The present application is based on Japanese priority application No. 2006-172829 filed on Jun. 22, 2006, the entire contents of which are hereby incorporated by reference.
The present invention generally relates to piezoelectric actuators and more particularly to a highly miniaturized and reliable piezoelectric actuator and a magnetic disk apparatus that uses such a piezoelectric actuator.
With recent trend of downsizing accompanied with augmentation of functional versatility in the information processing apparatuses, there is a demand for small and low-cost actuators capable of moving an object for minute distance but with high precision and high speed.
With an inkjet recording head of inkjet printers or a magnetic head of a magnetic disk apparatus, for example, there is a need for such a piezoelectric actuator capable of moving an object for minute distance with high precision and at high speed. Such a piezoelectric actuator is needed also in optical heads of optical disk apparatuses for focusing compensation or tilt control of the optical system used therein.
In these applications, it should be noted that the piezoelectric actuator itself is miniaturized with downsizing of the apparatus, and associated with this, the piezoelectric substance constituting the piezoelectric actuator also has a reduced layer thickness.
With such a piezoelectric actuator that uses a piezoelectric substance of small layer thickness, there is a tendency that the electric field applied to the piezoelectric substance is increased with decrease of the layer thickness. Thus, securing a reliable operation becomes a paramount problem with such a piezoelectric actuator.
In the case of the piezoelectric actuator used in magnetic disk apparatuses, in particular, the control distance or “stroke” required for the piezoelectric actuator is large, and thus, a very large electric field is applied to the piezoelectric substance. Further, the magnetic disk apparatuses have to guarantee proper operation also in various environmental conditions including high temperature and high humidity ambient, and thus, a particularly stringent demand is imposed for the piezoelectric actuator that is used in such a magnetic disk apparatus with regard to the reliability under various environmental conditions.
Japanese Laid-Open Patent Application 2004-30823 official gazette
Japanese Laid-Open Patent Application 2003-284362 official gazette
Japanese Laid-Open Patent Application 2003-61370 official gazette
Japanese Laid-Open Patent Application 2002-71871 official gazette
Japanese Laid-Open Patent Application 3-155180 official gazette
Japanese Laid-Open Patent Application 2002-319715 official gazette
Referring to
Further, electrode films 10A and 10B of Au, or the like, are provided at both ends of the piezoelectric laminated body.
Generally, such piezoelectric substance 11, 13, 15, 17 and 19 are formed by a green sheet process and the electrode patterns 12, 14, 16 and 18 are formed by a screen-printing process.
Meanwhile, with the piezoelectric actuator of such a construction, it should be noted that the electrode patterns 12, 14, 16 and 18 are exposed at the sidewall surfaces of the piezoelectric actuator, and because of this, such a construction raises a problem that the insulation resistance of the piezoelectric actuator is degraded severely at the sidewall surfaces thereof, particularly when the piezoelectric actuator is operated in a high temperature and high humidity ambient. Such severe degradation of insulation resistance leads to the problem of insulation breakdown.
It is thought that such severe degradation of insulation resistance is caused by a mechanism that there is caused a concentration of electric field at such a sidewall surface of the piezoelectric actuator where the electrode patterns are exposed and that such concentration of electric field facilitates the adversary process of electromigration, or the like.
When such insulation breakdown is caused at the sidewall surfaces of the piezoelectric actuator, the electrode patterns 12, 14, 16 and 18 may cause short circuit at the sidewall surfaces of the piezoelectric actuator.
As noted before, the problem of degradation of insulation resistance, and hence degradation of withstand voltage, is facilitated particularly in the high humidity ambient, and thus, there arise cases in which a piezoelectric actuator, operable stably for long time in a dry high temperature ambient, shows a serious degradation of insulation resistance after running only for about 100 hours in a high humidity ambient. As noted before, such severe degradation of insulation resistance is believed to be caused by water molecules of the ambient adsorbed on the sidewall surface of the laminated piezoelectric body and causing acceleration of electromigration.
Thus, in order to avoid insulation breakdown of the piezoelectric actuator at the sidewall surfaces thereof, Patent References 5 and 6 teach a technology of covering the sidewall surfaces of the piezoelectric laminated body constituting the piezoelectric actuator with various protective films.
When such a sidewall protective film is formed by an organic insulation film, however, there are cases in which the withstand voltage of the organic insulation film is lower than that of the piezoelectric substance itself and the protective film causes insulation breakdown first when the piezoelectric actuator is operated. Thus, such an approach is not effective for preventing the problem of insulation breakdown of the piezoelectric substance.
On the other hand, in the case such a sidewall protective film is formed by an organic insulation film, adherence of the protective film to the laminated piezoelectric body is tend to be deteriorated, and there arises a problem that the sidewall protective film drops out when the piezoelectric actuator is operated.
In order to attend to this problem, it is conceivable to form the sidewall protective films by a vacuum process such as sputtering process or CVD process. However, such an approach of using a vacuum process is expensive and also increases the time needed for the protective film, and hence manufacturing the piezoelectric actuator.
In a first aspect of the present invention, there is provided a piezoelectric actuator, comprising:
a body of a piezoelectric material;
electrode patterns embedded in said body; and
a sidewall protective film of a piezoelectric material covering at least a sidewall surface of said body,
said sidewall protective film covering said electrode patterns at said sidewall surface of said body.
Further, the present invention provides a magnetic disk apparatus that uses such a piezoelectric actuator.
In another aspect, the present invention provides a method for manufacturing a piezoelectric actuator, comprising the steps of:
forming a liquid state film of a piezoelectric ceramic source material containing therein an organic metal compound on a surface of a body of a piezoelectric material by a coating process, said body of piezoelectric material including therein electrode patterns; and
forming a protective film of a piezoelectric material on said surface of said body from said liquid state piezoelectric ceramic source material.
According to the present invention, in which the electrode patterns exposed at the sidewall surfaces of the piezoelectric body forming the piezoelectric actuator are covered with the sidewall protective film of the piezoelectric ceramic material, it becomes possible to avoid the insulation breakdown at the sidewall surfaces, even in the case the piezoelectric actuator is used in a high temperature and high humidity ambient, and it becomes possible to operate the piezoelectric actuator or an electronic apparatus such as a magnetic head assembly that uses the piezoelectric actuator stably, in wide variety of ambient and environments.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.
In order to solve the problems explained previously, it is conceivable to form the sidewall protective film integrally with the piezoelectric laminated body as in the case of a piezoelectric actuator 15 shown in
The construction of
Further, in
Further, in
With the piezoelectric actuator 15 of such a construction, in which the sidewall protective film protecting the sidewall surface is formed integrally with the piezoelectric lamination body, it is expected that the problem of insulation breakdown or dropping out of the sidewall protective film is eliminated successfully.
In the case of forming such a structure on a baked substrate shown in
When such a baking process is conducted, however, the piezoelectric lamination body shows a large shrinkage and it is difficult to suppress the positional error of the electrode patterns within several microns after the baking process.
Thus, when attempt is made to form a sidewall protective film covering the electrode patterns at the sidewall surface of the laminated body with the construction of
Thus, when the sidewall protective film is formed on the sidewall surface of the piezoelectric lamination body constituting the piezoelectric actuator with the approach of
However, when such a thick protective film having a thickness exceeding several ten microns is formed on the sidewall surface of the piezoelectric lamination body constituting a piezoelectric actuator, the protective film resists the deformation of the piezoelectric actuator and there is a possibility that the desired displacement is not attained for the piezoelectric actuator when the piezoelectric actuator is activated.
Referring to
Thus, formation of sidewall protective film on the piezoelectric actuator contradicts to the improvement of driving performance of the piezoelectric actuator, and it has been difficult to arbitrate these two contradictory requirements by using a low cost construction.
Referring to
As shown in the longitudinal cross-sectional view of
Further, a lead wire 23A of a temperature-resistant metal such as Au is bonded to the electrode pad 22A, while a similar lead wire 23B is bonded to the electrode pad 22B.
Typically, the piezoelectric actuator body 20A includes a piezoelectric lamination body 20B having a rectangular parallelepiped shape with a length of 1 mm, width of 0.25 mm and height of 0.25 mm, wherein the piezoelectric lamination body 20B is formed by laminating the piezoelectric substance 20a-20e and electrode patterns 21A-21D alternately as can be seen in the end view of
The piezoelectric substance 20C is formed by a coating process such as dip-coating process and is formed to have a thickness of 25 μm or less, preferably 10 μm or less, typically 2-3 μm. In view of obtaining excellent adherence to the lamination body 20B, it is preferable that the piezoelectric substance 20C has a crystal structure and a composition identical to those of the piezoelectric substance 20a-20e constituting the piezoelectric lamination body 20B. However, it is also possible that the piezoelectric substance 20C has a different composition.
In the case of forming the piezoelectric substance 20C to have a different composition, it is preferable that the piezoelectric substance 20C has a crystal structure identical to that of the piezoelectric substance 20a-20e, such as a perovskite structure.
Because the piezoelectric substance 20C is formed by a dip-coating process, it is easy to form the piezoelectric substance 20C to have a thickness of 25 μm or less. Preferably the piezoelectric substance 20C is formed to have a thickness of 10 μm or less, more preferably 2-3 μm, as noted previously.
As a result, the decrease of magnitude of displacement of the piezoelectric actuator is held minimum, even when there is caused the problem of decrease of displacement of the piezoelectric actuator because of formation of the piezoelectric substance 20C around the lamination body 20B of the piezoelectric actuator 20.
In
Further, in the case the piezoelectric substance 20C is formed with the thickness of 10 μm, it can be seen that a displacement exceeding 700 nm is attained. Further, in the case the piezoelectric substance 20C is formed with the thickness of 2-3 μm, a displacement of about 800 nm is attained, while it should be noted that this amount of displacement is quite close to the displacement attained in the case the piezoelectric substance 20C is not provided around the piezoelectric lamination body 20B in view of the relationship of
On the other hand, when the thickness of the piezoelectric substance 20C is reduced further and the layer thickness falls below 1 μm, there is a concern that sufficient insulation resistance may not be secured. Thus, there is a need of forming the piezoelectric substance 20C to have a thickness of 1 μm or more.
Here, it should be noted that the relationship of
Next, manufacturing process of the piezoelectric actuator 20 of
Referring to
The green sheets thus formed with the electrode patterns are then laminated and, after conducting a degreasing process, the resultant green laminate is subjected to a baking and crystallizing process. With this, a baked piezoelectric substrate is obtained such that the substrate includes therein the piezoelectric actuator elements in the state aligned in rows and columns.
Next, in the step of
Further, in the step of
Further, in the step of
After the step of
During such a crystallizing process, there can be a case in which volatile metal such as Pb in the piezoelectric material film 20C causes vaporization, and thus, there are cases in which the composition of the piezoelectric substance 20C does not coincide with the composition of the piezoelectric substance 20a-20e constituting the lamination body 20B, even when the liquid source 50 is prepared to provide the piezoelectric substance 20C with the composition identical to those of the piezoelectric substance 20a-20e.
Thus, in order to form the piezoelectric substance 20C with the composition as close to the composition of the piezoelectric substance 20a-20e, there are cases to increase the concentration of the volatile metal element such as Pb in the metal organic liquid source 50 beyond the nominal composition value corresponding to the composition of the piezoelectric substance 20C.
In the experiment of
In the experiment of
The experiment was conducted by applying a pulse voltage of 1 kH frequency with a peak-to-peak voltage of about 60V while holding the piezoelectric actuator in the ambient of 80° C. and humidity of 80%.
Further, with the experiment of
Referring to
In the case the piezoelectric substance 20C is provided by a PZT substance of the thickness of 2-3 μm (PZT-1, PZT-2), on the other hand, it can be seen that the insulation resistance exceeding 10 GΩ is maintained even when the operation of the actuator is continued over 200 hours.
It should be noted that, because the piezoelectric substance 20C is formed with a thickness of 2-3 μm, there arises no problem explained with reference to
While the example of
While the present embodiment was explained for the example of using a perovskite material containing Pb for the piezoelectric substance 10a-20e and further for the piezoelectric substance 20C, the present invention is not limited to such a specific piezoelectric material, and thus, it is also possible to use other piezoelectric materials. Further, the material of the electrodes 21A-21D is not limited to Pt but it is also possible to use other temperature-resistant metals such as a Pt—Rh alloy or a Pt—Ru alloy. Further, the electrode pads 22A and 22B or the lead wires 23A or 23B are not limited to Au.
Referring to
Further, there is provided a head slider 33 of a ceramic material and carrying a magnetic head is attached over the piezoelectric actuators 32A and 32B also by an adhesive so as to bridge the piezoelectric elements 32A and 32B.
With the magnetic disk apparatus that uses such a magnetic head assembly 30, degradation of insulation resistance of the piezoelectric actuator is suppressed even when the magnetic disk is operated under a high temperature and humid ambient, and stable and reliable operation is guaranteed.
Referring to
With the magnetic recording apparatus 105 of such a construction, the electrodes of the piezoelectric actuators are protected by a thin protective substance of a piezoelectric ceramic material not resisting the operation of the piezoelectric actuator on the sidewall surfaces thereof, and high reliability is attained even when the magnetic recording apparatus is operated in a high temperature and humid ambient.
While the present invention has been explained for preferred embodiments, the present invention is not limited to such specific embodiments but various variations and modifications may be made without departing from the scope of the invention.
Number | Date | Country | Kind |
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2006-172829 | Jun 2006 | JP | national |
Number | Date | Country | |
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Parent | 11541557 | Oct 2006 | US |
Child | 12458493 | US |