JPH1051041A - Compound piezoelectric material and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce dimension and enable application at higher frequencies, by making the section which is almost vertical to the longitudinal direction of a prism type body, a square whose side is a specified value or less, or a circle or a polygon whose area is equivalent to the square. SOLUTION: In compound piezoelectric material 100, many square prism type piezoelectric ceramic members 101 are regularly arranged in resin matrix 102, keeping specified intervals. The section almost vertical to the longitudinal direction of the prism type body 101 is made a square whose side is at most 75μm, or a circle or a polygon whose area is equivalent to the square. Thereby the dimension is reduced and application at higher frequencies is enabled. This compound piezoelectric material is suitable for an ultrasonic probe which requires high resolution, and in practice, for ultrasonic probes which are used in phased array electronic sector scanning system and linear scanning system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composite piezoelectric material and a method of manufacturing the same, and more particularly, to a composite piezoelectric material used for an ultrasonic probe and the like and a method of manufacturing the same.

[0002]

2. Description of the Related Art A composite piezoelectric material having a structure as shown in FIG. 1 has been used for an ultrasonic probe or the like of an ultrasonic medical diagnostic apparatus. In the composite piezoelectric material 100, a large number of quadrangular prism-shaped piezoelectric ceramic bodies 101 are regularly arranged in a resin matrix 102 at predetermined intervals. For example, in order to obtain an ultrasonic probe, an electrode including a strip electrode is formed on a main surface of such a plate-like material.

[0003] The composite material shown in FIG.
It was manufactured by a process as shown in FIG. A PZT ceramic plate 111 having a predetermined thickness is
After bonding on the upper surface (FIG. 2A), the ceramic is cut into a mesh shape using a dicing saw to form a large number of prismatic bodies (FIG. 2B). After the grooves formed by the cutting are filled with a resin material and solidified, the adhesive is dissolved to separate the ceramics from the substrate 112, whereby a composite piezoelectric material as shown in FIG. 2C is obtained.

For example, with respect to an ultrasonic probe, the frequency used tends to increase in order to improve the resolution. When it is desired to increase the operating frequency, it is necessary to reduce the width of the electrodes formed on the composite piezoelectric material and the size of the piezoelectric ceramic body in the composite piezoelectric material. According to the conventional manufacturing method using a dicing saw, it is difficult to form smaller piezoelectric ceramics in response to this demand. This is because, when grooves are formed in the piezoelectric ceramic plate, if the distance between the grooves is made smaller, the piezoelectric ceramics are easily damaged due to mechanical and thermal influences. Further, a process using a dicing saw takes time for groove processing.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite piezoelectric material having a smaller size piezoelectric ceramic body.

It is a further object of the present invention to provide a composite piezoelectric material that can achieve higher resolution.

It is a further object of the present invention to provide a method by which a composite piezoelectric material having a smaller size piezoelectric ceramic body can be manufactured with a relatively high yield.

[0008]

According to the present invention, there is provided a structure in which a plurality of pillars made of piezoelectric ceramics are arranged in a matrix made of an organic polymer material at intervals so that their longitudinal directions are parallel to each other. A composite piezoelectric material having a cross section substantially perpendicular to the longitudinal direction of the columnar body,
It is characterized by a square having a side of 75 μm or less, or a circle or polygon having an area equivalent thereto.

In the composite piezoelectric material according to the present invention, the ratio of the length of the column to the maximum width in a cross section substantially perpendicular to the longitudinal direction of the column can be 2 or more, or 3.3 or more.

[0010] In the composite piezoelectric material according to the present invention, the volume percentage of the piezoelectric ceramic is preferably in the range of 10 to 30%.

[0011] In the composite piezoelectric material of the present invention, the frequency constant in the direction perpendicular to the longitudinal direction of the columnar body is 560 kHz ·
It is desirably outside the range of mm to 940 kHz · mm.

In the composite piezoelectric material of the present invention, the shape of the column may be a truncated cone or a truncated pyramid, and the taper angle of the truncated cone or the truncated pyramid may be in the range of 0.1 ° to 20 °. it can.

Further, the present invention provides a composite piezoelectric material having a structure in which a plurality of columnar bodies made of piezoelectric ceramics are arranged in a matrix made of an organic polymer material at intervals so that their respective longitudinal directions are parallel to each other. A manufacturing method is provided. In this method, first, a layer made of a resin material for lithography is formed on a substrate. In the layer made of the resin material, a plurality of circles or polygons each having a square of 88 μm or less on one side or an area equivalent to the square are formed through a mask for forming a resist pattern having a pattern arranged at intervals. X by synchrotron radiation
A line is illuminated. Next, the layer made of the resin material is developed to obtain a patterned resin. After depositing the metal material on the patterned resin material, the resin material is removed to obtain a mold made of the metal material to which the shape of the patterned resin material is transferred. The obtained mold is filled with a resin material. The resin material is extracted from the mold to obtain a resin mold on which the shape of the mold has been transferred. The obtained resin mold is filled with a material for forming ceramics and solidified. Then
The resin mold is removed by vaporizing or sublimating the resin without melting the resin, or by dissolving the resin in a solvent. A ceramic structure having a structure in which the remaining solidified material is heated, and a plurality of columnar bodies having a cross section of a square having a side of 75 μm or less or a circle or polygon having an area equivalent thereto extend from the pedestal portion at intervals. Get. An organic polymer material is adhered on the obtained ceramic structure.
From the ceramic structure with the organic polymer material attached,
The pedestal is removed to obtain a composite material having a plurality of columns arranged in the organic polymer material at intervals.

In the manufacturing method according to the present invention, the step of irradiating X-rays with synchrotron radiation includes the step of irradiating the layer of the resin material with the diffracted light from the mask and the resin material so that the diffracted light of the synchrotron radiation through the mask is sufficiently irradiated. A step of providing a predetermined interval between the layers.
By the exposure accompanied by the diffracted light, it is possible to obtain a hole in the resin material, the opening area of which increases with distance from the substrate.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail by taking an ultrasonic probe of a medical ultrasonic diagnostic imaging apparatus as an example. When an electrode is formed on a composite piezoelectric material as shown in FIG. 1 to obtain an ultrasonic probe, the width of the electrode to be formed has a close relationship with the wavelength of the ultrasonic wave used in the body. For example, reference TRGururaja, “Piezoelectrics f
or medical ultrasonic imaging ”, American Ceramic
According to Society Bulletin vol. 73, No. 5, (1994), when this probe is used in the phased array electron sector scan method, the width of the electrode is one of the wavelength in the body.
/ 2, when using the linear scan method, the width of the electrode is preferably 3/2 of the body wavelength. On the other hand, at present, the frequency used tends to increase for the purpose of improving the resolution.
There is a high demand for inspection at 10 MHz. This trend is
This is remarkable in a probe used for a test for heart disease or a test for an intravascular test. Considering this, the width of the electrode to be formed is calculated as shown in Table 1. Here, the calculation was performed assuming that the sound speed in the body was 1500 m / s.

[0016]

[Table 1]

The main reason why a composite piezoelectric material as shown in FIG. 1 is used as a probe material in a medical ultrasonic diagnostic apparatus is as follows.

(A) In the composite piezoelectric material, the acoustic impedance is lower than that of the piezoelectric ceramic alone. Therefore, sound waves can be efficiently propagated in the body without providing an acoustic impedance matching layer.

(B) In the composite piezoelectric material, the vibration in the direction (lateral direction) parallel to the electrode surface, which causes image deterioration, is suppressed, and the required vibration in the vertical direction (longitudinal direction) is reduced to a single piezoelectric ceramic. There is no big difference compared with.

(C) In the composite piezoelectric material, the voltage piezoelectric constant in the direction perpendicular to the electrode surface is higher than that of the piezoelectric ceramic alone, and the sensitivity of ultrasonic waves is high.

In designing a composite piezoelectric material capable of fully exhibiting these advantages, the space factor of the piezoelectric ceramic is very important. Since the acoustic impedance is a weighted average of the constituent materials, it is desired to reduce the space factor of the piezoelectric ceramic as much as possible. Since the strength of vibration in the direction parallel to the electrode surface (distortion piezoelectric constant of transverse vibration) is approximately proportional to the piezoelectric ceramic space factor, the lower the piezoelectric ceramic space factor, the better. on the other hand,
Vibration in the direction perpendicular to the electrode surface (vertical strain piezoelectric constant)
Typically, the space factor of the piezoelectric ceramic increases sharply in the range of 0 to 10%, gradually increases in the range of 10 to 30%, and hardly changes in the range of 30 to 100%. The voltage piezoelectric constant is proportional to a value obtained by dividing a vertical strain piezoelectric constant by a dielectric constant. Since the dielectric constant is proportional to the space factor of the piezoelectric ceramic, the space factor of the piezoelectric ceramic is preferably about 10% in terms of the voltage piezoelectric constant. Taken together,
The volume percentage of the piezoelectric ceramic in the composite piezoelectric material is more preferably in the range of 10 to 30%.

From the requirements for the electrode width and the space factor of the piezoelectric ceramic as described above, preferred dimensions of each piezoelectric ceramic arranged in the composite piezoelectric material are next determined. Since the space factor of the piezoelectric ceramic in each element divided by the electrode is desirably in the range of 10 to 30%, when the cross section of each piezoelectric ceramic body is a square, the length of one side is 1/1 / the width of the electrode. It is desirable to set it to 4 or less. Table 2 summarizes the desired dimensions of the cross section of the piezoelectric ceramic. The frequency constant (the product of the resonance frequency and the thickness) in the thickness direction of the composite piezoelectric material is 1800 kHz.
Since it is about mm, the required probe thickness can be obtained as shown in Table 2 by dividing this constant by the operating frequency. Since the thickness of the probe may be に す る of the thickness calculated from the frequency constant, Table 2 shows two values. Furthermore, the ratio (aspect ratio) of the "thickness of the probe (this corresponds to the height of the piezoelectric ceramic)" to the "maximum width of the piezoelectric ceramic cross section (the length of the diagonal of the square)"
Are also shown in Table 2.

[0023]

[Table 2]

As is clear from Table 2, the operating frequency 7.
In the composite piezoelectric material desired for the phased array electronic sector scan method of 5 MHz or more, the length of one side of each square piezoelectric ceramic is 25 μm or less. That is, the cross section is desirably a square having a side of 25 μm or less, or a circle or polygon having an area equivalent thereto. Further, in a composite piezoelectric material desired for a linear scan method with a working frequency of 7.5 MHz or more, the length of one side of each square piezoelectric ceramic is 75 μm or less. That is, the cross section is desirably a square having a side of 75 μm or less, or a circle or polygon having an area equivalent thereto. The aspect ratio is preferably 2 or more in each case, and more preferably 3.3 or more in the phased array electronic sector scan system.

The use of a composite piezoelectric material for the ultrasonic probe suppresses lateral vibration, but it is advantageous if the lateral resonance frequency deviates from the used band. When the speed of sound in a living body is 1500 m / s,
The following relationship is established between the used frequency f and the electrode width w.

(Phased Array Electronic Sector Scan Method) fw = 750 (kHz · mm) or (MHz)
・ Μm) (Linear scan method) fw = 2250 (kHz ・
mm) or (MHz · μm) There is a certain band in the frequency used. Since this width is about 50% of the center value, the following is obtained by taking this into account.

(Phased array electronic sector scan system) fw = 560-940 (kHz.mm) (Linear scan system) fw = 1690-2810
(KHz · mm) If the frequency constant of the transverse mode of the composite piezoelectric material is a value in these bands, the transverse resonance frequency exists in the used frequency band. In this case, it is conceivable that the crosstalk between the image elements increases around the frequency, which causes a problem. On the other hand, when the frequency constant of the longitudinal mode is within the above range, the frequency characteristics in transmission and reception of the ultrasonic wave become not flat, which is not preferable. However, the image quality is not deteriorated by crosstalk or the like. PZ usually used as a probe material
At T, the required frequency constant of the longitudinal vibration mode is 2200 kHz · mm, and the required frequency constant of the obstructive transverse vibration mode is about 1400 kHz · mm. On the other hand, the frequency constant of the composite piezoelectric material is determined by the frequency constant of the piezoelectric ceramic and the Young's modulus of the resin to be composited. The frequency constant of the composite piezoelectric material in the longitudinal vibration mode is about 1600 to 1800 kHz · mm, and the frequency constant in the transverse vibration mode is 500 to 1100 kHz.
It is about z · mm. The lateral direction is more affected by the Young's modulus of the resin. In consideration of the above, it is desirable that the frequency constant in the lateral vibration mode is out of the range of 560 to 940 kHz · mm. Such a frequency constant can be controlled by, for example, the space factor of PZT or the Young's modulus of the composite resin.

In this specification, "piezoelectric ceramics"
The term refers to a ceramic material that exhibits a piezoelectric effect.
Piezoelectric ceramics include perovskite-type crystals such as barium titanate and lead zirconate-lead titanate solid solution, for example, lead zirconate titanate (PZT) and lanthanum lead zirconate titanate (PL
Zirconium titanate such as ZT) is preferably used. Further, lead titanate or the like can be used as the piezoelectric ceramic.

In the present invention, the organic polymer material includes
A resin such as an epoxy resin, a polyethylene resin, a polyurethane resin, or a rubber such as a silicone rubber, a urethane rubber, or a butadiene rubber can be used.

The height of the columnar bodies arranged in the organic polymer material can be, for example, 90 to 360 μm, and preferably 90 to 240 μm depending on the frequency used. The cross section of the columnar body may be a circle or a polygon, but a polygon may be a regular polygon such as a regular triangle, a square, a regular hexagon, or a rectangle. Further, as described later, the columnar body made of the piezoelectric ceramic can have a truncated cone or truncated pyramid shape. The taper angle of the truncated cone or truncated pyramid can be, for example, in the range of 0.1 ° to 20 °, and preferably in the range of 1 to 5 °. Such a shape can be easily formed by using diffracted light passing through a mask in a lithography step as described later.

A composite material having a piezoelectric ceramic body having a small size as described above can be prepared by the following process. Hereinafter, the manufacturing method according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 3A, a resin layer 2 for lithography is formed on a substrate 1 in the process of the present invention. As a substrate, for example, copper,
A substrate formed of a metal substrate such as nickel or stainless steel, a silicon substrate on which a metal such as titanium or chromium is sputter-deposited, or the like can be used. Examples of the material for forming the resin layer include a resist material mainly containing a polymethacrylate such as polymethyl methacrylate (PMMA), a chemically amplified resist material sensitive to X-rays, and the like. The thickness of the resin layer can be arbitrarily selected depending on the purpose, and usually 0.1 to 0.5 mm is used.

Next, as shown in FIG. 3B, a mask 3 is arranged on the substrate 1, and the resin layer 2 is irradiated with X-rays (hereinafter abbreviated as SR light) 10 of synchrotron radiation through the mask 3. You. The mask 3 has an X-ray absorption layer 3a formed in a predetermined pattern. The predetermined pattern is a plurality of 1
It includes a square having sides of 88 μm or less, or a pattern in which a plurality of circles or polygons having the same area as those are arranged at intervals. For example, silicon nitride, silicon, diamond, titanium, or the like can be used for the light-transmitting substrate that forms the mask, and for the X-ray absorption layer, for example, gold,
A heavy metal such as tungsten or tantalum or a compound thereof can be used. The thickness of the X-ray absorbing layer can be arbitrarily selected depending on the desired thickness of the resist pattern, but can be, for example, 3 to 10 μm. In some cases, a mask without a light-transmitting substrate can be used.

The wavelength of the SR light to be applied to the resin layer can be, for example, 1 to 10 °, and its energy is 1 °.
To 10 keV. The light source of the SR light is, for example, a small industrial SR device (with a stored electron energy of 0.6 to
1.5GeV), medium SR device (storage electron energy 1.
5 to 3 GeV).

The exposed resin layer is developed to form, for example, SR
When the portion altered by light is removed, a resin pattern 2 'as shown in FIG. 3C is obtained. Resin pattern 2 '
Has a plurality of holes 2'a. The shape of the hole corresponds to the shape of the piezoelectric ceramic of the composite piezoelectric material finally obtained. However, the size of the piezoelectric ceramic changes because it shrinks at a linear shrinkage rate of about 85% during firing. Therefore,
The cross section of the hole is a square having a side of 88 μm or less, or a circle or polygon having an area equivalent thereto. The ratio of the depth of the hole to the maximum width in the cross section of the hole is preferably 2 or more, and more preferably 3.3 or more.

Next, as shown in FIG. 3D, a metal 5 is deposited on the resin pattern 2 '. The metal 5 is deposited with a thickness in the range of 0.5 to 1 mm, for example, exceeding the thickness of the resin pattern 2 '. When plating is performed using the substrate 1 as a plating electrode, a metal can be easily deposited on the resin pattern 2 '. Metals such as nickel, copper,
Although gold and their alloys, permalloy, and the like can be used, nickel is more preferable because the metal 5 is used later as a mold.

Next, if the substrate is removed by wet etching or the like, and the resin is removed by wet etching or plasma etching, a mold 5 'as shown in FIG. 3E is obtained. The mold 5 'has a resin pattern 2'
The shape has been transcribed. Therefore, the convex portion 5'a corresponding to the hole of the resin pattern is a square having a cross section of 88 μm or less, or a circle or polygon having an area equivalent thereto.

Next, as shown in FIG. 4A, the resin 7 is injected into the mold 5 'obtained by the above process. Acrylic resin (methacrylic resin) such as polymethyl methacrylate (PMMA), polyurethane resin (PU
R), a thermoplastic resin such as polyacetal such as polyoxymethylene (POM), or a thermosetting resin such as epoxy or syrup-like acrylic. After the resin is cured, it is cooled to separate the resin from the mold 5 'to obtain a resin mold 7'.

After forming the resin mold, as shown in FIG. 4 (c), the resin mold 7 'is filled with a material for forming a fine structure. In the case of the present invention, a material for forming a ceramic is filled. The material is filled to the extent that it overflows the resin mold. As such a material, for example, a slurry containing ceramic particles can be used.
It is preferable to use a slurry having a higher viscosity than a slurry having a low viscosity. When a low-viscosity slurry is injected, injection under a vacuum is required. On the other hand, a high viscosity slurry can be pressed into a resin mold in the atmosphere. Pressure for press-fitting, for example, 100 kgf / cm ² or more, more preferably in the range of 100~150kgf / cm ^2. In addition, since the low-viscosity slurry contains a large amount of water, precise control is required in the subsequent drying step. High viscosity slurries do not require such precise control.

Next, as shown in FIG. 4D, the resin mold is removed. For removal, the resin is vaporized or sublimated without melting, or dissolved in a suitable solvent. When the resin is vaporized, the resin component can be evaporated, for example, by heating in a vacuum. In this case, for example, the resin can be decomposed and evaporated at a temperature of 500 ° C. under a pressure of 10 ⁻⁴ Torr or less. Further, the resin component can be vaporized by laser ablation. For example, an ArF excimer laser can be used as the laser. By irradiating the laser with an energy density of 350 mJ / cm ³ or less, only the resin can be removed without affecting the ceramics. Further, the resin may be etched by plasma such as oxygen plasma. For example, when etching is performed using oxygen and freon plasma, the decomposition rate of the resin is high, but the etching rate of the ceramic is extremely low. By utilizing such a difference in etching resistance between the ceramic and the resin, only the resin can be quickly removed. More specifically, for example, at a plasma power of 50 W and a reaction gas pressure of 0.5 Torr, a resin mold made of acrylic can be etched at about 3 μm / min. The conditions for the plasma can be appropriately selected depending on the thickness and the material of the resin. In addition, by dissolving the resin mold in the solvent, only the resin mold can be removed without damaging the ceramic structure. For example, in the case of an acrylic resin type, acetone can be used as a solvent. A suitable solvent can be appropriately selected depending on the material of the resin mold. All of these methods do not damage or destroy the ceramic structure,
This is a method that can quickly remove only the resin mold. By using these methods, a very fine structure can be formed in a resin mold. On the other hand, if the resin mold is removed under a condition that causes the resin to be in a molten state, there is a possibility that the fine columnar body may be collapsed by the molten resin.

By removing the resin, a fine structure as shown in FIG. 4E is obtained. When a slurry of ceramic particles is used, the dried and solidified product of the slurry is fired to obtain a fine structure 8 'made of a ceramic sintered body. This microstructure has a structure in which a plurality of columnar bodies 8'b made of piezoelectric ceramics extend at a predetermined interval from the base 8'a. The cross section perpendicular to the longitudinal direction of the columnar body 8'b is a square having a side of 75 μm or less, or a circle or polygon having an area equivalent thereto.
The height of the column depends on the frequency used and the scanning method.
For example, it is in the range of 90 to 360 μm, preferably 9
The range is from 0 to 240 μm. The aspect ratio of the columnar body is 2 or more, preferably 3 to 7. The columnar body is 40 to 7
It can be arranged at a density of 00 pieces / mm ² .

A composite piezoelectric material can be prepared by impregnating the thus-prepared piezoelectric ceramic structure with a resin. For example, as shown in FIG. 5A, a piezoelectric ceramic structure 121 is put in a cup 120 and impregnated with an organic polymer material 122 from above. This is cured, and the solidified product is removed from the cup 120 (FIG. 5).
(B)). Next, as shown in FIGS. 5C and 5D, the resin portion and the pedestal portion exceeding the height and width of the piezoelectric ceramic structure are removed by grinding or polishing, whereby a composite piezoelectric material 123 can be obtained.

In the present invention, a composite piezoelectric material having a truncated cone or truncated pyramid-shaped column can be prepared by the following process. First, as shown in FIG. 6A, a resin layer 2 for lithography is formed on a substrate 1. Next, as shown in FIG. 1B, a mask 3 is arranged above the substrate 1, and the SR layer 10 is irradiated on the resin layer 2 via the mask 3. The mask 3 has an X-ray absorption layer 3a formed in a predetermined pattern. In this case, the distance d between the mask 3 and the resin layer 2 is significantly large.
By arranging the mask at a considerable distance from the resin, the diffracted light 10b of the SR light by the mask 3 in addition to the straight light 10a of the SR light 10 also contributes to the deterioration of the resin layer 2. As shown in the figure, the diffracted light 10b reaches a portion of the resin layer slightly deviated from directly below (shown by a dotted line) the X-ray absorption layer of the mask. For example, the angle θ of the diffracted light 10b with respect to the straight light 10a as shown in FIG.
Can be in the range of 0.05 to 10 °, preferably 0.5 to 2.5 °. The interval d can be set so that the angle θ is in an appropriate range. The diffracted light 10b is
Since it has a longer wavelength than the straight light 10a and has a low intensity,
Transforms shallower parts than straight light. Therefore, the width of the portion 2a of the resin layer that has been altered by the exposure increases toward the surface. The wavelength of the SR light to be irradiated on the resin layer can be, for example, 1 to 10 °, and the energy can be 1 to 10 keV. In this case, it is particularly preferable to use without removing the long wavelength component of 5 to 10 °. These long wavelength components provide the appropriate diffracted light. As the light source of the SR light, those described above can be used. The distance d between the mask and the resin layer can be arbitrarily selected according to the required taper angle and the wavelength of the SR light to be irradiated.

When the exposed resin layer is developed to remove a portion altered by SR light, a resin pattern 2 'as shown in FIG. 6C is obtained. In the resin pattern 2 ′, the opening width W of the hole 2 ′ a increases as the distance from the substrate 1 increases. Therefore, the opening area of the hole increases as the distance from the substrate 1 increases. The side wall 2'b constituting the hole 2'a is inclined with respect to the thickness direction of the resin layer (indicated by an arrow). The holes can be in the shape of, for example, a truncated cone or a truncated pyramid. The cross section of the hole is 88 μm on one side
The following squares or circles or polygons having an area equivalent to the squares are used. The inclination of the side wall of the hole is determined by the two straight lines 6 and 6 'to intersect in the cross section as shown in FIG.
(Taper angle) α. The taper angle α can be in the range of 0.1 to 20 °, preferably in the range of 1 to 5 °.

Next, as shown in FIG. 6D, a metal 5 is deposited on the resin pattern 2 '. Next, if the substrate is removed by wet etching or the like, and the resin is removed by wet etching or plasma etching, a mold 5 'as shown in FIG. 6E is obtained. The shape of the resin pattern 2 'is transferred to the mold 5'. Therefore, the convex portion 5'a corresponding to the hole of the resin pattern has a taper angle α 'substantially equal to that of the resin pattern, and the width of the convex portion 5'a becomes narrower toward the tip. The taper angle α 'is in the range of 0.1 to 20 °, preferably 1 to 5
° range.

Next, as shown in FIG. 9A, the resin 7 is injected into the obtained mold 5 '. After the resin is cured, it is cooled to separate the resin from the mold 5 'to obtain a resin mold 7'. At this time, since the convex portion of the mold 5 'becomes thinner toward the tip at a predetermined taper angle as described above, the resin mold 7'
Can be easily removed from the mold 5 '. When removing
It is the initial adhesive force that works between the resin and the mold, and little frictional force works. Further, a component acting in the direction of breaking the mold convex portion in the adhesive force is small, and the mold convex portion is not destroyed at the time of removal. By obtaining a structure having a predetermined taper angle using the diffracted light in this manner, it is possible to more effectively prevent the destruction of the mold in the formation of the resin mold, and to prolong the life of the mold. it can.

After forming the resin mold, as shown in FIG. 9C, the resin mold 7 'is filled with a material 8 for forming ceramics. Next, as shown in FIG. 9D, the resin mold is removed. The resin is vaporized or sublimated without melting, or dissolved in a suitable solvent. By removing the resin, a fine structure as shown in FIG. 9E is obtained. By firing the dried and solidified ceramic slurry, a microstructure 8 'made of a piezoelectric ceramic sintered body is obtained. The microstructure 8 'includes a pedestal portion 8'a
And a plurality of columnar bodies 8'b formed on the pedestal portion 8'a. The cross section of the columnar body 8'b is a square having a side of 75 μm or less, or a circle or polygon having an area equivalent thereto. The height of the columnar body is, for example, in the range of 90 to 360 μm, and preferably in the range of 90 to 240 μm, depending on the frequency used and the scanning method. The aspect ratio of the columnar body is 2 or more, preferably 3 to 7. The pillars are
They can be arranged at a density of 40 to 700 pieces / mm ² . The taper angle of the columnar body having the shape of a truncated cone or a truncated pyramid is in the range of 0.1 to 20 °, preferably in the range of 1 to 5 °. From the obtained piezoelectric ceramic body, FIG.
A composite piezoelectric material is prepared as shown in FIG. The process is as described above.

In this method, a structure having a predetermined taper angle can be easily manufactured by controlling the distance between the X-ray mask and the substrate and positively using the diffracted light for lithography. According to this method, a structure having walls inclined with respect to the thickness direction can be basically obtained by one exposure step. The time required for fabrication is relatively short, and no complicated steps are required for exposure. A structure having inclined walls can also be obtained by a lithography step of irradiating SR light in a direction perpendicular to the substrate. In a process using diffracted light, the resolution is slightly lower than when only straight light is used. However, since the irradiation of the diffracted light can be controlled with good reproducibility, the required mold and microstructure can be obtained with high accuracy.

On the other hand, trying to obtain a similar structure by the conventional technique involves various difficulties as described below.
For example, as shown in FIG.
After irradiating the resist layer 22 on the substrate 21 with the R light 30 through the mask 23, as shown in FIG.
The SR light 30 can be emitted while changing the tilt angle.
However, in such a case, the resulting structure is shown in FIG.
As shown in FIG. 1 (c), a resist pattern 22 'having holes in which the width of the opening becomes narrower toward the surface is obtained. Such a resist pattern is the opposite of the shape required by the present invention. Also, as shown in FIG.
Substrate 3 coated with resist 32 with respect to SR light 40
A method of inclining and rotating 3 at a predetermined angle is also conceivable.
In this case, the exposure area 32 'has the shape of a truncated cone. However, in this method, it is difficult to realize a uniform irradiation amount as a whole because the moving speeds of the central portion and the peripheral portion of the exposure region are different. This method is not practical as a method for obtaining a highly accurate microstructure. In the method of irradiating the SR light obliquely, the method shown in FIG. 13 is considered to be more practical. In the method shown in FIG.
After irradiating the resist 42 on the substrate 41 obliquely with the SR light 50 as shown in (a), the position of the mask 43 is shifted and the angle of the substrate 41 is changed as shown in FIG.
Light 50 is applied. According to such a process, FIG.
A structure as shown in (c) is obtained. However, in this method, it is necessary to shift the mask with high accuracy, but to do so, it is necessary to match (align) the positional relationship between the mask and the substrate. It is impossible to perform such a process using one mask, and a plurality of different masks are required. In this method, the work time is lengthened due to the mask alignment, and the accuracy in manufacturing is reduced. Further, since it is necessary to perform SR light irradiation many times depending on the shape to be obtained, the exposure time becomes longer than necessary in a certain region. If the absorbed energy density exceeds the upper limit value, the positive / negative inversion occurs in the resist, and a desired resist pattern cannot be obtained. In this method, it is desirable to use light of a single wavelength. However, in the SR light, the light of a single wavelength has relatively low intensity, so that the exposure time is further increased. In addition, although a truncated pyramid resist pattern can be obtained, the shape is limited such that a truncated cone cannot be obtained. This method has many problems in terms of working time, cost, accuracy and efficiency. Comparing these methods with the method of the present invention, it should be easy to see how simple, accurate, efficient and low cost the method of the present invention is.

[0049]

EXAMPLE A composite piezoelectric material in which a number of pillars made of lead zirconate titanate (PZT) were dispersed in a resin was prepared as follows.

(1) Manufacture of a mold A mold for a PZT array structure was manufactured according to the processes shown in FIGS. First, an X-ray sensitive resist, a copolymer of methyl methacrylate and methacrylic acid (P (MMA + MAA)) was applied to a conductive substrate made of a silicon substrate on which titanium was sputter-deposited to a thickness of 180 μm. Next, a mask in which an absorption layer pattern made of tungsten nitride was formed on a light-transmitting substrate made of silicon nitride was arranged above the resist layer. The resist was irradiated with synchrotron radiation (SR light) through a mask. The SR apparatus was NIJI-3 (magnetic field of the deflection unit 4 Tesla, stored electron energy 0.6 GeV). SR
In the irradiation, usually, Kapton or the like is used as a filter to cut the super-wavelength light of 3 ° or more as much as possible, but in the case of this embodiment, the super-wavelength light was not cut. Although the peak wavelength of the light emitted from the SR apparatus itself was about 6 °, the peak wavelength of the SR light actually applied to the resist was about 4 ° because light passing through a 100 μm thick beryllium window was used. Was. Distance d between mask and resist layer
Was set to 50 μm or less, 5 mm, 14 mm, and 28 mm, respectively, and irradiation with SR light was performed. On the mask, circles having a diameter of 30 μm are regularly arranged at a relative angle of 60 ° and a pitch of 57 μm, or each side is 30 μm.
A pattern in which m square patterns were regularly arranged at intervals of 30 μm was used. The portion of the circle or square pattern is adapted to transmit X-rays. After irradiation with SR light, development was performed with methyl isobutyl ketone (MiBK) to obtain a resist pattern. When a mask having a circular pattern was used, when the distance d between the mask and the resist layer was 50 μm or less, many cylindrical holes having a diameter of 30 μm were formed. The distance d between the mask having a circular pattern and the resist layer is 5 mm, 14 mm and 28 mm.
mm, the taper angles are 2 °, 6 °, 1
A large number of holes having a 4 ° truncated cone shape were formed in the resist pattern. The diameter of the truncated cone on the substrate side is 30
μm. As described above, by remarkably increasing the distance between the mask and the resist layer, a taper angle in an appropriate range could be obtained by utilizing the diffraction effect of SR light. When a mask having a square pattern of 30 μm square was used, it was possible to obtain a resist pattern in which a large number of prism-shaped or truncated pyramid-shaped holes were formed. The taper angle of the truncated pyramid is 2 ° when the interval d is 5 mm, and the interval d is 14 mm
At 6 °, and 14 ° at an interval d of 28 mm.

Next, plating was performed using the conductive substrate as a plating electrode, and nickel was deposited to a thickness of 1 mm.
After dissolving the substrate with an aqueous potassium hydroxide solution, the resist was removed by oxygen plasma to obtain a mold. Fig. 1
4A or FIG. 15A. In the mold 55 shown in FIG.
A large number of cylindrical or prismatic fine columns 55b extend from 5a. In the mold 55 'shown in FIG. 15A, a fine column 55'b having a truncated cone or truncated pyramid shape extends from the pedestal portion 55'a. The upper surface of the pillar 55'b has a diameter of 3
It is a circle of 0 μm or a square of 30 μm on a side. The height of the columns 55b and 55'b is 180 μm. The columns 55b or 55'b are arranged at intervals of 30 μm.

(2) Preparation of Ceramic Microstructure A microstructure made of a PZT sintered body was formed according to the process shown in FIGS. First, a resin was filled in the obtained mold. An acrylic resin composed of polymethyl methacrylate (PMMA) was used as the resin. The syrup-shaped acrylic resin was poured into a mold, heated and cured, and then cooled to room temperature to separate the resin from the mold, thereby obtaining a resin mold. The resin mold is obtained by inverting the shape of a desired fine structure. Next, a slurry containing PZT particles was filled in a resin mold. The slurry was prepared using water and an organic binder. Next, the filled slurry was solidified by drying. Subsequently, ashing using oxygen plasma was performed to remove the resin mold. Ashing conditions were a reaction gas pressure of 0.5 Torr and an RF power of 50 W. The solidified product of the remaining slurry was calcined at 500 ° C., and further calcined at 1100 ° C. By firing, a fine structure made of a PZT sintered body was obtained. FIG. 14 (b) and FIG.
This is shown in FIG. In the fine PZT array structure 68, a large number of column-shaped or prism-shaped fine columns 68b extend from the plate-shaped pedestal portion 68a. Approximately 8
Since the column 68b contracts by 5%, the cross section of the column 68b is a circle having a diameter of 25 μm or a square having a side length of 25 μm. From the plate-shaped pedestal portion 68'a, a large number of fine columns 68'b in the shape of a truncated cone or truncated pyramid extend. The upper surface of the pillar 68'b is a circle having a diameter of 25 μm or a square having a side of 25 μm. The height of columns 68b and 68'b is 150 μm. The columns 68b and 68'b are both arranged at intervals of 25 μm.

By impregnating the PZT array produced as described above with a resin, a composite piezoelectric material could be produced. The fabrication method is, for example, as shown in FIGS. Epoxy resin was used as the resin. FIG. 5 (a)
As shown in FIG. 10A and FIG.
The T array 121 was put in, and the epoxy resin 122 was impregnated under vacuum from above. This was heated to cure the resin, and the solidified product was taken out of the cup 120 (FIGS. 5B and 10B). Subsequently, as shown in FIGS. 5 and 10C and 10D, when the resin portion exceeding the height and width of the PZT array and the pedestal portion of the PZT array are removed by grinding or polishing, the composite piezoelectric material 123 is removed. Could be formed. The thickness of the obtained composite piezoelectric material is 100 μ
m.

Gold was sputter-deposited on both surfaces of the composite piezoelectric material thus prepared to form electrodes. After polarization, cutting was performed to obtain an ultrasonic probe having a size of 5 mm × 5 mm. When the characteristics of the obtained probe were measured, the electromechanical coupling coefficient Kt in the longitudinal vibration mode was 60%.
~ 65%, the value obtained from PZT alone 43 ~
That was well over 45%. Distortion piezoelectric constant d of longitudinal vibration
₃₈ is about 300 × 10 ⁻¹² m / V, and this value is
It was about 80% of ZT alone. Regarding the lateral vibration mode,
K ₃₁ was about 15% and d ₃₁ was 60 × 10 ⁻¹² m / V, which was ４ to の of PZT alone. As a result, it was found that the transverse vibration mode that hinders the image diagnosis was suppressed, and the necessary longitudinal vibration mode was not much different from PZT. Also, a voltage piezoelectric constant g ₃₃ that gives the sensitivity to longitudinal vibration
Is 100 to 120 × 10 ⁻³ Vm / N, which is P
It is about 4 to 5 times of 23 × 10 ⁻³ Vm / M of ZT alone. Therefore, the obtained composite piezoelectric material has higher sensitivity than that of PZT alone. Regarding the acoustic impedance of the obtained composite piezoelectric material, a calculated value of 10 Mrayl was obtained. This is much closer to 1.5 Mrayl in the case of a living body (however, bone is 4 to 8 Mrayl) than 30 Mrayl in the case of PZT alone.

Regarding the frequency constant of the lateral vibration,
5.5 × 10 Young's modulus in several bands ⁸Pa or less
If the frequency constant is 560 kHz · mm or less,
The rate is 2.4 × 10⁹If Pa or more, frequency constant 940
Experiments show that the frequency is higher than kHz
Out of the range of 560 to 940 kHz · mm
It was found that it was possible to control with. The experiment
FIG. 16 shows the results. In practice, however, the capital of the manufacturing process
It is preferable to use the resin of the latter condition from the case. Ma
If the frequency band used is 50% or more of the center frequency,
In order to obtain the corresponding frequency constant,
It is necessary to control the Young's modulus.

[0056]

As described above, according to the present invention, a composite piezoelectric material which can be used at a higher frequency can be provided. The composite piezoelectric material according to the present invention is suitable for an ultrasonic probe requiring high resolution. The present invention provides a composite piezoelectric material suitable for an ultrasonic probe used in a phased array electronic sector scan system and a linear scan system. The present invention provides a composite piezoelectric material particularly suitable for a probe of a medical ultrasonic diagnostic imaging apparatus, but its use is not particularly limited to this. The present invention also provides a method capable of producing a composite piezoelectric material having excellent performance as described above with high yield.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a general structure of a composite piezoelectric material.

FIG. 2 is a perspective view showing a conventional process for manufacturing a composite piezoelectric material.

FIG. 3 is a schematic sectional view illustrating an example of a manufacturing process according to the present invention.

FIG. 4 is a schematic sectional view showing an example of a manufacturing process according to the present invention.

FIG. 5 is a schematic sectional view showing an example of a manufacturing process according to the present invention.

FIG. 6 is a schematic sectional view showing another example of the manufacturing process according to the present invention.

FIG. 7 is a schematic diagram illustrating an angle formed between straight-traveling light and diffracted light with respect to SR light.

FIG. 8 is a schematic sectional view showing a shape of a resist pattern obtained by X-ray lithography in another manufacturing process according to the present invention.

FIG. 9 is a schematic sectional view showing another specific example of the manufacturing process according to the present invention.

FIG. 10 is a schematic sectional view showing another embodiment of the manufacturing process according to the present invention.

FIG. 11 is a schematic sectional view showing a method for manufacturing a structure having inclined walls by a conventional method.

FIG. 12 is a schematic cross-sectional view showing a process for manufacturing a structure having inclined walls according to another conventional method.

FIG. 13 is a schematic sectional view showing a process for obtaining a structure having inclined walls similar to the present invention using a conventional method.

FIG. 14 is a partial cross-sectional view showing the shapes of a mold and a PZT array structure obtained according to an example.

FIG. 15 is a partial cross-sectional view showing another shape of the mold and the PZT array structure obtained in the example.

FIG. 16 relates to a composite piezoelectric material obtained by the present invention,
FIG. 3 is a diagram illustrating a relationship between a resin Young's modulus and a frequency constant of a transverse vibration mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Resin layer 3 Mask 5 Metal 5 'Die 7 Resin 7' Resin mold 8 Ceramic material 8 'Fine structure made of ceramics

Continued on the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location H01L 41/22 H01L 41/22 C H04R 17/00 330 Z

Claims (8)

[Claims] 1. A composite piezoelectric material having a structure in which a plurality of columnar bodies made of piezoelectric ceramics are arranged in a matrix made of an organic polymer material at intervals so that their respective longitudinal directions are parallel to each other, A composite piezoelectric material, wherein a cross section of the columnar body substantially perpendicular to the longitudinal direction is a square having a side of 75 μm or less, or a circle or polygon having an area equivalent thereto. 2. A ratio of a length of the columnar body to a maximum width in a cross section of the columnar body substantially perpendicular to the longitudinal direction,
2. The composite piezoelectric material according to claim 1, wherein the number is two or more. 3. A ratio of a length of the columnar body to a maximum width in a cross section of the columnar body substantially perpendicular to the longitudinal direction,
3. The composite piezoelectric material according to claim 1, wherein the composite piezoelectric material has a ratio of 3.3 or more. 4. The composite piezoelectric material according to claim 1, wherein a volume percentage of said piezoelectric ceramic in said composite piezoelectric material is in a range of 10 to 30%. 5. A frequency constant in a direction perpendicular to a longitudinal direction of the columnar body is 560 kHz · mm to 940 kHz · mm.
The composite piezoelectric material according to any one of claims 1 to 4, wherein the composite piezoelectric material is outside of the following. 6. The columnar body has a shape of a truncated cone or a truncated pyramid, and a taper angle of the truncated cone or the truncated pyramid is 0.1.
The angle is in the range of 20 ° to 20 °.
6. The composite piezoelectric material according to any one of items 5 to 5. 7. A method of manufacturing a composite piezoelectric material having a structure in which a plurality of columnar bodies made of piezoelectric ceramics are arranged in a matrix made of an organic polymer material at intervals so that their longitudinal directions are parallel to each other. A step of forming a layer made of a resin material for lithography on a substrate; and a plurality of circles or polygons each having a square of 88 μm or less or an area equivalent to the square, A step of irradiating X-rays by synchrotron radiation through a mask for forming a resist pattern having a pattern arranged at intervals, a step of developing the layer made of the resin material, and a step of forming a pattern by development. Depositing a metal material on the resin material that has been removed, and removing the resin material to change the shape of the patterned resin material. Obtaining a mold of the copied metal material, filling the obtained mold with a resin material, extracting the resin material from the mold, and transferring the resin mold onto which the shape of the mold has been transferred. Obtaining, filling the obtained resin mold with a material for forming ceramics, and solidifying; and evaporating or sublimating the resin mold without bringing the resin into a molten state, or dissolving it in a solvent. By doing
The step of removing, and heating the remaining solidified material, a plurality of columnar bodies each having a cross section of a square having a side of 75 μm or less or a circle or polygon having an area equivalent thereto extended from the pedestal portion at intervals. A step of obtaining a ceramic structure having a structure; a step of attaching an organic polymer material onto the obtained ceramic structure; and a step of attaching the organic polymer material to the ceramic structure.
Removing the pedestal portion to obtain a composite material in which the plurality of columnar bodies are arranged at intervals in the organic polymer material. 8. The step of irradiating the synchrotron radiation with the X-rays includes the step of irradiating the mask and the resin material such that the diffracted light of the synchrotron radiation through the mask is sufficiently irradiated to the layer made of the resin material. A step of providing a predetermined interval between the resin material and the layer made of, wherein the exposure with the diffracted light provides a hole in the resin material, the opening area of which increases with distance from the substrate. 7. The production method according to 7.