JP5384843B2 - Method for manufacturing piezoelectric element structure and piezoelectric element structure - Google Patents

Description

  The present invention relates to a method for manufacturing a piezoelectric element structure including a plurality of piezoelectric elements on a substrate, and a piezoelectric element structure.

  A piezoelectric element including a piezoelectric body having piezoelectricity that expands and contracts as the electric field application intensity increases and decreases and an electrode that applies an electric field to the piezoelectric body in a predetermined direction is used as an actuator mounted on an ink jet recording head. It is used.

  As a piezoelectric material, a composite oxide having a perovskite structure such as lead zirconate titanate (PZT) is known. Such a material is a ferroelectric material having spontaneous polarization when no electric field is applied. In a conventional piezoelectric element, by applying an electric field in a direction corresponding to the polarization axis of the ferroelectric material, the piezoelectric material extends in the direction of the polarization axis. It is common to use “effect”.

  In order to make the spontaneous polarization of the piezoelectric body coincide with the electric field application direction, the piezoelectric body has been conventionally subjected to polarization treatment. As the polarization treatment, a method of forming electrodes on the upper and lower sides of a piezoelectric body and applying an electric field between the electrodes is generally used.

  Patent Document 1 proposes a method of performing polarization by alternately applying electric fields in opposite directions to the piezoelectric body in order to improve the heat resistance of the piezoelectric body together with the polarization treatment.

  On the other hand, a piezoelectric element having a piezoelectric film formed on a substrate by sputtering is known, and the piezoelectric film formed by sputtering is formed without performing polarization treatment. It is known that it has spontaneous polarization from the substrate side to the film surface in the state immediately after (see FIG. 3).

When a piezoelectric film formed by sputtering on a substrate is used as a piezoelectric element, a piezoelectric film is formed on a substrate on which a lower electrode layer has been formed in advance, and an upper electrode layer is formed on the piezoelectric film. Form. When a piezoelectric element structure having a piezoelectric film having spontaneous polarization from the substrate side toward the film surface (from the lower electrode layer side to the upper electrode layer side) is put into practical use, the direction of the electric field during driving In order to match the direction of spontaneous polarization, the upper electrode needs to have a higher potential than the lower electrode. Therefore, (1) the upper electrode side is set as a ground potential and the lower electrode side is set as a positive potential using the address electrode, or (2) the lower electrode side is set as the ground potential and the upper electrode side is driven as the negative potential using the address electrode. There is a need. In the case of (1), the lower electrode, which is an electrode on the substrate side, needs to be an individual electrode, and in the case of (2), a driving IC for negative voltage is required.
JP 2007-258597 A

  However, when the lower electrode is an individual electrode, there is a problem that the manufacturing process is complicated, and the negative voltage driving IC for performing negative voltage driving is larger in size than the positive voltage driving IC, and thus the negative voltage driving IC is negative. Since the drive IC is provided, the size of the entire apparatus including the drive IC is increased, the number of elements that can be manufactured from one wafer needs to be reduced according to the IC size, and further, for the negative voltage drive. Since the IC itself is more expensive than the positive voltage, there is a problem that the cost is increased.

  Therefore, it is desired that the lower electrode layer is not a separate electrode for each element, but a solid electrode common to a plurality of elements and a positive voltage driver IC can be used. For this purpose, the spontaneous polarization of the piezoelectric film may be reversed. As the reversal polarization process for reversing the spontaneous polarization, it is conceivable to apply a method in which a voltage is applied between the upper and lower electrodes sandwiching the piezoelectric body, similarly to the conventional polarization process. In addition, in the piezoelectric element structure, it is desirable that the reversal polarization of the spontaneous polarization of the piezoelectric films of a plurality of piezoelectric elements is performed in a lump. In this case, a voltage is applied between the electrodes of each piezoelectric film. The collective polarization inversion is performed on the piezoelectric films of a large number of elements.

  However, according to the experiments by the present inventors, when the above-described collective polarization reversal process is performed on the piezoelectric element structure, the element defect rate due to film breakdown at the time of voltage application is as high as about 15-30%. The problem was that it was expensive and could not be practically used.

  In general, it is known that film breakdown at the time of voltage application starts with a part having relatively low resistance such as a composition defect or a structural defect, or a part where charge tends to be accumulated, such as surface defects or pores, at the time of voltage application. It has been. If an electric field is continuously applied to the piezoelectric film, heat is generated at the charge concentration portion of the trigger portion, and the temperature locally increases. It is considered that the breakdown due to the charge concentration is caused by the sudden drop in resistance at the part where the temperature is locally increased.

  In the polarization processing of the piezoelectric element structure, a voltage is collectively applied between a lower electrode that is a solid electrode common to a plurality of elements and an upper electrode provided for each element. The total amount of charges increases as the electrode area increases. Since the voltage is applied to a plurality of elements at once, the total electrode area increases, and breakdown due to charge concentration tends to occur. For this reason, it is difficult to invert a plurality of elements uniformly, the defect rate is very high, and practical application is difficult.

  The present invention has been made in view of the above circumstances, and in a piezoelectric element structure including a large number of piezoelectric elements, the direction of spontaneous polarization of the piezoelectric film is directed from the upper electrode layer side to the lower electrode layer side. An object of the present invention is to provide a method for manufacturing a practical piezoelectric element structure.

The method for manufacturing a piezoelectric element structure of the present invention includes a piezoelectric element for manufacturing a piezoelectric element structure including a plurality of piezoelectric elements in which a lower electrode layer, a piezoelectric film, and an upper electrode layer are laminated in this order on a substrate. In the manufacturing method of the structure,
The piezoelectric film is formed by sputtering,
With respect to the piezoelectric film in which spontaneous polarization is directed from the lower electrode layer toward the upper electrode layer by the film formation, the upper electrode layer has a magnitude greater than the coercive electric field of the piezoelectric film and the lower electrode. It is characterized by applying a pulse of an electric field directed to the layer.

  The piezoelectric film is preferably a perovskite oxide containing at least Pb.

  Note that the ratio B / A between the voltage application time A and the non-voltage application time B in the pulse application of the electric field is preferably 1 or more, and more preferably, the ratio B / A is 10 or more.

The piezoelectric element structure of the present invention is a piezoelectric element structure including a plurality of piezoelectric elements in which a lower electrode layer, a piezoelectric film formed by sputtering and an upper electrode layer are laminated in this order on a substrate. There,
The defect rate of the piezoelectric element in the piezoelectric element structure is 1% or less,
The spontaneous polarization of the piezoelectric film is directed from the upper electrode layer toward the lower electrode layer.

  Here, the defect rate is the number of piezoelectric elements in which a defect has occurred / the total number of piezoelectric elements provided in the piezoelectric element structure (= the number of upper electrode channels in which a defect has occurred / the number of upper electrode channels in the entire element).

  The piezoelectric film is preferably a perovskite oxide containing at least Pb.

  According to the method for manufacturing a piezoelectric element structure of the present invention, a piezoelectric film is formed by sputtering, and the spontaneous polarization is directed to the upper electrode layer from the lower electrode layer by the film formation. On the other hand, since the electric field directed from the upper electrode layer to the lower electrode layer is applied with a pulse having a magnitude greater than the coercive electric field of the piezoelectric film, the cooling time can be taken periodically, so that heat generation can be suppressed. This suppresses the destruction of the piezoelectric film that has been destroyed by the heat generated by voltage application during polarization, and suppresses the defect rate of piezoelectric elements such as cracks and voids compared to the case of using the polarization method by applying a continuous electric field. Thus, a piezoelectric element structure that can be put to practical use can be obtained.

  The piezoelectric element structure of the present invention is a piezoelectric element structure including a plurality of piezoelectric elements in which a lower electrode layer, a piezoelectric film formed by sputtering and an upper electrode layer are laminated in this order on a substrate. Since the defect rate of the piezoelectric element is 1% or less and the spontaneous polarization of the piezoelectric film is directed from the upper electrode layer toward the lower electrode layer, it is effective for practical use such as a piezoelectric actuator.

Embodiments of the present invention will be described below with reference to the drawings.
A method for manufacturing a piezoelectric element structure and a piezoelectric element structure according to an embodiment of the present invention will be described with reference to FIGS. 1 is a schematic plan view of a piezoelectric element structure 1 obtained by the manufacturing method of the present invention, FIG. 2 is a cross-sectional view of the main part of the piezoelectric element structure 1 obtained by the manufacturing method of the present invention, and FIG. FIG. 4 is a cross-sectional view of the main part of the piezoelectric element structure immediately after the film, and FIG. In addition, in order to make it easy to visually recognize, the scale of the component is appropriately changed from the actual one.

"Piezoelectric element structure"
First, the structure of the piezoelectric element structure obtained by the manufacturing method of this embodiment will be described. As shown in FIGS. 1 and 2, the piezoelectric element structure 1 includes a plurality of piezoelectric elements 2 on a substrate 11. In the present embodiment, the substrate 11 is a structure in which a plurality of diaphragm structures are formed, and the piezoelectric element 2 is provided on each diaphragm 12. The piezoelectric element 2 is an element in which a lower electrode layer 22, a piezoelectric film 23 formed by a sputtering method, and an upper electrode layer 24 are sequentially stacked on the substrate 11, and an electric field is formed in the thickness direction by the upper electrode and the lower electrode. Is applied.

  The lower electrode layer 22 is formed on substantially the entire surface of the substrate and serves as a common electrode for the plurality of piezoelectric elements 2, and the piezoelectric film and the upper electrode layer are configured in a separation pattern corresponding to each diaphragm 12. Although the piezoelectric film may be a continuous film, it is preferable that the piezoelectric element film be separated from each other because the expansion and contraction of each element occurs smoothly.

  In addition, when the piezoelectric film is separated for each element, it is preferable that the upper electrode layer provided on the piezoelectric film is formed to be smaller than the piezoelectric film at the center of the surface of the piezoelectric film. This is because when the piezoelectric film becomes very thin, the distance between the upper electrode and the lower electrode is small, and there is a risk of leakage from both ends of the piezoelectric film. However, in manufacturing the structure, the process can be simplified if the sizes of the piezoelectric film and the upper electrode layer are substantially the same.

  The direction of the spontaneous polarization dp of the piezoelectric film 23 of the piezoelectric element in the piezoelectric element structure 1 is the direction from the upper electrode layer 24 to the lower electrode layer 22, and the element defect rate is preferably 1% or less.

As the substrate 11, a silicon substrate is preferable because of its good thermal conductivity and workability. In particular, a stacked substrate such as an SOI substrate in which a SiO ₂ film and a Si active layer are sequentially stacked on a silicon substrate is preferably used. It is done. Further, a buffer layer for improving the lattice matching, an adhesion layer for improving the adhesion between the electrode and the substrate, or the like may be provided between the diaphragm 12 and the lower electrode layer 22. .

  The diaphragm is not limited to a part of the substrate 11 processed, and may be separated from the substrate and bonded to the substrate. When the substrate and the diaphragm are configured separately, not only silicon but also glass, stainless steel (SUS), yttrium stabilized zirconia (YSZ), alumina, sapphire, silicon carbide, etc. should be used as the substrate. Can do.

The main component of the lower electrode layer 22 is not particularly limited and includes metals or metal oxides such as Ir, Au, Pt, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof. The thicknesses of the lower electrode layer 22 and the upper electrode layer 24 are not particularly limited and are preferably 50 to 500 nm.

  The main component of the upper electrode layer 24 is not particularly limited, and the materials exemplified in the lower electrode layer 22, electrode materials generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof Is mentioned.

  The film thickness of the piezoelectric film 23 is not particularly limited, and is usually 1 μm or more, for example, 1 to 10 μm.

"Method for manufacturing piezoelectric element structure"
Next, a method for manufacturing the piezoelectric element structure according to this embodiment for manufacturing the piezoelectric element structure 1 will be described.
A substrate 11 formed with a plurality of diaphragm structures is prepared, and a lower electrode layer 22 is formed on the substrate 11. If necessary, a buffer layer or an adhesion layer may be formed before the lower electrode layer 22 is formed. Thereafter, the piezoelectric film 23 is formed on the lower electrode layer 22 by sputtering, and the upper electrode layer 24 is formed on the piezoelectric film 23. The upper electrode layer 24 and the piezoelectric film 23 are etched and separated so as to correspond to the diaphragm structure, thereby obtaining a piezoelectric element structure including a plurality of piezoelectric elements.

  As shown in FIG. 3, the direction of the polarization dp of the piezoelectric film 23 that has not been subjected to the polarization treatment is directed from the lower electrode to the upper electrode. An inversion polarization process for inverting the direction of the polarization dp by applying a pulse electric field to the piezoelectric film 23 is performed.

  The lower electrode of the piezoelectric film 23 is grounded, each upper electrode is set to a positive potential, and an electric field in a direction from the upper electrode to the lower electrode is applied between the upper and lower electrodes. The magnitude of the voltage is such that an electric field equal to or greater than the coercive electric field of the piezoelectric film 23 is applied to the piezoelectric film 23. The voltage holding time is about 1 to 30 minutes, and the pulse frequency (pulse period) is not particularly limited, but is about 0.1 kHz to 1 MHz, for example. The temperature of the piezoelectric film 23 at the time of polarization reversal is about room temperature to 100 ° C. When polarization is performed at a temperature higher than room temperature, it is desirable to apply the electric field after the temperature of the film has been raised in advance. When the temperature of the film is raised, the coercive electric field of the film is reduced, so that the polarization can be reversed with a voltage smaller than that at room temperature. However, as the film temperature approaches the Curie point, dark current increases with a rapid decrease in resistance, so the film temperature should be sufficiently lower than the Curie point in the range of room temperature to about 100 ° C. desirable.

  The applied voltage pulse waveform is preferably a rectangular wave as shown in FIG. 4 rather than a waveform that gradually rises and falls like a sine wave. This is because the rectangular wave can take more time during which no voltage is applied, and can secure more cooling time (non-voltage application time). Further, in order to increase the cooling efficiency, it is preferable that the ratio B / A between the voltage application time A in the pulse application and the non-voltage application time B is 1 or more, that is, A ≦ B in the waveform of FIG. It is more preferable that B / A is 10 or more.

  FIG. 5 shows the measurement results (temperature rise and temperature drop curves) of the temperature versus current value of the PZT thin film. Changes in dark current value during temperature rise or temperature drop while applying a voltage of 30 kV / mm to the PZT thin film. Is measured.

  From FIG. 5, it can be seen that the resistance rapidly decreases and the current value increases as the temperature approaches the Curie point (about 300 ° C.). At the time of temperature rise, the dark current value is almost 0 from the room temperature side to around 150 ° C., but when it exceeds 150 ° C., the dark current value starts to gradually increase, and when it exceeds 200 ° C., it increases. As described in the section of the prior art, when an electric field is applied in the polarization process, if heat generation proceeds at an electric field concentration point, the resistance rapidly decreases, which causes further charge concentration, which leads to film destruction. It is necessary to suppress the temperature of the film to a temperature lower than the temperature at which the resistance rapidly increases. For example, in the case of the PZT piezoelectric film shown in FIG. 5, it is considered that the film does not break unless the temperature is raised to 200 ° C. or higher. According to the polarization treatment in which the pulse electric field is applied in the present invention, even if charge concentration occurs in a portion where charges such as composition defects and structural defects in the piezoelectric film tend to accumulate due to voltage application, the cooling time ( There is a time during which no electric field is applied, and the presence of this cooling time makes it possible to suppress heat generation at the charge concentration portion and to suppress film breakdown.

  In particular, a film made of a perovskite oxide containing Pb, such as a PZT piezoelectric film, is prone to Pb composition defects when formed by sputtering, and this composition defect part tends to cause charge concentration. The effect of applying a polarization treatment that applies a pulse electric field is high.

  In addition, the thinner the film thickness, the greater the probability of breakdown due to charge concentration. Therefore, the polarization treatment by applying a pulsed electric field is applied to a piezoelectric film having a small film thickness, for example, 20 μm or less, or 10 μm or less. High effect.

  As in the manufacturing method of the above-described embodiment, a piezoelectric film is formed on the substrate by sputtering, and then a polarization process using a pulsed electric field is performed, so that the spontaneous polarization dp as shown in FIG. Thus, the piezoelectric element structure 1 in which the element defect rate in the direction (downward) toward the lower electrode 22 is suppressed can be obtained. In particular, when the ratio B / A between the voltage application time A and the non-voltage application time B in the pulse electric field application is 1 or more, the element defect rate is 1% or less, and the ratio B / A is 10 or more. The defect rate can be made zero (see the examples).

In the piezoelectric element structure 1, due to the positive voltage drive using the upper electrode layer 24 as an address electrode, the expansion and contraction accompanying the increase and decrease of the electric field applied intensity occurs effectively, and the piezoelectric effect due to the electric field induced strain is effectively obtained. That is, when an actuator using the piezoelectric element structure 1 is configured, the lower electrode layer 22 is a ground (GND) electrode to which an applied voltage is fixed, and the upper electrode layer 24 is an address electrode whose applied voltage is varied. Since the positive voltage drive driver D ⁺ can be used, the cost can be suppressed and the size of the entire apparatus can be reduced as compared with the case of using the negative voltage drive driver.

  The piezoelectric element structure 1 includes a voltage drive driver D +, and can be applied to an ink jet recording head, for example, as a pressurized liquid chamber for storing ink at the lower part of the diaphragm 12. Since the piezoelectric displacement is made uniform, the ink discharge amount becomes constant, which leads to an increase in image quality by increasing the in-plane uniformity. Further, if the manufacturing method of the present invention is used, the element breakdown rate can be suppressed to 1% or less, so that the yield can be increased and the cost can be reduced.

  In the present embodiment, the piezoelectric film to be formed may be any piezoelectric film that generates spontaneous polarization from the substrate toward the film surface by sputtering.

  In particular, it is preferable to form a film under the following film forming conditions because a piezoelectric film having very good piezoelectric characteristics can be obtained.

  The piezoelectric film is formed in a predetermined sputtering apparatus. In the sputtering method, factors that affect the characteristics of the film to be formed include the film formation temperature, the type of substrate, the composition of the substrate, the surface energy of the substrate, and the film formation pressure if there is a film previously formed on the substrate. The oxygen amount in the atmosphere gas, the input power, the substrate-target distance, the electron temperature and electron density in the plasma, the active species density in the plasma and the lifetime of the active species, etc. can be considered.

The applicant has studied the factors that have a great influence on the properties of the film to be formed, and found the film forming conditions that enable the formation of a good quality film. (Refer to Japanese Patent Application Nos. 2006-263978, 2006-263379, and 2006-263980, which have been filed earlier.)
Specifically, the film formation temperature Ts, Vs−Vf (Vs is the plasma potential in the plasma during film formation, Vf is the floating potential), Vs, and the substrate-target distance D are optimized. Thus, it has been found that a high-quality film can be formed. In other words, when the film characteristics are plotted with the film formation temperature Ts as the horizontal axis and any of the vertical axes of Vs−Vf, Vs and the substrate-target distance D, the film quality is good within a certain range (the conditions shown below). It was found that a simple film can be formed. The film formation temperature Ts is higher than the Curie point of the piezoelectric film to be formed.

(First film formation conditions)
This is a film formation condition in which the film formation temperature Ts and Vs−Vf are optimized. The film formation temperature Ts (° C.), the plasma potential Vs (V) in the plasma during film formation, and the floating potential Vf (V) The film is formed under the film forming conditions satisfying the following formulas (1) and (2) with Vs−Vf (V) which is the difference between the two. Note that it is particularly preferable to perform film formation under film formation conditions that satisfy the following formulas (1) to (3).
Ts (° C.) ≧ 400 (1),
−0.2Ts + 100 <Vs−Vf (V) <− 0.2Ts + 130 (2),
10 ≦ Vs−Vf (V) ≦ 35 (3)
(Second film formation condition)
This is a film forming condition that optimizes the film forming temperature Ts and the distance (substrate-target distance) D (mm) between the substrate B and the target T. The film forming temperature Ts (° C.) and the substrate-target distance D The film is formed under the condition that (mm) satisfies the following formulas (4) and (5), or the film forming condition that satisfies (6) and (7).
400 ≦ Ts (° C.) ≦ 500 (4),
30 ≦ D (mm) ≦ 80 (5),
500 ≦ Ts (° C.) ≦ 600 (6),
30 ≦ D (mm) ≦ 100 (7)

(Third film forming conditions)
This is a film forming condition in which the film forming temperature Ts and the plasma potential Vs (V) in the plasma during film formation are optimized. The film forming temperature Ts (° C.) and the plasma potential Vs (V in the plasma during film formation). ) Are formed under film forming conditions that satisfy the following formulas (8) and (9) or film forming conditions that satisfy (10) and (11).
400 ≦ Ts (° C.) ≦ 475 (8),
20 ≦ Vs (V) ≦ 50 (9),
475 ≦ Ts (° C.) ≦ 600 (10),
Vs (V) ≦ 40 (11)

  Note that a piezoelectric film made of a perovskite oxide represented by the following general formulas (P-1) and (P-2), for example, under a condition that satisfies any of the first to third film forming conditions described above. By forming the film, a highly oriented piezoelectric film can be obtained.

Pb _a (Zr _b1 Ti _b2 X _b3 ) O ₃ (P-1)
(In Formula (P-1), X is at least one metal element selected from the group consisting of Nb, W, Ni, and Bi. A> 0, b1> 0, b2> 0, b3 ≧ 0. (It is standard that a = 1.0 and b1 + b2 + b3 = 1.0, but these values may deviate from 1.0 within a range where a perovskite structure can be taken.)
(Pb _a X _a1 ) (Zr _b1 Ti _b2 ) O ₃ (P-2)
(In Formula (P-2), X is at least one metal element selected from the group consisting of La, Bi, and W. a> 0, a1 ≧ 0, b1> 0, b2> 0, a + a1 = (The standard is 1.0 and b1 + b2 = 1.0, but these values may deviate from 1.0 within a range where a perovskite structure can be taken.)
Vs−Vf can be changed by installing a ground between the substrate and the target. Note that the plasma space potential can be adjusted by a simple method by using the film forming apparatus described in Japanese Patent Application No. 2006-263881 filed earlier by the present inventor (not disclosed at the time of this application). . This film forming apparatus includes a shield that surrounds the outer periphery of the target holder that holds the target on the film forming substrate side, and is configured so that the potential state of the plasma space can be adjusted by the presence of the shield.

  The piezoelectric film thus obtained has a high degree of crystal orientation and the direction of spontaneous polarization is directed from the surface of the piezoelectric film to the substrate (from the lower electrode to the upper electrode).

In the above, an example has been given particularly for a PZT-based piezoelectric film. However, by using a sputtering method to form a piezoelectric material such as BaTiO ₃ or LiNbO ₃ other than the PZT-based film, the same spontaneous polarization as in the PZT system can be obtained. Therefore, these piezoelectric films may be provided.

  The structure shown below was subjected to polarization treatment under the conditions of Examples and Comparative Examples and evaluated. 6 and 7 are conceptual diagrams showing a structure subjected to polarization processing and a configuration at the time of polarization processing, FIG. 6 is a schematic cross-sectional view of the main part, and FIG. 7 is a schematic plan view of the main part.

  In the structure 4 subjected to the polarization treatment of the example and the comparative example, the Ti layer 32a and the Ir layer 32b are formed as the lower electrode layer 32 on the Si substrate 31, and the film thickness is formed on the lower electrode layer 32 by sputtering. A PZT piezoelectric film 33 having a thickness of 5 μm is formed, and an upper electrode 34 including a Ti layer 34 a and an Ir layer 34 b is formed on the PZT piezoelectric film 33 by patterning. Here, electrodes for 200 channels (corresponding to 200 elements) were formed on the PZT piezoelectric film 33. Furthermore, a lead wiring 36 was formed from each upper electrode 34, and an electrode pad 35 was formed at the end thereof. In the region where the lead wiring 36 and the electrode pad 35 are formed, a polyimide resin layer 37 is provided on the piezoelectric film 33, and the wiring 36 and the pad 35 are formed on the resin layer 37.

  The electrode pad 35 was connected to the polarization inversion drive power supply 40 by a probe, wire bonding, or FPC (Flexible Printed Circuit) wiring, and the lower electrode 32 was grounded.

Example 1
Applied voltage: 10 kV / mm
Voltage holding time: 10 minutes Pulse frequency 0.1 kHz to 1 MHz
Ratio of voltage application time and non-application time B / A = 1
Temperature of piezoelectric film: room temperature to 100 ° C
(If the temperature is higher than room temperature, the temperature is raised before applying the voltage.)
Within the range of the electric field application conditions, each electrode layer (200 channels) of the structure 4 having the above configuration was simultaneously subjected to a polarization inversion process by applying a pulse electric field, and the destruction rate was examined from the number of broken channels in the 200 channels. .

  As a result, in the above pulse frequency range, no significant frequency dependence was confirmed, and the destruction rate was 0-1% in all cases.

(Comparative Example 1)
A continuous electric field is applied instead of a pulsed electric field under the conditions of Example 1 above, and polarization inversion processing is performed by applying a continuous electric field when the temperature of the piezoelectric film is room temperature (25 ° C.) and when the temperature is 100 ° C. The destruction rate was examined.

  As a result, among the structures subjected to the polarization treatment by the continuous electric field, the destruction rate in the case where the treatment was performed at room temperature was 15%, and the destruction rate in the case where the treatment was performed at 100 ° C. was 30%.

  From the results of Example 1 and the comparative example, it was confirmed that if the polarization treatment by applying a pulsed electric field is used, a remarkable destruction rate reducing effect can be obtained as compared with the case of the polarization treatment by applying a continuous electric field.

(Example 2)
Applied voltage: 10 kV / mm,
Voltage holding time: 10 minutes Pulse frequency: 100 kHz
Ratio of voltage application time and non-application time B / A = 0.01-100
Temperature of piezoelectric film: room temperature (25 ° C.), 100 ° C. (in the case of 100 ° C., the temperature is increased before voltage application)
With respect to the plurality of structures, a pulse electric field was applied within the above condition range to perform polarization inversion, and the breakdown rate was examined. FIG. 8 shows the result of changing the ratio B / A between the voltage application time and the non-application time for each film temperature.

  As shown in FIG. 8, when the temperature of the piezoelectric film at the time of polarization is room temperature or 100 ° C., the specific breakdown rate decreases as the ratio B / A at the time of applying the pulse electric field increases. did. In particular, it was confirmed that the B / A with a voltage application time and a non-application time of 1: 1 was 1 or more and the destruction rate was 1% or less, and a significant reduction in the destruction rate was confirmed. Further, when the ratio B / A was 10 or more, the destruction was stable. It was confirmed that the rate was zero.

  Here, the breakdown rate in the polarization treatment is synonymous with the element defect rate in the structure after the polarization treatment.

  The piezoelectric element structure of the present invention can be preferably used for a piezoelectric actuator mounted on an ink jet recording head, a magnetic recording / reproducing head, a MEMS (Micro Electro-Mechanical Systems) device, a micro pump, an ultrasonic probe, and the like.

Schematic plan view of a piezoelectric element structure obtained by a manufacturing method according to an embodiment of the present invention Sectional drawing of the principal part of the piezoelectric element structure obtained by the manufacturing method of embodiment which concerns on this invention Sectional drawing of the principal part of the structure body immediately after film-forming of the piezoelectric film in the manufacturing method of embodiment which concerns on this invention The figure which shows the applied voltage pulse waveform at the time of polarization processing The figure which shows the temperature dependence of the dark current in a PZT piezoelectric material film. Schematic cross-sectional view of the main part showing the structure of the structure of the example and the structure during polarization treatment Schematic plan view of the main part showing the structure of the structure of the example and the structure during polarization processing The figure which shows the ratio B / A dependence of the voltage application time of a breakdown rate at the time of a polarization process, and non-application time

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element structure 2 Piezoelectric element 4 Piezoelectric element structure (before polarization process)
11, 31 Substrate 12 Diaphragm 22, 32 Lower electrode layer 23, 33 Piezoelectric film 24, 34 Upper electrode layer

Claims (6)

In the manufacturing method of a piezoelectric element structure for manufacturing a piezoelectric element structure including a large number of piezoelectric elements in which a lower electrode layer, a piezoelectric film, and an upper electrode layer are laminated in this order on a substrate,
Forming the lower electrode layer on the substrate as a common electrode;
Forming the piezoelectric film on the lower electrode layer by sputtering;
On the piezoelectric film, the upper electrode layer is formed as an individual electrode,
With respect to the piezoelectric film in which spontaneous polarization is directed from the lower electrode layer toward the upper electrode layer by the film formation, the upper electrode layer has a magnitude greater than the coercive electric field of the piezoelectric film and the lower electrode. A method of manufacturing a piezoelectric element structure, wherein an electric field directed to a layer is applied with a pulse.   2. The method of manufacturing a piezoelectric element structure according to claim 1, wherein the piezoelectric film is a perovskite oxide containing at least Pb.   3. The method for manufacturing a piezoelectric element structure according to claim 1, wherein a ratio B / A between a voltage application time A and a non-voltage application time B in pulse application of the electric field is 1 or more.   4. The method of manufacturing a piezoelectric element structure according to claim 3, wherein a ratio B / A between the voltage application time A and the non-voltage application time B in the pulse application of the electric field is 10 or more. A piezoelectric element structure comprising a plurality of piezoelectric elements in which a lower electrode layer, a piezoelectric film formed by sputtering and an upper electrode layer are laminated in this order on a substrate,
The piezoelectric element structure produced by the method according to any one of claims 1 to 4, wherein the lower electrode layer is a common electrode and the upper electrode layer is an individual electrode.
The defect rate due to film breakage due to the polarization inversion process of the piezoelectric film of the piezoelectric element in the piezoelectric element structure is 1% or less,
The piezoelectric element structure according to claim 1, wherein the spontaneous polarization of the piezoelectric film is directed from the upper electrode layer toward the lower electrode layer.   6. The piezoelectric element structure according to claim 5, wherein the piezoelectric film is a perovskite oxide containing at least Pb.

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