HK1069015B - Piezoelectric device and its manufacturing method - Google Patents

Description

Piezoelectric element and method for manufacturing the same

Technical Field

The present invention relates to a piezoelectric element having a piezoelectric thin film and a method for manufacturing the same.

Background

In recent years, piezoelectric thin films have been processed into various piezoelectric elements according to different needs, and are widely used in functional electronic components such as actuators that generate deformation by pressurization and sensors that generate voltage by element deformation. For example, as disclosed in japanese patent application laid-open No. 2002-279742, the position of the magnetic head of the magnetic disk can be finely controlled by using a piezoelectric element. This is because the recording density of the magnetic disk increases and the area of the recording region of one magnetic head becomes small, but it is difficult to control the position of the magnetic head with high accuracy by the conventional voice coil motor. Therefore, in addition to the position determination by the voice coil motor, the structure of the 2-stage actuator in which the position is determined with high accuracy in a minute area by the piezoelectric element is being studied. The piezoelectric element unit used is composed of a pair of piezoelectric elements, and when one element is extended, the other element is contracted, so that the magnetic head attached to the tip of the element can be moved on the disk surface minutely and accurately.

The piezoelectric element is generally manufactured by the following method. For example, a magnesium oxide single crystal substrate (MgO substrate) is used as the substrate. A (100) -oriented platinum film (Pt film) was formed on the MgO substrate. Then, a (001) -oriented lead zirconate titanate (PZT) thin film was formed on the Pt film. Further, after forming an electrode thin film on the PZT thin film, these thin films are processed into a certain shape by photolithography (フオトリソグラフイ - プロセス) and etching (エ ツ チ ン グ プロセス). Thereafter, the MgO substrate is removed by etching or the like, thereby preparing a piezoelectric element.

The PZT thin film is generally prepared by a sputtering method (スパツタリング method) at a film forming temperature of 550 ℃ to 650 ℃. When sputtering is performed at such a high temperature, lead (Pb) is re-evaporated from the PZT thin film during the sputtering film formation process, and therefore, the PZT thin film finally formed is a film having a reduced Pb composition and an offset stoichiometric composition. Therefore, in order to obtain a PZT thin film of a stoichiometric composition, Takayama et al prevent the reduction of Pb component in the PZT thin film by forming a film using a target (タ - ゲツト) for sputtering in which the Pb content is excessive by 20%. (J.appl.Phys.65(4), 1666 (1989)).

However, in order to obtain a PZT thin film of a stoichiometric composition prepared using a target containing excess Pb, it is necessary to perform sputtering film formation under a relatively high pressure condition by adding oxygen gas to an inert gas as a discharge gas. However, the film formation rate under such conditions cannot be large. Since the thickness of the PZT thin film used as the piezoelectric element must be controlled to about 1 μm to 10 μm, the mass productivity is very low at a small film formation rate.

Jp-a-6-49638 a discloses that in forming a PZT thin film for use in a semiconductor memory, sputtering is performed with a discharge gas pressure in a vacuum apparatus set to a low pressure in order to increase a film forming rate. Since the Pb component in the prepared film is more easily reduced when the discharge gas pressure is low, a target having an excessive Pb component corresponding to the discharge gas pressure is used in order to prepare a PZT thin film having a stoichiometric composition.

Further, Japanese patent No. 3341357 discloses that a film made to improve the piezoelectric characteristics of a PZT thin film contains excess Pb over the stoichiometric composition and has a rhombohedral crystal structure, thereby increasing the piezoelectric constant d₃₁。

However, in both of the above 1 st and 2 nd examples, the object is to produce a PZT thin film having a stoichiometric composition, and therefore, it is necessary to form a film by sputtering in a discharge gas having a high oxygen partial pressure. At the high oxygen contentPiezoelectric constant d of PZT thin film formed under pressure₃₁Generally, the film formation rate during sputtering cannot be increased. Therefore, high voltage characteristics cannot be obtained, and mass productivity cannot be improved.

In example 3, the amount of Pb in the PZT thin film was excessive compared to the amounts of titanium (Ti) and zirconium (Zr) added, but the amounts of oxygen (O) and Pb in the PZT thin film increased in the same ratio and oxygen deficiency was not caused. Therefore, it is necessary to add a large amount of oxygen during film formation and perform sputtering under a high discharge gas pressure, and the film formation rate cannot be increased, and as a result, the mass productivity cannot be improved.

Summary of The Invention

If the oxide piezoelectric thin film can be set to an appropriate oxygen deficiency amount, the piezoelectric constant d can be expected to be improved₃₁Thus, a piezoelectric element having excellent piezoelectric characteristics can be obtained. Based on this knowledge, the present invention provides a piezoelectric element having excellent piezoelectric characteristics, and capable of increasing the film formation rate and improving mass productivity, and a method for manufacturing the same.

In view of the above problems, a piezoelectric element according to the present invention has the following structure: the piezoelectric film is an oxide piezoelectric film having an oxygen deficiency of 0% or more, 10% or less relative to the stoichiometric composition, and includes a 1 st electrode film, a 2 nd electrode film, and a piezoelectric film sandwiched between the 1 st electrode film and the 2 nd electrode film.

By using an oxide piezoelectric thin film having oxygen deficiency, a piezoelectric element having larger piezoelectric characteristics than the original piezoelectric characteristics can be obtained, and film formation can be performed at high speed, so that improvement of characteristics of the piezoelectric element and improvement of mass productivity thereof are expected.

Brief Description of Drawings

Fig. 1 is an oblique view of a piezoelectric body element in an embodiment of the invention;

FIGS. 2A to 2D are sectional views showing the main steps in the method for manufacturing the piezoelectric element in the same embodiment;

fig. 3 is a graph showing the relationship between the displacement amount and the oxygen partial pressure of a piezoelectric body element produced using a target composed of Y ═ 0.25 in the same example;

FIG. 4 is a graph showing the relationship between the displacement amount of the piezoelectric element and the oxygen partial pressure corresponding to the oxygen deficiency ratio in the same example;

FIG. 5 is a schematic view showing a relationship between the oxygen deficiency amount ratio and the displacement amount of a piezoelectric element obtained in the same example;

FIG. 6 is a schematic view showing the relationship between the displacement amount and the oxygen partial pressure of a piezoelectric body element prepared by changing the composition of a target in the same example;

FIG. 7 is a view showing an example of head position confirmation using a piezoelectric element in the same embodiment for a magnetic disk apparatus;

FIG. 8A is a plan view showing a shape of the vicinity of a piezoelectric element in the magnetic disk device in the same embodiment;

FIG. 8B is a cross-sectional view taken along the X-X ray shown in FIG. 8A.

Description of the symbols

1,1081 No. 1 electrode film (Pt film)

2,1082 oxide piezoelectric thin film (PZT thin film)

3,1083 No. 2 electrode film (Pt film)

5 drive power supply

10, 108, 108A, 108B piezoelectric elements

15MgO substrate

100 magnetic head supporting structure

102 slider (スライダ one)

103 flexible portion (フレクシヤ one)

103A electrode pad

103B piezoelectric electrode wire

103C magnetic head electrode wire

104 floating device (サスペンション)

105 reed

106 arm

107 adhesive layer

109 wire

110 bearing part

112 voice coil

200 magnetic disk

220 rotary driving device

Detailed description of the preferred embodiments

Embodiments of the present invention are described below with reference to the drawings. In the drawings described below, the same elements are denoted by the same reference numerals, and the description thereof may be omitted.

Example 1

Fig. 1 is a perspective view of a piezoelectric element according to embodiment 1 of the present invention. Further, fig. 1 also shows a driving power supply 5 for driving the piezoelectric body element 10.

The piezoelectric element 10 includes a 1 st electrode film 1, an oxide piezoelectric thin film 2 formed on the 1 st electrode film 1, and a 2 nd electrode film 3 formed on the oxide piezoelectric thin film 2. The 1 st electrode film 1, the oxide piezoelectric thin film 2, and the 2 nd electrode film 3 are each formed by a thin film forming technique such as sputtering, and are processed into a nearly rectangular parallelepiped shape shown in fig. 1 by photolithography and etching.

The dimensions of the piezoelectric element 10 are, for example, about 2mm in the longitudinal direction (direction shown by B in the figure), about 0.5mm in the width direction, and about 3 μm in thickness, which is the direction in which the piezoelectric body expands and contracts. In order to use the piezoelectric element 10, it is necessary to perform initial polarization on the oxide piezoelectric thin film 2, and in the present embodiment, the polarization direction is the direction indicated by the arrow a as shown in fig. 1. The polarization vector does not necessarily have to be perpendicular to the film surface, and when the polarization vector is inclined, the perpendicular component thereof may be considered. That is, it is not necessary that all the regions of the oxide piezoelectric thin film 2 be polarized in the film thickness direction.

When spontaneous polarization occurs naturally in the state after film formation, the spontaneous polarization can be used as it is. The shape of the piezoelectric element 10 does not necessarily have to be a rectangular parallelepiped. For example, various shapes such as a trapezoidal shape and a triangular shape may be adopted in accordance with the shape of the device to be used.

The driving power source 5 is a power source for applying a predetermined voltage to the piezoelectric element 10, and when a voltage is applied to the 1 st electrode film 1 and the 2 nd electrode film 3, the oxide piezoelectric thin film 2 can be extended and contracted by the voltage.

With the above configuration, the piezoelectric element 10 can be moved in the direction indicated by the arrow B by the voltage of the driving power source 5. In the present embodiment, this telescopic motion is used as the driving force. That is, the top end in one direction is fixed, and the top end in the other direction is used as a free end to which an object to be controlled is fixed, whereby the precise position of the object to be controlled can be determined. The displacement amount of the unit voltage depends on the piezoelectric constant d₃₁(one of piezoelectric indexes), d₃₁The larger the element displacement amount.

The present invention is characterized in that the oxygen deficiency in the oxide piezoelectric thin film 2 is controlled to 0% or more and 10% or less, preferably 2% or more and 7% or less, and more preferably 2% or more and 5% or less. The present inventors have found that a piezoelectric element including an oxide piezoelectric thin film having the above oxygen deficiency amount has a larger piezoelectric property than an oxide piezoelectric thin film in an oxidized state of a stoichiometric composition. Further, the film formation rate can be increased and the mass productivity can be improved by the production under such conditions.

When the oxygen deficiency is set to 0% or more and 10% or less, the piezoelectric constant d can be increased₃₁As a result, the displacement amount of the piezoelectric body can be increased. For example, use is made of a compound of the formula Pb_1+Y(Zr_XTi_1-X)O_3+ZIn the case of the PZT thin film of (3), the oxygen deficiency ratio (Y-Z)/(Y +3) may be 0 or more and 0.1 (i.e., 10%) or less.

Further, if the oxygen deficiency amount is made to be 2% or more to 7% or less, irregularities in the degree of crystal orientation can be controlled, and even if irregularities occur in the oxygen deficiency amount, the variation in the amount of displacement can be made relatively small. Therefore, the production yield is expected to be improved. If the oxygen deficiency amount is 2% or more and 5% or less, the variation of the displacement amount corresponding to the oxygen deficiency amount will be smaller. Therefore, it is expected to further improve the production yield.

Further, the crystal orientation is preferably such that the polarization axis is in the film thickness direction. For example, the orientation (001) direction is preferable for a tetragonal PZT thin film, and the orientation (111) direction is preferable for a rhombohedral PZT thin film.

Next, as the oxide piezoelectric thin film 2, an oxide piezoelectric thin film having a general formula A was prepared by a sputtering method_1+YBO_3+Z(wherein A and B represent elements) and the degree of crystal orientation in the direction parallel to the polarization axis thereof is 70% or more, indicating the general formula Pb_1+Y(Zr_XTi_1-X)O_3+ZThe specific production method of the PZT thin film and the measurement result of the piezoelectric property are shown.

Fig. 2A to 2D are sectional views of main steps of the method for manufacturing the piezoelectric element 10 according to the present embodiment.

The MgO substrate in the (100) direction is used as the substrate. A Pt film 1, which is a (100) -oriented 1 st electrode film having a film thickness of 100nm, was formed on the MgO substrate 15 by a sputtering method using argon (Ar) gas under conditions of a substrate temperature of 500 ℃ and a discharge gas pressure of 0.5 Pa.

Then, a PZT thin film 2 of an oxide piezoelectric thin film having a thickness of 5 μm was formed on the Pt film 1. FIG. 2A is a sectional view showing a state where a PZT thin film 2 is formed. General formula Pb for target composition_1+Y(Zr_XTi_1-X)O_3+ZWhen (0 < X < 1), a target of X ═ 0.58 or Y ═ 0.25 was used. In this case, the Z value is the same as the Y value.

The discharge gas pressure during sputtering was set to 0.5Pa, and the substrate temperature was set to 600 ℃. At this time, the composition of the discharge gas is Ar gas and oxygen (O)₂) The mixed gas of (3) is formed into a film under the condition that the oxygen ratio in the discharge gas is 0.5% -50% of that of Ar gas. Further, in the film formation including the PZT thin film 2, the composition of the discharge gas in the discharge space between the target and the substrate is measured by mass filtration (マスフイルタ I). The PZT thin film 2 thus produced was evaluated for crystallinity by quantitative Analysis of film composition and X-ray diffraction using Electron probe micro Analysis (hereinafter referred to as EPMA).

Next, a 2 nd electrode Pt film 3 on the PZT thin film 2 was prepared by sputtering using Ar gas under a discharge gas pressure of 0.5PA at normal temperature. Fig. 2B is a cross-sectional view showing a state where the Pt film 3 is formed. Further, it was confirmed that the PZT thin film 2 produced under the above conditions was spontaneously polarized naturally in the upper direction of the substrate surface without applying a voltage thereto.

Then, as shown in fig. 2C, a predetermined piezoelectric element shape was prepared on the MgO substrate by photolithography and etching. As shown in FIG. 1, the length direction of the plate was 2mm, and the width direction was 0.5 mm.

After having been processed into a predetermined shape in this manner, as shown in fig. 2D, the MgO substrate 15 is removed by etching, and the piezoelectric element 10 having the shape shown in fig. 1 is obtained.

Then, the drive power source 5 shown in fig. 1 was connected to the piezoelectric element 10, and the displacement in the direction indicated by the arrow B was measured. The applied voltage was set to 10V. The displacement is a displacement in the direction indicated by the arrow B when a voltage of 10V is applied. The displacement amount can be measured by a laser doppler vibrometer.

Fig. 3 is a graph showing the relationship between the displacement amount of the piezoelectric element 10 and the oxygen partial pressure corresponding to the degree of crystal orientation, obtained using a target having a composition of Y ═ 0.25. The horizontal axis represents the percentage of oxygen partial pressure in total pressure, the left side of the vertical axis represents the amount of displacement, and the right side represents the degree of crystal orientation.

The degree of crystal orientation of the PZT thin film 2 was obtained by an X-ray diffraction apparatus. X-ray diffraction the theta-2 theta can be measured using a CuK alpha radiation source. The angle 2 theta is in the range of 20 deg. -40 deg.. Since the polarization direction of the tetragonal PZT thin film 2 was the (001) direction, the crystal orientation degree was determined by the peak intensity ratio (001)/∑ (hkl) of X-ray diffraction. The polarization direction is determined by (001)/∑ (hkl) for the material in the (001) direction, and the polarization direction is determined by (111)/∑ (hkl) for the material in the (111) direction. Here, ∑ (hkl) is the sum of intensities of reflection peaks due to PZT when the upper limit and the lower limit of 2 θ are set within the minimum range in which the reflection from (001) reflectometry (111) can be performed when θ -2 θ is measured by the CuK α radiation source. Hereinafter, the degree of crystal orientation may be simply referred to as the degree of orientation.

As is clear from fig. 3, when the oxygen partial pressure is 2% or less, the degree of orientation decreases, but even if the oxygen partial pressure is 0.5%, the degree of orientation can reach 60%. When the oxygen partial pressure is 50%, the degree of orientation is drastically reduced, but even in this case, the degree of orientation can reach 65%. When the oxygen partial pressure is in the range of 0.5% to 10%, the degree of orientation is 95% when the oxygen partial pressure is 1.5%, the degree of orientation increases gradually when the oxygen partial pressure is increased, and the degree of orientation reaches 100% when the oxygen partial pressure is 10%. When the oxygen partial pressure is in the range of 10% to 30%, the degree of orientation is 100%, and when the oxygen partial pressure is 40%, the degree of orientation is 96%, and at a higher oxygen partial pressure than that, the degree of orientation sharply decreases.

On the other hand, as the oxygen partial pressure increases from 0.5% to 2%, the displacement amount also sharply increases. However, beyond 2%, the displacement will decrease. The degree of reduction was different before and after the oxygen partial pressure was 10%, and an inflection point appeared.

Fig. 4 is a graph showing the relationship between the displacement amount and the oxygen deficiency amount ratio (Y-Z)/(Y +3) of the piezoelectric element 10 obtained by using a target composed of 0.25 as Y, and by using the oxygen partial pressure. The horizontal axis represents the percentage of oxygen partial pressure relative to the total pressure, the left side of the vertical axis represents the amount of displacement, and the right side represents the oxygen deficiency ratio (Y-Z)/(Y + 3). FIG. 5 is a graph showing the relationship between the oxygen deficiency amount ratio (Y-Z)/(Y +3) and the amount of displacement.

Next, a method of calculating the oxygen deficiency amount ratio will be described. First, the composition of the ferroelectric thin film necessary for determining the oxygen deficiency amount was measured by the above-mentioned EPMA method. In this analysis method, a very fine electron beam is irradiated onto the surface of a sample, and the wavelength and intensity of characteristic X-rays emitted from this portion are measured by an X-ray spectrometer, thereby determining the composition of the sample.

The quantitative analysis method of the PZT thin film is specifically performed as follows. That is, the initial X-ray intensity was measured using a standard sample in which the concentrations of each of Pb, Zr, Ti and O are known. The following description will be given taking Pb as an example. Pb concentration of the reference sample W_Pb(std)The X-ray intensity of the sample is set as I_Pb(std). When a PZT thin film of unknown concentration is measured, the X-ray intensity of Pb is set as I_Pb. By performing a first approximation (first approximation) from these data, the Pb concentration W of the PZT thin film of unknown concentration_PbThis can be found by the following equation:

W_Pb＝W_Pb(std)×I_pb/I_pb(std)

I_pband I_pb(std)Is the X-ray intensity per unit current after the dead time correction and the background correction.

By the same method, the concentrations W of Zr, Ti and O can be determined separately_Zr、W_TiAnd W_O。

Next, ZAF correction coefficients are calculated. Z is the atomic number correction, and the numerical value of Duncumb-Reed is calculated by a least square method. A is the absorption correction, calculated by Philibert equation. F is fluorescence correction, calculated by Reed equation. From W_Pb、W_Zr、W_TiAnd W_ONormalized (size) values of (A) can be calculated for each elementThe first ZAF correction coefficients Z, A and F were substituted into the formula to obtain the corrected concentration. The density value thus obtained is used to calculate a ZAF correction coefficient again. The corrected concentration is further obtained by using the correction coefficient. This was repeated until the calculation error reached 0.001%, and a quantitative value was calculated.

The device used for the analysis was a wavelength dispersive EPMA (JXA-8900R, manufactured by Japan Electron Ltd.). The sample is processed into a square with the size of about 5mm, and the sample is stuck on a sample table by carbon paste, conducted and coated with carbon (カ - ボンコ - テイング).

In the actual measurement, the sample is first subjected to a full qualitative analysis in order to confirm the film thickness and to check the presence or absence of impurities. Accordingly, it is possible to confirm whether or not the electron beam has entered the bottom layer. Thereafter, PZT of the standard sample is measured, and the value of the standard sample is read to perform quantitative analysis of the sample. The analysis conditions at this time were: the acceleration voltage was 15kV, the irradiation current was 70mA, and the beam diameter (ビ - ム diameter) was 10 μm. Whether the measurement is abnormal or not is checked, and if the measurement is normal, the measurement value is normalized to obtain a measurement result. The quantitative values of Pb, Zr, Ti and O were obtained by the above-mentioned measurement methods.

The oxygen deficiency ratio (Y-Z)/(Y +3) is defined as the ratio of the oxygen deficiency in the PZT thin film 2 when Pb takes a valence of 2 and Zr and Ti take a valence of 4. That is, if the oxidation of Pb is completely performed stoichiometrically, the amount of oxygen (O) at this time is the same as Pb, and Y +1, the oxidation of Zr is also completely performed stoichiometrically, the amount of oxygen (O) at this time is 2 times 2X that of Zr, and the amount of oxygen (O) at this time is 2 times 2(1-X) that of Ti, when the oxidation of Ti is performed in the same manner. In the stoichiometric composition state, the total oxygen amount is (Y +1) +2X +2(1-X) ═ Y + 3.

Further, the actual oxygen amount of the prepared PZT thin film 2 was (3+ Z), and the insufficient amount of oxygen was (Y +3) - (3+ Z) ═ Y-Z. The total oxygen amount in the stoichiometric composition was (Y +3), and the oxygen deficiency ratio, i.e., the ratio of the two, was (Y-Z)/(Y + 3). That is, (Y-Z)/(Y +3) represents the ratio of the oxygen deficiency amount. W can be calculated from the results of the quantitative analysis of EPMA_Pb、W_Zr、W_TiAnd W_OTherefore, X, Y and Z values are easily obtained by calculation based on these values.

As shown in FIG. 4, when the oxygen partial pressure is 1% or less, the oxygen deficiency ratio (Y-Z)/(Y +3) increases sharply with a decrease in the oxygen partial pressure. That is, when the oxygen partial pressure is 1% or less, a large amount of oxygen deficiency occurs in the PZT thin film 2. When the oxygen partial pressure is more than 1%, the oxygen deficiency amount is gradually decreased, and when the oxygen partial pressure is 10%, the oxygen deficiency amount ratio is 0.2% (0.002), and above this oxygen partial pressure, a PZT thin film of a stoichiometric composition is obtained.

As shown in fig. 4, when the oxygen deficiency ratio is 0.2%, the oxygen partial pressure is 10%, and when the oxygen deficiency ratio is 5% (0.05), the oxygen partial pressure is 2%, and it is seen that the amount of displacement tends to increase almost linearly with the increase in the oxygen deficiency ratio. However, when the oxygen deficiency amount ratio is greater than 5% (0.05), the displacement amount becomes smaller, and there is no correlation with the oxygen deficiency amount ratio in this region. The reason for this is because the degree of orientation becomes low (as shown in fig. 3).

FIG. 5 is a graph showing the relationship between the calculated oxygen deficiency amount ratio (Y-Z)/(Y +3) and the amount of displacement. When the oxygen deficiency ratio is about 5%, the displacement amount shows the maximum value. When the oxygen deficiency ratio is less than about 5%, the displacement amount gradually decreases. On the other hand, when the oxygen deficiency rate is 5% or more, the displacement amount is similarly decreased, but an inflection point appears at the displacement amount in the vicinity of the oxygen deficiency of 10%.

From the above results, it is effective to increase the displacement amount of the piezoelectric element 10 and to generate some oxygen deficiency in the PZT thin film 2. When the degree of orientation of the PZT thin film 2 is 70% or more, the upper limit of the oxygen deficiency ratio is 0.1. As can be seen from FIG. 4, in order to ensure that the amount of displacement is larger than the amount of displacement when the degree of orientation is 100% and there is no oxygen deficiency, the oxygen deficiency ratio must be controlled to 0.1 or less. The oxygen partial pressure at this time must be controlled in the range of 1% or more to 10% or less.

Further, if the oxygen deficiency ratio is controlled to be in the range of 2% (0.02) to 7% (0.07), as is clear from fig. 5, since this range includes the displacement peak, the variation in displacement is relatively small even if the oxygen deficiency varies. This is preferable because the manufacturing yield can be improved. And, if the oxygen deficiency amount ratio is controlled to be 2% or more to 5% or less, the shift variation corresponding to the oxygen deficiency ratio is smaller. The manufacturing yield can be further improved, and therefore, this is more preferable.

When the oxygen deficiency amount ratio is in the range of 2% to 7%, the oxygen partial pressure must be set in the range of 1.5% or more to less than 5%.

As shown in FIG. 6, the composition of the target is represented by the general formula P b_1+Y(Zr_XTi_1-X)O_3+ZIn the case of expression (0 < X < 1), X is constant at 0.58, and the PZT thin film 2 is formed using a target having three compositions of Y0, Y0.25, and Y1, and fig. 6 shows the relationship between the oxygen partial pressure in the discharge gas and the displacement of the piezoelectric element 10 during film formation.

With the target of Y ═ 0, the oxygen partial pressure showed a peak of displacement in the range of 10% to 20%, and the amount of displacement was small as a whole. The reason is that the PZT thin film made by the sputtering method using this target is in a Pb deficient state when Y is 0.

When the target was used with Y being 1, the peak of the amount of displacement was locally observed in the vicinity of 1% oxygen partial pressure.

On the other hand, it was found that when a target having Y of 0.25 was used, the range in which a large displacement amount was obtained was increased, and the PZT thin film 2 could be produced with high yield.

As can be seen from fig. 6, as the Y value indicating the Pb composition in the target increases from 0, the oxygen partial pressure value indicating the peak of the displacement amount tends to move in a small direction. Although not shown, we studied the relationship between the displacement and the target in which the Y value was variously changed, and as a result, found that when 0 < Y < 1, the piezoelectric characteristics were good and the mass productivity and the yield were improved by forming the film in the range of 1% to 10% of the oxygen partial pressure. During sputtering, the discharge gas is analyzed by mass filtration while controlling the introduction of argon (Ar) gas and oxygenGas (O)₂) The oxygen partial pressure can be controlled. Or, for Pb_1+Y(Zr_XTi_1-X)O_3+ZAr and O as discharge gas are introduced when the target Z is 0 or the like₂The flow rate ratio of (a) to (b) is set within the above range, and a similar piezoelectric thin film can be obtained.

In this example, the general formula Pb was used_1+Y(Zr_XTi_1-X)O_3+ZWhen X is 0.58 constant (0 < X < 1), a target having the same value as Z and Y is used. However, the oxygen composition value Z of the target is not limited to the case where it is equal to the Pb composition value Y, and may be set separately. That is, if the amount of oxygen in the discharge gas during sputtering is within the above range in which Z is 3. ltoreq. Y, a piezoelectric thin film having excellent piezoelectric characteristics can be produced by appropriately controlling the film formation rate.

In the present embodiment, the MgO substrate having the (100) orientation is used as the substrate, but the present invention is not limited thereto. For example, a single crystal silicon substrate, a single crystal strontium titanate substrate, a sapphire (サフアイヤ) substrate, a sintered alumina substrate, a zirconia substrate, or the like may be used. When spontaneous polarization cannot be generated by using these substrates, the oxide piezoelectric thin film may be formed and then subjected to polarization treatment.

In the present embodiment, a Pt film is used as the 1 st electrode film, but the present invention is not limited thereto. For example, gold (Au), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), or an oxide thereof and a material having conductivity may be similarly used.

In the present embodiment, a Pt film is used as the 2 nd electrode film, but the present invention is not limited thereto. For example, the same material as the first electrode film 1, or a metal material such as aluminum (Al), copper (Cu), or nickel (Ni) may be used without particular limitation.

In the present embodiment, the piezoelectric element is fabricated by photolithography and etching, but the present invention is not limited thereto. For example, the predetermined shape can be formed by sputtering or vapor deposition using a mask (マスク).

Example 2

This example is an actuator prepared from a piezoelectric element (prepared as described in example 1), and the following description will be given of the determination of the head position of a magnetic disk device using this actuator. FIG. 7 is a schematic diagram showing the structure of an apparatus for determining the position of a head on a magnetic disk apparatus using a piezoelectric element in this embodiment. The magnetic disk device is characterized by a 2-stage actuator structure in which an actuator made of a piezoelectric element of the present invention is attached to an actuator made of an original voice coil motor. The head support structure 100 includes a suspension 104 having low rigidity, a reed 105, an arm 106 having high rigidity, a flexible portion 103, a slider 102 attached to the device 103 on a surface facing the magnetic disk 200, a magnetic head (not shown) mounted on the slider 102, and a piezoelectric element 108 bonded and fixed to the flexible portion 103.

The suspension 104 is less rigid and the other end forms a spring 105, the spring 105 being fixed to an arm 106. The voice coil 112 attached to the arm 106 and a magnet not shown constitute a voice coil motor. The head support structure 100 is rotatable within a certain angular range in a direction parallel to the surface of the magnetic disk 200 by the voice coil motor.

In order to accurately position the head mounted on the slider 102 at a predetermined track position of the magnetic disk 200, the piezoelectric element 108 is driven. That is, the head support structure 100 is a two-stage actuator structure in which the position is roughly determined by a voice coil motor and then fine-tuned by the piezoelectric element 108.

Hereinafter, the movement of the magnetic disk device will be described. The magnetic disk 200 is rotated at a certain rotational speed by the spin-drive unit 220. When recording and reproducing are performed in the magnetic disk apparatus, the slider 102 is floated by a predetermined amount by a force balance between a floating force caused by an air flow generated by the rotation of the magnetic disk 200 and an attractive force of the slider 102 pressing against the surface of the magnetic disk 200, and the magnetic head performs recording and reproducing in the floating state. Although recording and reproduction are performed in a floating state. In order to position the magnetic head at a certain track position, the arm 106 is rotated about the bearing portion 110 by a voice coil motor. While the position of the conventional magnetic disk device is determined only by the voice coil motor, the magnetic disk device of the present embodiment also performs highly accurate position determination by the piezoelectric element 108.

Fig. 8A and 8B show the shape of the portion near the piezoelectric element 108. Fig. 8A is a plan view and fig. 8B is a sectional view taken along X-X rays shown in fig. 8A. In the flexible portion 103, a pair of piezoelectric elements 108A and 108B are bonded and fixed to positions axially symmetric to the center line Y-Y in the longitudinal direction of the suspension by an adhesive layer 107. Each of the piezoelectric elements 108A and 108B has a symmetrical shape along the Y-Y line, as well as its cross-sectional configuration. That is, the piezoelectric elements 108A and 108B are formed by the 1 st electrode film 1081 and the 2 nd electrode film 1083 sandwiching the PZT thin film 1082. An insulating protective resin film may be formed on the surfaces of the piezoelectric elements 108A and 108B. The 1 st electrode film 1081 and the 2 nd electrode film 1083 of each of the piezoelectric elements 108A and 108B are connected to the lead wires 109(ワイヤリ - ド) via the electrode pads 103A of the flexible portion 103. Piezoelectric electrode lines 103B led out from the electrode pads 103A and connected to a disk device control unit (not shown) are formed on the flexible portion 103. A head electrode line 103C connecting the head mounted on the slider 102 and a disk device control unit (not shown) is formed in the flexible portion 103 located at the center of the pair of piezoelectric elements 108A and 108B.

In the magnetic head support structure 100 having the above-described structure, a voltage of 10V was applied to the piezoelectric element 108, and the displacement of the magnetic head (not shown) was measured. As a result, it was found that in the case of a PZT thin film having an oxygen deficiency ratio of 0 < (Y-Z)/(Y +3) > 0.1 or less, a displacement of 2 times or more is generated as compared with a piezoelectric element using the conventional PZT thin film. Therefore, the fine position can be specified in a wider range than that of the conventional piezoelectric element, and a magnetic disk device with a large recording density can be realized.

In the piezoelectric elements 108A and 108B shown in fig. 8A and 8B, the PZT thin film 1082 is sandwiched between the 1 st electrode film 1081 and the 2 nd electrode film 1083, and the PZT thin film 1082 has only one layer, or the films having such a structure may be bonded with an adhesive or the like to form a laminated structure of a plurality of PZT thin films. A greater displacement driving force can be achieved by lamination.

The crystal structure of the PZT thin film of this example was tetragonal, (001) oriented. This is because the (001) orientation is advantageous in piezoelectric properties because the polarization of tetragonal PZT faces the (001) direction. In the case of a rhombohedral PZT thin film, polarization is oriented in the (111) direction, and in this case, a high degree of orientation of (111) can be secured, which is advantageous in terms of piezoelectric characteristics.

In example 1 and example 2, the general formula P b_1+Y(Zr_XTi_1-X)O_3+ZThe case where X is 0.58 has been described, but the present invention is not particularly limited thereto. The composition of PZT in which the crystal structure depends on X and the value of X in the vicinity of the boundary between tetragonal and rhombohedral systems is called mpb (morphotropic phase boundary) composition, and it is known that its piezoelectricity is high. If a composition in the vicinity of this is used, a piezoelectric element having a high piezoelectric property can be obtained without limiting X to 0.58. The value of the boundary X between the tetragonal system and the rhombohedral system depends on the method of forming the film, the amount of the additive, and the like, and thus can be appropriately adjusted.

In example 1 and example 2, although PZT was described as a material of the piezoelectric thin film, additive elements may be added as necessary to adjust the material characteristics. In this case, the oxygen deficiency amount may be calculated by considering the amount of the additive and the valence thereof. The elements as the additive elements and the valences thereof are as follows. Typical group 1 elements (typical group 1 elements) are monovalent, typical group 2 elements, Mn, Ni, Cu, Zn, Sm, Eu, Yb are 2 valent, Sc, Y, Cr, B, Al, Ga, In, Sb, Bi, La, Nd, Pm, Gd, Dy, Ho, Er, Tm, Lu are 3 valent. Hf. Ir, Si, Ge, Sn, Ce, Pr, Tb are 4-valent.

In examples 1 and 2, the PZT thin film was directly formed on the Pt film, and in order to improve the crystallinity and crystal orientation of the PZT thin film, a base film may be formed on the Pt film, and then the PZT thin film may be formed thereon.

In examples 1 and 2, it was confirmed that the piezoelectric property was improved by forming a film having oxygen deficiency in the PZT thin film formed by sputtering, but not limited to sputtering, and laser grinding (レ - ザ - アブレ - ション). The present invention is not limited to PZT thin films, and the effects of the present invention can be achieved if the thin film is an oxide piezoelectric thin film.

In the piezoelectric element of the present invention, the crystal structure of the piezoelectric thin film may be a perovskite tetragonal system, and the crystal may be oriented in the (001) direction. The crystal structure of the piezoelectric thin film may be perovskite type rhombohedral system, and the crystal may be oriented in the (111) direction. Thus, a piezoelectric element manufactured using a tetragonal PZT thin film or a rhombohedral PZT thin film as a piezoelectric material has a large piezoelectric characteristic.

In the piezoelectric element of the present invention, Pb has the general formula_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1), a part of Pb may be substituted with at least 1 element selected from the group consisting of group 2 typical elements, manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), samarium (Sm), europium (Eu) and ytterbium (Yb). In the composite oxide piezoelectric thin film to which one or more of the above elements are added, if the oxygen deficiency amount is more than 0% and less than 10%, the piezoelectric characteristics can be further improved.

In the piezoelectric element of the present invention, Pb has the general formula_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1), a part of at least one element selected from the group consisting of Ti and Zr may be substituted with at least one element selected from the group consisting of hafnium (Hf), iridium (Ir), silicon (Si), germanium (Ge), tin (Sn), cerium (Ce), praseodymium (Pr), and terbium (Tb). In the complex oxide piezoelectric thin film obtained by substituting a part of at least one element of Ti and Zr with the above element, if the oxygen deficiency is more than 0% and less than 10%, the piezoelectric characteristics can be further improved.

In the piezoelectric element of the present invention, Pb has the general formula_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1), a part of at least one element selected from the group consisting of Pb, Ti and Zr may be selectedAt least one element selected from the group consisting of monovalent group 1 typical elements, scandium (Sc), yttrium (Y), chromium (Cr), boron (B), aluminum (Al), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi), lanthanum (La), neodymium (Nd), promethium (Pm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and lutetium (Lu). In the composite oxide piezoelectric thin film obtained by substituting a part of at least one element selected from Pb, Ti and Zr with these elements, if the oxygen deficiency amount is more than 0% and less than 10%, the piezoelectric characteristics can be further improved.

In examples 1 and 2, a method of manufacturing a piezoelectric thin film by a sputtering method was described, but the present invention is not limited thereto. For example, the general formula A can be formed on the 1 st electrode film by laser ablation_1+YB O_3+Z(A and B represent elements) represents an oxide piezoelectric thin film having a crystal orientation degree of 70% or more in a direction parallel to the polarization axis thereof. When the film is formed in a discharge gas atmosphere in which the oxygen partial pressure in the vacuum apparatus during the film formation process is controlled with high precision, the amount of oxygen deficiency can be controlled precisely, and the amount of oxygen deficiency can be distributed uniformly in the film.

On the other hand, when a piezoelectric body is formed by, for example, a powder sintering method, if it is fired in a low oxygen environment, oxygen deficiency may occur, but in this case, oxygen deficiency is likely to occur locally, and reliability is lowered. Further, if a Chemical Vapor Deposition (CVD) method is used, unlike the sputtering method and the laser ablation method, a film is formed by oxidation and decomposition of a reaction gas, and therefore, it is difficult to form a piezoelectric thin film having good piezoelectric characteristics under a low oxygen partial pressure.

On the other hand, in the oxide piezoelectric thin film produced by the sputtering method and the laser milling method, a predetermined oxygen deficiency amount is uniformly present in the film, and therefore, a piezoelectric thin film having high piezoelectric characteristics and high reliability can be obtained. However, when sputtering is performed in a state where the oxygen partial pressure exceeds 10%, oxygen deficiency does not occur, and the film formation rate is not increased. On the other hand, when the oxygen partial pressure is 1% or less, the proportion of crystals parallel to the polarization axis decreases, and the piezoelectric characteristics cannot be improved. That is, in order to obtain the necessary piezoelectric characteristics, the degree of crystal orientation must be 70% or more. Therefore, the oxygen partial pressure is required to be 1% or more than 1%. In addition, sputtering at a low oxygen partial pressure as described above can improve the film formation rate and mass productivity.

In the sputtering or laser milling method, the ratio of the oxygen gas introduction flow rate to the total gas introduction flow rate as the gas introduction flow rate into the vacuum apparatus may be 0.01 or more and less than 0.1. Thus, even under a condition of a relatively low discharge gas pressure, an oxide piezoelectric thin film having a predetermined oxygen deficiency ratio can be obtained, and a high-speed film formation can be performed, thereby greatly improving mass productivity.

Claims (8)

1. A piezoelectric body element comprising the following composition: a piezoelectric element includes a 1 st electrode film, a 2 nd electrode film, and a piezoelectric thin film sandwiched between the 1 st electrode film and the 2 nd electrode film, wherein the piezoelectric thin film is an oxide piezoelectric thin film having an oxygen deficiency amount of 0% or more and 10% or less with respect to a stoichiometric composition.

2. The piezoelectric element according to claim 1, wherein said piezoelectric thin film is of the general formula Pb_1-Y(Zr_XTi_1-X)O_3+ZWherein 0 < X < 1, and 0 < Y-Z)/(Y +3) is 0 to 0.1 when the oxygen deficiency ratio in the piezoelectric thin film is represented by (Y-Z)/(Y + 3).

3. The piezoelectric element according to claim 2, wherein a degree of crystal orientation of an orientation parallel to a polarization axis of the piezoelectric thin film is 70% or more.

4. The piezoelectric element according to claim 2, wherein a crystal structure of the piezoelectric thin film is a perovskite tetragonal system, and a crystal is oriented in a (001) direction.

5. The piezoelectric element according to claim 2, wherein the crystal structure of said piezoelectric thin film is a perovskite type rhombohedral system, and the crystal orientation is in the (111) direction.

6. The piezoelectric element according to claim 2, wherein said general formula Pb is_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1) a part of Pb is substituted with at least one element selected from the group consisting of group 2 typical elements, manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), samarium (Sm), europium (Eu) and ytterbium (Yb).

7. The piezoelectric element according to claim 2, wherein said formula Pb is_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1), a part of at least one element selected from the group consisting of Ti and Zr is substituted with at least one element selected from the group consisting of hafnium (Hf), iridium (Ir), silicon (Si, germanium (Ge), tin (Sn), cerium (Ce), praseodymium (Pr) and terbium (Tb).

8. The piezoelectric element according to claim 2, wherein said formula Pb is_1+Y(Zr_XTi_1-X)O_3+Z(wherein 0 < X < 1), a part of at least one element selected from Pb, Ti and Zr is represented by a monovalent group 1 typical element, scandium (Sc), yttrium (Y), chromium (Cr), boron (B), aluminum (Al), gallium (Ga), indium (In), antimony (Sb), bismuth (Bi)At least one element selected from (Bi), lanthanum (La), neodymium (Nd), promethium (Pm), gadolinium (Gd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm) and lutetium (Lu).