JPH0937392A - Piezoelectric element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element having sensitivity necessary for flaw detection inside a material. SOLUTION: The piezoelectric element has a lower electrode 2 formed on a base 1, a zinc oxide thin film 3 formed on the surface of the electrode film 2 and an upper electrode 4 formed on the surface of the thin film 3. Sapphire is used as the base 1 and the value of c-axis orientation (σZnO) of the thin film 2 is 0 deg.<(σZnO)<=2.5 deg., preferably 0 deg.<(σZnO)<=1.5 deg.. The lower electrode 2 consists of a gold (Au) thin film and the value of c-axis orientation (σAu) of the Au thin film is 0 deg.<(σAu)<=4.5 deg., preferably 0 deg.<(σAu)<=2.2 deg.. The piezoelectric element is used as an ultrasonic nondestructive inspection probe for surface search and internal search.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a piezoelectric element.
In particular, it relates to the relationship between crystallinity and sensitivity of a piezoelectric element using a zinc oxide (ZnO) thin film.

[0002]

2. Description of the Related Art A gold (Au) electrode film formed on a substrate,
A piezoelectric element having a zinc oxide thin film formed on the gold electrode film and a metal (eg, Au) upper electrode formed on the zinc oxide thin film is a sensor portion for nondestructive observation of the inside of the material. Widely used as an ultrasonic probe.

Zinc oxide, which is sandwiched by the upper and lower electrodes, undergoes strain deformation when a voltage is applied to the electrodes, and ultrasonic waves can be emitted inside the substrate.
Converts electrical signals into ultrasonic waves. In addition, when ultrasonic waves are received by the zinc oxide thin film and distortion deformation occurs, a voltage difference occurs between both electrodes, and it becomes possible to convert ultrasonic signals into electrical energy.

An example of a nondestructive inspection device using such an ultrasonic probe is shown in FIG. In FIG. 8, reference numeral 8
0 indicates an ultrasonic probe, and 81 indicates a subject. The ultrasonic probe 80 is held on stages 83 and 83 ′ that are movable in the X direction, the Y direction, and the Z direction.
Are arranged in the water tank 82. One end of the ultrasonic probe 80 has a suitable transmission medium (eg, a wire or an optical fiber).
Is connected to the visualization device 84. The apparatus shown in FIG. 8 is used, for example, for the purpose of taking an image of the inside of a subject. The ultrasonic probe 80 or the subject 81 is mechanically scanned in two dimensions (xy, xz, yz) by a scanner, and 1
Using one ultrasonic probe or two ultrasonic probes separately for transmission and reception, the reflected wave and the transmitted wave from the inside of the subject are A / D converted and the image is displayed with the brightness of the image according to the signal strength. .

The crystal structure of zinc oxide (ZnO) has a hexagonal wurtzite ore structure as shown in FIG.
Not only does it have good piezoelectric characteristics (bulk electromechanical coupling coefficient = 0.3) in the c-axis [0001] direction, but it can be made into a thin film relatively easily, so it can be used as a piezoelectric element or a surface acoustic wave filter (SAW device). It's being used.

The frequency of ultrasonic waves emitted from the piezoelectric element is determined by the thickness resonance of the piezoelectric element. Since this piezoelectric element made of zinc oxide can be formed by a thin film process, it is used in a thin region (high frequency region of about 100 MHz or more).

The thin film of zinc oxide can be formed by vapor deposition, sputtering, chemical vapor deposition (CVD) or the like. Here, a manufacturing method of performing sputtering in a mixed gas atmosphere of Ar and oxygen using sintered zinc oxide as a sputtering target will be described. First, an Au thin film to be a lower electrode is formed on a substrate such as glass by a vapor deposition method.

At this time, in order to favorably orient the zinc oxide thin film on the C-axis, the Au thin film is preferably [111] oriented.
This is because the unit cell of the (0001) plane, which is the plane orientation of the zinc oxide thin film, has the structure of the face-centered cubic lattice of (111) of Au.
This is because it is equivalent to a unit cell of the plane, and thus the [111] orientation of the Au electrode previously formed on the substrate promotes the C-axis orientation of zinc oxide formed thereon. A
An Au electrode to be an upper electrode is further formed by vapor deposition on the zinc oxide thin film formed by sputtering on the u electrode to have a desired thickness.

Japanese Patent Publication No. 5-41080 discloses a piezoelectric element using a gold electrode film formed on a quartz glass substrate and having a standard deviation of a (111) diffraction line rocking curve of 3 degrees or less. There is. However, even if the piezoelectric element having such a structure is used, sufficient sensitivity cannot be obtained. Especially, in the device for observing the internal structure of the material, 3
Although a sensitivity of about% is required, this sensitivity cannot be achieved by the piezoelectric element having the structure disclosed in Japanese Patent Publication No. 5-40080.

[0010]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a piezoelectric element having the sensitivity required for internal flaw detection in materials.

[0011]

In order to achieve the above object, the present invention provides a lower electrode formed on a substrate, a zinc oxide thin film formed on the lower electrode film, and a zinc oxide thin film formed on the zinc oxide thin film. In the piezoelectric element having the above-described upper electrode, sapphire is used as the substrate, and the standard deviation σ of the rocking curve of the zinc oxide thin film by X-ray is 0 ° <σZnO.
≦ 2.5 ° and / or the standard deviation σ of the rocking curve of the gold (Au) thin film forming the lower electrode by X-ray is within the range of 0 ° <σAu ≦ 4.5 °. A piezoelectric element characterized by the above.

Further, according to the present invention, a lower electrode of gold (Au) is formed on a substrate by electron beam (EB) vapor deposition to a predetermined thickness, and a zinc oxide thin film is formed on this electrode by a high frequency magnetron sputtering method. A sapphire is used as a substrate material in a method of manufacturing a piezoelectric element, which is formed to have a predetermined thickness and further includes an upper electrode formed on zinc oxide,
Provided is a method for manufacturing a piezoelectric element, which comprises optically polishing an end face of a sapphire substrate, depositing a gold thin film of a lower electrode on the optically polished sapphire end face, and further forming a zinc oxide thin film on the gold thin film. .

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Zinc oxide has a high piezoelectric property in the c-axis direction. When a zinc oxide thin film is formed by sputtering or vapor deposition, it usually becomes polycrystalline and it is difficult to form a film having a composition close to an ideal single crystal. In this case, when a crystal is grown on the substrate, a crystal axis other than the c-axis also grows, and the directivity of the c-axis varies. Therefore, the c-axis orientation is improved by optimizing the substrate material and film forming conditions. The improvement of the c-axis orientation can be expected to improve the sensitivity.

Single crystal sapphire has the same crystal structure as zinc oxide (see FIG. 9), and the (111) plane of Au, which is the lower electrode, is the C plane of sapphire and zinc oxide ((00
It is equivalent to the (01) plane). Therefore, Au formed on sapphire is affected by the crystal structure of the sapphire substrate depending on the vapor deposition conditions, and the (111) plane orientation is facilitated, and sometimes epitaxial growth occurs. Sapphire substrates are difficult to process, whereas conventional quartz substrates have the advantage of being easy to process. However, in a quartz substrate, Au and zinc oxide crystals formed on the substrate surface grow randomly in a direction parallel to the plane. That is, the c-axis orientation becomes poor. Therefore, when the sapphire substrate is used rather than the quartz substrate, the zinc oxide formed on the Au lower electrode can have a better c-axis orientation due to the influence of the orientation of Au in the lower portion.

When the piezoelectric element of the present invention is used in a probe for nondestructive inspection, in order to probe the surface of the subject, only the reflection on the surface of the subject needs to be captured. That is, the propagation loss is only the transmission loss between the acoustic lens and the propagation medium and the attenuation in the propagation medium. Therefore, in this case, the c-axis orientation (σZnO) of the zinc oxide thin film may be 0 ° <σZnO ≦ 2.5 °. However, when the inside of the subject is searched, the transmission loss into the subject, that is, the attenuation inside the subject is very large. Therefore, in this case, the c-axis orientation (σZnO) of the zinc oxide thin film must be 0 ° <σZnO ≦ 1.5.

In the case of the quartz substrate, the c-axis orientation (σZnO) of the zinc oxide thin film formed on the substrate was about 2 to 3 °. Therefore, if only the surface inspection of the object is to be performed, a quartz substrate can be sufficiently used. However, it is not possible to obtain σZnO of 1.5 ° or less on a quartz substrate. In other words, in the case of a probe using a quartz substrate, it is not possible to obtain the sensitivity required for exploring the inside of the subject.

Similarly, when exploring the surface of the subject, Au is used.
The c-axis orientation (σAu) of the thin film may be 0 ° <σAu ≦ 4.5 °, but when probing the inside of the object, the c-axis orientation (σAu) of the Au thin film is 0 ° <σAu ≦ 2. It must be 2 °.

The c-axis orientation (σZnO) of the zinc oxide thin film is not necessarily affected by the c-axis orientation (σAu) of the Au thin film. Therefore, when exploring the surface of the subject, 0 ° <σZ
It is only necessary that the requirement of nO ≦ 2.5 ° is satisfied, and at the same time, the requirement of 0 ° <σAu ≦ 4.5 ° may not be satisfied. However, in order to obtain good measurement results, it is preferable that both requirements are satisfied at the same time. Similarly, when exploring the inside of the subject, the c-axis orientation of the zinc oxide thin film (σZnO)
Is 0 ° <σZnO ≦ 1.5, and c of the Au thin film
The axial orientation (σAu) does not need to be 0 ° <σAu ≦ 2.2 °. However, to get the best measurement results, 0
It is preferable to simultaneously satisfy both the requirements of ° <σZnO ≦ 1.5 and 0 ° <σAu ≦ 2.2 °.

The shape and size of the substrate are not particularly limited. An appropriate shape and size can be selected according to the application of the piezoelectric element. Those skilled in the art can easily make such a selection. For example, when the piezoelectric element is used as a probe for ultrasonic nondestructive inspection, the substrate can be in the shape of a cylinder having a diameter of 30 mm or less. This substrate is used as an acoustic lens. If the diameter of the substrate is small,
When forming a zinc oxide thin film, a film having a uniform film thickness distribution over the entire surface of the substrate can be formed.

The zinc oxide thin film in the piezoelectric element of the present invention is produced by the high frequency magnetron sputtering method. The radio frequency magnetron sputtering method itself is known to those skilled in the art.
An example of an apparatus used to carry out this film forming method is shown in FIG. A target 26 is arranged in the chamber 21. The target 26 (for example, sintered zinc oxide (ZnO)) is held by the target holder 27. The substrate 1 is arranged above the target 26 so as to face the target 26. Substrate 1 is substrate holder 2
Held by 8. The substrate 1 is heated to a predetermined temperature by the heater 20. Atmospheric gas such as Ar and O ₂ is fed into the chamber 21 through the atmospheric gas supply pipe 22. Further, the inside of the chamber 21 can be evacuated from the exhaust duct 23 to a predetermined degree of vacuum.

When forming a film, the inside of the chamber is filled with argon (A
A mixed gas atmosphere of r) and oxygen (O ₂ ) is formed. The mixing ratio of argon and oxygen is not particularly limited.
The gas pressure is not particularly limited, but is generally 1.0 to
Gas pressures in the range of 4.0 Pascal (Pa) can be used. The range of 1.5 to 3.0 Pa is preferable.

When the substrate 1 is heated by the heater 20, the substrate can be heated to a temperature within the range of 100 ° C to 500 ° C. The heating temperature is preferably in the range of 260 ° C to 400 ° C. If the heating temperature is too low, the inconvenience that migration of sputtered particles is difficult to occur occurs, while if the heating temperature is too high, the film cracks due to thermal stress, which is not preferable.

In a mixed gas atmosphere of argon and oxygen,
When ZnO target is irradiated with heavy charged particles such as Ar ⁺ ions, the impact causes ZnO to jump out of the target.
The particles are attached to the opposite substrate surface. The high frequency output to be applied is not particularly limited, but is generally 100 W to 40 W.
It is within the range of 0 W. The range of 150 to 300 W is preferable. If the output is too low, the film deposition rate will be too slow, and on the other hand, if the output is too high, the crystallinity will be deteriorated.

Although the film forming rate varies depending on the distance between the substrate and the target, the film forming rate of the zinc oxide thin film in the piezoelectric element of the present invention is generally 0.5 to 2.5.
It is in the range of μm / h. It is preferably within the range of 0.8 to 2.0 μm / h.

[0025]

EXAMPLE FIG. 1 shows a specific example of use of the piezoelectric element of the present invention. FIG. 1 is a schematic sectional view of a focus probe for ultrasonic nondestructive inspection. This probe is basically a sapphire substrate 1 that serves as an acoustic lens, a lower electrode 2 made of an Au thin film deposited on the plane of this sapphire substrate, a zinc oxide thin film 3 provided on this lower electrode, and this zinc oxide. Thin film 3
An upper electrode 4 made of an Au thin film deposited on the upper surface of the above, and a concave portion 5 having a concave lens-like function are provided on the surface opposite to the surface on which the lower electrode 2 is provided. The surface of the acoustic lens on which the concave portion 5 is provided is the surface side in contact with the subject (not shown). An acoustic matching layer 6 is provided on the inner surface of the recess 5. Needless to say, the piezoelectric element of the present invention can be used for a non-focus probe that does not have this recess.

Next, a method of manufacturing the focus type probe of FIG. 1 will be described. As the substrate / acoustic lens, one end surface of sapphire optically polished was used. A recess was formed on the surface of the sapphire opposite to the polished surface. At this time,
First, the lower electrode 2 was formed on the optically polished end surface by a vacuum deposition method. A conventional electron beam (EB) vapor deposition apparatus was used for vapor deposition. Keep the substrate temperature at 300 ℃,
Evaporated to a thickness of 0 nm.

A zinc oxide thin film 3 was formed on this Au thin film by a high frequency magnetron sputtering method. Using a high frequency magnetron sputtering apparatus as shown in FIG. 2, in an (Ar (50%) + O ₂ (50%)) atmosphere,
Substrate temperature 300 ° C, gas pressure 2Pa, high frequency output 200
W, space between target material and substrate bottom electrode surface 8
cm, and the deposition rate was 0.95 μm / h, to form a zinc oxide thin film. Further, using the same EB vapor deposition apparatus as described above, chromium and Au to be the upper electrode 4 were vapor deposited at room temperature on this zinc oxide thin film. In order to make the size of the upper electrode 4 equal to the size of the concave lens machined on the tip of the sapphire, there is a hole S of a predetermined size.
Vapor deposition was performed by covering the zinc oxide thin film 3 with a US mask. Furthermore, the acoustic matching layer 6 (S
iO ₂ ) was formed by sputtering. The presence of the acoustic matching layer 6 improves the transmission efficiency of ultrasonic waves from the tip of the sapphire 1 to the propagation medium.

The thickness of the zinc oxide thin film 3 can be designed so that the frequency when the piezoelectric element thickness-resonates is the frequency actually used, depending on the target frequency. When the piezoelectric element is formed on the sapphire 1 as in the present invention, the acoustic impedance of the sapphire 1 (44 × 1
Since 0 ⁶ kg / cm ² ) is larger than the acoustic impedance of zinc oxide 3 (34 × 10 ⁶ kg / cm ² )), the piezoelectric element resonates ¼λ (λ is the wavelength). For example, 50
If you want to create a piezoelectric element having a MHz frequency characteristics, its thickness, (1/4) × (6400 × 10 6/5
0 × 10 ⁶ ) = 32 μm. When used in SAW devices, acousto-optic elements, optical waveguides, etc., the thickness of the zinc oxide thin film is usually 1 μm or less, but when used in a probe, the thickness of the zinc oxide thin film depends on its frequency. Is. The film thickness of the Au thin film of the lower electrode is about 0.15 μm.

When quartz is used as the substrate material, since quartz has a resonance of 1 / 2λ, it is necessary to have a film thickness twice as large as that of the zinc oxide thin film formed on the sapphire substrate. But,
As the film thickness increases, the film thickness distribution becomes non-uniform, which causes product defects. As a result, the yield of products deteriorates with the quartz substrate.

The sensitivity of the piezoelectric element depends on the crystallinity of the formed piezoelectric element. Therefore, the sensitivity of the piezoelectric element can be determined by examining the crystallinity and orientation of zinc oxide with an X-ray diffractometer. The angle at which the c-axis of zinc oxide 3 appears is measured by diffraction line measurement, and the rocking curve is measured by scanning the angle of only the sample with X-rays incident at this angle. Since the lattice constant of c-axis of zinc oxide is about 2.5Å, the peak value in X-ray diffraction appears around 34 °.

FIG. 3 shows the appearance of diffraction lines after the formation of zinc oxide. A diffraction line peak (34 °) of the c-plane (0001) of zinc oxide 3 is observed in the diffraction line.

FIG. 4 shows the rocking curve measurement results measured by making X-rays incident at an angle of 34 ° of the peak value in X-ray diffraction. The measured rocking curve shows the orientation of the c-axis of the zinc oxide thin film, that is, the variation in the growing direction of the c-axis, and can be regarded as a nearly normal distribution as shown in the figure. Therefore, the standard deviation (σ) of this rocking curve is measured, and this value is used for quantitative evaluation. Therefore, the value of σ becomes large when the c-axis orientation is poor and the variation in the crystal growth direction is large, and conversely, when the orientation is good, the value of σ becomes small.

FIG. 5 shows a method of evaluating the sensitivity.
The pulsar 5 is formed on the zinc oxide thin film 3 formed on the sapphire 1.
Impulse voltage V _P is applied from 6. Reference numeral 57 indicates an attenuator, which is used for adjusting the applied voltage.
The ultrasonic wave radiated from the zinc oxide thin film 3 passes through the inside of the sapphire 1 which is an acoustic lens, is reflected by the end opposite to the zinc oxide thin film, is received again by the zinc oxide thin film 3, and is converted into an electric signal. . After the ultrasonic signal received here is amplified by the amplifier 58, the waveform monitor 59 measures the signal strength V _R thereof. From the signal intensity thus measured, the sensitivity of the zinc oxide thin film 3 is determined by the following relationship. Sensitivity _{= (V R / V P)} × 100

FIG. 6 shows the relationship between the c-axis .sigma. Value and the sensitivity of the zinc oxide thin film measured using the apparatus shown in FIG. Figure 6
Therefore, the σ value of the c-axis rocking curve of the zinc oxide thin film has a good correlation with the sensitivity, and the smaller the σ value, the better the sensitivity. In fact, the sensitivity of the piezoelectric element required to measure the inside of the material is about 3%. With such sensitivity, it is possible to detect internal defects. From FIG. 6, the condition for satisfying the minimum required sensitivity of 3% is that the c-axis orientation (σ) of the zinc oxide thin film is 1.
Understand that it must be less than 5 °.

Further, FIG. 7 shows the experimental results of examining the relationship between the c-axis orientation of the zinc oxide thin film and the c-axis orientation of the lower electrode Au. FIG. 7 is a characteristic diagram measured by an X-ray diffractometer. The c-axis orientation of the zinc oxide thin film and the c-axis orientation of Au as the lower electrode have a good correlation, and this relationship is expressed by the following equation. σZnO = 0.67σAu−0.03

From the above relational expression, the c-axis orientation (σ) of the zinc oxide thin film for having the sensitivity necessary for the internal measurement of the subject is obtained.
The condition that (ZnO) is 1.5 ° or less is satisfied is
It can be understood that the case where the c-axis orientation (σAu) of Au of the lower electrode is 2.2 ° or less.

[0037]

As described above, according to the present invention,
In a piezoelectric element having a lower electrode formed on a substrate, a zinc oxide thin film formed on the lower electrode film and an upper electrode formed on the zinc oxide thin film, sapphire is used as a substrate, The value of c-axis orientation (σZnO) is 0 ° <σZnO ≦ 2.5 °, especially 0 ° <σZnO.
≦ 1.5 and / or the value of c-axis orientation (σAu) of the gold (Au) thin film forming the lower electrode is 0 ° <σ
If Au ≦ 4.5 °, especially 0 ° <σAu ≦ 2.2,
The sensitivity of the ultrasonic probe can be improved, and minute internal defects that could not be observed conventionally can be observed.

Further, the performance of the probe can be controlled during the probe manufacturing process by evaluating the orientation after forming the lower electrode of Au or forming the zinc oxide thin film.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a focus type probe for ultrasonic nondestructive inspection including a piezoelectric element of the present invention.

FIG. 2 is a schematic configuration diagram of an example of a high frequency magnetron sputtering apparatus used for forming a zinc oxide thin film for a piezoelectric element of the present invention.

FIG. 3 is a waveform diagram of an X-ray diffraction analysis of a zinc oxide thin film formed in an example.

FIG. 4 is a characteristic diagram showing a rocking curve measurement result measured by making X-rays incident on a zinc oxide thin film at a diffraction line peak angle (34 °).

FIG. 5 is a schematic diagram showing a device configuration for measuring the sensitivity of a probe.

FIG. 6 is a characteristic diagram showing a relationship between c-axis orientation (σZnO) of zinc oxide thin film and sensitivity.

FIG. 7: c-axis orientation (σZnO) and Au of zinc oxide thin film
FIG. 6 is a characteristic diagram showing a relationship with c-axis orientation (σAu) of a thin film.

FIG. 8 is a schematic configuration diagram showing an example of a conventional nondestructive inspection apparatus using an ultrasonic probe.

FIG. 9 is a schematic constitutional diagram showing a crystal structure of zinc oxide, (a) showing a crystal coordination constitution, and (b) showing a schematic crystal structure.

[Explanation of symbols]

 1 Sapphire Lens (Substrate) 2 Lower Electrode 3 Zinc Oxide Thin Film 4 Upper Electrode 5 Recess 6 Acoustic Matching Layer 20 Heater 21 Chamber 22 Atmospheric Gas Inlet Tube 23 Exhaust Duct 26 ZnO Target 27 Target Holder 28 Substrate Holder 56 Pulser 57 Attenuator 58 Amplifier 59 Waveform monitor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location C23C 14/35 C23C 14/35 Z G01L 1/16 G01L 1/16 G01N 29/24 G01N 29/24 H01L 21/203 H01L 21/203 S 41/09 41/08 C 41/08 Z 41/18 41/18 101A 41/22 41/22 Z

Claims (12)

[Claims] 1. A piezoelectric element having a lower electrode formed on a substrate, a zinc oxide thin film formed on the lower electrode film, and an upper electrode formed on the zinc oxide thin film, wherein sapphire is used as the substrate. A piezoelectric element characterized in that the zinc oxide thin film has a c-axis orientation (σZnO) value of 0 ° <σZnO ≦ 2.5 °. 2. A c-axis orientation (σZnO) of a zinc oxide thin film.
2. The piezoelectric element according to claim 1, wherein the value of 0 ° <σZnO ≦ 1.5 °. 3. The lower electrode is made of a gold (Au) thin film, and the value of c-axis orientation (σAu) of the Au thin film is 0 ° <σAu.
The piezoelectric element according to claim 1, wherein ≦ 4.5 °. 4. The piezoelectric element according to claim 1, wherein the value of c-axis orientation (σAu) of the Au thin film is 0 ° <σAu ≦ 2.2 °. 5. A zinc oxide thin film c used as a probe for ultrasonic nondestructive inspection for probing the surface of a subject.
The value of axial orientation (σZnO) is 0 ° <σZnO ≦ 2.5.
And the value of c-axis orientation (σAu) of the Au thin film is 0.
The piezoelectric element according to claim 1, wherein the relation of <° Au ≦ 4.5 °. 6. A zinc oxide thin film c used as a probe for ultrasonic nondestructive inspection for probing the inside of a subject.
The value of axial orientation (σZnO) is 0 ° <σZnO ≦ 1.5.
And the value of c-axis orientation (σAu) of the Au thin film is 0.
2. The piezoelectric element according to claim 1, wherein the relationship of <° Au ≦ 2.2 °. 7. A method for manufacturing a piezoelectric element, which comprises forming a lower electrode on a substrate, forming a zinc oxide thin film on the electrode, and further forming an upper electrode on the zinc oxide thin film, wherein sapphire is used as a substrate material. Is used to optically polish the lower electrode formation surface of the sapphire substrate, the lower electrode is formed on this optically polished surface, and a zinc oxide thin film is formed by a high frequency magnetron sputtering method. The c-axis orientation (σZnO The method of manufacturing a piezoelectric element is characterized in that the value of 2) is 0 ° <σZnO ≦ 2.5 °. 8. A c-axis orientation (σZnO) of a zinc oxide thin film.
8. The method for manufacturing a piezoelectric element according to claim 7, wherein the value of is 0 ° <σZnO ≦ 1.5 °. 9. A gold thin film is formed by evaporating gold (Au) on an optically polished surface of a substrate by an electron beam evaporation method, and the value of c-axis orientation (σAu) of the Au thin film is 0 ° <.
The method for manufacturing a piezoelectric element according to claim 7, wherein σAu ≦ 4.5 °. 10. The method for manufacturing a piezoelectric element according to claim 9, wherein the value of c-axis orientation (σAu) of the Au thin film is 0 ° <σAu ≦ 2.2 °. 11. A c-axis orientation (σZnO) value of a zinc oxide thin film, which is used as a probe for ultrasonic nondestructive inspection for probing the surface of an object, is 0 ° <σZnO ≦ 2.
It is 5 °, and the value of c-axis orientation (σAu) of the Au thin film is
The method of manufacturing a piezoelectric element according to claim 7, wherein 0 ° <σAu ≦ 4.5 °. 12. The c-axis orientation (σZnO) value of a zinc oxide thin film, which is used as a probe for ultrasonic nondestructive inspection for probing the inside of a subject, is 0 ° <σZnO ≦ 1.
It is 5 °, and the value of c-axis orientation (σAu) of the Au thin film is
The method for manufacturing a piezoelectric element according to claim 7, wherein 0 ° <σAu ≦ 2.2 °.