JPS6098799A - Layer-built ultrasonic transducer - Google Patents

Abstract

PURPOSE:To enable coping with different frequency by one transducer by forming a piezo-electric layer and an electrode alternately into a layer shape. CONSTITUTION:An ultrasonic transducer 21 is formed by alternately laminating four-layer electrodes 23-1-23-4 and three-layer piezo-electric diaphragms 24-1- 24-3 in a base body 22. For example, the transducer can be resonated at a frequency of 400MHz whose wavelength resonance length is 1/2, by using the electrodes 23-1 and 23-2 which are close to the base body 22. Utilization of said 23-1 and 23-3 makes it possible to use 200MHz. Utilization of said 23-1 and 23-4 makes it possible to use the device as the ultrasonic transducer 21 at 133MHz.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a stacked ultrasonic transducer that can generate and transmit ultrasonic waves of a plurality of frequencies with a single transducer.

[Technical background of the invention and its problems] The idea of observing the microscopic structure of objects using ultrasound instead of light has been around for a long time, and a mechanical scanning ultrasound microscope has recently been developed. In principle, this ultrasound microscope mechanically scans the sample surface with a narrowly focused ultrahigh-frequency ultrasound beam, collects the ultrasound waves scattered by the sample, converts them into electrical signals, and converts the signals into electrical signals. The image is displayed two-dimensionally on a display screen such as a cathode ray tube to obtain a microscopic image. The configuration depends on how the ultrasound is detected; in other words, there are two methods: detecting ultrasound that has passed through the sample while being scattered or attenuated, and detecting ultrasound that has been reflected due to differences in acoustic properties within the sample. Depending on the type, it can be divided into transmissive type and reflective type.

FIG. 1 is a diagram showing the principle of a reflection type ultrasonic microscope, in which a signal from a high frequency oscillator 1 is supplied to an ultrasonic wave generator 3 which serves both as a transmitter and receiver via a directional coupler or circulator 2. This signal is converted into an ultrasonic wave, and this is an ultrasonic focusing lens (acoustic lens) consisting of an ultrasonic propagation medium such as sapphire that is attached to one surface (upper end surface) for both transmitting and receiving waves.
The waves are radiated inward from one side of the 4 and transmitted to the other side. The other surface of this acoustic lens 4 is hollowed out into a spherical shape to form a spherical lens portion 4a, and a sample holding plate 5 is disposed (into it) facing the spherical lens portion 4a.

Water 6, which is an ultrasonic propagation medium, is interposed between the acoustic lens 4 and the holding plate 5, so that the sample 7 can be attached to the holding plate 5 at the focal position of the spherical lens portion 4a. The holding plate 5 is moved in the x and y directions by a scanning device 8 so as to two-dimensionally scan a plane. Of course,
It is also possible to move the acoustic lens 4 in the X and Y directions instead of the holding plate 50, or, for example, it is also possible to move the acoustic lens 4 in the X direction and move the force holding plate 5 in the Y direction. can.

The scanning device 8I is controlled by a scanning circuit 9.

The ultrasonic waves incident on the acoustic lens 4 from the ultrasonic transducer 3 are focused and reach the sample 7. The reflected waves are again collected by the acoustic lens 4 and transmitted to the transducer 3.
The signal is converted into an electrical signal and supplied to the display device 10 through the directional coupler or circulator 2.

By the way, the ultrasonic transducer 3 used in the above-mentioned ultrasonic microscope is used while being closely fixed to the acoustic lens 4, and the resonant frequency is determined by the thickness of the piezoelectric material forming the ultrasonic transducer 3. ,
Conventional ultrasonic transducers have been limited in that they can only be used at a single frequency. Therefore, in order to observe at an appropriate frequency depending on the sample, a large number of acoustic lenses to which ultrasonic transducers are fixed are required.
There was a problem in that the price of ultrasonic microscopes increased.

Furthermore, there is the inconvenience that the acoustic lens must be removed even when observing the same sample at different frequencies.

OBJECT OF THE INVENTION The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a laminated ultrasonic transducer that can be used for generating or receiving ultrasonic waves at multiple frequencies. shall be.

[Summary of the Invention] The present invention enables piezoelectric layers and electrodes to be alternately formed in a laminated manner, thereby selecting and using two N poles corresponding to the thickness of the piezoelectric layer depending on the frequency used. frequency.

[Embodiments of the invention] Hereinafter, the present invention will be specifically described with reference to the drawings.

2 and 3 show one embodiment of the present invention, FIG. 2 shows a cross section of the embodiment as seen from the side, and FIG. 3 shows a partially cutaway view from the top side. .

As shown in FIG. 2, the (laminated) ultrasonic transducer 21 of one embodiment includes alumina constituting an acoustic lens,
On the 220 surface of the substrate such as sapphire or fused silica,
The first electrode 23-1 is made of a nickel-chromium alloy or gold or the like and has a film thickness of, for example, several hundred layers.
is formed.

The electrode 23-1 includes a circular portion 23-1a that is concentric with the circular upper end surface of the substantially cylindrical base 22, and
- A straight lead portion 2 extending radially outward from 18.
3-1b and the circular portion 23-18 at the lead portion 23-1b.
The electrode 23-1 can be formed by vapor deposition using an electrode forming mask cut out in the above shape.

(Nth (n = 2.3.4') electrode 23- to be described later)
Each part in n, such as a circular part, is represented by 23-na. ) Zinc oxide 2110 as a piezoelectric material is sputtered onto the first electrode 23-1 of the base 22 on which the first electrode 23-1 is formed to a film thickness of, for example, 7.5 mm.
A first piezoelectric film (piezoelectric layer) 24-1 having a thickness of 5JJl is formed.

From above the first piezoelectric film 24-1, the electrode forming mask is rotated several times, for example, 90 degrees, and then vapor-deposited again in a state in which the second electrode 23-2 is formed on the first electrode 23. The first piezoelectric film 24-1 formed on -1 is nH-treated so that the circular portions 23-1a and 23-28 overlap with each other.

A second piezoelectric film 24-2 is formed on the second electrode 23-2 of the base 22 on which the second electrode 23-2 is formed.
2 is formed with the above film thickness by sputtering. The electrode forming mask is further rotated 90 degrees and placed on the second piezoelectric film 24-2, and the third electrode 23 is deposited again.
-3 is formed, the mask is removed and a third piezoelectric film 24-3 is formed with the above film thickness by sputtering thereon, and on this third piezoelectric film 24-3, an additional 90 The fourth electrode 23-4 is formed using a mask placed with rotation. In this way, the three-layer piezoelectric film 24 is attached to the base 22.
-1.24-2,213 (hereinafter abbreviated as 24-1 to 24-3. The same applies to electrodes) and the four-layer electrode Vi
The arcuate portion 23-1 on the outer circumferential side of each electrode 23-1 to 4 is formed by immersing it in dilute sulfuric acid, etc.
Each arcuate portion 23- is exposed so that a to 4a are exposed.
The piezoelectric films 24-1 to 24-3 in the portions adjacent to 1a to 4a are removed to form the ultrasonic transducer 21 of the first embodiment.

According to the ultrasonic transducer 21 of the first embodiment, the piezoelectric material is ZnO and the film thickness of each piezoelectric body DI 24-1 to DI 24-3 is 7.5 times, so that adjacent electrodes, for example, the base 2
The first electrode 23-1 and the second electrode 23-2 close to the second side
If you use
It can resonate at a frequency of , and can be used for generating ultrasonic waves at this frequency or for receiving ultrasonic waves.

Furthermore, if an electrode having two layers of piezoelectric films interposed therebetween, for example, the first electrode 23-1 and the third electrode 23-3, is used, the
Can be used at MHz.

Furthermore, by utilizing the space between the first and fourth electrodes 23-1.2:14, it can be used as an ultrasonic I transducer at 133 MHz.

If the third piezoelectric film 24-3 is formed to have a thickness of 15 mm, it can be used at 100 MHz by using the first and fourth electrodes 23-1, 23-4i.

As described above, according to one embodiment, a single ultrasound transducer 21 can be used at three different frequencies, reducing the number of required transducers compared to the conventional example. can significantly reduce product prices.

Furthermore, when used in an ultrasonic microscope for observation, the need for replacement can be greatly reduced, making it extremely convenient.

In addition, when observing the same sample at different frequencies, it may be possible to cover it with a single ultrasonic transducer 21, and in such cases, in the conventional example, after replacing and installing it, it is necessary to set it for observation. However, in the first embodiment, observation can be made by simply adjusting the distance while maintaining the same state, which is very effective.

As in the first embodiment, a part of the outer periphery of the piezoelectric film 24-3 may be dissolved with dilute sulfuric acid to expose each electrode 23-1 to 23-4, or may be formed by sputtering. When doing so, it is also possible to form a mask in advance so that at least a part of the six-electrode tffi 23-1 to 23-4 is exposed.

Note that the present invention is not limited to the three-layer piezoelectric films 24-1 to 24-3 as in the above-mentioned embodiment, but also includes two-layer piezoelectric films or four or more layers. It is. In this case, the number of electrodes is greater than the number of piezoelectric films. Note that each piezoelectric film may be formed to have a film thickness depending on a desired frequency.

Furthermore, the above-mentioned embodiments are for ultrasonic microscopes that use high frequencies ranging from 100 MHz to several GHz, and in this case, the piezoelectric film has a thickness of several turns or several tens of moons. Therefore, the sputtering method or vapor deposition method is suitable for forming the piezoelectric film, but at lower frequencies, or even in the case of the above-mentioned ultrasonic microscope, in the low frequency region, the piezoelectric film is formed into a thin plate using a diamond cutter or the like. There is also a transducer in which electrodes are formed by vapor deposition on both sides of each cut thin plate-like piezoelectric material, and each electrode is fixed with an adhesive to form a laminated type. It belongs to the present invention. Further, in this case, the piezoelectric material is not limited to 2+10, and other piezoelectric materials such as PZT, crystal, etc. can be used.

As shown in FIG. 1, the first embodiment described above is an ultrasonic microscope in which an acoustic lens is formed on the upper end surface of an acoustic lens having a flat surface on one (upper end) surface and a spherical concave surface on the other surface. Although the present invention is described as an ultrasonic transducer, the present invention is not limited thereto, and may be formed on a substrate of other shapes, such as a flat substrate, and used for ultrasonic diagnosis, etc. These also belong to the present invention.

[Effects of the Invention] As described above, according to the present invention, piezoelectric layers and electrodes are alternately formed in the form of WA layers, so that one piece can be used as an ultrasonic transducer that can handle different frequencies. It has the advantage of being possible. It also has the advantage that it can be used for different frequencies without being replaced. Furthermore, in devices such as ultrasonic microscopes that require observation at a large number of different frequencies, the number of acoustic lenses can be reduced by forming the present invention on them, and the overall price of the product can be greatly reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the principle of an ultrasonic microscope, Figs. 2 and 3 show one embodiment of the present invention, Fig. 2 is a sectional view of one embodiment, and Fig. 3 is a cross-sectional view of one embodiment. FIG. 2 is a partially cutaway plan view. 21...(Laminated type) ultrasonic transducer 22...
- Base body 23-1. ..., 23-4... electrode 24-1.24
-2.24-3...Piezoelectric film -, /'

Claims (3)

[Claims] (1) In an ultrasonic transducer in which an electrode is attached to a piezoelectric body, ultrasonic waves are excited by a high-frequency electric signal applied to the electrode, and the excitation by the ultrasonic wave can be converted from the electrode into a high-frequency electric signal, A laminated ultrasonic transducer characterized in that piezoelectric layers and electrodes are alternately laminated. (2) The laminated ultrasonic transducer according to claim 1, wherein the electrode is formed by vapor-depositing a nickel-chromium alloy or gold. (3) The laminated ultrasonic transducer according to claim 1, wherein the piezoelectric layer is formed by sputtering zinc oxide.