JP3782282B2 - Method for manufacturing piezoelectric driving body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric driving body that can be driven by voltage by arranging electrodes on the piezoelectric element, and more particularly to a method for manufacturing the piezoelectric driving body. The invention relates to a manufacturing method.
[0002]
[Prior art]
A piezoelectric driving body using a thin film piezoelectric element for controlling movement of a minute amount, such as an actuator for head tracking of an HDD having a high track density, has attracted attention.
[0003]
FIG. 5 is a diagram showing a conventional method for manufacturing a piezoelectric driving body. A platinum (Pt) film 2 and a lead titanate (PLT) film 3 are formed on a magnesium oxide (MgO) 1 serving as a substrate by sputtering or vapor deposition. A PZT (Pb—Zr—Ti) film 4 that is a piezoelectric element is formed thereon by the same method, and a chromium (Cr) film 5 that is an electrode is formed thereon.
[0004]
Here, a state in which an electrode film is added to a piezoelectric element film is referred to as a piezoelectric driving body (hereinafter the same). The reason why MgO1 is used for the substrate is that the coefficient of thermal expansion is higher than that of the PZT film 4, thereby applying a compressive stress to the inside of the PZT film 4 during film production. It is known that applying a compressive stress during film formation has a great effect on improving the displacement characteristics of the PZT film 4 after film formation.
[0005]
As described above, when the piezoelectric element thin film is formed, the MgO substrate plays a role of applying compressive stress to the inside of the film, but is removed after the piezoelectric element film is formed because it becomes unnecessary.
[0006]
FIG. 6 is a reverse of FIG. 5 and shows a step of removing MgO1 serving as a substrate by etching with phosphoric acid (7 indicates the etching direction). At this time, the side surfaces of the elements such as directions 12a, 12b, 12c, and 12d shown in the figure are sealed with resin or the like to prevent phosphoric acid from entering each thin film during etching. FIG. 7 shows a state in which the voltage power source 9 is connected between the Pt film 2 and the Cr film 5 after the MgO 1 that has become the substrate when the piezoelectric film is formed is removed by phosphoric acid. The operation as a piezoelectric driving body is started by applying an AC voltage from this voltage source.
[0007]
For example, when the fixed end is 11, it moves in a direction such as 10 as the displacement direction. This is because the piezoelectric film PZT4 expands and contracts in the length direction 13 by the applied voltage and moves like a bimetal due to the influence of the highly rigid Cr layer 5.
[0008]
[Problems to be solved by the invention]
However, in the piezoelectric driving body configured as shown in FIG. 7, when operated by applying a voltage, a rust-like electro-corrosion area 8 is generated and eventually spreads over the entire film, and finally the piezoelectric driving. There was a problem of losing the displacement characteristics of the body. In view of such a problem, the present inventor has intensively studied. As a result, when the etching with phosphoric acid is performed in FIG. 6, the cause is that the battery is generated by passing the small hole existing in the upper electrode substrate Pt layer 2 and the phosphoric acid entering the PZT4 layer and applying a voltage thereto. It was found that the electric corrosion spreads depending on the effect. Since the upper electrode substrate Pt layer 2 is made very thin (usually a thickness of submicron), a portion where the film is not sufficiently integrated is generated and becomes a small hole.
[0009]
In order to solve this problem, it is conceivable to increase the thickness of the Pt film 2. However, if the Pt layer 2 is increased, it depends on the thermal expansion coefficient generated between the MgO substrate 1 and the PZT layer 4 during film formation. The Pt layer 2 absorbs the compressive stress in the PZT layer 4 and no compressive stress is applied during film formation. On the other hand, if the phosphoric acid etching in FIG. 6 is stopped halfway and the MgO substrate 1 is left on the Pt layer 2, an electrode cannot be formed on the Pt layer 2.
[0010]
In order to solve the above-mentioned conventional problems, the present invention prevents the penetration of phosphoric acid into the PZT layer during etching, prevents the occurrence of galvanic corrosion that occurs at the time of driving, and achieves a greater displacement characteristic. It aims at providing a body and its manufacturing method.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a piezoelectric driving body according to the present invention includes a step of forming a groove on an electrical insulator substrate made of MgO , filling the groove with a conductor made of Pt , and forming a first electrode film thereon A piezoelectric element film is formed thereon, a second electrode film is formed thereon, and phosphorous is exposed until the conductor made of Pt with the electrically insulating substrate made of MgO buried in the groove is exposed. It is characterized by being removed by an acid etching process .
[0012]
In the method, it is preferable that the first electrode film is formed of Pt and the second electrode film is formed of Cr .
[0013]
Further, it is preferable that both the first electrode film and the second electrode film are formed of Pt .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a part to be an electrode end is formed on the MgO substrate 1 in advance, and a Pt layer 2, a PLT layer 3, a PZT layer 4 and a Cr layer 5 are formed thereon as shown in FIG. In the removal process of the substrate 1, the MgO layer is etched until the end of the electrode is exposed, and finally an electrode is formed which leaves a part of the MgO layer and leads to the Pt layer 2 below. In the above, the MgO layer needs to have a thickness that does not allow the phosphoric acid solution to pass through the PZT layer when the Pt layer is etched, and the thickness is several μm to several tens of μm, preferably 3 nm to 15 nm. . By doing so, phosphoric acid is prevented from entering the PZT layer 4 which is a piezoelectric element film through the Pt layer 2 which is an electrode layer, and the electrode is formed even if a part of the MgO substrate 1 is left. Can be formed. Further, although MgO does not exist outside the portion formed as the electrode end, the membrane pressure is sufficiently thick, so that intrusion of phosphoric acid from this portion can also be prevented.
[0017]
(Embodiment 1)
Embodiment 1 according to the present invention will be described below with reference to the drawings. FIG. 1 shows a piezoelectric driver having an electrode according to the present invention. Compared with FIG. 7, the MgO layer 1 as a substrate is still left above the Pt layer 2, and an electrode end Pt 21 is formed as an electrode that communicates with the Pt layer 2. Although this Pt layer 21 exists in the same plane as the MgO layer 1, its surface is exposed and this portion can be used as an electrode.
[0018]
FIG. 2 is a view showing a cross section from the 14 direction of FIG. The Cr layer 5, the PZT layer 4, the PLT layer 3, and the Pt layer 2 have the same configuration as the conventional one, but a part of the MgO substrate 1 remains on the Pt layer 2 and the electrode ends. It can be seen that a portion of Pt21 is formed. As shown in FIG. 2, when the power source 9 is arranged between the electrode end Pt layer 21 and the Cr layer 5 and the fixed end is 11 and a driving voltage is applied, driving is performed in a variation direction as indicated by 10.
[0019]
Since the Pt layer 21 serving as the electrode end exists as a thick film between the MgO substrate 1 and the PZT layer 4 when the PZT layer 4 which is a piezoelectric element film is formed, the in-film compression effect of the MgO substrate on the PZT layer 4 is exerted. It is thought that it is hard to act. That is, when viewed in FIG. 2, a part of the PZT layer 4 below the Pt layer 21 that is the electrode end has a small displacement characteristic. Therefore, the electrode end Pt21 should have a narrow width and should be formed at the end of the piezoelectric driving body.
[0020]
Further, as shown in FIGS. 1 and 2, the electrode ends formed on the piezoelectric driving body do not have to be two places, and may be one place, and the shape of the present invention is also to ensure conduction. It is not limited to a belt shape.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0022]
Example 1
Hereinafter, manufacturing of the piezoelectric element having the electrode terminal according to the present invention shown in FIG. 1 will be described with reference to FIG. As the substrate, MgO having a length of 20 mm, a width of 20 mm, and a thickness of 0.3 mm was prepared (FIG. 3A).
[0023]
In order to draw an electrode terminal pattern on the substrate, a photosensitive resin resist 30 was applied to a thickness of 5 μm, and an electrode pattern was formed by exposure using a separately prepared electrode pattern mask. The resist of the part which becomes is removed (FIG. 3B).
[0024]
At this time, the width of the electrode portion was 30 μm. After removing the resist to be the electrode part, the whole was etched with a phosphoric acid solution of 20% by weight aqueous solution at 80 ° C., and a part to be the electrode end having a depth of 10 μm was formed in the MgO substrate (FIG. 3C )).
[0025]
Pt was formed thereon by a 10 μm vapor deposition method. By doing so, the portion 32 where the surface of the MgO substrate shown in FIG. 3C is removed by etching can be filled with Pt, and this portion becomes a later electrode end. By removing the resist 30 after this, the MgO substrate 1 having the electrode end on the film surface can be produced (FIG. 3D). The above method is a so-called lift-off method.
[0026]
A Pt layer 2, a PLT layer 3, a PZT layer 4 and a Cr layer 5 are formed on the MgO substrate thus prepared in the same manner as the conventional method, and then the Pt layer 21 is exposed by the phosphoric acid etching process 7. Until then, the MgO layer 1 was removed. At this time, it is needless to say that the side surface direction of the film is sealed with resin as described with reference to FIG. 6 to prevent damage due to phosphoric acid penetration into the film.
[0027]
In this example (FIG. 3E), the Pt layer was 0.1 μm, the PLT layer 3 was 0.05 μm, the PZT layer 4 was 2.5 μm, and the Cr layer 5 was 5 μm. The phosphoric acid solution used in the phosphoric acid etching was an aqueous solution containing 20% by weight phosphoric acid. Etching conditions were performed at a temperature of 80 ° C., and the etching rate was controlled by time.
[0028]
Gold (Au) 22 is deposited to a thickness of 0.05 to 0.07 μm on the side where the electrode end Pt21 of the piezoelectric driving body with the electrode end of the Pt21 thus made exposed from the MgO substrate is present, and the entire upper surface is conductive. The body. When a drive voltage of 1 KHz and 5 V was applied between the Au layer 22 and the Cr layer 5, a displacement of about 0.5 μm could be observed at the free end opposite to the fixed end.
[0029]
In the piezoelectric element having the electrode according to the present invention as described above, a part of MgO1 serving as the substrate is left, so that the phosphoric acid of the phosphoric acid etching treatment 7 used for removing the MgO substrate 1 is the Pt layer. 2 did not enter the PZT layer 4, and no electrolytic corrosion occurred even during long-time driving.
[0030]
(Example 2)
In Example 1, the Cr layer 5 and the MgO layer 1 having high elastic modulus remain on both sides of the PZT layer 4 that is a piezoelectric element, and the bimetal effect works to cancel it on both sides of the PZT layer 4, resulting in displacement characteristics. It is thought that it is causing loss. In other words, if there is a film that does not easily deform (has a high elastic modulus) on both sides of the piezoelectric element that expands and contracts due to the drive voltage, the overall displacement characteristics become small.
[0031]
Therefore, it was considered that a Pt layer having a low elastic modulus was provided instead of the Cr layer 5 to form an electrode on the side opposite to the electrode end Pt21. In other words, the piezoelectric element PZT that expands and contracts and the MgO film that is difficult to deform formed on one surface of the piezoelectric element PZT substantially perform a bimetallic operation.
[0032]
FIG. 4 shows the specific structure. As compared with FIG. 3 (f), it can be seen that a Pt layer 23 is formed instead of the Cr layer 5. In this state, when a drive voltage of 1 kHz and 5 V was applied as before, a displacement of about 1 μm could be observed at the free end opposite to the fixed end. Thus, by replacing the Cr layer with the Pt layer 23 having low rigidity, the bimetal effect is generated between the PZT layer 4 and the MgO layer 1, and a larger displacement characteristic can be obtained.
[0033]
As described above, in the embodiment of the present invention, the Pt layer 2 serving as an electrode and the conductive electrode Pt21 are formed while leaving a part of the MgO layer removed by phosphoric acid, so that the PZT layer 4 is infiltrated by phosphoric acid. This eliminates the problem of electric corrosion that occurs during driving. Further, since the opposite side of the MgO layer 1 is the electrode Pt23 having a low elastic modulus, a larger displacement characteristic can be obtained.
[0034]
【The invention's effect】
According to the present invention, the piezoelectric drive body is formed so that the electrode end can be formed on a part of the MgO substrate left at a constant thickness while leaving the MgO serving as the substrate at the same time, so that PZT by phosphoric acid at the time of etching is formed. It is possible to provide a piezoelectric driver and a method for manufacturing the same that can prevent intrusion into the layer, prevent the occurrence of electrical corrosion that occurs during driving, and obtain even greater displacement characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing a piezoelectric driving body having an electrode portion according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a driving state of the piezoelectric driving body according to an embodiment of the present invention. FIG. 4 is a diagram showing a manufacturing process of a piezoelectric driving body according to an embodiment of the present invention. FIG. 4 is a diagram showing a cross-section of a piezoelectric driving body according to another embodiment of the present invention. FIG. 6 is a view showing a process of removing a substrate with phosphoric acid during a manufacturing process of a conventional piezoelectric drive body. FIG. 7 is a view showing a state of driving a conventional piezoelectric drive body.
1 Electrical insulator (MgO)
2 electrodes (Pt)
3 Lead titanate film (PLT)
4 Piezoelectric element film (PZT)
5 Electrode (Cr)
6 Bonding direction to substrate 7 Etching direction 8 Electrolytic corrosion area 9 Voltage power supply 10 Displacement direction 11 Fixed ends 12a, 12b, 12c, 12d Resin sealing portion

Claims (3)

A groove is formed on an electrical insulator substrate made of MgO , the groove is filled with a conductor made of Pt, a first electrode film is formed thereon, a piezoelectric element film is formed thereon, and a first electrode film is formed thereon . 2. A method for manufacturing a piezoelectric driver, comprising: forming an electrode film 2 and removing the electric insulator substrate made of MgO by a phosphoric acid etching process until a conductor made of Pt buried in the groove is exposed. The method for manufacturing a piezoelectric driving body according to claim 1, wherein the first electrode film is formed of Pt, and the second electrode film is formed of Cr. The method for manufacturing a piezoelectric driver according to claim 1, wherein both the first electrode film and the second electrode film are formed of Pt.

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