JPH0352025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a probe for an ultrasound microscope using high-frequency ultrasound energy, and particularly to a matching device thereof.

[Background of the invention]

In recent years, it has become possible to generate and detect sound waves with frequencies as high as 1 GHz, making it possible to achieve sound wave lengths of up to approximately 1 μm underwater, and as a result, it has become possible to obtain high-resolution sound wave imaging devices. In other words, a concave lens is used to create a focused acoustic beam, achieving a resolution as high as 1 μm. A sample is inserted into the beam, and the reflected and transmitted sound waves from the sample are detected to obtain information reflecting the elastic properties of the sample.
Alternatively, a two-dimensional image is created by relatively mechanically scanning the sample or the sensor that generates the beam. (A by Mr. RA Lemon and Mr. CF Quates)
IEEE entitled Scanning Acoustic Microscope
cat.No.73CH14829SU-pp423-426, paper published in 1973).

A conventional example of an ultrasonic microscope for obtaining such a sound wave image will be explained with reference to FIGS. 1 and 2.

FIG. 1 is a diagram showing a schematic configuration of a probe system for obtaining reflected signals from a sample. In the figure, a sound wave lens 20 is made of a cylindrical material such as sapphire or quartz, and one end surface is an optically polished flat surface, and the other end surface is formed with a concave spherical hole lens surface 30. A piezoelectric thin film 10 sandwiched between an upper electrode and a lower electrode is formed on the above plane, and a pulse is applied to this piezoelectric thin film 10 by a pulse oscillator 5.
An RF pulsed sound wave in the form of a plane wave is radiated into the sound wave lens 20 by the RF pulsed electric signal. When this planar sound wave reaches the lens surface 30 of the spherical hole, a positive focusing lens formed at the interface between the lens surface 30 and the medium 40 focuses the sample 5 at a predetermined focus.
0 is irradiated with focused ultrasound. The sound waves reflected by the sample 50 are collected by the same lens, converted into plane waves, propagated within the sound wave lens 20, and finally converted back into RF electrical signals by the piezoelectric thin film 10.

If we look at the state of this received signal in the video band after detecting the RF electric signal, it will look like the one shown in Fig. 2. Here, the horizontal axis represents the time axis, and the vertical axis represents the signal strength. In FIG. 2, waveform A represents the launch signal (the above applied signal), and waveform B represents the lens 2.
Echo from the interface 30 between 0 and the medium 40
Also, waveform C shows a reflected echo from the sample 50. Such a waveform is repeated with a repetition time _tR . Since the reflected echo C changes each time it is repeated depending on the acoustic properties of each sample location and the scanning of the sample, this reflected echo C is sampled by the receiving circuit 6 in synchronization with the repetition period.
Only the intensity is extracted and used as an image signal. That is, an ultrasonic microscope can be obtained by scanning the sample in the xy plane by the mechanical scanning system 60 and displaying the image signal on the cathode ray tube 70 in synchronization with this mechanical scanning.

By the way, in such devices, CdS or ZnO is usually used as the material for the piezoelectric thin film 10, which is the main part that transmits and receives ultrasonic waves.In order to transmit and receive ultrasonic waves as efficiently as possible, RF
It is necessary to insert a matching device between the pulse oscillator 5 and the probe made of a piezoelectric thin film.

As is well known, the equivalent circuit of such a contact seen from the electrical terminal side is shown in Figure 3, and the braking capacity is
It consists of Cd, reactance components La and Ca that reflect the mass and stiffness of the piezoelectric body, and Ra that reflects acoustic radiation resistance. When applying high frequency power to the contact from an RF pulse oscillator, the braking capacity of the probe
Cd gives a short circuit effect as the frequency increases.

Conventionally, a matching device composed of a strip line, a slot line, a coplanar waveguide, etc. is used, but in this case, first, when attempting to approach the thin film and integrate it with the acoustic lens, the matching device becomes The large size makes the contact large and heavy, making it difficult to mechanically scan drive it. Second, if a matching device is provided outside the end contact, there is a problem that sufficient matching cannot be achieved because of the connector or cable that connects the two.

FIG. 4 is a diagram showing an example of a conventional configuration, in which the probe has a lower electrode 11 formed on the lens 20 by vapor deposition of a metal such as Cr-Au, and an upper electrode 9 formed by vapor deposition of a metal such as Al or Au. , the piezoelectric thin film 10 formed between
Consisting of As a matching part, pattern 1 such as copper foil is placed on the upper and lower surfaces of an insulator such as a glass epoxy board.
2 and 14, this length L is selected to be 1/4 wavelength at the frequency used, and the upper pattern 12 is formed into a tapered shape.
Alternatively, they were formed in an exponential manner.

In such a conductor line type, the free space wavelength λ is short-circuited at the wavelength λ' in the substrate using the dielectric constant ε _r of the substrate as follows: λ'=λ/√ε _r (1). Above, in the case of glass epoxy, ε _r
= about 2, so at 1 GHz, λ' = 21.2 m, and λ'/4 = 5.3 cm. Lens dimensions are 5
mmφ and about 5 mmt, so if these probes and matching device were to be integrated, the probe would be extremely large.

[Purpose of the invention]

The present invention has been made in view of the above points, and
By integrally molding a matching device and a piezoelectric thin film on a sonic lens, a small and lightweight probe is provided.

[Summary of the invention]

The gist of the present invention is to integrally form a matching device and a piezoelectric thin film using a piezoelectric material having a high dielectric constant and requiring polarization treatment for piezoelectric activation. With this configuration, firstly, it is possible to provide a probe that is small, lightweight, and suitable for mechanical scanning, and secondly, since alignment is achieved very close to the thin film, it is not affected by contact resistance, cable loss, connector loss, etc. Optimum alignment can be easily achieved without any interference, and this greatly contributes to improving the image quality of imaging devices such as ultrasound microscopes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments with reference to the drawings.

[Embodiments of the invention]

In the present invention, ceramics capable of realizing piezoelectricity, such as those with high dielectric constants such as zirconate, barium titanate (PZT), and lead titanate (PbTiO ₃ ), are used as the substrate material. For these dielectrics, ε _r
is as large as 100 to 1000, so the short-circuit wavelength λ' in equation (1) above is 1/10 to 1/30, which is extremely suitable for integration. In the case of 1/4 wavelength matching mentioned above, λ'/4 = 7.5 mm (ε _r
= 100, for 1 GHz), λ'/4 = 2.5 mm (ε _r = 1000,
1GHz).

FIG. 5 is a diagram showing an embodiment of the present invention, in which a lower electrode 11 (Au, Cr, Pt) is provided on a lens 20, and the ceramic material 10 is formed thereon by means such as sputtering. Two upper electrodes (made of metal such as Au, Cr, Al, or Pt) are provided on the top. Therefore, the piezoelectric thin film 10 made of ceramic material is sandwiched between two pairs of upper and lower electrodes, that is, the electrode 102 and the lower electrode 11, and the electrode 101 and the lower electrode 11.

Here, between the upper electrode 101 and the lower electrode 11,
When a DC electric field of about 10 KV/mm is applied, a so-called polarization process is performed, and the ceramic becomes piezoelectrically active. When RF power is applied to this sandwich structure, ultrasonic waves are emitted to the lens surface 30 as before. On the other hand, the ceramic at the portion sandwiched between the upper electrode 102 and the lower electrode 11 has a high dielectric constant but is piezoelectrically inactive, and no ultrasonic waves are generated even if RF power is applied to both ends of the ceramic. Therefore, by selecting the shape of the electrode 102, this portion can be operated as a matching portion. Further, the electrode 101 and the electrode 102 are connected using a gold wire 15 or the like. Thanks to the high dielectric constant of the ceramic used in the present invention, L is
The length is shortened to 2.5 to 7.5 mm, and the sounding part and the matching part can be integrated on the lens without significantly increasing the size of the lens 20. In this embodiment, the upper electrode 1
Although a rectangular shape was presented as the shape of 02,
Other shapes suitable for alignment such as tapered, exponential, etc. may also be used. Alternatively, as shown in FIG. 6, the part that acts as a piezoelectric body may be made of a material 11a that does not require polarization treatment, such as ZnO, and the matching part may be made of a ceramic thin film 10b with a high dielectric constant.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain an ultra-high frequency ultrasonic probe which is small in size and lightweight, and which can easily be optimally matched with a transmitting/receiving circuit.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the conventional configuration of an ultrasonic microscope to which the present invention is applied, Fig. 2 is a waveform diagram showing its operation, Fig. 3 is an equivalent circuit diagram of a contact, and Fig. 4 is a conventional ultrasonic microscope. Perspective view showing the feeler and alignment part, No. 5
6 are a plan view and a sectional view, respectively, showing an embodiment of the present invention. 10... Ceramic thin film, 11... Lower electrode,
101, 102...electrode, 20...sonic wave lens.

Claims (1)

[Claims] 1. An integral ceramic thin film is formed on the flat surface of a sound wave lens with a lens surface formed on one end and a flat surface formed on the other end via one lower electrode, and an upper electrode for generating sound waves is formed on this ceramic thin film. an upper electrode for alignment, and a portion of the ceramic thin film sandwiched between the ultrasound generating electrode and the lower electrode is piezoelectrically activated. probe.