JP2005353876A - Piezoelectric material laminate structure, piezoelectric element, piezoelectric material device, and liquid discharge head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a piezoelectric element of multilayer structure whose piezoelectric characteristic and response are satisfactory without using PZT etc. containing an adhesive or lead. <P>SOLUTION: A first electrode 2 is deposited on a base body 1, a piezoelectric laminate 5 is formed of 3 layers where an intermediate layer 4 is inserted between piezoelectric bodies 3 made of e.g. zinc oxide and the like, and a second electrode 2 is deposited on it. Regarding the two piezoelectric bodies 3, the polarization directions of crystal are opposite to each other with the intermediate layer 4 inserted therebetween, so that displacement etc. are canceled to obtain satisfactory piezoelectric characteristic. Compared with the case of using an adhesive, the variation of resonance frequencies is reduced to realize a high-definition resonator, liquid discharge head, etc. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric laminated structure widely used in various piezoelectric devices such as robots, microactuators, liquid ejection heads, piezoelectric vibrators, piezoelectric resonators, filters, ultrasonic transducers, surface acoustic wave devices, sensors, etc. The present invention relates to an element, a piezoelectric device, and a liquid discharge head.

  The multilayer piezoelectric laminated structure used in conventional piezoelectric elements is obtained by polarizing a plurality of piezoelectric bodies using ceramic plates or single crystals and bonding the piezoelectric bodies with an adhesive so that the polarization directions are opposite to each other. It was a structure that was laminated. As a method for reversing the polarization direction in a crystal, a method has been reported in which titanium is diffused in a lithium niobate single crystal so that the polarization direction of the titanium diffusion portion is an inversion layer (see Non-Patent Document 1).

In addition, a piezoelectric body using lead zirconate titanate (PZT) having excellent piezoelectric characteristics as a piezoelectric material is used in various piezoelectric application fields such as actuators. As piezoelectric materials other than PZT, inorganic materials such as lithium niobate, bismuth titanate, quartz crystal, zinc oxide, and aluminum nitride, and polymer materials such as polyvinylidene fluoride have been put into practical use.
Nakamura et al., IEICE Technical Report, CPM86-17 (1986)

  However, the conventional technology as described above uses a ceramic plate or a single crystal as the piezoelectric body, and thus is not suitable for increasing the frequency of the device. Further, since the thickness of each piezoelectric body is usually 10 μm or more, the laminated body becomes large, and since the machining is the center, it is difficult to form a precise structure as compared with the fine processing of the semiconductor. Furthermore, since the resonance frequency is lowered when the piezoelectric body is thick, it is unsuitable for increasing the frequency of the device, and there is a problem that the usable drive frequency cannot be increased.

  Furthermore, the method of laminating piezoelectric bodies with an adhesive cannot normally be used at high temperatures because the adhesive is organic. In addition, since the thickness of the adhesive also has a large distribution, variations in piezoelectric characteristics have occurred.

  Further, the method of diffusing titanium into lithium niobate requires a high temperature of 1000 ° C. or more to reverse the diffusion and polarization direction of titanium, and the lithium niobate single crystal is very expensive. The crystal orientation is also limited. Furthermore, since the diffusion range of titanium is also limited, there is a limit in controlling the thickness of the piezoelectric body whose polarization direction is reversed. Further, in the method of diffusing titanium using lithium niobate, a two-layer structure can be formed, but there is a problem that it is difficult to increase the number of layers.

  PZT as a piezoelectric material is used in various application fields including actuators, but due to global environmental problems, restrictions on the use of lead constituting PZT are being studied. Already outside the field of piezoelectric application, materials that do not contain lead at all, such as solder and lenses, have come to be used. As described above, in the field of piezoelectric material application, simply having excellent piezoelectric characteristics cannot be said to be a practical material, and there is an urgent need to realize excellent piezoelectric characteristics with a material having a low environmental load.

  In addition, miniaturization of device products for various piezoelectric materials is also important. For this purpose, it is necessary to reduce the thickness of the piezoelectric material to cope with fine processing that is impossible by machining.

  The present invention has been made in view of the above-mentioned unsolved problems of the conventional technology, and can realize excellent piezoelectric characteristics without using an adhesive or a piezoelectric material having a large environmental load. An object of the present invention is to provide a piezoelectric laminated structure, a piezoelectric element, a piezoelectric device, and a liquid discharge head that enable not only machining but also fine machining.

  In order to achieve the above object, the piezoelectric laminated structure of the present invention is a piezoelectric laminated structure having a plurality of piezoelectric bodies and at least one intermediate layer between a pair of electrodes, and a film structure between the electrodes. Is provided with one or a plurality of laminated portions that become “piezoelectric body / intermediate layer / piezoelectric body”, and the piezoelectric bodies through the intermediate layer have polarization directions opposite to each other. .

  It has a laminated structure in which an intermediate layer is disposed at the interface between piezoelectric bodies, and the polarization directions of the piezoelectric bodies via the intermediate layer are opposite to each other. Therefore, the piezoelectric bodies through the intermediate layer are displaced in the opposite directions when a voltage is applied, and both the displacement and the force can be improved. Compared with a piezoelectric body formed with only one layer with the same film thickness. Large piezoelectric characteristics can be obtained.

  In order to ensure mechanical durability and performance improvement, the piezoelectric body and the intermediate layer are made of oxide or nitride, and the electrode may be made of any material as long as the adhesion to the piezoelectric body is not a problem in practice. It is preferable to use an oxide when it is required to be used in an environment with large fluctuations or when durability is required.

  For example, when zinc oxide is used as the piezoelectric body, a metal electrode is generally used in many cases. However, in this case, a problem remains in adhesion with zinc oxide, and problems such as electrode peeling may occur. is there. In order to avoid this, an electrode made of zinc oxide doped with conductivity (for example, gallium) to provide conductivity is used. With this configuration, it is possible to stack the piezoelectric body and the electrode with less interface strain.

  Also in the high frequency application field, there is an intermediate layer between the layers of the piezoelectric body, and the presence of this intermediate layer makes the polarization direction of the piezoelectric body clear, so that the resonance frequency is higher than when using a conventional adhesive. Variations can also be reduced. As a result, the Q value indicating the degree of resonance can be greatly improved.

  As shown in FIG. 1A, a piezoelectric laminate 5 having a piezoelectric laminate structure in which a first electrode 2 is laminated on a substrate 1 and an intermediate layer 4 is sandwiched between two piezoelectric bodies 3. Is formed. The piezoelectric laminate 5 is a laminate in which the intermediate layer 4 is disposed at the interface between the two layers of the piezoelectric bodies 3, and the polarization directions of the piezoelectric bodies 3 through the intermediate layer 4 are opposite to each other. A second electrode 2 made of a conductive material is disposed on the piezoelectric laminate 5.

  As a manufacturing method of each piezoelectric body 3 and intermediate layer 4, various vacuum deposition methods such as sputtering method, ion plating method, MOCVD method, MBE method and the like can be generally used. Also, a sol-gel method, a hydrothermal method, various plating methods, a sintering method, and the like can be used. FIG. 1A shows a piezoelectric laminated structure having a film configuration “electrode / piezoelectric body / intermediate layer / piezoelectric body / electrode”, but the polarization directions of mutually opposite directions of three or more layers sandwiching the intermediate layer are shown. A film configuration in which piezoelectric bodies having the above structure are stacked may be used.

  Further, as shown in FIG. 1B, a film structure “electrode / intermediate layer / piezoelectric body / intermediate layer / piezoelectric body / with an intermediate layer 14 added between the upper and lower electrodes 12 and the adjacent piezoelectric bodies 13 respectively. The piezoelectric laminate 15 having “intermediate layer / electrode” may be used. Furthermore, a film configuration in which three or more piezoelectric bodies having polarization directions opposite to each other are stacked with the intermediate layer interposed therebetween, and the intermediate layer is interposed between the upper and lower electrodes.

  The thickness of each piezoelectric body can be arbitrarily set according to the intended application, but the thickness of one layer is preferably less than 20 μm. Needless to say, the thicknesses of the piezoelectric bodies are not necessarily the same. As the piezoelectric material, any material can be used as long as it is an oxide or nitride having piezoelectric characteristics. Furthermore, the piezoelectric material does not need to be the same material, and piezoelectric materials having different compositions, different crystal structures, and different crystal states may be combined. However, in view of environmental problems, it is needless to say that the piezoelectric material is desirably a stable material that does not release harmful elements such as heavy metals such as lead, mercury, cadmium, and chromium due to temperature changes.

  The thickness of the intermediate layer can be arbitrarily set according to the intended use. It is desirable that the thickness T1 of the intermediate layer satisfies the relationship of 0 <T1 ≦ T2 with respect to the film thickness T2 of the thinnest piezoelectric body among the piezoelectric bodies constituting the laminated body. The material used for the intermediate layer is not limited, but a material having a lattice constant or a thermal expansion coefficient similar to that of the piezoelectric material is preferable.

  The electrode material may be any conductive material, but an oxide conductive material is preferable. Typical materials are zinc oxide doped with gallium or the like, ITO or the like.

  As described above, each piezoelectric body is manufactured by a thin film manufacturing technique such as a vacuum deposition method without using a ceramic plate or a crystal, so that the thickness of each piezoelectric body can be reduced and mainly an organic material. There is no need to use an adhesive consisting of Similarly, since the intermediate layer is also manufactured by a vacuum deposition method or the like, the thickness of the intermediate layer can be reduced.

  Therefore, it is possible to cope with microfabrication that is impossible with machining, so that not only machining but also microfabrication using semiconductor processing technology and processing using laser light, etc. are applied to process piezoelectric elements. Is possible.

In the piezoelectric element as described above, for example, when the piezoelectric constant d ₃₁ is used, when an AC voltage is applied to the upper and lower electrodes, the polarization direction of the piezoelectric bodies through the intermediate layer is reversed, so that the intermediate layer The piezoelectric bodies are displaced in directions opposite to each other via the.

  For this reason, compared with the case where a piezoelectric body is used independently, it is possible to improve both displacement and force, and it is possible to realize excellent piezoelectric characteristics. In particular, by forming a structure in which a plurality of piezoelectric bodies are laminated, the hysteresis of the displacement characteristics with respect to the applied voltage is alleviated, and it can be used as an actuator capable of controlling precise displacement. In addition, since the piezoelectric characteristics are greatly improved, excellent piezoelectric characteristics can be realized even when the above-described material with low environmental load is used.

  The number of piezoelectric layers can be arbitrarily set according to the intended application. For example, when a high frequency is used, the resonance frequency of the piezoelectric laminate and the value of Q become a problem. The target resonance frequency may be set according to the thickness, the number of layers, the area, etc. of the piezoelectric body constituting the laminate. For this reason, with the above film configuration, it is possible to realize vibrators and resonators of several tens of MHz to several hundreds of GHz.

  In the film configuration of FIG. 1, all are cases where an electric field is applied in the thickness direction of the laminated body. However, for example, an electrode is provided in one of the desired arrangements and used by applying an electric field in the in-plane direction. It goes without saying that it is also possible to do.

  In this example, a piezoelectric element having the piezoelectric laminate 5 of FIG. 1 was prepared by the following method.

  First, the first electrode 2 was formed on the substrate 1 made of quartz glass (thickness 0.3 mm) by sputtering. In this example, a zinc oxide sintered body doped with 3% gallium was used as a target to form an electrode having a thickness of 200 nm.

  Next, a zinc oxide film having a thickness of 5 μm was formed by RF sputtering using zinc oxide as a target material to form the first piezoelectric body 3, and then a 100 nm magnesium oxide film was formed to form the intermediate layer 4.

  Thereafter, a zinc oxide film having a thickness of 5 μm is formed on the magnesium oxide film by RF sputtering using metal zinc as a target material to form the second piezoelectric body 3, and subsequently, the second electrode 2 is oxidized by doping with gallium. A zinc film was laminated to 200 nm to obtain a piezoelectric laminate 5.

  A voltage was applied to the piezoelectric element produced as described above, and the displacement was measured with an optical displacement meter. As shown in FIG. 2, the measurement method is as follows. In the state where the piezoelectric element having the piezoelectric laminate 5 is cantilevered on the base 6, a lead wire is attached to the lower electrode 2 and a power source 7 (in this embodiment, An AC voltage was applied at a low frequency AC power source of 5 Hz to 50 Hz. When the voltage is applied in this way, the piezoelectric body 3 contracts or expands in the direction perpendicular to the stacking direction, that is, in the longitudinal direction of the substrate 1 due to the lateral effect of the piezoelectric body 3. For this reason, the piezoelectric laminate 5 is bent and deformed perpendicularly to the longitudinal direction of the substrate 1 as a whole. The piezoelectric characteristics were examined by detecting this deformation with the optical displacement meter 8. In this example, the piezoelectric laminate 5 cut by machining so as to have a width of 2 mm and a length of 10 mm was used as a sample. The measurement results are shown in FIG.

  For comparison, a piezoelectric element in which a zinc oxide film of 10 μm is formed using metal zinc as a target material instead of the piezoelectric laminate 5 of the present embodiment to form a single-layer piezoelectric element, and zinc oxide Displacement was measured in the same manner as described above for a piezoelectric element in which a 10 μm zinc oxide film was formed as a target material and a single-layer piezoelectric body was formed. The measurement result when metallic zinc is used as the target material is shown in FIG. 4, and the measurement result when zinc oxide is used as the target material is shown in FIG. As can be seen from FIG. 4 and FIG. 5, it was confirmed that the phase of displacement was changed by changing the target material from zinc metal to zinc oxide.

  In this example, as can be seen from FIG. 3, it was confirmed that even when the total film thickness of the plurality of piezoelectric bodies was the same as 10 μm, the displacement amount increased approximately twice.

  FIG. 6 shows a thin film resonator having the piezoelectric laminated structure shown in FIG. 1A. A silicon oxide film 1a is deposited on a silicon (100) wafer S to a thickness of 2.5 μm by RF sputtering. The silicon oxide film 1a is formed and used as a substrate having a piezoelectric layered structure. Next, an electrode 2 as a lower electrode was formed by RF sputtering. The material is a zinc oxide film doped with gallium, and the film thickness is 150 nm. The electrode 2 was patterned by photolithography technique as shown in the figure after film formation.

  On the electrode 2, piezoelectric bodies and intermediate layers constituting the piezoelectric laminate 5 are alternately formed. First, a ZnO film was formed to a thickness of 2.2 μm using a ZnO sintered body as a target. Subsequently, an alumina film was formed to a thickness of 0.1 μm, and ZnO was formed to a thickness of 2.2 μm using Zn metal as a target. Then, Cr / Au was formed in the thickness of 10 nm / 200 nm as the electrode 2 used as an upper electrode, respectively.

  Finally, a silicon oxide film of 2 μm is formed on the back surface of the silicon (100) wafer S, patterned to serve as a mask, and then etched with EDP solution (46% ethylenediamine + 4% pyrocatechol + 50% water). Thus, an opening 1b was formed to manufacture a resonator.

  When power was supplied between the upper and lower electrodes 2 and the admittance of the vibration mode in the thickness direction of the piezoelectric laminate 5 was measured, the result was as shown in FIG. The resonance frequency was 466.4 MHz and Q was 6000. This result shows that the piezoelectric laminated structure of this example exhibits a sufficient function as a thin film resonator. In contrast, when the ZnO film is one layer, the thickness is 4.5 μm, and the silicon oxide film is 2.5 μm, the resonance frequency is almost the same as 466 MHz, but Q is 730. It was.

  A resonator having a piezoelectric element having the film configuration shown in FIG. 8 was prepared. First, Au / Cr used as the 1st electrode 22 is formed in the epoxy board used as a base | substrate by RF sputtering method. After patterning the electrode 22 into a desired shape, the portion other than the electrode portion is covered with an epoxy resin. Next, an aluminum nitride film piezoelectric body 23 having a thickness of 8 nm is formed using metal aluminum as a target. Further, a magnesium oxide sintered body is used as the intermediate layer 24 to form a magnesium oxide film with a thickness of 1 nm, and an aluminum nitride sintered body as a target to form an aluminum nitride film piezoelectric body 23 with a thickness of 8 nm. In this way, the film formation of the nitrogen aluminum sintered body and the piezoelectric body 23 targeting metal aluminum was alternately repeated 2000 times with the intermediate layer 24 interposed therebetween. Thereafter, a second electrode 22 of Cr / Au was formed, and finally the epoxy resin was removed to form a resonator.

  When the admittance characteristics of the resonator manufactured in this way were measured, it was as shown in FIG. 9, and a resonator having a resonance frequency of 60 GHz and Q of 60000 was obtained. In contrast, when a single layer film of an aluminum nitride film was used with an aluminum nitride sintered body as a target, the resonance frequency was the same, but Q was 590. It was confirmed that it could be greatly increased.

  As shown in FIG. 10, first, the silicon wafer 30 is anisotropically etched to form a liquid supply port 30 a, a liquid chamber 30 b, a nozzle 30 c, and the like, and a diaphragm 31 made of heat-resistant glass serving as a substrate on the surface of the silicon wafer 30. Were anodically bonded. Subsequently, a first electrode 32 of zinc oxide doped with gallium was formed. Further, an intermediate layer of a silicon oxide film (film thickness 0.1 μm) is formed using a silicon oxide sintered body as a target, and then a zinc oxide film (film thickness 6 μm) formed using a zinc oxide sintered body as a target. Piezoelectric material, an intermediate layer of a silicon oxide film (film thickness 0.1 μm) formed using a silicon oxide sintered body as a target, a zinc oxide film (film thickness 7 μm) piezoelectric film formed using metal zinc as a target, An intermediate layer of a silicon oxide film (thickness: 0.1 μm) targeting a silicon oxide sintered body is continuously formed, and a piezoelectric laminate 35 similar to the piezoelectric laminate 15 shown in FIG. Was formed on the liquid chamber 30b. Thereafter, Cr / Au was attached as the second electrode 32. Finally, patterning was performed to a width of 200 μm and a length of 3 mm by photolithography to form a liquid discharge head.

  Here, when a liquid (for example, water, alcohol, color ink, etc.) was supplied from the liquid supply port 30a and a pulse voltage was applied to the piezoelectric laminate 35, the discharge of the liquid from the nozzle 30c was observed. The liquid discharge speed at this time was a maximum of 13 m / s when isopropyl alcohol was used as the liquid.

  On the other hand, a liquid discharge head in which a zinc oxide film was formed to a thickness of 10 μm to form a single-layer piezoelectric body was prepared, and a similar experiment was conducted. May not be observed, and even when liquid discharge is observed, the discharge speed of isopropyl alcohol is a maximum of 2 m / s.

It is a figure which shows the structure of the piezoelectric element by two embodiment. 6 is a diagram for explaining a method for measuring displacement of a piezoelectric element according to Example 1. FIG. 3 is a graph showing the measurement results of displacement of a piezoelectric element according to Example 1. It is a graph which shows the displacement measurement result of the piezoelectric element by one comparative example. It is a graph which shows the displacement measurement result of the piezoelectric element by another comparative example. 6 is a cross-sectional view showing a film configuration of Example 2. FIG. It is a figure which shows the high frequency response of Example 2. 6 is a sectional view showing a film configuration of Example 3. FIG. It is a figure which shows the high frequency response of Example 3. 6 is a schematic cross-sectional view showing a liquid ejection head according to Embodiment 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base | substrate 1a Silicon oxide film 2, 12, 22, 32 Electrode 3, 13, 23, 33 Piezoelectric body 4, 14, 24, 34 Intermediate | middle layer 5, 15, 25, 35 Piezoelectric laminated body 30 Silicon wafer 30a Liquid supply port 30b Liquid chamber 30c Nozzle 31 Diaphragm

Claims (7)

  A piezoelectric laminated structure having a plurality of piezoelectric bodies and at least one intermediate layer between a pair of electrodes, and a laminated portion having a film configuration of “piezoelectric body / intermediate layer / piezoelectric body” between the two electrodes is 1 A piezoelectric laminate structure in which one or a plurality of piezoelectric bodies via the intermediate layer are provided such that their polarization directions are opposite to each other.   A piezoelectric laminated structure having a plurality of piezoelectric bodies and at least three intermediate layers between a pair of electrodes, and the film configuration between both electrodes is “intermediate layer / piezoelectric body / intermediate layer / piezoelectric body / intermediate layer”. One or a plurality of laminated parts to be provided are provided, and the piezoelectric bodies via the intermediate layer have polarization directions opposite to each other.   3. The piezoelectric layered structure according to claim 1, wherein the maximum thickness of the intermediate layer is not more than the minimum thickness of the piezoelectric body.   4. The piezoelectric laminated structure according to claim 1, wherein the piezoelectric body and the intermediate layer are oxides or nitrides, and at least one of the electrodes is an oxide.   5. A piezoelectric element comprising: the piezoelectric multilayer structure according to claim 1; and a base that supports the piezoelectric multilayer structure.   A piezoelectric device comprising the piezoelectric element according to claim 5 and a drive unit driven by the piezoelectric element.   6. A liquid discharge head comprising: the piezoelectric element according to claim 5; and a liquid chamber pressurized by the piezoelectric element.

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