JP4920867B2 - Actuator and inkjet head - Google Patents

Description

  The present invention relates to an actuator that generates a mechanical displacement and an ink jet head using the actuator. These are actuators and inkjet heads that can be finely processed suitable for micromachines. In particular, it is a high-density inkjet head and an actuator that can embody it.

  Various things are known as an actuator which generates a mechanical displacement. Among them, unimorph type and bimorph type actuators have a simple structure and are suitable as a structure of a micromachine.

  The structure of the above type actuator has a piezoelectric film having an elastic body and electrodes. As an ink jet head using this actuator, it is used as a bender type head. However, due to the characteristics of the piezoelectric film, a head having high density and ejecting power cannot be realized.

  Among them, studies have been made to reduce the rigidity of the displacement portion and increase the density. For example, Patent Document 1 describes a method of manufacturing an inkjet head in which a piezoelectric film is thinned. However, the above-mentioned patent does not have a detailed description regarding the composition of the piezoelectric film, and only uses general-purpose materials. On the other hand, Patent Document 2 describes an invention in which characteristics of a thin film are improved by making the composition of a piezoelectric film mainly composed of lead zirconate titanate (PZT) lead-excess. .

  In general, PZT of ceramic body is processed and manufactured at high temperature, so adding excessive lead that tends to disappear is a technique that has been used conventionally, and in the case of ceramic body, As a result, a material with good characteristics could be obtained.

However, according to the study by the present inventors, even when lead is added excessively in a preferentially oriented or single crystal type piezoelectric / electrostrictive film, only the grain boundary portion is increased and the piezoelectric characteristics can be positively affected. It has been found that not only the crystallinity is poor, but also the electrical resistance is lowered, which gives undesirable results.
US Patent 5,265,315 JP 2000-299510 A

  Accordingly, the present invention provides an actuator that can exhibit high performance even when microfabricated, and provides an inkjet head with high density and high discharge power. In particular, it is an object of the present invention to provide an actuator and an ink jet head having a single-oriented crystal or a single-crystal thin film having a thin film with excellent piezoelectric characteristics.

The present invention relates to an actuator and an ink jet head having a piezoelectric film having a perovskite structure and having an A site component having a composition component smaller than the stoichiometric ratio by 1 than the B site component. Further, when the component amount of the A site element per unit volume of the perovskite structure of the piezoelectric film is a and the component amount of the B site element is b, a / b is greater than 0.8 and 0.96 or less. An actuator and an inkjet head, wherein the width of the grain boundary in the cross section of the piezoelectric film is 0.02 μm or more and 0.05 μm or less. More preferably, a / b is greater than 0.85.

  The a / b ratio can be measured by ICP emission spectroscopy.

  When a / b is 0.8 or less, the occupancy of the A site of the perovskite structure is too low, and it is not preferable because the piezoelectric property cannot be enlarged even if the film structure has good crystallinity. Absent. In addition, when a / b is 1.0 or more, the A-site component contained exceeding 1.0 creates a grain boundary, which causes dripping of crystallinity or a decrease in electrical resistance. It is also expected that the A site element is contained in the B site and oxygen site, which is a factor that inhibits the expression of piezoelectric characteristics.

  Since the piezoelectric / electrostrictive film of the present invention has an a / b ratio in a specific range, it is possible to obtain a high-quality film having a grain boundary width of 0.05 μm or less with a single orientation crystal or single crystal film. Further, the film has an area occupied by the grain boundary portion of 0.5% or less.

  Examples of the piezoelectric / electrostrictive film material of the present invention include lead-based materials and non-lead-based materials having a perovskite crystal structure. Examples of the piezoelectric film material include lead zirconate titanate and barium titanate. A trace amount of additive elements may be added to these.

  The ratio of Zr and Ti in the lead zirconate titanate is preferably 40% to 70%.

  Electrostrictive film materials include: lead zinc niobate, lead magnesium niobate, lead niobate zinc titanate, lead niobate magnesium titanate, lead niobate scandate titanate, titanium indium niobate Lead acid, nickel niobate, lead zirconate titanate, potassium diobate, lithium diobate and the like. A small amount of additive elements may be added to these.

  The crystallinity of the piezoelectric / electrostrictive film of the present invention is a single-orientation crystal film or a single-crystal film, and the single-orientation crystal film has a specific crystal orientation of 80% or more, preferably 95% by X-ray analysis. This is the above film. The measurement of the crystallinity is calculated by dividing the peak intensity of the main peak by the sum of the peak intensities obtained by crystal analysis by out-plane measurement with an X-ray analyzer (Rigaku RINT in-plane). For example, when the peak intensity of [001] is 100,000 and the peak intensity of [110] and the peak intensity of [111] are 10,000 and 1000, respectively, the crystallinity of this film is 100000 ÷ 111000 = 0.090 Thus, the crystallinity is 90.1%.

  In measuring the grain boundary part of the piezoelectric / electrostrictive film, the width and occupied area of the grain boundary part can be measured by TEM observation of the cross section of the film.

  The crystal structure is tetragonal, rhombohedral, orthorhombic or monoclinic, preferably tetragonal or rhombohedral.

  The crystal orientation of the above crystal structure is <100>, <110>, <111>, and is preferably <100> because of good piezoelectric characteristics.

  In order to make the a / b ratio within the specific range in the present invention, this is achieved by charging the raw material at the time of production with an A-site component equal to or less than the stoichiometric ratio. In particular, when the A-site component is lead, even if it is not less than an equal amount, it disappears by the heat treatment step, so a / b is less than 1.0.

The piezoelectric / electrostrictive film production method of the present invention can be formed by sputtering, sol-gel method, hydrothermal method, MO-CVD method, gas deposition method, molecular beam epitaxy method, laser ablation method or the like.
Of these, sputtering and MO-CVD are preferred because they facilitate the formation of a single orientation crystal or single crystal film.

  Next, the structure of the actuator of the present invention will be described. As shown in FIG. 1, the actuator of the present invention includes an elastic film 1, a lower electrode 2, a piezoelectric / electrostrictive film 3, and an upper electrode 4. An adhesive layer may be provided between the elastic film 1 and the lower electrode 2 to prevent peeling. By making the piezoelectric / electrostrictive film and the elastic film into thin films, the rigidity can be lowered and the displacement can be increased. The film thickness of the piezoelectric / electrostrictive film is preferably 1 μm to 10 μm. A preferable film thickness of the elastic film is 2 to 15 μm.

  FIG. 2 shows the structure of the inkjet head of the present invention. FIG. 2 shows a cross section of the inkjet head. Reference numeral 11 denotes an individual liquid chamber into which a liquid enters. Reference numeral 12 denotes a communication hole connecting the individual liquid chamber and the discharge port 14. Reference numeral 2 denotes a lower electrode which is not patterned because it is used as a common electrode. On the other hand, the piezoelectric / electrostrictive film 3 and the upper electrode 4 are patterned according to the width of the individual liquid chamber. Although it is possible to configure the piezoelectric / electrostrictive film without patterning, it is preferable to perform patterning in order to increase the amount of displacement. Reference numeral 13 denotes a partition for making the individual liquid chamber and the communication hole independent. If the partition wall portion is too thin, the partition wall portion also vibrates due to the vibration of the elastic film 1, and the discharge of droplets from the discharge port 14 becomes unstable or impossible.

  FIG. 3 shows a longitudinal section of the inkjet head. In FIG. 3, 22 is a common liquid chamber provided to carry the liquid into the individual liquid chamber. The liquid placed in the common liquid chamber 22 is sent through the throttle portion 21 connected to the individual liquid chamber 11. Since the narrowed portion 11 has a smaller cross-sectional area than the individual liquid chamber and the common liquid chamber, the back flow of liquid to the common liquid chamber when the elastic film 1 is displaced and the liquid is discharged from the discharge port 14. Can be prevented.

  The common liquid chamber 22 communicates with a liquid tank (not shown), and is prepared to fill the common liquid chamber with the discharged liquid as needed. Although the width w of the individual liquid chamber in FIG. 2 and the width l of the individual liquid chamber in FIG. 3 are different, l / w is preferably 5 to 100, but the amount of ejected droplets May be less than 5.

The discharge port 14 may take various shapes such as a circle and a star shape, but preferably has a size of 10 to 40 μm.
In particular, a circular shape having a diameter of 10 to 25 μm is preferable. In the present invention, the form in which the discharge ports are arranged in a straight line is illustrated, but a form in which the discharge ports are alternately arranged in a zigzag form may be used.

The material of the lower electrode and the upper electrode of the actuator and the inkjet head of the present invention is a metal, an alloy, a conductive oxide, and the like. Specifically, as the metal, for example, Pt, Au, Ir, Ni, Sn, Al, Cu, In, Ti, Ag, Pd, Cr and the like. Examples of the alloy include Au—In, Mo—Ag, Au—Pd—In, Ag—Ni, Ag—Cu, Cu—Ti, and Ag—Cu—Ti. Examples of the conductive oxide include perovskite oxides such as SuRuO ₃ , (La—Sr) TiO ₃ , LaNiO ₃ , LaCrO ₃ , CaRuO ₃ , BaPbO ₃ , and IrO ₂ , InO, In—SnO, and the like. It is a component oxide or a two-component oxide.

  The film thickness of the lower electrode and the upper electrode of the actuator and the ink jet head of the present invention is 50 nm to 1 μm, preferably 100 nm to 500 nm.

Examples of the adhesive layer inserted to prevent peeling between the elastic film and the lower electrode include metals such as Ti, TiO ₂ , Ir, IrO, and Cr, and metal oxides. The thickness of the adhesive layer is 5 nm to 100 nm.

The elastic film of the present invention has a Young's modulus of 10 to 300 GPa, preferably 30 to 200 GPa.
Examples of the material include metals and ceramics. Specifically, metals such as Cr, SUS, Si, Pt, and Ir, and ceramics such as ZrO ₂ , Al ₂ O ₃ , and SiO ₂ are used.

  Since the actuator and the inkjet head of the present invention have the above characteristics, they are elements excellent in displacement amount and displacement speed. In particular, as an inkjet head, an element having a high density and a large ejection force can be obtained.

  Next, an Example is given and this invention is demonstrated.

  As described above, the actuator of the present invention and the ink jet head using the actuator of the present invention can obtain very good characteristics by adjusting the composition ratio of the A site and B site of the piezoelectric / electrostrictive film to a specific range. I understand.

  In particular, it can be understood that a large discharge droplet is possible from an ink jet head having individual liquid chambers of the same size, and that the material and configuration have excellent piezoelectric characteristics of the element.

( Example 1, 2, reference example 1 , comparative example 1)
FIG. 4 shows a cross-sectional view of an inkjet head having the actuator of the present invention. In FIG. 4, reference numerals 1 and 4 denote an elastic film and a piezoelectric / electrostrictive film as described above. Reference numeral 31 denotes a partition wall of the individual liquid chamber portion, which is a Si substrate. Reference numerals 32 and 33 denote separate substrates for producing the discharge port and the throttle portion, and an SUS substrate is used. The width w of the individual liquid chamber is 60 μm, the length l is 1.2 mm, and the depth is 250 μm. These liquid chamber structures were fabricated by an ICP process using an SOI substrate.

The elastic film is B-doped Si and has a thickness of 2 μm. On the liquid chamber side, an SiO ₂ film as an insulating layer of the SOI substrate is attached to Si with a thickness of 0.2 μm. The lower electrode is Pt (0.2 μm) / TiO ₂ (0.05 μm), the upper electrode is Au (0.3 μm), 3 is a Pb (Zr _0.55 Ti _0.45 ) O ₃ thin film with a thickness of 2.5 μm, as shown in Table 1. Various films were formed. The thicknesses of the 32 and 33 SUS substrates are 50 μm and 80 μm, respectively, and a discharge port having a diameter of 17 μmΦ is formed on the 33 substrate.

As can be seen from Table 1, in Example 1, the composition ratio of Pb to B site element is 0.97 , 0.91 in Reference Example 1 , and 0.87 in Example 2 . On the other hand, the composition ratio of the film produced in Comparative Example 1 was 1.05. Table 2 shows the results of evaluating the characteristics of these inkjet heads. Table 2 shows the maximum value of the discharged droplets of each head, the discharge speed at that time, and the maximum drive frequency that can be displaced. As can be seen from Table 2, the maximum drive frequency of the device of Comparative Example 1 is lower than that of the example. This is presumably because the above-mentioned frequency cannot be displaced with good followability to the drive frequency. In addition, since the maximum discharge droplet amount is small, it can be seen that the displacement amount is small compared to the cases of Examples 1 and 2 and Reference Example 1 .

( Example 3 )
The piezoelectric film was changed to [Pb (Mg _1/3 Nb _2/3 ) O ₃ ] _0.65- [PbTiO ₃ ] _0.35 of the electrostrictive film as compared with Examples 1 and 2 and Reference Example 1. Elements were fabricated in the same manner as in Examples 1 and 2 and Reference Example 1 . Since the thin film was produced by the MO-CVD method, it became a thin film with good crystallinity (crystallinity 97.2%) and adhesion. The composition ratio of Pb of the A site element was 0.96 with respect to Mg, Nb, and Ti of the B site element. As a result of the discharge characteristics, the maximum discharge droplet was 14 pl or more, and the discharge speed at that time was 15 m / sec or more, which was good.

The structure of the actuator of this invention is shown. The structure of the inkjet head of this invention is shown. A longitudinal section of an ink jet head is shown. 1 is a cross-sectional view of an ink jet head having an actuator of the present invention.

Claims (6)

An actuator having a piezoelectric film having a perovskite structure,
The relationship between the component amount a of the A site component of the perovskite structure and the component amount b of the B site component is 0.8 <a / b < 0.96 , and the grain boundary in the cross section of the piezoelectric film is An actuator having a width of 0.02 μm or more and 0.05 μm or less. The actuator according to claim 1 , wherein the component of the A site is lead.   3. The actuator according to claim 1, wherein the component of the B site includes at least one element selected from Zr, Ti, Nb, Zn, Mg, Sc, Ni, and In.   The actuator according to claim 1, wherein the piezoelectric film is a single orientation crystal film.   The actuator according to claim 1, wherein the piezoelectric film has a thickness of 1 μm or more and 10 μm or less.   An ink jet head comprising the actuator according to claim 1.

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