JP2011222792A - Method of manufacturing laminated piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a compact laminated piezoelectric actuator capable of obtaining a larger amount of displacement compared with a conventional one.SOLUTION: Slurry manufactured by mixing ceramic powder and organic solvent is formed into a film having a predetermined thickness to manufacture a green sheet. An internal electrode layer is printed on the green sheet and the desired number of the green sheet is laminated and then pressure-bonded by a heat press or the like to manufacture a plate laminated body in which piezoelectric ceramic layers and the internal electrode layers are alternately laminated. The laminated body is sintered after a debinder process and the sintered flat laminated body is then cut in one direction so as to form a plurality of rectangular and rod-shaped laminated bodies, each having a cut surface perpendicular to its laminating direction. A side electrode is then formed on a side having the cut surface. A voltage is then applied between both side electrodes to perform first polarization processing. Thereafter, the rectangular and rod-shaped laminated body is cut perpendicularly to the length direction thereof to obtain a discrete laminated body having a rectangular shape. Finally, a lead wire is soldered thereon and a voltage is applied to the lead wire to perform second polarization processing.

Description

  The present invention relates to a method for manufacturing a laminated piezoelectric actuator produced by alternately laminating piezoelectric ceramic layers and internal electrode layers, and more particularly to a method for producing a laminated piezoelectric actuator suitable for manufacturing a small-sized laminated piezoelectric actuator.

  Piezoelectric actuators are characterized by high positioning accuracy and large generated force. In particular, laminated piezoelectric actuators produced by alternately laminating piezoelectric ceramic layers and internal electrode layers and firing them integrally are the fine features of semiconductor manufacturing equipment. It is used in many fields, including positioning mechanisms. In recent years, applications have also been developed for a camera-shake prevention mechanism of a digital still camera (DSC) and an autofocus (AF) of a camera unit of a mobile phone, and accordingly, downsizing of the shape has been remarkably advanced. For example, the shape that was about 10 mm x 10 mm x 40 mm for precision positioning applications of semiconductor manufacturing equipment becomes about 2 mm x 2 mm x 5 mm for DSC applications, and small to about 1 mm x 1 mm x 1.5 mm for AF applications for mobile phones. Is progressing.

  The configuration of the laminated piezoelectric actuator is described in Patent Document 1 and the like, and a typical configuration is shown in FIG. As shown in FIG. 4, a rectangular parallelepiped laminated piezoelectric actuator having a height T, width W1, and W2 in the laminating direction, which is produced by alternately laminating piezoelectric ceramic layers 1 and internal electrode layers 2 and firing them integrally. 10, every other internal electrode layer 2 is exposed to the surface of two side surfaces having a width W2 facing each other, side electrode 3 is installed on the side surface, and a part of side electrode 3 is soldered by solder 5. The lead wire 4 is connected and fixed. A voltage is applied to each piezoelectric ceramic layer 1 sandwiched between the internal electrode layers 2 by applying an external drive signal between the opposing side electrodes through a lead wire 4. Since the internal electrode layer 2 does not exist in the entire width direction of the width W1 and the portion sandwiched between the internal electrode layers 2 remains inside, it is called a partial electrode structure.

  FIG. 5 is a diagram showing an example of a conventional general manufacturing process of a laminated piezoelectric actuator. First, a slurry 12 in which a ceramic powder 11 and an organic solvent are mixed is formed to a predetermined thickness to produce a green sheet 13, and then an internal electrode layer is printed, and the required number of layers is laminated and then subjected to pressure bonding with a hot press or the like to thereby produce piezoelectric ceramic A flat laminate 14 in which layers and internal electrode layers are alternately laminated is produced. Through a binder removal process for removing unnecessary organic components, the flat laminate 14 is sintered at around 1000 ° C. Thereafter, the sintered plate-like laminate is cut in one direction so as to form a plurality of rectangular rod-like laminates 15 having cut surfaces perpendicular to the stacking direction, and side electrodes are formed on the side surfaces that are the cut surfaces. Provide. Here, the side electrodes of the two cut surfaces facing each other of the rectangular bar-shaped laminate 15 are electrically connected to the internal electrode layer every other layer and are insulated from each other. Further, after applying a resist to the side electrode surface in order to prevent the spread of solder in a portion to be soldered later, the rectangular bar-shaped laminated body 15 is cut again perpendicularly in the length direction to form a rectangular parallelepiped laminated product having a product size. A body 16 is obtained. Finally, after being soldered to the lead wire, a polarization treatment is performed by applying a voltage to the lead wire to complete a laminated piezoelectric actuator.

JP 2004-296585 A

  Conventionally, one of the problems in manufacturing a small laminated piezoelectric actuator having a height of less than 2 mm is a deterioration in characteristics when an external terminal such as a lead wire is connected by soldering. FIG. 6 is a schematic diagram showing the internal state when the piezoelectric ceramic is polarized. As shown in FIG. 6, the polarization is a phenomenon in which a direct current electric field is applied to the piezoelectric ceramic to cause distortion in the crystal lattice, and positive and negative charge centers in the crystal lattice are separated to develop piezoelectricity. If a solder having a high rigidity equivalent to that of the layer is preliminarily present on the surface of the laminated body, generation of distortion due to polarization is suppressed in the portion directly under the solder, and as a result, the piezoelectric characteristics of the portion are deteriorated. FIG. 7 is a diagram schematically showing a state in which the displacement amount of the laminated piezoelectric actuator is reduced by restraint by solder. Compared to the case where the solder is not present on the side surface, when the solder 5 is present on the side surface, there is a restraint due to the solder, and because the distortion and deformation in that part are different, the finally obtained characteristics are different, In particular, the amount of displacement is reduced.

  In addition, the thickness per layer of the piezoelectric ceramic layer (hereinafter referred to as the interlayer) has been reduced with downsizing, and the reduction in relative permittivity, which is the main factor that determines the piezoelectric characteristics, has become significant due to the reduction in thickness. It is also known to appear, and the cause is presumed to be the effect of the internal stress of the laminate. FIG. 8 is a diagram showing the result of comparing the relative permittivity when the firing temperature is changed in the case of forming a 50-layer laminate with 38 μm and 20 μm per layer. Although it is influenced by the firing temperature, it is shown that the relative permittivity changes greatly when the layers are different. FIG. 9 is a diagram showing the result of measuring the relative permittivity when the laminate is configured by further changing the interlayer. However, when the interlayer is 1000 μm, it indicates the relative dielectric constant of the bulk piezoelectric ceramic, not the laminate. FIG. 9 shows that the relative permittivity is greatly affected by the interlayer, and the relative permittivity tends to decrease greatly as the film thickness is reduced.

  Accordingly, an object of the present invention is to provide a method of manufacturing a laminated piezoelectric actuator that can obtain a larger displacement than a conventional one in a small shape.

  In order to solve the above-mentioned problems, a method for manufacturing a laminated piezoelectric actuator of the present invention includes a step of alternately laminating piezoelectric ceramic layers and internal electrode layers to produce a flat laminate, and sintering the laminate. A step of cutting the sintered plate-like laminate to produce a plurality of rectangular rod-like laminates having a cut surface perpendicular to the lamination direction, and the rectangular rod-like laminates facing each other. A step of forming side electrodes that are electrically connected to the internal electrode layer every other layer on two cut surfaces and insulated from each other; and a plurality of rectangular parallelepiped shapes by cutting the rectangular bar-shaped laminated body perpendicularly in the length direction. In the method of manufacturing a laminated piezoelectric actuator, including a step of manufacturing a laminated body having a step, and a step of connecting a lead terminal to a part of the side electrode of the laminated body having the rectangular parallelepiped shape by soldering. A first polarization treatment step of applying a voltage to a side electrode of the body to perform polarization, and a second polarization treatment step of applying a voltage to the lead terminal of the laminate having the rectangular parallelepiped shape to perform polarization. It is characterized by that.

  Furthermore, in the first polarization treatment step, polarization may be performed in a state where compressive stress is applied in the stacking direction. In this case, it is desirable that the compressive stress is 200 MPa or more.

  In addition, it is desirable that an electric field applied to the piezoelectric ceramic layer in the first polarization treatment step is larger than an electric field applied to the piezoelectric ceramic layer in the second polarization treatment step. The electric field applied to the piezoelectric ceramic layer in the polarization treatment step may be 2000 V / mm or more, and the electric field applied to the piezoelectric ceramic layer in the second polarization treatment step may be 1000 to 1500 V / mm.

  In the present invention, when a rectangular parallelepiped small stacked piezoelectric actuator is connected to an external terminal by soldering, polarization is performed even before the solder is added. This process is simplified by collectively performing this polarization in the shape of an elongated rectangular bar to which a plurality of actuators are connected, and after being soldered after being cut into a rectangular parallelepiped shape, Perform polarization. Thereby, the deterioration of the piezoelectric characteristics due to the soldering to the side electrode as in the conventional case can be improved, and a larger displacement than in the conventional case can be obtained.

  In the present invention, in order to alleviate the internal strain of the laminate due to the thinning of the layers, the piezoelectric characteristics are further improved by performing polarization in a rectangular rod state with a compressive stress applied in the lamination direction. Can do.

  Furthermore, in the partial electrode structure, the inactive portion sandwiched between every other internal electrode layer is not polarized in the vicinity of the side electrode, so there is little distortion, and it is sandwiched between the internal electrode layers on both sides inside it. In consideration of the fact that the active portion to be polarized is in a state of large strain and the difference in internal stress between the two portions is large, the electric field during the first polarization treatment and during the second polarization treatment after being cut into pieces. By making these different, the occurrence of defects such as internal cracks can be prevented.

  As described above, according to the present invention, it is possible to obtain a method of manufacturing a laminated piezoelectric actuator that can obtain a larger displacement than a conventional one in a small shape.

The figure which shows the flowchart of the manufacturing process of 1st Embodiment of the manufacturing method of the laminated piezoelectric actuator by this invention. The perspective view which shows the direction of the compressive stress at the time of the 1st polarization process of a rectangular-bar-shaped laminated body. The figure which shows the measurement result of the relative dielectric constant of the magnitude | size of a compressive stress, and the obtained laminated piezoelectric actuator. The figure which shows the typical structure of a laminated piezoelectric actuator. The figure which shows an example of the conventional general manufacturing process of a laminated piezoelectric actuator. The schematic diagram of the inside state when polarizing a piezoelectric ceramic. The figure which shows typically a mode that the displacement amount of a laminated piezoelectric actuator reduces by restraint by solder. The figure which shows the result of having compared the dielectric constant at the time of comprising the laminated body of 50 layers by making interlayer 38 micrometers and 20 micrometers. The figure which shows the result of having measured the dielectric constant when a laminated body is comprised by changing the interlayer further greatly.

  Embodiments of the present invention will be described below.

  FIG. 1 is a view showing a flowchart of manufacturing steps of a first embodiment of a method for manufacturing a laminated piezoelectric actuator according to the present invention. The manufacturing method of this embodiment is similar to the conventional manufacturing method shown in FIG. 5, in which a slurry prepared by mixing ceramic powder and an organic solvent is formed into a predetermined thickness to form a green sheet, The electrode layer is printed, and the required number of sheets is laminated and then subjected to pressure bonding by hot pressing or the like, thereby producing a flat laminated body in which piezoelectric ceramic layers and internal electrode layers are alternately laminated. After the binder removal step, the laminated body is sintered, and the sintered flat plate-like laminated body is cut in one direction so as to form a plurality of rectangular bar-like laminated bodies having cut surfaces perpendicular to the lamination direction, and the cutting Side electrodes are formed on the side surfaces. In the present embodiment, after that, the first polarization treatment is performed by applying a voltage between both side electrodes. After that, as in the conventional case, a rectangular bar-shaped laminate is cut perpendicularly in the length direction to obtain a rectangular parallelepiped laminate, and finally a voltage is applied to the lead wire after soldering with the lead wire. Thus, the second polarization process is performed to complete the laminated piezoelectric actuator.

Example 1
A specific example of the manufacturing method of this embodiment will be described below. The outer dimensions of the finished product of the laminated piezoelectric actuator manufactured in this example are W1 = 0.8 mm, W2 = 0.8 mm, and T = 1.5 mm in FIG. 4, and an Ag—Pd alloy is used for the internal electrode layer. Used, the layer number is 20 μm and the number of layers is 60 layers. Production of a flat laminate is carried out by the conventional manufacturing method of FIG. 5 and firing thereof. After firing, the laminate is cut in parallel with a dicing saw at a pitch of 0.8 mm to obtain a rectangular rod-like laminate. Next, after providing side electrodes made of an Ag film on the cut surfaces on both sides by sputtering, a voltage is applied to the side electrodes to perform a first polarization treatment. Next, a rectangular parallelepiped laminate having the above-described shape is obtained by cutting again at a pitch of 0.8 mm in a direction perpendicular to the cut surface. Finally, a lead wire is soldered to a part of the side electrode, a voltage is applied to the lead wire, and the second polarization treatment is performed to complete the multilayer piezoelectric actuator manufactured according to the first embodiment.

  Here, in order to confirm the effect of the present embodiment, at the same time as the fabrication in the present embodiment, the conventional manufacturing method, that is, the first polarization process is not performed, but only the second polarization process is performed and completed. A laminated piezoelectric actuator of a comparative example was also produced. The conditions of the first polarization process of Example 1 and the second polarization process of Example 1 and the comparative example are both performed by applying DC 40 V for 1 minute, and the temperature during the polarization process is 150 ° C. Identical.

  Table 1 shows an example of electrical characteristics of the laminated piezoelectric actuator manufactured by the manufacturing methods of Example 1 and Comparative Example. In Example 1, the capacitance is increased by 7% compared to the comparative example, and accordingly, the displacement amount when 6 V is applied is increased by about 8%.

  As is generally known, the polarization characteristics of piezoelectric ceramics are almost reversible when an electric field exceeding the coercive electric field is applied, and the electrical characteristics such as capacitance finally obtained by multiple times of polarization treatments. It does not fluctuate. The difference between Example 1 and the comparative example is not that the polarization process is performed only twice, but the polarization distortion that is uniform in the state of the rectangular bar before the solder that suppresses the distortion due to polarization is provided. It is thought to be due to having given.

(Example 2)
Next, a second embodiment of the method for manufacturing a laminated piezoelectric actuator according to the present invention will be described. The manufacturing method of this example is the same as the manufacturing method of Example 1 except that in the first polarization treatment step, polarization is performed in a state where compressive stress is applied in the stacking direction of the rectangular bar-shaped stacked body. In addition to the effects of the first embodiment, the present embodiment aims to alleviate the internal strain of the laminate due to the thinning of the layers. FIG. 2 is a perspective view showing the direction of compressive stress during the first polarization treatment of the rectangular bar-shaped laminate 20. In this embodiment, compressive stress 21 in the stacking direction was applied.

  Specific examples and operational effects of the manufacturing method of this embodiment will be described below. The outer dimensions, the internal electrode layers, the layers, the number of layers, etc. of the finished product of the multilayered piezoelectric actuator manufactured in the second embodiment are the same as those in the first embodiment. The steps other than the first polarization treatment step are the same as in the first embodiment. As a factor for reducing the piezoelectric characteristics when the piezoelectric ceramic layer is thinned, it was possible to find the manufacturing method of the present embodiment by specifying the direction assuming the strain generated inside the ceramic after firing. Therefore, in Example 2, in order to confirm that the decrease in the dielectric constant is caused by stress strain, the direction and magnitude of the compressive stress is performed when the first polarization treatment is performed on the rectangular rod-shaped laminate. The change in capacitance, that is, the change in relative permittivity was measured while changing.

  The compressive stress was applied by sandwiching the laminated piezoelectric actuator between preload jigs. The capacitance of the completed multilayer piezoelectric actuator was measured with an LCR meter, and the relative dielectric constant was determined. The preload jig can change the pressure according to the rotation angle of the screw. As shown in FIG. 2, as a result of comparative measurement between the time of applying the compressive stress 21 in the stacking direction, that is, the d33 direction of the piezoelectric ceramic, and the time of applying the compressive stress 22 in the direction perpendicular to the stacking direction, that is, the d31 direction, In the case of the compressive stress 21, the relative permittivity increased as the pressure increased, but in the case of the compressive stress 22, the relative permittivity slightly decreased. This suggests that the compressive stress in the d31 direction and the tensile stress in the d33 direction are acting inside the piezoelectric ceramic layer of the laminated body after sintering, which influences the relative dielectric constant. It is.

  In this example, in order to increase the relative permittivity, the first polarization treatment was performed while applying the compressive stress 21, and the change in relative permittivity due to the magnitude of the compressive stress was measured. As in Example 1, both the first and second polarization treatments were performed by applying DC 40 V for 1 minute. FIG. 3 shows the measurement results of the magnitude of the compressive stress and the relative dielectric constant of the obtained multilayer piezoelectric actuator. It can be seen that the relative permittivity recovers greatly as the pressure is increased. It is presumed that by applying pressure, strain tends to be released during polarization, and the relative permittivity is thereby recovered. It can be seen that the relative dielectric constant tends to saturate when the magnitude of the compressive stress is 200 MPa or more.

(Example 3)
Next, a third embodiment of the method for manufacturing a laminated piezoelectric actuator according to the present invention will be described. In the manufacturing method of this example, the electric field applied to the piezoelectric ceramic layer in the first polarization treatment step is 2000 V / mm or more, and the electric field applied to the piezoelectric ceramic layer in the second polarization treatment step is 1000 to It is the same as that of the manufacturing method of Example 2 except setting it to 1500V / mm. In addition to the effects of the second embodiment, this embodiment prevents the occurrence of defects such as internal cracks in the vicinity of the side electrode due to the difference in internal stress between the non-polarized inactive portion and the polarized active portion. The purpose is to do.

  As described above, in a conventional laminated piezoelectric actuator having a partial electrode structure, a portion where one of the internal electrode layers does not reach the side electrode is generally referred to as an inactive portion, and is an active portion that is sandwiched and polarized by both inner poles. There is a tendency that a difference in polarization distortion easily occurs at the boundary between the two and, in some cases, due to internal stress due to the difference in distortion, the presence of minute cracks or the like causes a decrease in strength. The laminated piezoelectric actuator manufactured according to Examples 1 and 2 increases the piezoelectric characteristics further than the conventional manufacturing method and can increase the amount of displacement, so that it is sufficient for the internal stress at the boundary. Careful attention is required.

  Therefore, in this embodiment, the conditions of the first polarization process with the rectangular rod-shaped laminate and the second polarization process with the lead terminals connected by soldering are adjusted, and the strength of the multilayer piezoelectric actuator is maintained optimally. Conditions can be used.

  A specific example of the manufacturing method of this embodiment will be described below. The outer dimensions, the internal electrode layers, the layers, the number of layers, etc. of the finished product of the multilayered piezoelectric actuator produced in this Example 3 are the same as those in Example 2. The steps other than the first and second polarization treatment steps are the same as in the second embodiment. The conditions of the first polarization treatment in this example were performed by applying a direct current of 40 V for 1 minute as in the second example, with the magnitude of the compressive stress in the stacking direction being 200 MPa. However, the second polarization treatment was performed under four conditions of applied voltage.

  That is, in the second polarization treatment, the temperature and voltage application time during polarization are constant, and the coercive electric field of the piezoelectric ceramic material used in this example is 500 V / mm. Four voltage values were used: condition (1) for mm, condition (2) for 1000 V / mm, condition (3) for 1500 V / mm, and condition (4) for 2000 V / mm. The electrical characteristics and the bending strength of the actuator were measured for the completed laminated piezoelectric actuator produced under these four conditions.

  Table 2 shows measurement results of relative permittivity, capacitance, displacement amount when applying a voltage of 1 kHz, 6 Vpp, and bending strength as typical examples of electrical characteristics. Table 2 also shows the laminated piezoelectric actuator manufactured by the above-described comparative example, Example 1, and Example 2 when the compressive stress is 200 MPa. In the third embodiment, in the first polarization process to which no solder is added, a voltage of 40 V that is an electric field of 2000 V / mm is applied in order to saturate the polarization as much as possible at this stage. Depending on the magnitude of the electric field of the second polarization process in the state of the above, the values of the dielectric constant, capacitance, displacement, and bending strength are different. In Example 2 and condition (4) of Example 3 equivalent thereto, the electrostatic capacity and the displacement amount are maximum, but the bending strength is reduced. On the other hand, the condition (1) of Example 3 where the electric field in the second polarization treatment is the lowest is high in strength, but the displacement is small and the difference from the comparative example is small. When the target value of the displacement is 200 nm and the target value of the bending strength is 100 MPa, the conditions (2) and (3) of Example 3 satisfy both the above-mentioned targets and have a balanced characteristic.

  As described above, according to the method for manufacturing a laminated piezoelectric actuator of the present invention, even a small laminated piezoelectric actuator having a height of less than 2 mm can obtain a larger displacement than in the past.

  Needless to say, the present invention is not limited to the above-described embodiments and examples, and the design can be changed depending on the structure of the laminated piezoelectric actuator to be manufactured. For example, depending on the shape of the laminated piezoelectric actuator, the piezoelectric ceramic material used, the number of layers, the number of layers, the soldering conditions to the side electrodes, etc., the magnitude of the compressive stress and the magnitude of the electric field during the first and second polarization processes Can be optimized.

DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic layer 2 Internal electrode layer 3 Side electrode 4 Lead wire 5 Solder 10 Laminated piezoelectric actuator 11 Ceramic powder 12 Slurry 13 Green sheet 14 Flat laminated body 15, 20 Rectangular rod laminated body 16 Rectangular laminated body 21, 22 Compressive stress

Claims (5)

A step of alternately laminating piezoelectric ceramic layers and internal electrode layers to produce a flat laminate, a step of sintering the laminate, and cutting the sintered laminate in the stacking direction A step of producing a plurality of rectangular bar-shaped laminates having a vertical cut surface, and two conductive surfaces of the rectangular bar-shaped laminate opposite to each other are electrically connected to the internal electrode layer and insulated from each other. A step of forming a side electrode; a step of cutting the rectangular bar-shaped laminated body perpendicularly to a length direction to produce a laminated body having a plurality of rectangular parallelepiped shapes; and the side electrode of the laminated body having the rectangular parallelepiped shape. In a method for manufacturing a laminated piezoelectric actuator including a step of connecting a lead terminal by soldering to a part,
A first polarization treatment step in which a voltage is applied to a side electrode of the rectangular bar-shaped laminate and polarization is performed; and a second polarization in which a voltage is applied to the lead terminal of the laminate having the rectangular parallelepiped shape to perform polarization. A method of manufacturing a laminated piezoelectric actuator, comprising: a processing step.   2. The method for manufacturing a laminated piezoelectric actuator according to claim 1, wherein in the first polarization treatment step, polarization is performed in a state where compressive stress is applied in the lamination direction.   The method for manufacturing a laminated piezoelectric actuator according to claim 2, wherein the compressive stress is 200 MPa or more.   The electric field applied to the piezoelectric ceramic layer in the first polarization treatment step is larger than the electric field applied to the piezoelectric ceramic layer in the second polarization treatment step. A manufacturing method of the multilayer piezoelectric actuator according to claim 1.   The electric field applied to the piezoelectric ceramic layer in the first polarization treatment step is set to 2000 V / mm or more, and the electric field applied to the piezoelectric ceramic layer in the second polarization treatment step is set to 1000 to 1500 V / mm. The method for manufacturing a laminated piezoelectric actuator according to claim 4.

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