JPH03252554A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To accurately measure a sound velocity in a fine area on the surface of a sample by propagating a reflected wave in the vicinity of the center of the concave surface of a lens which transmits and receives an ultrasonic wave signal on the surface of the sample and transmitting/receiving ultrasonic waves which reach the lens individually. CONSTITUTION:This probe is provided with a transmission/reception part 14b which transmits/ receives the ultrasonic wave in the vicinity of the center of the concave surface 11a and a 2nd transmission/reception part 14a which transmits an ultrasonic wave to the sample 15 and also receives the ultrasonic wave propagated in the surface part of the sample 15 and reaching the edge part of the concave surface 11a. Consequently, the ultrasonic wave 16 which is sent by the reception part 14b is reflected by the surface of the sample 15 and received as an echo by the transmission/reception part 14b again. Further, the ultrasonic wave 17 which is transmitted by the transmission/reception part 14a is made incident partially on the sample 15 at the Rayleigh critical angle and propagated as a surface wave on the surface and the wave is projected at the Rayleigh critical angle similarly and received as the echo 19 by the transmission/reception part 14a again. The other part of the ultrasonic wave 17 is reflected by the surface of the sample 15 and propagated as an echo 18 toward the ultrasonic probe, but no transmission/reception parts 14a and 14b is present on its reception part and the wave is not received.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to an ultrasonic probe suitable for use in measuring the sound speed of surface acoustic waves in 5AW (surface acoustic wave) devices and the like.

B. Prior Art FIG. 4 is a sectional view showing a conventional example of an ultrasonic concave probe used for measuring the sound velocity of surface acoustic waves in SAW devices and the like. In the figure, 1 is a lens, and a concave surface 1a is formed at the bottom of this lens 1. 2 is lens 1
3 is a piezoelectric material provided on the surface of the lower electrode 2, 4 is an upper electrode formed on the surface of the piezoelectric material, and these lenses 1. The lower electrode 2, the piezoelectric material 3, and the upper electrode 4 constitute an ultrasonic concave probe.

In the ultrasonic concave probe with such a configuration, when a high frequency voltage is applied to the lower electrode 2 and the upper electrode 4, the piezoelectric material 3 vibrates, causing the piezoelectric material 3 to vibrate and move in front of the upper electrode 4 (lower side as shown in FIG. 4).
Ultrasonic waves are transmitted toward the sample 5 placed at. In particular, since this ultrasonic probe is formed with a concave surface, the emitted ultrasonic waves are converged at a focal position defined by the curvature of the concave surface.

Then, the piezoelectric material 3 vibrates due to the reflected echo reflected by the sample 5, and this is received as a potential difference between the lower electrode 2 and the upper electrode 4.

In FIG. 5, the vertical axis represents the relative intensity with the received intensity of 0 (dB) when the focal position is set on the surface of the sample 5, and the horizontal axis represents the distance between the focal position and the surface of the sample 5. so-called V
(z) This is a diagram showing a relationship called a curve, and lens 1
It is obtained by taking out the signal from the electrode while approaching the sample 5 in the Z-axis direction.

This V (z) curve shows that the reflected echo 6 that propagates near the center axis of the lens 1 and is reflected from the sample 5 and the ultrasonic wave 7 that is incident on the sample 5 at a Rayleigh critical angle unique to the sample 5 strike the surface of the sample 5. It is known that this wave propagates as a surface wave and is obtained by interference with an echo 9 that is similarly obtained by being emitted at Rayleigh's critical angle. Then, by measuring the period of this interference (the interval between the "r peaks" of the V (z) curve that appears conspicuously on the left side of FIG. 5), the sound speed of the surface acoustic wave of the sample 5 can be determined.

Problem to be Solved by the C0 Invention However, this V (z) curve is affected by the reflected echo 8 obtained when the ultrasonic wave 7 incident from all directions including the Rayleigh critical angle is directly reflected on the surface of the sample 5. I have also received In particular, when the focal position is set near the surface, this reflected echo 8 enters the ultrasonic probe in a nearly perpendicular state, so as shown in Figure 5, near the focal position, the above-mentioned interference occurs. Therefore, conventionally, by using the measurement results at a surface position far from the focal position and having a large amount of defocus, V (z) shown in Fig. 5 is not clearly observed. The speed of sound of surface acoustic waves was measured at locations where the "r-mountain" was conspicuous.

However, the transmitted ultrasonic wave has a large beam diameter at a position away from the focal position, and the ultrasonic probe receives echoes from a wide area on the surface of the sample 5.

Therefore, it was not possible to divide the sample 5 into minute regions and measure the sound speed of the surface acoustic waves with high precision.

A technical object of the present invention is to accurately measure the sound velocity of a surface wave in a micro region on a sample surface using an ultrasonic probe.

00 Means for Solving the Problems The present invention will be explained with reference to FIG.
1, a first transmitting/receiving section 14b provided on the concave surface 11a and transmitting and receiving ultrasonic waves near the center of the lens 11; and a second transmitting/receiving section 14a that receives the ultrasonic waves that reach the lens 11# section.
The above technical problem is achieved.

E0 action The ultrasonic wave 16 emitted from the first transmitting/receiving section 14b is reflected on the surface of the sample 15, and is transmitted again to the first transmitting/receiving section 14b.
is received as an echo. On the other hand, the second transmitter/receiver 14
A part of the ultrasonic wave 17 emitted from a enters the sample 15 at Rayleigh's critical angle, propagates as a surface wave on the surface of the sample 15, exits at the Rayleigh's critical angle, and returns as an echo 19. The signal is received by the second transmitter/receiver 14a.

Further, the ultrasonic wave 17 transmitted from the second transmitter/receiver 14a
The other part is reflected on the surface of this sample 15 and becomes an echo 18.
However, since the echo 18 is received at a location where the transmitting/receiving sections 14a and 14b are not provided, it is not detected as a received signal.

In the above-mentioned sections and section E, which describe the present invention in detail, figures of embodiments are used to make the present invention easier to understand, but the present invention is not limited to the embodiments.

F. Examples Examples of the present invention will now be described in detail with reference to the drawings.

Embodiment of Part 1 - A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG.

FIG. 1(a) is a sectional view showing a first embodiment of the ultrasonic probe according to the present invention. In FIG.
The focal position of the ultrasound probe is determined by the spherical surface of this concave surface 11a. That is, this ultrasonic probe is of a so-called point focus type. Note that, for example, a so-called line focus type device having a concave surface cut by cutting the side surface of a cylinder along a plane parallel to the axis of the cylinder may be used.

Reference numeral 12 denotes a lower electrode made of a conductive film such as a metal film, and this lower electrode 12 is provided so as to cover substantially the entire surface of the concave surface 11a. Reference numeral 13 denotes a piezoelectric material formed in the form of a film, and this piezoelectric material 13 is provided so as to cover substantially the entire surface of the lower electrode 12. The material of the piezoelectric material 13 is appropriately selected from known piezoelectric materials depending on the frequency of the ultrasonic waves emitted by the ultrasonic probe. Since ultrasonic waves in a relatively high frequency range (MHz=GHz) are used, materials such as ZnO can be suitably used. Further, the thickness of the piezoelectric material 13 is also appropriately determined by the frequency of the ultrasonic probe, as described above.

14 is an upper electrode formed from a conductive film such as a metal film, like the lower electrode 12. This upper electrode 14
As shown in Figure (b), an upper electrode 14a serving as a second transmitting/receiving section provided in an annular shape at the edge of the surface of the piezoelectric material 13;
The piezoelectric material 13 includes an upper electrode 14b, which is a first transmitting/receiving section, provided in a circular shape at the center of the surface of the piezoelectric material 13.

Further, a lead wire (not shown) is connected to the lower electrode 12 and the upper electrode 14, and one or more lenses 11 to which a voltage is applied from a voltage supply source (not shown) is connected to the lower electrode 12 and the upper electrode 14.
, the lower electrode 12, the piezoelectric material 13, and the upper electrode 14 constitute an ultrasonic probe according to the present invention.

The operation of the first embodiment having such a configuration will be explained.

The sample 15 is placed in front of the ultrasonic probe, that is, in a position facing the upper electrode 14. In this state, a voltage is applied to the lower electrode 12 and the upper electrode 14 from a voltage supply source (not shown). Note that since the ultrasonic probe of this embodiment is a transmitting/receiving type probe, the voltage applied to these electrodes 12 and 14 may be one in which pulses are repeated at a constant period.

When a voltage is applied to the electrodes 12, 14, the piezoelectric element 13 vibrates due to the piezoelectric effect, generating ultrasonic waves.

In particular, in this embodiment, the upper electrode is not provided on the entire surface of the piezoelectric material 13, and ultrasonic waves are mainly generated at the upper electrode, that is, the concave edge 14a and the center 14b.

A part of this ultrasonic wave propagates within the lens 11.

If the lens 11 is an effective ultrasonic absorber, the ultrasonic waves will be sufficiently absorbed within the lens 11. On the other hand, since the piezoelectric material 13 is formed into a concave surface, the ultrasonic waves emitted forward propagate so as to converge near the center of the concave surface, in other words, at the focal point.

That is, the ultrasonic wave 16 emitted from the first upper electrode 14b is reflected on the surface of the sample 15 and is received again as an echo by the first upper electrode 14b. On the other hand, a part of the ultrasonic wave 17 emitted from the second upper electrode 14a enters the sample 15 at the Rayleigh critical angle, propagates as a surface wave on the surface of the sample 15, and similarly reaches the Rayleigh critical angle. The light is emitted and received again as an echo 19 by the second upper electrode 14a. Further, another part of the ultrasonic wave 17 emitted from the second upper electrode 14a is reflected on the surface of this sample 15 and propagates toward the ultrasonic probe as an echo 18.
Since the echo 18 is received at a location where the upper electrode 14 is not provided, it is not detected as a received signal.

Therefore, in the ultrasonic probe of this embodiment, the midpoint between the lens center and the edge, which causes an error when measuring the sound velocity of a surface wave using a V(z) curve in a conventional ultrasonic probe, is Since it is dangerous to remove the influence of echoes from the
Accurate sound velocity measurement is possible even when the focal position of the ultrasonic probe is slightly deeper than the surface of the sample 15. Thereby, it is possible to accurately measure the sound velocity in a minute area on the surface of the sample 15.

Figure 2 shows the measurement results of the V (z) curve according to this example. Even when the focus position is near the surface of sample 15, a "mountain" appears on the V (Z) curve, making it possible to measure the sound velocity sufficiently. I can understand that.

In the above embodiment, the piezoelectric material 13 is provided on the entire surface of the lower electrode, but it is clear that it may be provided in accordance with the shape of the electrodes 14a and 14b.

-Second Example- A second embodiment of the present invention will be explained with reference to FIGS. 3(a) and 3(b).

FIG. 3(a) is a sectional view showing a second embodiment of the ultrasonic probe according to the present invention. In addition, in the following explanation,
Components that are the same as those in the first embodiment are given the same reference numerals and their explanations will be omitted.

The difference between this embodiment and the first embodiment is that a matching layer is provided in the ultrasonic probe. Namely.

In the figure, the upper electrode 14 is provided so as to cover almost the entire surface of the piezoelectric material 13, and the upper electrode 14
A matching layer 20 is provided on the surface of 4. As shown in FIG. 3(b), this matching layer 20 includes a first matching layer 20a provided in a circular shape and an annular shape at the center and edge of the surface of the upper electrode 14, respectively, and the other upper electrodes. and a second matching layer 20b provided on the surface of 14.

The first matching layer 20a has a thickness of 1/4λ (λ is the wavelength of the ultrasonic wave), and the second matching layer 20b has a thickness of 1/2λ. Also, these first. The second matching layers 20a and 20b both have an acoustic impedance of 2.

z=fI7了1] zl: Acoustic impedance of the piezoelectric material 13 z2: Acoustic impedance of a medium such as water in front of the ultrasonic probe.

Therefore, the ultrasonic waves incident on the first matching layer 20a are emitted from the matching layer 20a to the sample in a state where they are strengthened by the superposition of the reflected waves reflected between the interfaces, while
Similarly, the ultrasonic waves incident on the second matching layer 20b cancel each other out due to the superposition of reflected waves reflected between the boundary surfaces.

Almost no radiation is emitted from this matching layer 20b to the sample.
That is, the location where the second matching layer 20b is provided (the first
Ultrasonic waves are neither emitted nor received from the area (corresponding to the area where the upper electrodes 14a and 14b are not provided in the fifth embodiment).Therefore, the fifth embodiment also achieves the same effect as the first embodiment. I can do it.

G0 Effects of the Invention As described above, according to the present invention, the concave surface of the lens, where ultrasonic signals are transmitted and received, includes a first transmitting/receiving section that transmits and receives reflected waves near the center of the lens, and a first transmitting/receiving section that transmits and receives reflected waves near the center of the lens, and a first transmitting/receiving section that transmits and receives reflected waves near the center of the lens. Since a second transmitting/receiving section that transmits and receives ultrasonic waves reaching the lens is provided, it is possible to eliminate the influence of ultrasonic echoes that are incident at the Rayleigh angle of incidence and are reflected without propagating on the surface. Therefore, it is possible to measure the sound velocity with high precision even when the focal position of the ultrasonic probe is close to the surface, and it is possible to measure the sound speed of a minute area on the sample surface with high precision.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of an ultrasonic probe according to the present invention, in which (a) is a longitudinal sectional view and (b) is a bottom view thereof. FIG. 2 is a diagram showing an experimental example of the V (z) curve according to the same embodiment. FIG. 3 shows a second embodiment of the ultrasonic probe according to the present invention, in which (a) is a longitudinal sectional view and (b) is a bottom view thereof. FIG. 4 is a sectional view showing a conventional ultrasonic probe. FIG. 5 is a diagram showing a V (z) curve according to the conventional example. 11: Lens 11a: Concave surface 12: Lower electrode 13: Piezoelectric material 14a: Second upper electrode (second transmitter/receiver) 14b: First upper electrode (
1st transmitter/receiver) 15: Sample

Claims (1)

[Scope of Claims] A lens having a concave surface formed therein; a first transmitting/receiving section provided on the concave surface and configured to transmit and receive ultrasonic waves near the center of the lens; and a first transmitting/receiving section provided on the concave surface configured to transmit ultrasonic waves to a sample. An ultrasonic probe comprising: a second transmitting/receiving section that receives ultrasonic waves that propagate through the surface of a sample and reach a lens.