the sample, and capture the returning sound wave signal. , an acoustic image of the microstructure of the sample can be obtained. On the other hand, by using a cylindrical lens in addition to a spherical lens, it was discovered that the anisotropy of the elastic properties of a sample can be identified in JP-A-58-906.
This is stated in Publication No. 3. According to this method,
Since the sound waves are converged into a line (referred to as a line focused beam), elastic properties in a direction perpendicular to this line within the sample plane can be identified, but there are disadvantages such as first order. That is, since the information is averaged over the length of the axis of the cylindrical surface, it is not possible to obtain a resolution on the order of several μm as obtained with a spherical lens.

Furthermore, unless the positional relationship between the sample and the cylindrical lens is rotated, information in only one direction can be obtained.

[Problem to be solved by the invention]

According to the above conventional technology, when obtaining an image with high resolution,
When measuring the anisotropy of a sample, it was necessary to examine the sample using different lenses. As a result, even if an acoustic image was obtained, it was impossible to measure the anisotropy of the sample at that specific location.

The aim of the invention is to obtain an acoustic image and at the same time to make it possible to measure the anisotropy of the sample at specific positions therein. Furthermore, conventional cylindrical lenses could only measure characteristics in one direction, but by making it possible to measure characteristic values in multiple directions without changing the positional relationship between the sample and the lens. be.

[Means to solve the problem]

To achieve the above objective, we invented a polyhedral lens instead of the conventional spherical or cylindrical lens.In this lens, electrodes that emit plane waves and electrodes that receive signal waves are formed corresponding to each face of the polyhedron. has been done.

[Effect]

In the above polyhedral lens, the pair of lens planes has the role of transmitting and receiving sound waves.

Since the plurality of pairs of planes are placed at constant angles to each other with respect to the central axis of the lens, the elastic properties of the sample in multiple directions can be determined. Furthermore, if this lens is used, plane waves emitted from all planes can be converged on one point, so an acoustic image can be obtained with high resolution.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The lens body has a lens surface 2 consisting of a four-pyramidal concave surface at one end thereof, and piezoelectric elements 31 to 34 positioned corresponding to each of the four pyramidal surfaces are independently formed at the other end. There is. By applying a voltage to each piezoelectric element, an elastic plane wave is generated within the lens body, and a sound wave is transmitted from the pyramidal surface located directly below to the sample through a medium (mainly water). Furthermore, the sound waves returning from the sample travel in the opposite direction to the piezoelectric element, where they are detected as a voltage signal. The contour shape of the piezoelectric element is determined as follows. That is, the shape is slightly smaller than the outline of four mutually touching isosceles triangles formed by projecting the four pyramidal surfaces at one end of the lens body onto the plane at the other end.

This prevents one piezoelectric element from interfering with other adjacent lens surfaces.

FIG. 2 shows a cross-sectional view of the lens body in FIG. 1 taken along plane A. Each of the piezoelectric elements 31 and 32 in FIG.
and 52, and gold upper electrodes 61 and 62 are stacked on top of each other.

These piezoelectric elements can be connected to a plane wave generating circuit 5 or a receiving circuit 6, and connection to either circuit can be selected by an electric switch 7.

With this lens, (1) an acoustic image can be obtained; (2)
) The fact that line focused beams in two orthogonal directions can be generated independently will be explained below.

To obtain an acoustic image, a synchronous voltage is applied to all the piezoelectric bodies 31 to 34 from the plane wave generation circuit 5 so that the sound waves emitted from the lens body pass through the medium 3 and are focused into the sample 8. The traveling direction of the plane wave emitted from the piezoelectric bodies 51 and 52 of the pair of piezoelectric elements 31 and 32 is as shown by the arrow 9 of the 21s. It is clear that the plane waves emitted from the other pair of piezoelectric elements 33 and 34 travel in the same way and are focused.

The sound waves containing information about the sample reflected from this focal point are
The piezoelectric elements 31 to 34 are reached by following the path indicated by the arrow 9 in the opposite direction.If the voltage signal generated here is guided to the receiving circuit 6 via the switch 7, an acoustic image of the sample can be obtained.The principle of detection of 0 or more is as follows. , which is essentially the same as detecting an acoustic image using a conventional spherical acoustic lens. The convergence of sound waves in a spherical acoustic lens is as shown in FIG. 3. A plane wave 11 emitted from a piezoelectric element 12 is refracted by the spherical part of the lens body 10, converged at a focal point, and then passes through the opposite path to form a reflected wave. is the piezoelectric element 12
Return to FIG. 5 schematically shows the distribution of acoustic intensity near the focal point in the sample.

The sound waves emitted from the spherical lens converge in a rotationally symmetrical manner, with a point-like strong convergence appearing at the center, but in addition to this, an annular astigmatism appears around the center. On the other hand, the lens consisting of four surfaces shown in FIG. 1 shows an acoustic intensity distribution in the xy plane of the sample as shown in FIG. 7, in which a four-fold symmetrical distribution appears.

Similar to FIG. 5, a point-like strong convergence portion appears on the central axis.

This spot provides an acoustic image with high resolution, similar to a spherical lens.

Next, we will discuss the principle of measuring the anisotropy of a sample. When the lens body is brought closer to the sample from the position where the acoustic intensity has converged to one point as shown in FIG. 7, linear focused beams appear on the X and Y axes as shown in FIG. The focused beam on the x-axis is formed by piezoelectric elements 31 and 32 of FIG.
formed by. In other words, if you use a focused beam that falls on the
You can see the elastic anisotropy in the direction.

This is done using the same principle as determining the elastic anisotropy of the sample in the y direction using a focused beam formed by the cylindrical lens shown in FIG. 4 (FIG. 6). We have explained how to obtain signals by independently generating focused beams that appear on the x- and y-axes, but
Signals can also be obtained when rotating the axis and y-axis. At this time, by slightly shifting the frequency of the X-axis circumferential focused beam and the Y-axis circumferential focused beam frequency and adding a phase detection means to the receiving circuit, it is also possible to obtain signals for each axis without interference. What should be noted here is that with a conventional cylindrical lens, elastic information can only be obtained in one direction unless the positional relationship between the sample and the lens is rotated, whereas with the polyhedral lens of the present invention, elastic information can be obtained from the sample and the lens. While keeping the positional relationship of the lenses fixed, elastic information in the two directions of X and y can be obtained independently by selecting a pair of piezoelectric elements.

Further, according to the present invention, after capturing an acoustic image of a sample, it is possible to measure the elastic anisotropy at a specific position of the image using a single lens.

A signal from the sample is stored in a memory (not shown).

This operation is repeated as the sample moves, and all signals obtained as a result of scanning the entire surface of the sample are stored in memory. Thereafter, the data is converted into an image by an imaging device (not shown) and displayed as an image on a monitor.

This section describes one method for determining the When setting the lens at a desired location on the sample while looking at the screen, the sample stage (not shown) is moved at the same time as the marker is moved.

After the movement, a voltage is applied to the piezoelectric elements 31 and 32, and a signal indicating the elastic characteristics from the sample obtained by the line focused beam on the y-axis is stored in a memory.

Next, a voltage is applied to the piezoelectric elements 33 and 34 to generate a line focused beam on the X axis, and a signal from the sample in a direction perpendicular to the above direction is stored in the memory in the same manner as above.

Next, move the lens in two axial directions as indicated by X above.

A signal indicating elastic characteristics for the line focused beam on the y-axis is detected. Repeat the operation in this way,
Then, using the signals from the stored memory, the orthogonal 2
For each direction, the V(z) characteristics (characteristics obtained by observing the signal from the piezoelectric element while moving the sample closer to the lens direction; as is generally known, the elastic anisotropy of the material can be determined). demand.

The elastic anisotropy at a desired position can be specified while obtaining an acoustic image of the obtained V (z) characteristic graph on the same monitor, resulting in more efficient and highly accurate measurements.

Although the sample was moved here, the same results can be obtained by moving the lens.

An example of the method for manufacturing the polyhedral lens of the present invention will be described below. Here, a silicon single crystal is used as the lens body.

As shown in FIG. 9(a), both surfaces of a single crystal silicon plate 13 with a plane orientation of (100) are oxidized to form an oxide film 14.14'.
form. The oxide film on the portion forming the polyhedron (here, a square pyramid surface) is removed, and a portion of the oxide film is also removed on the polyhedron. When silicon in this state is etched with a KOH aqueous solution, due to the anisotropy of etching, the 9th
As shown in Figure (b), a concave surface 15 of a quadrangular pyramid composed of the (111) plane of the crystal and an inclined surface 16 on the outside thereof are formed. It is clear from the geometric relationship of the crystal that all of these planes form exactly 54.7@ with respect to the (100) plane. After that, the oxide film on the front surface is removed, and the electrode of ZnO piezoelectric body 17 mm φu is patterned on the back surface.
If this is further cut into an appropriate size, a polyhedral lens can be obtained as shown in FIG. 9(d).

〔Effect of the invention〕

According to the present invention, the acoustic image of the sample and the elastic anisotropy of the sample can be specified with a single lens. In particular, the present invention has made it possible to measure the anisotropy of a sample at a specific position in an acoustic image, which was previously impossible. Furthermore, in measurements using conventional cylindrical lenses, the elastic properties of the sample could only be measured in one direction unless the lens was rotated, but with the lens of the present invention, elastic properties can be measured from at least two directions. I can do it.

Further, by using anisotropic etching of a silicon single crystal as a method for manufacturing a polyhedral lens, a polyhedral lens having an accurate shape can be processed.

[Brief explanation of drawings]

Fig. 1 is an overview of the polyhedral lens of the present invention, Fig. 2 is a cross-sectional view of the lens shown in Fig. 1 taken along plane A, and a circuit configuration diagram as a microscope. Fig. 3 is a cross-section of a conventional spherical lens. Figure 4 is an overview of a conventional cylindrical lens, Figures 5 to 8 are schematic diagrams showing the intensity distribution of sound waves in a sample, and Figure 9 shows the manufacturing process of the lens of the present invention. FIG. l... Lens body, 2... Polyhedron, 3... Medium, 4
... Electrode, 5 ... Plane wave generation circuit, 6 ... Receiving circuit, 7 ... Switch, 8 ... Sample, 9 ... Sound wave,
31-34... piezoelectric element, 51.52... piezoelectric body,
61.62... Electrode. Hatame Hachitatsumi 31-34 Pressure V performance 3rd prisoner Shodai Zufu■ Waiting for the day meeting/8

Claims (1)

[Claims] 1. An acoustic lens characterized in that the lens body has a plurality of planes. 2. The acoustic lens according to claim 1, wherein the lens body is made of single crystal silicon. 3. The acoustic lens according to claim 1 or 2, characterized in that the acoustic lens has electrodes having a divided structure independent of each other. 4. The method of processing an acoustic lens according to claim 1, which applies anisotropic etching of a single crystal. 5. A sonic microscope device using the acoustic lens according to any one of claims 1 to 4. 6. Using the acoustic lens according to any one of claims 1 to 4, the elastic properties of the object to be measured are measured by electrically switching the voltage applied to the electrode in a plurality of directions. A sonic microscope system characterized by: