JPH04214000A - Ultrasonic transducer - Google Patents

Abstract

PURPOSE:To constitute the above transducer by laminating piezoelectric films having a nonvolatile memory function in order to form desired electrode patterns, to suppress the sound fields of the transducer and to recognize the patterns. CONSTITUTION:The plural lower electrodes 12, the piezoelectric films 13 having the nonvolatile memory function, the plural upper electrodes 14 extending in the direction intersecting with the above-mentioned lower electrode 12, and an acoustic matching layer 15 covering the entire surface of the upper electrodes 14 are provided on a supporting base 11 for element mounting. Terminals 16 and 17 for various kinds of signal lines are provided on the above-mentioned lower electrodes 12 and upper electrodes 14. The piezoelectric films 13 are cut and arranged to stripe shapes of 50 to 95% of the thickness from the front surface and are further similarly cut in the direction intersecting with the cut direction on the front surface. The bipolar directions of the polarization processing are set when the electric field above the antielectric field is impressed so as to match the desired electrode patterns.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer having a memory function, and more particularly to an ultrasonic transducer having a memory function and using a piezoelectric film.

0002

[Prior Art] Conventionally, ferroelectric materials such as PZT (lead zirconate titanate) and PbTi have been used as materials exhibiting piezoelectricity.
Inorganic materials such as O3 (lead titanate) and organic materials such as polymers such as PVDF (polyvinylidene fluoride) or its copolymers are well known. These piezoelectric materials are widely used in ultrasonic transducers for ultrasonic diagnosis, ultrasonic flaw detection, etc. by utilizing the thickness vibration of the piezoelectric body.

[0003] Also, with the improvement of ferroelectric film forming technology,
Attempts to realize large-capacity nonvolatile memory by utilizing the fact that ferroelectric materials have two remanent polarization states with different polarities are attracting attention. However, ultrasonic transducers using piezoelectricity do not have a nonvolatile memory function.

[0004] In general, piezoelectric materials are not necessarily ferroelectric, and conventional ultrasonic transducers that utilize piezoelectricity do not take memory functions into consideration. Therefore, conventional ultrasonic transducers do not have the nonvolatile memory function that ferroelectric materials have.

[0005]

[Problems to be Solved by the Invention] Conventionally used ultrasonic transducers have the following drawbacks because they do not have a memory function. (i) Because the desired electrode pattern cannot be easily formed,
It is difficult to suppress the sound field by changing the size of the transducer aperture. (ii) Pattern recognition is not possible. In the above (i), an ultrasonic transducer used in an electronic scanning method such as a linear scan or a sector scan is used by cutting a ceramic piezoelectric material such as PZT and its electrode layer into strips and separating them.

FIG. 6 shows a conventional ultrasonic transducer for electronic scanning, in which a plurality of signal electrodes 2 and a flat piezoelectric material 3 are arranged in a predetermined direction on a support base 1 that absorbs sound waves.
is provided. Then, these signal electrodes 2 and piezoelectric bodies 3 are cut and separated using a dicing saw or the like. Terminals 4 for various signal lines are provided on one side of the signal electrode 2, and a ground electrode 5 is provided on the piezoelectric body 3 on the opposite side from these terminals 4 so as to be connected to the adjacent piezoelectric body. is provided. In an ultrasonic transducer obtained through such a process, the electrode pattern cannot be easily changed.

The above electronic scanning ultrasonic transducer has an optimal electrode pitch and aperture size according to each frequency, and uses a thin beam to reduce side lobes to increase resolution and improve image quality. It is necessary to control the field. Therefore, for example, 2.5MHz, 3.5M
Transducers with different pitches are available for Hz and 5MHz. Furthermore, regarding (ii) above, the conventional ultrasonic transducer using the reflected echo method does not have a function of checking the pattern of an image using echoes.

The present invention has been made in view of the above points, and it is possible to form a desired electrode pattern, and it is not difficult to suppress the sound field by changing the size of the aperture of the transducer. Another object of the present invention is to provide a high-performance ultrasonic transducer that can perform pattern recognition.

[0009]

[Means for Solving the Problems] That is, the present invention comprises a support means for absorbing sound waves, a lower electrode layer formed on the support means, and a piezoelectric material provided on the lower electrode layer to make the piezoelectric material thinner. It is characterized by comprising a piezoelectric thin film having a memory function for selectively retaining information, and an upper electrode layer formed on the piezoelectric thin film.

0010

[Operation] The ultrasonic transducer according to the present invention includes a piezoelectric film having a nonvolatile memory function utilizing the hysteresis characteristics of ferroelectric material on an insulating support having an electrode layer on its surface, and a piezoelectric film formed on the surface of the piezoelectric film. The piezoelectric film having the memory function is laminated with a plurality of piezoelectric films having the same or different types of memory functions. By using a piezoelectric film having a memory function, an electric field higher than the coercive electric field can be applied to match a desired electrode pattern, and the dipole direction of the polarization process can be set. In addition, piezoelectricity is used to generate and receive ultrasonic waves by simultaneously driving or driving with phase difference in mind, depending on the size of the aperture of the transducer that matches the electrode pattern, focus, scanning method, etc. That's what I do. Furthermore, by stacking a plurality of piezoelectric films with the memory function mentioned above, the thickness of the piezoelectric film can be used as a parameter, and not only the frequency can be made variable, but also the piezoelectric film with the memory function can generate ultrasonic waves. The piezoelectric film, which has a memory function, is used to recognize the echo image of the ultrasonic wave as a pattern.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention. In the figure, a plurality of lower electrodes 12 extending in a first direction are mounted on a support base 11 for mounting an element which also serves as an acoustic damper, and a non-volatile electrode is arranged on each of the lower electrodes 12. A piezoelectric film 13 having a memory function is provided. Further, on this piezoelectric film 13, a plurality of upper electrodes 14 extending in a second direction intersecting the lower electrode 12 and an acoustic matching layer 15 covering the entire surface of these upper electrodes 14 are provided. . Further, terminals 16 and 17 for various signal lines are connected to the lower electrode 12 and the upper electrode 14, respectively.

The support base 11 is made of silicone rubber or other rubber-like material containing ferrite, epoxy resin mixed with tungsten powder, Bakelite, glass epoxy resin, or the like. Further, the piezoelectric film 13 is made of PZT,
It is composed of an inorganic material such as PbTiO3 or an organic material such as PVDF and its copolymer. The lower electrode 12 and the upper electrode 14 are made of, for example, Al, Cu, Ag,
It is formed by sputtering or vapor deposition of Au or the like. The acoustic matching layer 15 is made of epoxy resin, polyester,
It is made of polyimide, polysulfone resin, optical glass, etc., and is inserted for acoustic matching between the piezoelectric film 13 and the medium.

The piezoelectric film 13 has a non-volatile memory function, and the surface of the piezoelectric film 13 has a non-volatile memory function. They are cut into stripes by 50 to 95% of their thickness and arranged in rows as shown in the figure. Further, in the direction crossing the cutting direction on the front surface, stripes are similarly cut from the back surface by 50 to 95% of the thickness. An insulator with low acoustic impedance is embedded between adjacent piezoelectric bodies. In addition, the surface shape of the piezoelectric film 13 may be formed into a convex or concave surface, instead of being flat, and may have a curvature in the front and back arrangement direction. Next, the operation of this embodiment will be explained.

In the piezoelectric film 13 having a memory function,
Upper electrode 14 as the front surface and lower electrode 12 as the back surface
Each element in which two types of striped electrodes intersect has a memory function that can record data using hysteresis characteristics in addition to piezoelectricity. That is, by applying an electric field greater than or equal to the coercive electric field, the polarization is reversed and the dipole direction of each element is set. This allows the electrode pattern to be easily changed.

FIGS. 2 and 3 show other examples of the shapes of the electrode patterns as second and third embodiments of the present invention. For example, the electrode pattern 18 shown in FIG.
are formed in a hexagonal shape on a piezoelectric film 19 having a memory function. In this case, the direction of arrow A in the figure is the direction of ultrasonic wave generation, and the direction of arrow B in the figure is the polarization direction. According to the electrode pattern 18 having such a shape, polarization treatment is performed to reduce side lobes, and the piezoelectric film 19
are simultaneously driven to transmit ultrasound and receive echoes.

Further, a plurality of electrode patterns 20 shown in FIG. 3 are arranged in a strip shape on a two-layer piezoelectric film 21 having a memory function. In this case as well, the direction of the arrow A in the figure is the ultrasonic generation direction, the direction of the arrow B in the figure is the polarization direction, and the polarization process is performed in the form of a strip. Then, by driving each strip-shaped electrode pattern 20 with a predetermined phase difference, the ultrasonic waves are focused, and linear scanning, sector scanning, etc. are possible. Moreover, the piezoelectric film 21 having two layers stacked on top of each other allows the thickness of the piezoelectric film to be changed as a parameter, thereby providing a transducer with variable frequency.

In this way, arbitrary electrode patterns can be easily changed, so a single transducer as shown in FIG. 2 or an electronic scanning transducer (two-dimensional one) as shown in FIG. (including linear scan, sector scan, etc.), ring division transducer, surface wave transducer, etc. In addition, the transducer aperture size and frequency electrode pitch can be changed to optimize the sound field so that the sidelobes are small with a narrow beam.

It should be noted that FIG. 1 shown in the above-mentioned first embodiment
In the ultrasonic transducer, its control circuit is
The material described in Japanese Patent Application No. 63-170471 by the present applicant can be used.

FIG. 4 is a perspective view of a transducer having two layers of piezoelectric films, which is a fourth embodiment of the present invention. In the same figure, a plurality of lower electrodes 23 extending in the first direction are mounted on an element mounting support 22 which also serves as acoustic damping, and a non-volatile electrode is arranged on each of the plurality of lower electrodes 23. A lower piezoelectric film 24 having a memory function is provided. Furthermore, a plurality of middle electrodes 25 are provided on the lower piezoelectric film 24 and extend in a second direction intersecting the lower electrode 23 . And these middle electrodes 2
5, an upper piezoelectric film 26 having a nonvolatile memory function as a second piezoelectric film, an upper electrode 27 extending in the same direction as the lower electrode 23, and a protective film 28 covering the entire surface of the upper electrode 27. are stacked in sequence. In addition, the lower electrode 2
3, a terminal 29 is connected to the middle electrode 25, a terminal 30 is connected to the upper electrode 27, and a terminal 31 is connected to the upper electrode 27. Among these terminals, terminals 29 and 30 are used when transmitting waves, and terminals 30 and 31 are used when receiving waves.

The lower piezoelectric film 24 and the upper piezoelectric film 26 are
It is a different type of piezoelectric film, and the lower piezoelectric film 24 contains P.
Acoustic impedance like ZT 34×106 [kg
/m2 s] is used, and the upper piezoelectric film 26 is made of P.
Acoustic impedance 4.5x like VDF copolymer
106 [kg/m2 s] is used. The upper piezoelectric film 26 is made of polymer and has high reception sensitivity, and can be switched so that it acts as a piezoelectric element only when receiving waves, and acts as an acoustic matching layer for the lower piezoelectric film 24 when transmitting waves. do. By doing so, an ultrasonic transducer with high transmitting sensitivity and high receiving sensitivity can be obtained. In addition, in the above piezoelectric film, the thickness required to make the coercive electric field 5 to 10 V is 1 to 2 μm for PZT, and 1 to 2 μm for PZT.
It is assumed that the VDF has a thickness of about 0.1 to 0.2 μm. Next, the operation of this embodiment will be explained.

First, a predetermined electrode pattern is written in the memory function of the lower piezoelectric film (PZT) 24 in advance. Here, polarization processing is performed into a matrix array (two-dimensional array), and ultrasonic waves are sequentially switched and transmitted from each element. The generated ultrasonic waves are focused at a predetermined depth by an acoustic lens (not shown), and the echoes reflected from the target object at that depth are received by the upper piezoelectric film 26 made of polymer. (C mode image). In the memory of this upper piezoelectric film 26, a pattern of an object is written in order to be recognized and polarization processing is performed in advance. When matched with this pattern, the wave reception sensitivity of the upper piezoelectric film 26 becomes high. In this way, image pattern recognition based on reflected echoes becomes possible. Further, the film thicknesses of the lower piezoelectric film 24 and the upper piezoelectric film 26 do not need to be the same. Furthermore, a fifth embodiment of the present invention will be described with reference to FIG.

In the figure, the ultrasonic transducers 32 divided and arranged in a matrix also serve as a memory cell section, and are connected to a memory write/read circuit via a column switching control section 33 and a row switching control section 34. It is connected to a switching circuit 36 that performs switching between the 35 and 35. When receiving ultrasonic waves, this switching circuit 36 applies the output of the transmitting circuit 37 to the ultrasonic transducer 32, and when receiving ultrasonic waves, the intensity of the received echo is applied to the signal processing circuit 39 via the preamplifier 38.
supplied to The output from the signal processing circuit 39 is sent to an A/D converter 40, a digital scan converter (D
SC) 41 and is supplied to a television monitor 43 via a D/A converter 42. Next, the operation of this embodiment will be explained.

First, in the transducer 32, writing is performed in each cell in the polarization direction by the write/read circuit 35, the column switching control section 33, and the row switching control section 34. Next, the transducer 32 that has finished writing,
The switching circuit 36 sets it as an ultrasonic transducer capable of transmitting and receiving ultrasonic waves. Here, the elements or element groups of the transducer 32 selected by the column switching control section 33 and the row switching control section 34 are driven simultaneously by the transmission pulse from the transmission circuit 37 as in the second embodiment described above, or As in the third embodiment, a predetermined phase difference is applied to drive. When the ultrasonic waves are sequentially switched and transmitted from each selected element as in the two-dimensional array shown in the fourth embodiment, the write/read circuit 35
By also serving as a crosstalk prevention circuit, it becomes possible to transmit and receive ultrasonic waves while reducing crosstalk to other elements. In addition, the ultrasonic pulse emitted to a medium such as a living body is reflected as an echo from the living body.
received by the same transducer 32.

Since the received signal converted into an electrical signal by the transducer 32 has a wide dynamic range,
After being amplified by a wide preamplifier 38 with a good S/N ratio, the signal is supplied to a signal processing circuit 39 comprising an STC, a logarithmic amplifier, a detection circuit, etc., which increases the gain for weaker echoes located at a farther distance. The signal processed by this signal processing circuit 39 is then passed through an A/D converter 40 to convert the image data obtained asynchronously with the television signal into a television signal.
The signal passes through the SC 41 and is further displayed on the television monitor 43 via the D/A converter 42.

[0026]

As described above, according to the present invention, a desired electrode pattern can be easily formed, and it is not difficult to suppress the sound field by changing the aperture size and frequency of the transducer. Furthermore, it is possible to provide a high-performance ultrasonic transducer that can perform pattern recognition.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of an ultrasonic transducer according to the present invention.

FIG. 2 is a diagram showing another shape of an electrode pattern as a second embodiment of the invention.

FIG. 3 is a diagram showing another shape of an electrode pattern as a third embodiment of the present invention.

FIG. 4 is a perspective view of a transducer having two layers of piezoelectric films according to a fourth embodiment of the present invention.

FIG. 5 is a block configuration diagram showing a fifth embodiment of the invention.

FIG. 6 is a perspective view of a conventional electronic scanning ultrasonic transducer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11, 22... Indicator stand, 12, 23... Lower electrode, 13... Piezoelectric film, 14, 27... Upper electrode, 15... Acoustic matching layer, 16
, 17, 29, 30, 31... terminal, 24... lower piezoelectric film,
25... Middle electrode, 26... Upper piezoelectric film, 28... Protective film.

Claims (5)

[Claims] 1. A support means for absorbing sound waves, a lower electrode layer formed on the support means, and a memory provided on the lower electrode layer for selectively retaining information by thinning a piezoelectric material. An ultrasonic transducer comprising a functional piezoelectric thin film and an upper electrode layer formed on the piezoelectric thin film. 2. The ultrasonic transducer according to claim 1, wherein the piezoelectric thin film having a memory function is further laminated with a combination of a plurality of piezoelectric films having a memory function. 3. The ultrasonic transducer according to claim 1, wherein the piezoelectric thin film having a memory function has an arbitrary curvature. 4. The ultrasonic transducer according to claim 1, wherein an electric field greater than a coercive electric field is applied to the piezoelectric thin film having a memory function. 5. An electroacoustic device consisting of a plurality of elements divided and arranged in a matrix, each element having a memory function capable of writing and reading information on polarization directions, and capable of transmitting and receiving ultrasonic pulses. In an ultrasonic transducer having a conversion function, a first switching means for selecting each of the elements, a means for operating the transducer for transmitting and receiving the ultrasonic waves, and a means for receiving and amplifying the signal received by the transducer. means and
a second switching means for writing and reading information into each of the above elements; a means for reading out the information written in each of the above elements; and a display for displaying image data according to the information read by the reading means. An ultrasonic device comprising: means.