JP2007134561A - Method for forming multilayer piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve reliability of a multilayer piezoelectric element by eliminating a stretch (burr) of a metallic layer occurring on a part of an internal electrode layer on a cut surface when cutting the multilayer piezoelectric element from a baked block. <P>SOLUTION: The multilayer piezoelectric element is formed under a condition of T1<T2 where T1 is a temperature for first heat treatment (baking) by stacking a plurality of piezoelectric ceramic sheets having an internal electrode layer formed, and T2 is a temperature for second heat treatment (baking) after the multilayer piezoelectric element is prepared by cutting it from the baked block. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a highly reliable multilayer piezoelectric element, and in particular, in a multilayer piezoelectric element manufacturing process, a piezoelectric ceramic sintered body having an internal electrode layer is cut to form individual piezoelectric elements. The present invention relates to a method for effectively suppressing the occurrence of defects such as occurrence of burrs in which internal electrode layers extend vertically on a cut surface, resulting in short-circuiting between internal electrodes.

  In recent years, information devices have been miniaturized and refined, and there has been an increasing demand for high reliability of piezoelectric elements used in small actuators capable of controlling a minute moving distance with high accuracy. For example, the capacity of magnetic disk devices has been increasing year by year, and since it is necessary to reduce the track width of the disk, it is required to control the position of the magnetic disk head in the track direction with high reproducibility and high accuracy. High reliability of a small piezoelectric element used for a head actuator is indispensable.

Such a piezoelectric element, in particular, a small-sized and highly drivable multilayer (or multi-layer) piezoelectric element has heretofore been manufactured by a manufacturing process using a flow as shown in FIG. (For example, the conventional method shown by patent document 1.)
That is, first, a piezoelectric ceramic powder, a binder, and a solvent are mixed to create a slurry, which is formed into a sheet to form a piezoelectric ceramic sheet. An internal electrode layer is formed on one surface of the piezoelectric ceramic sheet by screen printing using a paste containing a conductive metal. After the required number of sheets are laminated, the sheets are multilayered, pressed and pressure-bonded, debindered, and then fired at a high temperature of, for example, about 1200 ° C. to obtain a fired body of the sheet. Next, the fired body is divided into blocks of a desired size using, for example, a dicing saw, and driving electrodes are formed on the opposite side surfaces where the internal electrode layer is exposed among the divided side surfaces. Thereafter, the block is cut and separated into a required multilayer piezoelectric element in which piezoelectric ceramics and internal electrode layers are alternately stacked on comb teeth. Thereafter, the lead was attached to the external electrode in a form according to the application and the exterior was applied to complete the actuator piezoelectric element. That is, in many of the conventional methods, a ceramic element is laminated and then fired once to form a piezoelectric element.

  On the other hand, in Patent Document 1 described above, the firing temperature after lamination is 1120 ° C. (2 hours), cut into piezoelectric elements, and then subjected to heat treatment at 300 to 500 ° C. (10 minutes), whereby lubricating oil and cleaning liquid As a result of the decomposition and the release of residual stress, the insulation failure of the glass insulator introduced during the process is improved.

Further, in Patent Document 2, the firing temperature after lamination is performed at about 1200 ° C. (several hours), cut out into a piezoelectric element, and then subjected to heat treatment at 800 ° C. (2 hours). It is said that microcracks can be repaired.
Japanese Patent Laid-Open No. 04-179285 JP-A-6-252469

  FIG. 7 (7-1) shows a schematic diagram of a typical multilayer piezoelectric element. The multilayer piezoelectric element 100 includes a first internal electrode layer 103 that is laminated in multiple layers as shown in the figure and connected to a driving electrode 102 (also formed on the opposing surface), and is not shown in the figure. The internal electrode layer and the piezoelectric ceramic are alternately crossed in a comb-like shape by the second internal electrode layer 104 connected to the drive electrode on the other side facing the drive electrode 102, and the two internal electrodes The intersecting portion of the electrode layers becomes an active portion 105 where the piezoelectric driving force is activated. In the case of the illustrated multilayer piezoelectric element 100, the active part 105 is composed of four layers.

  FIG. 7 (7-2) shows a part A in the diagram of (7-1) in the multilayer piezoelectric element manufactured by the above-described conventional method (method of firing only the multilayer ceramic sheet), that is, the multilayer piezoelectric element 100. It is a figure when the side surface of this active part 105, ie, the cut surface of the active part 105 when it cuts out from a block with a dicing saw, is observed with a microscope (SEM: secondary electron microscope). In the figure, the layer of the piezoelectric ceramic 101, the first internal electrode layer 103, and the second internal electrode layer 104 are observed. In the piezoelectric element shown in this figure, the thickness of the piezoelectric ceramic layer 101 obtained by firing the piezoelectric ceramic powder is about 35 μm, and the thickness of each internal electrode layer using a paste made of Pt (platinum) as the metal material is about 2 μm. It is. A multilayer piezoelectric element having such a thin layer is used to realize a required displacement amount, dimensional restriction, etc., for example, in an actuator for a head of a large-capacity magnetic disk device.

  As shown by part B in FIG. 7 (7-2), it can be seen that the vertical extension (burr) of the electrode layer of about 5 μm occurs in the second internal electrode layer 104 here. . This phenomenon occurs regardless of the first internal electrode layer 103 and the second internal electrode layer 104, and the length of the burr varies, but it is observed that the length reaches from ˜5 μm to beyond.

  The cause of this burr generation is that when the block is cut with a dicing saw, the internal electrode layer, which is a metal layer, is cut so that it is shredded, so that burr is generated outside the metal layer, or the cut It is considered that due to the melting of the metal layer due to the frictional heat at that time, the metal spreads above and below the original metal layer thickness at the cut surface, and burrs are generated.

  Such relatively long burrs generated in the internal electrode layer work to narrow the interval between the internal electrodes, and cause a short circuit between the internal electrodes in a piezoelectric element having a thin ceramic layer. .

  Therefore, an object of the present invention is to effectively suppress the occurrence of vertical elongation (burrs) of the electrode layer at such a cut surface, particularly in a multilayer piezoelectric element formed by laminating thin layers. An object of the present invention is to provide a method for forming a highly reliable piezoelectric element.

  An object of the present invention is to form a sheet laminate in which a plurality of piezoelectric ceramic sheets each having an internal electrode layer formed on one surface are laminated, and to heat-treat the sheet laminate to form a sheet fired body. 1 heat treatment step, dividing the sheet fired body to cut out the block fired body, separating it into multilayer piezoelectric elements, and a second heat treatment step for heat treating the multilayer piezoelectric element, The heat treatment temperature in the heat treatment step can be achieved by the multilayer piezoelectric element forming method, wherein the heat treatment temperature is lower than the heat treatment temperature in the second heat treatment step.

  The heat treatment temperature in the first heat treatment step is a temperature not exceeding the densification temperature of the piezoelectric ceramic, and the heat treatment temperature in the second heat treatment step is a temperature exceeding the densification temperature of the piezoelectric ceramic. It is characterized by that.

  The piezoelectric ceramic is composed of PNN (lead nickel niobate), PT (lead titanate), and PZ (lead zirconate) components.

  The heat treatment temperature in the first heat treatment step is in a range of 900 to 1000 ° C., and the heat treatment temperature in the second heat treatment step is in a range of 1150 to 1250 ° C.

  The piezoelectric ceramic is composed of PNN (lead nickel niobate), PT (lead titanate), and PZ (lead zirconate).

  By the method of the present invention, the occurrence of vertical elongation (burrs) from the internal electrode layer on the cut surface of the multilayer piezoelectric element cut out by a dicing saw or the like is suppressed. This makes it possible to reduce obstacles such as a short circuit between internal electrodes in a multilayer piezoelectric element formed by laminating thin piezoelectric ceramic layers in particular, and a highly reliable multilayer piezoelectric element can be manufactured. .

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

(Embodiment)
1 to 3 are process schematic diagrams for forming a multilayer piezoelectric element used to describe an embodiment of the present invention. In this example, first, PNN (lead nickel niobate), PT (lead titanate) and PZ (lead zirconate) powders are used as the piezoelectric ceramic powder, and the molar ratio is, for example, 0.5 PNN. : 0.35PT: 0.15PZ. This is mixed with a predetermined amount of an organic binder, for example, PVB (polyvinyl butyral) to form a slurry, and by a doctor blade method, as shown in FIG. A ceramic sheet 1 (green sheet) is obtained.

  On this piezoelectric ceramic sheet 1, an internal electrode pattern having a film thickness of about 5 μm is applied by a screen printing method using a Pt (platinum) paste containing 20% by volume of the PNN-PT-PZ powder. Then, as shown in FIG. 1 (1-2), the required number of piezoelectric ceramic sheets 1 coated with the internal electrodes 2 are prepared, laminated, pressed, and pressure-bonded. ), A sheet laminate 3 is produced.

  Next, the sheet laminate 3 is held in an electric furnace at 500 ° C. in an atmosphere in the air, and after performing binder removal, this is performed in an atmosphere in the atmosphere, an electric furnace at 900 ° C. A first heat treatment (firing) is performed for about 3 hours to produce a sheet fired body 4 shown in FIG. And this is divided | segmented into a block in a predetermined direction using a dicing saw, and the block baking body 5 is produced as shown to FIG. 2 (2-2).

  Next, driving electrodes made of Pt (platinum) are formed on both exposed side surfaces where the internal electrode layer is exposed on the opposite side surfaces of the block fired body 5. This is shown in FIG. 2 (2-3). (A) of the figure is a top view and (b) is a side view. As can be seen from these drawings, the drive electrode 6 is formed on the block fired body 5. (B) As can be seen from the side view, the driving electrode 6 is formed on the exposed side surface of the internal electrode 2 (the same applies to the opposite side surface).

  Next, as shown in FIG. 3 (3-1), the block fired body 5 on which the driving electrode 6 is formed is cut into a predetermined size in a predetermined direction using a dicing saw, and the piezoelectric ceramic layer and the internal The multilayer piezoelectric element 7 having a structure in which the electrode layers are alternately stacked in a comb shape is cut out. As shown in the drawing, driving electrodes 6 are formed on the side surfaces of the multilayer piezoelectric element 7 (the same is true for the opposite side surfaces not shown). Further, the multilayer piezoelectric element 7 is subjected to a second heat treatment (firing) for about 3 hours in an electric atmosphere at 1150 ° C. in order to carry out the firing treatment again. As shown in FIG. 2, the second heat-treated multilayer piezoelectric element 8 according to the present invention is produced.

  The multilayer piezoelectric element thus fabricated had a ceramic layer thickness of about 35 μm and an internal electrode layer thickness of about 2 μm. Of course, these thicknesses can be appropriately controlled by the thickness of the piezoelectric ceramic sheet 1 (green sheet) and the thickness of the paste during screen printing.

The above embodiment is shown as a process flow in FIG. As apparent from the process flow of the conventional method of FIG. 6, the heat treatment (firing) is performed twice, and the first heat treatment temperature T1 is higher than the heat treatment temperature T2 of the second heat treatment (firing temperature). )
The cut surface of the multilayer piezoelectric element according to the present embodiment and the conventional multilayer piezoelectric element formed under the same conditions except for one heat treatment (lamination in the air at 1150 ° C. for 3 hours after lamination pressing) as in the past. A comparison with the cut surface is shown in FIG.

  FIG. 5 (5-1) is a view of the cut surface of the piezoelectric element obtained by the conventional one-time heat treatment process when observed with a microscope (SEM). The first internal electrode layer 11 is sandwiched by sandwiching the piezoelectric ceramic layer 10. The second internal electrode layer 12 is formed, and in each internal electrode layer, the vertical extension (burr) of the internal electrode layer of about 5 μm or more is observed. On the other hand, FIG. 5 (5-2) is a view when the cut surface of the piezoelectric element by the two heat treatments according to the present invention is observed with a microscope (SEM). As can be seen from the above, the first internal electrode layer 14 and the second internal electrode layer 15 are formed with the piezoelectric ceramic layer 13 interposed therebetween, but almost no burrs are observed in any of the internal electrode layers. Thus, it was possible to form a multilayer piezoelectric element in which the generation of burrs was remarkably suppressed (the maximum was 2 μm or less).

  In this embodiment, the first heat treatment temperature is 900 ° C. and the second heat treatment temperature is 1150 ° C., but the first heat treatment temperature is changed in the range of 900 to 1000 ° C. and the second heat treatment temperature is 1150 ° C. It was confirmed that the same effect was obtained even when the temperature range was changed to 1250 ° C.

  Thus, by setting the first heat treatment temperature to a relatively low temperature within the above range, the piezoelectric ceramic has not been sufficiently densified, and the internal electrode layer variability generated during cutting has not been achieved. However, by performing the subsequent second heat treatment at a higher temperature, it is considered that the burr also shrinks when the piezoelectric ceramic and the internal electrode layer are sufficiently densified.

  In Patent Documents 1 and 2 described above, both heat treatments are performed (the device is subjected to heat treatment after separation). However, both of the piezoelectric ceramic layers are sufficiently dense at high temperatures first. The heat treatment (firing) is performed, and the heat treatment is performed at a temperature lower than the first heat treatment after the element is separated. For this reason, the suppression effect with respect to the generation | occurrence | production of the burr | flash which becomes a problem with the multilayer piezoelectric element by the thin lamination especially obtained by this invention is not acquired.

  Further, in the examples, the volume ratio of 0.5PNN: 0.35PT: 0.15PZ was used as the composition of the piezoelectric ceramic powder, but the composition ratio is not limited to this, and the composition ratio is changed as appropriate. Thus, a piezoelectric element having a required piezoelectric effect can be formed.

  The piezoelectric ceramic material has been described using a mixed powder of PNN-PT-PZ in the embodiments, but is not limited thereto. For example, lead nickel niobate, lead titanate, lead zirconate, lead magnesium niobate, lead zinc niobate, lead manganese niobate, lead antimony stannate, lead manganese tungstate, lead cobalt niobate, barium titanate, titanium Examples thereof include ceramics containing sodium bismuth oxide, potassium sodium niobate, strontium bismuth tantalate, etc. alone or as a mixture. Depending on these materials, the same effects as in the embodiment can be obtained by appropriately selecting the first heat treatment temperature and the second heat treatment temperature by the method of the present invention.

  In the examples, a metal conductor (Pt) paste containing 20% by volume of powder having the same composition as the piezoelectric ceramic was used as the internal electrode paste. Mixing the powder having the same composition as the piezoelectric ceramic in this way is an effective method for improving the adhesion between the piezoelectric ceramic layer and the internal electrode layer. Further, the mixing ratio is not limited to 20% by volume, but is preferably 5% by volume or more and 50% or less and 10 to 30% by volume, whereby a required resistance value can be appropriately obtained.

  Further, in this embodiment, as the driving electrode, in the manufacturing process of this embodiment, the driving electrode is formed on the block fired body, and then divided into piezoelectric elements and subjected to heat treatment again. Pt is used as a representative material that can withstand temperature, but is not limited thereto. Further, if a step of forming the driving electrode after dividing the piezoelectric element is employed, a material having a lower heat-resistant temperature can be applied.

  The following supplementary notes are further disclosed with respect to the embodiments including the above examples.

(Appendix 1)
Forming a sheet laminate in which a plurality of piezoelectric ceramic sheets having an internal electrode layer formed on one surface are laminated;
A first heat treatment step of heat-treating the sheet laminate to form a sheet fired body;
Dividing the sheet fired body to cut out the block fired body and separating it into multilayer piezoelectric elements;
A second heat treatment step of heat treating the multilayer piezoelectric element,
The method of forming a multilayer piezoelectric element, wherein a heat treatment temperature in the first heat treatment step is lower than a heat treatment temperature in the second heat treatment step.

(Appendix 2)
The heat treatment temperature of the first heat treatment step is a temperature that does not exceed the densification temperature of the piezoelectric ceramic, and the heat treatment temperature of the second heat treatment step is a temperature that exceeds the densification temperature of the piezoelectric ceramic. The method for forming a multilayer piezoelectric element according to Supplementary Note 1, wherein

(Appendix 3)
The method for forming a multilayer piezoelectric element according to appendix 1 or 2, wherein the piezoelectric ceramic is composed of components of PNN (lead nickel niobate), PT (lead titanate) and PZ (lead zirconate).

(Appendix 4)
The heat treatment temperature of the first heat treatment step is in a range of 900 to 1000 ° C., and the heat treatment temperature of the second heat treatment step is in a range of 1150 to 1250 ° C. The formation method of the multilayer piezoelectric element of description.

(Appendix 5)
The internal electrode layer is formed using a metal conductor paste containing a powder having the same composition as that of the piezoelectric ceramic and containing 5 to 50 volume percent, preferably 10 to 30 volume percent. The method for forming a multilayer piezoelectric element according to appendix 1 or 3.

(Appendix 6)
The method for forming a multilayer piezoelectric element according to appendix 5, wherein the metal conductor is Pt (platinum).

(Appendix 7)
The molar ratio of each component of PNN (lead nickel niobate), PT (lead titanate) and PZ (lead zirconate) in the piezoelectric ceramic is 0.5: 0.35: 0.15 in order. The method for forming a multilayer piezoelectric element according to Supplementary Note 3, wherein

Process schematic diagram for forming the multilayer piezoelectric element of the present invention (part 1) Process schematic diagram for forming the multilayer piezoelectric element of the present invention (part 2) Process schematic diagram for forming the multilayer piezoelectric element of the present invention (part 3) Manufacturing process flow of the method of the present invention for forming a multilayer piezoelectric element The figure for demonstrating the effect of this invention Manufacturing process flow of a conventional method for forming a multilayer piezoelectric element The figure explaining the burr | flash which arises in the cut surface of the multilayer piezoelectric element by the conventional method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic sheet 2 Internal electrode 3 Sheet laminated body 4 Sheet fired body 5 Block fired body 6, 102 Drive electrode 7 Multilayer piezoelectric element (before 2nd heat processing)
8 Multi-layer piezoelectric element (after second heat treatment)
10, 13, 101 Piezoelectric ceramic layer 11, 14, 103 First internal electrode layer 12, 15, 104 Second internal electrode layer 100 Multilayer piezoelectric element 105 Active part

Claims (5)

Forming a sheet laminate in which a plurality of piezoelectric ceramic sheets having an internal electrode layer formed on one surface are laminated;
A first heat treatment step of heat-treating the sheet laminate to form a sheet fired body;
Dividing the sheet fired body to cut out the block fired body and separating it into multilayer piezoelectric elements;
A second heat treatment step of heat treating the multilayer piezoelectric element,
The method of forming a multilayer piezoelectric element, wherein a heat treatment temperature in the first heat treatment step is lower than a heat treatment temperature in the second heat treatment step.   The heat treatment temperature of the first heat treatment step is a temperature that does not exceed the densification temperature of the piezoelectric ceramic, and the heat treatment temperature of the second heat treatment step is a temperature that exceeds the densification temperature of the piezoelectric ceramic. The method for forming a multilayer piezoelectric element according to claim 1, wherein:   3. The method of forming a multilayer piezoelectric element according to claim 1, wherein the piezoelectric ceramic is composed of components of PNN (lead nickel niobate), PT (lead titanate), and PZ (lead zirconate).   The heat treatment temperature of the first heat treatment step is in a range of 900 to 1000 ° C, and the heat treatment temperature of the second heat treatment step is in a range of 1150 to 1250 ° C. A method for forming a multilayer piezoelectric element as described in 1.   The internal electrode layer is formed using a metal conductor paste containing a powder having the same composition as that of the piezoelectric ceramic and containing 5 to 50 volume percent, preferably 10 to 30 volume percent. A method for forming a multilayer piezoelectric element according to claim 1 or 3.

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