1. Field of the Invention
The present invention relates to a “laminate including a lower electrode, a dielectric layer, and an upper electrode,” which is formed on a support, and more particularly, to a laminate that includes a piezoelectric layer as a dielectric layer and functions as a piezoelectric/electrostrictive film type element.
2. Description of the Related Art
Hitherto, there has been widely known a piezoelectric/electrostrictive film type element that is a laminate including a plate-like lower electrode formed on a support, a piezoelectric layer that is a fired body formed on the lower electrode, and a plate-like upper electrode formed on the piezoelectric layer so as to be opposed in parallel to the lower electrode (see, for example, Japanese Patent Application Laid-open No. 2010-219153). Such a piezoelectric/electrostrictive film type element is widely used as, for example, a drive source of an ink jet head (part for ejecting, in an atomized manner, liquid stored inside a pressure chamber in the support) of an ink jet printer.
Japanese Patent Application Laid-open No. 2010-219153 discloses, referring to
By the way, as described above, when the sectional shape of the piezoelectric layer is a “trapezoid that expands toward the lower electrode side,” the ratio of the area of the upper electrode to the area of the lower electrode (when viewed from above) decreases. As a result, the ratio of the “area of a part of the piezoelectric layer, which is sandwiched between the upper and lower electrodes (that is, a part relating to the drive)” to the “area of the lower electrode” (when viewed from above) decreases. This fact leads to reduction in drive efficiency of the piezoelectric/electrostrictive film type element.
To address this problem, it is conceivable to form the sectional shape of the piezoelectric layer into, instead of a “trapezoid,” a “rectangle” (or a shape close to a rectangle, hereinafter called a “substantially rectangular shape”), that is, a shape in which the side surface of the piezoelectric layer extends upwardly and (substantially) perpendicularly from the upper surface of the lower electrode. With this, (when viewed from above,) “the ratio of the area of the upper electrode to the area of the lower electrode,” that is, “the ratio of the area of the part of the piezoelectric layer, which is sandwiched between the upper and lower electrodes (that is, the part relating to the drive) to the area of the lower electrode” can be increased. In this manner, the drive efficiency of the piezoelectric/electrostrictive film type element can be improved.
However, when the sectional shape of the piezoelectric layer is a “rectangle” as described above, as compared to the case where the sectional shape is a “trapezoid,” a distance between upper and lower ends of the side surface of the piezoelectric layer (that is, a distance between end portions of the opposing upper and lower electrodes) is reduced. As a result, when a voltage is applied between the upper and lower electrodes, a leak current that flows through the piezoelectric layer is easily generated. When a large amount of leak current flows, there may arise problems in that the drive efficiency of the piezoelectric/electrostrictive film type element decreases, etc.
The inventors of the present invention assume the following dielectric layer. A dielectric layer (piezoelectric layer) that is a fired body included in a laminate such as the above-mentioned piezoelectric/electrostrictive film type element is formed so that a “shape that is represented by a virtual line obtained by approximating a contour of a sectional shape in a thickness direction of the dielectric layer is a quadrilateral having a height of 0.5 μm or more and 15 μm or less and an angle at an end point of a base of 85° or more and 105° or less” (in other words, the sectional shape of the dielectric layer is a substantially rectangular shape having a height of 0.5 μm or more and 15 μm or less). Further, “the dielectric layer is formed of particles of a dielectric material, which each have an average particle diameter d of 0.5 μm or more and 10 μm or less.”
In this case, it is preferred that the length of the base of the rectangle be 30 μm or more and 500 μm or less. The quadrilateral may be a rectangle, a square, a trapezoid, or a parallelogram. Further, in a case where the shape of the laminate (piezoelectric/electrostrictive film type element) when viewed from above has a longitudinal direction, the sectional shape of the dielectric layer is a sectional shape in a “thickness direction of the dielectric layer” and a “direction perpendicular to the longitudinal direction.”
The inventors of the present invention have found that, in the laminate including the dielectric layer assumed as described above, the magnitude of the leak current is closely related to the surface roughness of the side surface of the dielectric layer. Specifically, the inventors of the present invention have found that, when the surface roughness of the side surface of the dielectric layer is 0.05 dμm or more at the maximum height roughness Rz, the leak current becomes significantly smaller as compared to a case with a different surface roughness (details are described later).
In addition, the inventors of the present invention have found that, when the surface roughness of the side surface of the dielectric layer is 0.5 dμm or less at the maximum height roughness Rz, as compared to a case with a different surface roughness, “particle shedding” (phenomenon that the particles forming the side surface fall from the side surface) from the side surface of the dielectric layer when a voltage is applied between the upper and lower electrodes (in particular, when the voltage is applied for a long period of time) is more significantly prevented (details are described later).
Based on the above-mentioned findings, the laminate according to one embodiment of the present invention has a feature in that the surface roughness of the side surface of the dielectric layer is 0.05 dμm or more and 0.5 dμm or less at the maximum height roughness Rz. With this, it is possible to prevent both of “generation of a leak current that flows through the dielectric layer” and “occurrence of ‘particle shedding’ from the side surface of the dielectric layer” when a voltage is applied between the upper and lower electrodes.
In the laminate according to one embodiment of the present invention, the dielectric layer is a piezoelectric layer that is a fired body formed of particles of a piezoelectric material. Therefore, when the laminate functions as a piezoelectric/electrostrictive film type element, it is preferred that the angle present at the end point of the base in the sectional shape of the piezoelectric layer be 90° or more and 105° or less.
In a case where the dielectric layer is a piezoelectric layer (therefore, in a case where the laminate is a piezoelectric/electrostrictive film type element), when a voltage is applied between the upper and lower electrodes at a predetermined pattern, the piezoelectric layer is driven, and as a result, the center portion of the piezoelectric/electrostrictive film type element (when viewed from above) is displaced in the up-down direction with respect to the peripheral edge portion (when viewed from above). The inventors of the present invention have found that, when the “angle” is 90° or more and 105° or less, as compared to the case where the “angle” is 85° or more and less than 90°, the level of the displacement (displacement amount) of the piezoelectric/electrostrictive film type element is significantly increased (details are described later).
Now, additional remarks are made of the dielectric layer (piezoelectric layer) of the laminate according to one embodiment of the present invention. The dielectric layer (piezoelectric layer) may be produced with use of a so-called “thin film method” such as sputtering and CVD, but is preferred to be produced with use of a so-called “thick film method” such as screen printing, spin coating, and tape casting. The “thick film method” as used herein refers to a method of forming a film of produced/synthesized powder (slurry) on a substrate, and firing the obtained compact to obtain a sintered film.
In order to set the average particle diameter of each of the particles of the dielectric material forming the dielectric layer to fall within the range of 0.5 μm to 10.0 μm, the dielectric layer is preferred to be produced with use of the so-called “thick film method.” When the dielectric layer is produced with use of the so-called “thin film method,” the average particle diameter of each of the particles becomes a value markedly smaller than values within this range.
Further, the entire region of the surface (except the side surface) of the dielectric layer (piezoelectric layer) of the laminate (piezoelectric/electrostrictive film type element) according to one embodiment of the present invention is a sintered surface formed of an aggregate of the plurality of particles of the dielectric material, which each have an average particle diameter of the above-mentioned range (surface formed by firing, surface that is not subjected to any additional processing after the firing). The side surface of the dielectric layer (piezoelectric layer) may be the sintered surface, or may be a surface (etched surface) that is formed (appears) by etching after the firing.
In the accompanying drawings:
(Configuration)
Now, the configuration of a piezoelectric/electrostrictive film type element according to an embodiment of the present invention is described with reference to the drawings. As illustrated in
As illustrated in
As illustrated in
The support S is a fired body made of an electrically insulating material (for example, zirconia (ZrO2)). At a position inside the support S corresponding to each of the piezoelectric/electrostrictive film type elements 10, a pressure chamber S1 is formed. On the lower side of the pressure chamber S1, an ejection nozzle S2 that communicates to the pressure chamber S1 and is opened on the lower side is formed. On the upper side of the pressure chamber S1, a vibration film S3 is formed. The vibration film S3 has a thin rectangular parallelepiped shape that extends in the longitudinal direction (y-axis direction) and has a thickness (z-axis direction) of 1 μm to 10 μm, a width (length in the x-axis direction) of 30 μm to 500 μm, and a length (y-axis direction) of 500 μm to 5,000 μm. Note that, the material for forming the support S is not limited to ceramics, and may be glass, a resin, or the like as long as the support S exhibits an electrically insulating property. Further, the material may be any one of single crystal, polycrystal, and amorphous.
The lower electrode 20 is a thin plate-like fired body made of an acid-resistant conductive material (for example, platinum (Pt)). Each of the lower electrodes 20 is formed on the upper surface of the corresponding vibration film S3 so that the entire lower electrode 20 is included in a range of the corresponding vibration film S3 when viewed from above. Each of the lower electrodes 20 has a thin rectangular parallelepiped shape that extends in the longitudinal direction (y-axis direction) and has a thickness (z-axis direction) of 0.1 μm to 10.0 μm, a width (length in the x-axis direction) of 30 μm to 500 μm, and a length (y-axis direction) of 500 μm to 5,000 μm. Note that, the material for forming the lower electrode 20 is not limited to a noble metal, and may be a conductive polymer, a conductive oxide, or the like as long as the lower electrode 20 exhibits an electrical conductivity.
The piezoelectric layer 30 is a fired body made of a polycrystalline piezoelectric material (for example, a lead zirconate titanate based material, in particular, lead zirconate titanate (PZT)). Each of the piezoelectric layers 30 is formed on the upper surface of the corresponding lower electrode 20 so that the entire piezoelectric layer 30 is included in a range of the corresponding lower electrode 20 when viewed from above. Each of the piezoelectric layers 30 has a thin plate shape that extends in the longitudinal direction (y-axis direction), and the reference cross-section thereof is a rectangle (alternatively, a shape close to a rectangle, hereinafter referred to as “substantially rectangular shape”). That is, the side surface of each of the piezoelectric layers 30 extends upwardly and (substantially) perpendicularly from the upper surface of the lower electrode 20. The piezoelectric layer 30 is described in detail later.
The upper electrode 40 is a thin plate-like fired body made of an acid-resistant conductive material (for example, gold (Au)). Each of the upper electrodes 40 is formed on the upper surface of the corresponding piezoelectric layer 30 so that the entire upper electrode 40 is included in a range of the corresponding piezoelectric layer 30 when viewed from above. Each of the upper electrodes 40 has a thin rectangular parallelepiped shape that extends in the longitudinal direction (y-axis direction) and has a thickness (z-axis direction) of 0.01 μm to 1.0 μm, a width (length in the x-axis direction) of 30 μm to 500 μm, and a length (y-axis direction) of 500 μm to 5,000 μm. Note that, the material for forming the upper electrode 40 is not limited to a noble metal, and may be a conductive polymer, a conductive oxide, or the like as long as the upper electrode 40 exhibits an electrical conductivity.
Now, the operation of the ink jet head illustrated in
(Manufacturing Method)
Next, a method of manufacturing the piezoelectric/electrostrictive film type element 10 described above is described with reference to
First, as illustrated in
Subsequently, as illustrated in
Next, as illustrated in
Subsequently, as illustrated in
Next, as illustrated in
Subsequently, as illustrated in
As the etchant, one that contains acid as the main component was used. For example, an etchant obtained by doping, into dilute hydrochloric acid having a concentration of 10%, a trace of ammonium fluoride, a thickener, a complexing agent, a surfactant, etc. (fluorine concentration of less than 1%) was used. The etchant stored in a nozzle and the film 30 were heated and maintained at a temperature higher than room temperature (for example, about 40° C.). From an opening of a leading end portion of the nozzle directed downward (z-axis negative direction) at a position above the upper surface of the film 30 (position in the z-axis positive direction) by a predetermined distance (spraying distance, for example, 8 cm), the etchant was sprayed downward toward the upper surface of the film 30 (in particular, between adjacent protective films R and R) at a predetermined spraying pressure (for example, 0.2 MPa) for a predetermined spraying time period (for example, 2 minutes). After that, the etched film 30 was cleaned with pure water. Such spraying and cleaning were alternately performed by a predetermined number of times, and the etching was completed.
In this embodiment, the piezoelectric layer 30 obtained after the patterning is completed by etching has, in the reference cross-section, the above-mentioned “substantially rectangular shape,” that is, a “shape in which the side surface of the piezoelectric layer 30 extends upwardly and (substantially) perpendicularly from the upper surface of the lower electrode 20 (θ≈90° in
In this case, when the etching rate (rate of removal of the film by etching) decreases as the etching progresses downward in the thickness direction of the film 30 (z-axis direction), the range in the x-axis direction of the film 30 in a part between the adjacent protective films R and R to be removed by etching is reduced as the etching progresses downward in the thickness direction of the film 30 (z-axis direction). As a result, the shape of the reference cross-section of the piezoelectric layer 30 is a “trapezoid in which the upper base is shorter than the lower base (θ<90°).” On the other hand, when the etching rate increases as the etching progresses downward in the thickness direction of the film 30 (z-axis direction), the range in the x-axis direction of the film 30 to be removed by etching increases as the etching progresses downward in the thickness direction of the film 30 (z-axis direction). As a result, the shape of the reference cross-section of the piezoelectric layer 30 is a “trapezoid in which the upper base is longer than the lower base (θ>90°).” Therefore, in order to form the shape of the reference cross-section of the piezoelectric layer 30 into the above-mentioned “substantially rectangular shape” (θ≈90°), the etching rate needs to be adjusted to be substantially constant in the thickness direction of the film 30 (z-axis direction).
The etching rate may be adjusted by controlling, for example, the concentration of the etchant, the spraying distance, the spraying pressure, the spraying time period, the opening diameter of the nozzle, and the temperature of the etchant and the film 30. Specifically, the etching rate increases as the concentration of the etchant is higher, the spaying distance is shorter, the spraying pressure is higher, the spraying time period is longer, the opening diameter of the nozzle is larger, and the temperature of the etchant and the film 30 is higher.
In this embodiment, as described above, the etching rate is adjusted to be substantially constant in the thickness direction of the film 30 (z-axis direction). In this manner, the angle θ is adjusted to fall within a range of 85° to 105°. After the etching of the film 30 is completed, the respective protective films R are removed, and the film 30 is subjected to dewaxing.
Then, as illustrated in
As described above, as illustrated in
(Feature of Piezoelectric Layer)
Next, the feature of the piezoelectric layer 30 (fired body) of the piezoelectric/electrostrictive film type element 10 formed by the above-mentioned manufacturing method is described with reference to
The average particle diameter of each of the particles of the piezoelectric material, which are distributed inside the piezoelectric layer 30, is 0.5 μm to 10 μm. Note that, the particle diameter of a certain particle can be defined as a diameter of a circle having an area that is equal to an area of a region corresponding to the particle that can be recognized in the cross-section. The range of the average particle diameter of each of the above-mentioned particles of the piezoelectric material can be obtained with use of, for example, a plurality of reference cross-sections obtained by cutting the piezoelectric layer 30 at different positions in the longitudinal direction (y-axis direction). For example, the lower limit value of the range of the average particle diameter of each of the particles of the piezoelectric material described above is the minimum value of the average particle diameters obtained from the respective reference cross-sections, and the upper limit value of the range of the average particle diameter of each of the particles of the piezoelectric material described above is the maximum value of the average particle diameters obtained from the respective reference cross-sections. The average particle diameter of each of the particles of the piezoelectric material forming the piezoelectric layer 30 ranges from 0.5 μm to 10 μm. This is based on the fact that the piezoelectric layer 30 is produced with use of a so-called “thick film method” such as spin coating and tape casting. When the piezoelectric layer is produced by a so-called “thin film method,” the average particle diameter of each of the particles becomes a value that is markedly smaller than values within this range.
The substantially rectangular shape represented by the virtual line obtained as described above has a lower-side length L4 of 30 μm to 500 μm and a height L5 of 0.5 μm to 15 μm. As described above, the angle θ at the end point of the lower side is 85° to 105°. The lower limit value of the range of each of the above-mentioned length, height, and angle is the minimum value of the minimum values of each of the length, height, and angle obtained from the above-mentioned plurality of reference cross-sections, or an average value of the respective minimum values. The upper limit value of the range of each of the above-mentioned length, height, and angle is the maximum value of the maximum values of each of the length, height, and angle obtained from the above-mentioned plurality of reference cross-sections, or an average value of the respective maximum values. Note that, the above-mentioned ranges of L4 and L5 are ranges that are suitable for the demand for, in the case where the piezoelectric/electrostrictive film type element 10 is used as a drive source of an ink jet head of an ink jet printer, appropriately jetting fine ink droplets from the ink jet head. When the piezoelectric/electrostrictive film type element 10 is used for other applications, the ranges of L4 and L5 are not limited to the above-mentioned ranges, and may be set to ranges appropriate for those applications.
(Prevention of Leak Current and Particle Shedding from Side Surface of Piezoelectric Layer)
As described above, in this embodiment, the following piezoelectric layer is assumed. The piezoelectric layer 30 of the piezoelectric/electrostrictive film type element 10 has a “shape that is represented by the virtual line, the shape being a quadrilateral having the length L4 of 30 μm to 500 μm, the height L5 of 0.5 μm to 15 μm, and the angle θ of 85° to 105°” (in other words, the sectional shape of the piezoelectric layer 30 is a substantially rectangular shape having a length of 30 μm to 500 μm and a height of 0.5 μm to 15 μm). Further, “the average particle diameter d of each of the particles of the piezoelectric material forming the piezoelectric layer 30 is 0.5 μm to 10 μm.”
In the piezoelectric/electrostrictive film type element 10 including the piezoelectric layer 30 having an extremely small thickness as described above, when a voltage is applied between the upper and lower electrodes 20 and 40, a leak current that flows through the piezoelectric layer 30 is easily generated. When an amount of the leak current is large, there easily occur problems such as reduction in drive efficiency of the piezoelectric/electrostrictive film type element 10.
The inventors of the present invention have worked on various experiments and the like to prevent the above-mentioned leak current. As a result, the inventors of the present invention have found that the magnitude of the above-mentioned leak current is closely related to the surface roughness of the side surface of the piezoelectric layer 30. Specifically, the inventors of the present invention have found that, when the average particle diameter of the piezoelectric material is set in the order of “d”μm, the leak current becomes significantly smaller in a case where the surface roughness of the side surface of the piezoelectric layer 30 is 0.05 dμm or more at the maximum height roughness Rz (defined by JIS B 0601:2001) as compared to a case with a different surface roughness. In the following, the testing that confirms this fact is described.
(Testing)
In this testing, a plurality of samples of the piezoelectric/electrostrictive film type element 10 were produced in accordance with the procedure illustrated in
In each of the samples, the layer width and the layer thickness are adjusted by adjusting the width and the thickness of the film 30g for the piezoelectric layer 30 (see
Further, as is understood from Table 1, each of the samples has the width L4 (see
Each of the produced samples was subjected to “polarization treatment” at a temperature of 75° C., a voltage corresponding to a DC electric field of 15 kV/mm, and a voltage application time period of 10 seconds. After that, the leak current between the upper and lower electrodes was evaluated with respect to each of the samples under a high humidity situation with humidity of 85%. Specifically, in the leak current evaluation, the maximum leak current value when an electric field of 30 kV/mm was applied between the upper and lower electrodes was measured. The results (average values of the samples (N=10) for respective levels) are shown in Table 1.
As is understood from levels 1 to 24 (in particular, levels 9 to 15) of Table 1, as the surface roughness of the side surface of the piezoelectric layer 30 becomes larger, the leak current value tends to decrease. This reason is considered as follows. As the surface roughness increases, a “distance (passage) between the upper and lower ends of the side surface of the piezoelectric layer 30 in a case considering fine irregularities as well,” that is, “the passage through which the electron flows between the end portions of the opposing upper and lower electrodes” becomes long. Further, when the surface roughness is 0.05 dμm or more at the maximum height roughness Rz (see levels other than levels 9, 10, and 22), the leak current becomes significantly smaller as compared to a case with a different surface roughness (when the surface roughness is less than 0.05 dμm) (see levels 9, 10, and 22).
Further, for each of the samples, the displacement amount of the piezoelectric/electrostrictive film type element 10 when an electric field having a pattern of a triangular wave of 1 Hz and having an electric field intensity of 10 kV/mm was applied was measured. The displacement amount was measured by measuring the displacement amount in the up-down direction (z-axis direction) at the center portion of the upper surface of the piezoelectric/electrostrictive film type element 10 by a laser Doppler displacement meter. The results (average values of the samples (N=10) for respective levels) are also shown in Table 1.
As is understood from levels 1 to 24 (in particular, levels 1 to 8) of Table 1, it can be said that, when the angle θ is 90° to 105° (see levels other than levels 6 to 8, 16, and 22), as compared to the case where the angle θ is 85° or more and less than 90° (see levels 6 to 8, 16, and 22), the displacement amount of the piezoelectric/electrostrictive film type element 10 is significantly larger. The reason is considered as follows. When the angle θ is 90° to 105°, as compared to the case where the angle θ is 85° or more and less than 90°, the “ratio of the area of a part of the piezoelectric layer 30, which is sandwiched between the upper and lower electrodes (that is, a part relating to the drive) to the area of the lower electrode 20” can be increased, and thus the drive efficiency of the piezoelectric/electrostrictive film type element 10 can be improved.
In addition, evaluation was performed of whether or not “particle shedding” (phenomenon that the particles forming the side surface fall from the side surface) occurred from the side surface of the piezoelectric layer 30 when an electric field was applied for a long period of time at a pattern similar to that when the above-mentioned “displacement amount” was measured (that is, a pattern of a triangular wave of 10 kV/mm and 1 Hz). As a result (not shown in Table 1), it was found that, when the surface roughness of the side surface of the piezoelectric layer 30 was 0.5 dμm or less at the maximum height roughness Rz, as compared to a case with a different surface roughness (when the surface roughness was more than 0.5 dμm), the “particle shedding” from the side surface of the piezoelectric layer 30 was more significantly prevented.
As described above, the following has been found. The piezoelectric layer 30 of the piezoelectric/electrostrictive film type element 10 is formed so that a “sectional shape that is represented by the virtual line (see
In the above, description is made of the case where the “dielectric layer” according to the present invention is the piezoelectric layer 30, and the “laminate” according to the present invention is the piezoelectric/electrostrictive film type element 10. However, the following fact has been separately confirmed. Also in a case where the “dielectric layer” according to the present invention is a dielectric layer other than the piezoelectric layer (for example, a layer made of a dielectric material such as barium titanate or strontium titanate), similarly to the above, the dielectric layer is formed so that the “shape that is represented by the virtual line (see
Number | Date | Country | Kind |
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2012-220296 | Oct 2012 | JP | national |