JP2003179997A - Manufacturing method of piezoelectric element and ultrasonic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a piezoelectric element by which a piezoelectric element used for an ultrasonic oscillator can be worked with a high manufacturing yield, and to provide a manufacturing method of an ultrasonic oscillator employing the same. <P>SOLUTION: At least the piezoelectric element 1 having parallel grooves 11 formed on one side surface at prescribed intervals is incorporated, and then array working is executed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a piezoelectric element and a method for manufacturing an ultrasonic oscillator.

[0002]

2. Description of the Related Art An ultrasonic oscillator used in a medical ultrasonic diagnostic apparatus forms an array type in which a large number of strip-shaped vibrators are arranged. Thereby, the ultrasonic beam can be electronically controlled to obtain a high-resolution tomographic image in real time.

FIG. 8 is a structural diagram of a general ultrasonic oscillator. Electrodes 42a (not shown) on both surfaces of the piezoelectric element 41,
42 b is formed, and a rubber-based backing material 43 is provided on the lower surface of the piezoelectric element 41 by being fixed with an epoxy adhesive. An acoustic matching layer 44 in which alumina is dispersed in epoxy resin is formed on the upper surface of the piezoelectric element 41.
The piezoelectric element 41 and the acoustic matching layer 44 are array processed. The array pitch of the array oscillator is 0.1
It is about mm. Acoustic lens 45 on acoustic matching layer 44
Are formed. Ultrasonic waves are transmitted and received through the acoustic lens 45. The electrodes formed on both sides of the piezoelectric element 41 are connected to a diagnostic device via a flexible printed wiring board (FPC) or a cable.

The ultrasonic oscillator having the structure shown in FIG.
And the method shown in FIG. First, as shown in FIG. 9, electrodes 42 are formed on both surfaces of an integrally formed piezoelectric element 41.
a and 42b are formed. The piezoelectric element 41 is bonded onto the backing material 43. On the other hand, the acoustic matching layer 44 is formed on the upper surface of the piezoelectric element 41.

Next, as shown in FIG. 10, the thickness is 50 μm.
A piezoelectric element 41 is cut from the acoustic matching layer 44 side using a dicing saw having a diamond blade (thin blade grindstone) 48 of about 100 μm in depth in the backing material 43.
The dicing is performed at one time so as to form the groove 49. Then, the acoustic lens 45 is formed on the acoustic matching layer 4, and the acoustic lens 45 shown in FIG.
The ultrasonic oscillator having the structure shown in Fig. 3 is completed.

As the material of the piezoelectric element 41, ceramics of lead zircon titanate (PZT) have been conventionally used in many cases, but recently, a piezoelectric element having a large electromechanical coupling coefficient representing the conversion efficiency of electric energy and ultrasonic energy. Piezoelectric single crystals are drawing attention as a material. Medical devices and non-destructive inspection machines that employ an ultrasonic oscillator that uses a piezoelectric single crystal material can significantly improve resolution and sensitivity. For example, Pb ((Zn _1/3
Nb _2/3 ) _0.91 Ti _0.09 ) O ₃ typified by a solid solution of lead zinc niobate and lead titanate (PZNT) from a solid solution of lead magnesium niobate and lead titanate And a single crystal of lithium niobate. When these materials are used, particularly in the fields of medical equipment and nondestructive inspection equipment, when the above-mentioned piezoelectric single crystal is used as the material of the piezoelectric element 41 of the ultrasonic oscillator,
It is possible to significantly improve the resolution and sensitivity.

Next, a method of manufacturing the piezoelectric element 41 will be described. FIG. 11 is a schematic view showing the manufacturing process of the piezoelectric element 41 when PZNT is used as the piezoelectric single crystal. After growing the crystal by the Bridgman method or the like, the grown crystal is sliced with a wire saw. Subsequently, the sliced crystal is subjected to a dicing process to form a plate having a desired size. After that, a desired thickness (for example, 120 to 260 μm) is finished by double-sided lapping, and after cleaning, electrodes are formed on both sides by a sputtering method or the like. Through these manufacturing methods, a piezoelectric element 41 having electrodes 42a and 42b on both surfaces of a piezoelectric single crystal plate as shown in FIG. 12 is formed.

[0008]

As described above, in the manufacturing process of the ultrasonic oscillator, the piezoelectric element is array-processed by the dicing saw together with the acoustic matching layer. Since the number of array elements formed by array processing ranges from several tens to several hundreds, variations in the characteristics between array elements due to the difference in the cut surface affect the image quality of the tomographic image displayed on the diagnostic device connected to the ultrasonic oscillator. High homogeneity is required due to the influence.

As shown in FIG. 13 which shows a cut portion by a dicing saw at the time of array processing described above, PZT ceramics has relatively good workability so that a desired cut surface can be obtained.
Since the ZNT piezoelectric single crystal is a hard-to-cut material having a hard and brittle property, it often has a rough cut surface and cracks 50 and chipping often occur. They are a major factor in reducing the manufacturing yield.

The present invention has been made based on these circumstances, and a method of manufacturing a piezoelectric element capable of processing a piezoelectric element used in an ultrasonic oscillator with good manufacturing yield, and a method of manufacturing an ultrasonic oscillator using the same. Is intended to provide.

[0011]

According to the means according to the invention of claim 1, an electrode forming step of forming electrodes on both surfaces of a piezoelectric material cut into a predetermined shape and polished, and on at least one side surface of the piezoelectric material. And a groove forming step of forming parallel grooves at predetermined intervals.

According to the second aspect of the present invention,
The groove forming step is a method of manufacturing a piezoelectric element, which is performed by photoetching.

According to the third aspect of the invention,
The parallel groove in the groove forming step has a plate thickness Ct of the piezoelectric element,
When the groove depth is Bd and the inter-groove element width is Cw, it is a method of manufacturing a piezoelectric element, which is characterized by forming into a shape having a relationship of 10 μm <(Ct−Bd) <Cw.

According to the means of the invention of claim 4,
An electrode forming step of forming electrodes on both sides of the piezoelectric element and applying an electric field to the piezoelectric element to polarize; a wiring step of connecting a signal line to one of the electrodes and a ground line to the other; A groove forming step of forming a groove in the piezoelectric element by the method for manufacturing a piezoelectric element according to any one of claims 1 to 3, and a backing on a side of the piezoelectric element having the groove connected to the signal line. A backing material joining step of joining materials, an acoustic matching layer forming step of joining an acoustic matching layer to a side of the piezoelectric element in which the groove is formed, to which the ground wire is connected,
In a state where the signal line, the ground line, the backing material, and the acoustic matching layer are joined to the piezoelectric element having the groove formed therein, the piezoelectric element is joined to the piezoelectric element by aligning with the groove with a dicing blade. And a dicing step of performing groove processing on each of the formed portions, and a method for manufacturing an ultrasonic oscillator.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the structure of an ultrasonic oscillator. Electrodes 2a and 2b are formed on both surfaces of the piezoelectric element 1, and a backing material 3 is provided on the lower surface side of the piezoelectric element 1 via a chipping prevention layer 4 formed of an epoxy adhesive or the like. The chipping prevention layer 4 is for preventing chipping of the piezoelectric element 1 during array processing.

On the other hand, an acoustic matching layer 5 is formed on the upper surface side of the piezoelectric element 1, and the piezoelectric element 1 and the acoustic matching layer 5 form an array oscillator 7 which is array processed. The array pitch of the array oscillators 7 is narrow and is about 0.1 mm. The acoustic lens 7 is formed on the acoustic matching layer 5. Ultrasonic waves are transmitted and received through the acoustic lens 7.

Electrodes 2a formed on both sides of the piezoelectric element 1,
A flexible printed wiring board for signal (signal FPC 8) is fixed to the electrode 2a on the backing material 2a side of 2b by soldering. The signal FPC 8 is connected to an ultrasonic diagnostic apparatus (not shown).

A grounding FPC 9 is fixed to the electrode 2b formed on the other surface of the piezoelectric element 1 by soldering.

A piezoelectric single crystal is used as the material of the piezoelectric element 1. The piezoelectric single crystal is not particularly limited, and Pb ((Zn
_1/3 Nb _2/3 ) _0.91 Ti _0.09 ) O ₃ represented by solid solution of lead zinc niobate and lead titanate (PZN)
A single crystal made of T), a single crystal made of a solid solution of lead magnesium niobate and lead titanate, a lithium niobate single crystal, or the like can be used as appropriate. Since the piezoelectric single crystal has a low Curie point of about 180 ° C., polarization deterioration easily occurs due to heat of soldering or array processing. Therefore, the piezoelectric single crystal needs to be repolarized after array processing.

The acoustic matching layer 5 is formed of a composite material in which alumina powder is dispersed in epoxy resin.

In the medical probe, the backing material 3 is a rubber-based material such as a material in which ferrite powder is mixed with neoprene rubber or a material in which chloroprene rubber and epoxy resin are mixed as the backing material 3. ing.

Next, a method of manufacturing the ultrasonic oscillator will be described. First, the electrodes 2a and 2b are formed on the lower surface and the upper surface of the piezoelectric element 1, respectively. The electrodes 2a and 2b are polarized by applying an electric field to the piezoelectric element 1. The conductive layer of the grounding FPC 9 is soldered to the end of the upper surface electrode 2b of the piezoelectric element 1. In addition, the lower surface electrodes 2a, 2b of the piezoelectric element 1
The conductive layer of the signal FPC is soldered to the end of the.

A rubber-based backing material 3 is bonded to the lower surface of the piezoelectric element 1 by using an epoxy adhesive except for the connection portion with the conductive layer of the FPC. On the other hand, the acoustic matching layer 5 is formed on the upper surface of the piezoelectric element 1. The acoustic matching layer 5 is made of a composite material in which alumina powder is dispersed in an epoxy resin and has a first thickness of a predetermined value.
The acoustic matching layer 5a is formed, and the second acoustic matching layer 5b made of a resin sheet and having a predetermined thickness is further bonded thereon.

Next, the FPCs 8 and 9 are bent downward along the side surface of the backing material 3. In this state, the first acoustic matching layer 5 is set on the dicing saw at a predetermined pitch.
a, second acoustic matching layer 5b, piezoelectric element 1, electrodes 2a, 2
b, the FPCs 8 and 9 and the backing material 3 are cut.
After that, the array processing which will be described in detail when the method of manufacturing the piezoelectric element 1 is described later is performed.

Since the piezoelectric single crystal causes polarization deterioration after array processing, a voltage of 0.5 to 2 is applied at a temperature of 80 ° C.
DC voltage of kV / mm, time 0.2-5min is F
Repolarization is performed by applying from the conductive layer of PC. After that, the cut groove is filled with silicone resin, and the acoustic lens 7 is bonded onto the second acoustic matching layer 5b. Further, a cable (not shown) is connected to the ends of the FPCs 8 and 9 and housed in a case to manufacture an ultrasonic oscillator.

Next, a method of manufacturing the piezoelectric element 1 will be described. FIG. 2 is an explanatory view schematically showing the manufacturing process of the piezoelectric element 1.

First, a crystal is grown by the Bridgman method. From the grown crystal, using a Laue camera [10
[0] axis is taken out and slice processing is performed in parallel with this axis with a wire saw to cut a wafer to a thickness of about 0.3 to 10 mm.

Next, the wafer is subjected to a dicing process,
For example, it is cut out into a plate shape having a size of about 15 × 20 mm.

The obtained plate-shaped wafers are # 1000- #.
Both sides are polished by lapping or the like using about 4000 abrasive grains. Wafer thickness at this point is 100-500μ
m. The thickness differs depending on the frequency of ultrasonic waves used as the ultrasonic oscillator.

After the polishing process, washing and drying are performed, and thereafter, electrodes 2a and 2b of Au or Ag are formed on both surfaces of the wafer by a sputtering method or the like. The steps up to this point are the same as the conventional steps.

After this, a photo-etching process is applied to the surface of one electrode 2b (the side to which the acoustic matching layer 5 will be joined later). In this photo-etching process, first, the electrode 2b
The resist 10 is applied to the surface of the substrate and then exposed through a mask (not shown) having a predetermined pattern. Hereinafter, the grooves 11 arranged in parallel are formed in the piezoelectric element 1 by a photo-etching step generally used in a semiconductor device manufacturing process such as development, dry etching, resist stripping and cleaning.

Finally, at a high temperature of 200 ° C., 0.1-2
The polarization is terminated by cooling to room temperature with a voltage of kV / cm applied.

As a result, the grooved piezoelectric element 1 as shown in FIG. 3A is obtained. If the same photo-etching process is performed on the other surface of the piezoelectric element 1, as shown in FIG.
The piezoelectric element 1 having the grooves 11 formed on both surfaces as shown in (b) is obtained.

As the groove forming method, grinding processing using a thin blade having elasticity can be used instead of the etching step. In that case, the elasticity of the thin blade is used to absorb the impact when the groove is formed.

In the above case, the grooves 2 are formed after the electrodes 2a and 2b are formed on both surfaces of the piezoelectric element 1. However, the grooves are formed before the electrodes 2a and 2b are formed, and then the electrodes 2a and 2b are formed. 2b may be formed.

Next, the array processing will be described with reference to the schematic diagram of the array processing shown in FIG. The same parts as those in FIG. 1 are designated by the same reference numerals, and their description will be omitted. A groove is formed in advance in the piezoelectric element 1 incorporated in the ultrasonic oscillator by the groove forming process described above.

The ultrasonic oscillator in which the acoustic lens 7 is not bonded is set on the dicing saw, and the first acoustic matching layer 5 is formed along the groove 11 formed in the piezoelectric element 1 in advance.
a, second acoustic matching layer 5b, piezoelectric element 1, electrodes 2a, 2
b, the FPC and the rubber-based backing material 3 with the blade 12
The array processing is performed by cutting with.

In order to compare the operation of the processing points of the array processing in this case with the conventional case, FIG. 5 shows the operation of the processing points in the case of the array processing of the prior art, and FIG. 6 shows the operation of the above-described embodiment. The action of processing points during array processing is shown.

The thickness of the piezoelectric element 1 which is a difficult-to-cut material is reduced and
The 3 component force (X direction, Y direction, Z direction) at the work point is
(Fx, Fy, Fz) and the case of the above embodiment (F
x₁, Fy₁, Fz₁) And Fx> F
x₁, Fy> Fy₁, Fz> Fz ₁And the above implementation
In the case of the above form, the stress generation at the processing point can be suppressed.

Further, in the case of the above-mentioned embodiment, since the groove bottom has a structure in which the mechanical strength is the weakest, cracks are generated only in the groove bottom during array processing. Since the crack generated at the groove bottom serves as a removed portion in the array processing, cracks, chipping and chipping in the remaining portion in the array processing are extremely reduced, and the ultrasonic oscillator can be manufactured with high yield.

FIGS. 7A to 7D are explanatory views comparing the groove shape of the piezoelectric element 1 and the processing model of the array processing between the conventional case and the above-described embodiment.

FIG. 7A shows a groove 11 formed on the conventional piezoelectric element 1.
It is an array processing model in the state where is not formed.
When the stress 12 is generated in the vicinity of the processing point, the material strength is weak because the adjacent cutting groove side portions that have already been cut have the smallest wall thickness. For this reason, the cracks 14 are most likely to be generated in the portion of the piezoelectric element 1 to be left uncut, which is a main factor of reducing the manufacturing yield.

FIG. 7B shows a relationship of (Ct-Bd)> Cw when the plate thickness Ct, the array element width Cw of the piezoelectric element 1 and the depth Bd of the cutting groove 11 provided in advance are set. It is an array processing model in the case. Although the groove 11 which is cut in advance is provided, the element width Cw is larger than the plate thickness Ct-Bd in the initial cutting stage. Also in this case, cracks 14 are most likely to occur at the portion of the array element to be left uncut,
It is difficult to obtain the effect of providing the cutting groove in advance, as shown in FIG. 7 (c).
Is an array processing model in the relationship of 10 μm <(Ct−Bd) <Cw. In this case, the thickness of the bottom wall of the groove formed by the array processing is set to 10 μm. The groove 11 provided in advance is deep and thinner than the array element width (Ct-Bd) <
Since there is a relationship of Cw, the material strength of the groove bottom portion is the weakest at the time of array processing, and the crack 14 is likely to occur. But,
Even if a crack is generated at the bottom of the groove, it is cut and removed thereafter, so that it does not affect the performance of the ultrasonic oscillator. Therefore, the rate of crack occurrence in the piezoelectric element 1 to be left is extremely small, and the piezoelectric element 1 can be manufactured with high yield.

However, as shown in FIG. 7 (d), when the thickness of the bottom portion of the groove 11 provided in advance is 10 μm or less, cracks 14 and fractures occur at the stage of handling the material before the array processing, and before the manufacturing and assembling. The function of parts as a material of the piezoelectric element 1 cannot be maintained.

From these results, the shape of the groove 11 of the piezoelectric element 1 is preferably 10 μm <(Ct−Bd) <Cw.

As described above, according to the above-described embodiment, in the array processing by dicing, which is performed when manufacturing the ultrasonic oscillator, cracks and chippings which have been conventionally generated are reduced, and The production yield of the sonic oscillator was improved.

In particular, a great effect can be obtained in manufacturing using the piezoelectric element 1 made of a piezoelectric single crystal, but the processing accuracy in the array processing is improved even in the case of PZT ceramics conventionally used for the piezoelectric element 1, and the manufacturing is improved. The yield can be increased.

[0049]

According to the present invention, it is possible to manufacture a piezoelectric element and an ultrasonic oscillator using the same with high accuracy and with high manufacturing yield.

[Brief description of drawings]

FIG. 1 is a perspective view of an ultrasonic oscillator.

FIG. 2 is an explanatory view schematically showing the manufacturing process of the piezoelectric element of the present invention.

FIG. 3A and FIG. 3B are perspective views of a grooved piezoelectric element.

FIG. 4 is a schematic view of array processing of the present invention.

FIG. 5 is an explanatory view of the action of processing points during array processing according to the related art.

FIG. 6 is an explanatory view of the action of processing points during array processing of the present invention.

7A to 7D are explanatory views of the groove shape of a piezoelectric element and a processing model of array processing.

FIG. 8 is a structural diagram of a general ultrasonic oscillator.

FIG. 9 is an explanatory diagram of a method of manufacturing an ultrasonic oscillator.

FIG. 10 is an explanatory view of a method of manufacturing an ultrasonic oscillator.

FIG. 11 is a schematic view showing a manufacturing process of a conventional piezoelectric element.

FIG. 12 is a perspective view of a piezoelectric element.

FIG. 13 is an explanatory view of a cutting portion by a dicing saw at the time of conventional array processing.

[Explanation of symbols]

1 ... Piezoelectric element, 2a, 2b ... Electrode, 3 ... Backing material,
4 ... Chipping prevention layer, 5 ... Acoustic matching layer, 7 ... Acoustic lens, 10 ... Resist, 11 ... Groove, 12 ... Blade

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04R 31/00 330 H01L 41/22 Z // H03H 3/02 41/08 C F term (reference) 2G047 CA01 EA11 GB02 GB17 GB21 GB23 GB28 GB32 GB33 4C301 EE12 GB04 GB18 GB20 GB22 GB33 GB34 4C601 EE10 GB01 GB02 GB03 GB04 GB19 GB20 GB24 GB25 GB26 GB41 GB42 5D019 HH03 5J108 AA08 BB01 JJ04 KK01 KK07 MM08 MM11 MM15 NA04 MM11 MM15 NA04

Claims (4)

[Claims] 1. An electrode forming step of forming electrodes on both surfaces of a piezoelectric material cut into a predetermined shape and polished, and a groove forming step of forming parallel grooves at a predetermined interval on at least one side surface of the piezoelectric material. A method for manufacturing a piezoelectric element, comprising: 2. The method of manufacturing a piezoelectric element according to claim 1, wherein the groove forming step is performed by photoetching. 3. The parallel groove in the groove forming step has a relationship of 10 μm <(Ct−Bd) <Cw, where Ct is the plate thickness of the piezoelectric element, Bd is the groove depth, and Cw is the inter-groove element width. 2. Forming into a shape according to claim 1.
Alternatively, the method for manufacturing the piezoelectric element according to claim 2. 4. An electrode forming step of forming electrodes on both surfaces of a piezoelectric element and applying an electric field to the piezoelectric element for polarization; a wiring step of connecting a signal line to one of the electrodes and a ground line to the other of the electrodes. A groove forming step of forming a groove in the piezoelectric element by the method for manufacturing a piezoelectric element according to any one of claims 1 to 3, and the signal line of the piezoelectric element in which the groove is formed is connected. A backing material joining step of joining a backing material to the formed side, an acoustic matching layer forming step of joining an acoustic matching layer to a side of the piezoelectric element in which the groove is formed, to which the ground wire is connected, and the formation of the groove In the piezoelectric element, the signal wire, the ground wire, the backing material and the acoustic matching layer are joined to the piezoelectric element and each portion joined to the piezoelectric element by aligning the groove with a dicing blade. Groove processing Method for producing an ultrasonic oscillator and having a single step.