JP5790835B2 - Method for manufacturing piezoelectric element - Google Patents

Description

The present invention relates to a method for manufacturing a piezoelectric element including a first electrode, a piezoelectric layer, and a second electrode.

  A piezoelectric element used in a liquid ejecting head such as an ink jet recording head is an element in which a piezoelectric layer made of a piezoelectric material exhibiting an electromechanical conversion function is sandwiched between two electrodes. For example, a material using titanium, for example, lead zirconate titanate (PZT) has been proposed (for example, see Patent Document 1).

JP 2001-223404 A

  In order for a piezoelectric element used in a liquid ejecting head or the like to have excellent piezoelectric characteristics that can obtain a large amount of displacement at a low voltage, it is important to have a vector component of a polarization moment in the direction of an applied electric field. This is because a domain having a polarization moment opposite to the direction of the electric field contributes to lowering the piezoelectric characteristics.

  For this reason, for example, after forming the piezoelectric layer, an electric field in the same direction as the driving electric field applied during liquid ejection is applied to the piezoelectric layer to perform initialization to align the directions of the polarization moments.

  However, since initialization was performed by applying a relatively large electric field when performing initialization to align the polarization moments of the piezoelectric layer, a large amount of energy was required, resulting in increased costs and piezoelectricity by applying a large electric field. There was a risk of deterioration or destruction of the body layer.

  Such a problem is not limited to the ink jet recording head, and similarly exists in a liquid ejecting head that ejects liquid other than ink.

In view of such circumstances, an object of the present invention is to provide a method for manufacturing a piezoelectric element that can suppress deterioration and destruction of a piezoelectric layer and improve piezoelectric characteristics with low energy.

An aspect of the present invention that solves the above problem is a method of manufacturing a piezoelectric element that includes a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode that causes a pressure change in a pressure generation chamber that communicates with a nozzle opening. The piezoelectric layer has a perovskite structure, the piezoelectric layer is preferentially oriented in the (100) plane, and the electric field direction applied to the piezoelectric layer is provided by the second electrode. When the <001> direction is perpendicular to a given plane, it is greater than the energy required to change the <111> direction polarization direction to the <110> direction, and the <111> direction polarization direction is <00 1 >. The piezoelectric element manufacturing method includes a polarization step of applying polarization of the piezoelectric layer by applying an electric field having an energy smaller than that required for the direction.
In such an aspect, the polarization treatment can be performed by applying an electric field having a relatively low electric field strength, the cost can be reduced, and the destruction of the piezoelectric layer can be suppressed.

Here, in the polarization step, when the polarization direction of the piezoelectric layer changes from the <111> direction to the <11 1 > direction by applying an electric field, the polarization direction in the middle of the change is directed to the <110> direction. Is preferred. According to this, the polarization direction in the <111> direction can be changed to the <11 1 > direction through the <110> direction with a relatively small applied voltage.

  In the polarization step, it is preferable that the piezoelectric layer does not enter a paraelectric state in which the polarization moment disappears. According to this, when the polarization moment is reversed during the polarization process, if it is in the paraelectric state, a considerably high energy state is required. However, by preventing the paraelectric state from occurring, the polarization moment can be reduced with a small applied voltage. Therefore, the dielectric breakdown of the piezoelectric layer can be suppressed.

  The piezoelectric layer preferably contains lead, zirconium and titanium. According to this, a piezoelectric element excellent in piezoelectric characteristics can be realized.

  The lattice constant in the direction perpendicular to the surface on which the second electrode is provided is preferably smaller than the lattice constant in the surface direction on which the second electrode of the piezoelectric layer is provided. According to this, a piezoelectric element excellent in piezoelectric characteristics can be realized.

  The piezoelectric layer is preferably monoclinic. According to this, a piezoelectric element excellent in durability and piezoelectric characteristics can be realized.

FIG. 3 is an exploded perspective view of the recording head according to the first embodiment. 2A and 2B are a plan view and a cross-sectional view of the recording head according to the first embodiment. 3 is a diagram illustrating a crystal lattice model according to Embodiment 1. FIG. FIG. 4 is a cross-sectional view illustrating the recording head manufacturing method according to the first embodiment. FIG. 4 is a cross-sectional view illustrating the recording head manufacturing method according to the first embodiment. FIG. 4 is a cross-sectional view illustrating the recording head manufacturing method according to the first embodiment. FIG. 4 is a cross-sectional view illustrating the recording head manufacturing method according to the first embodiment. 3 is a diagram schematically showing a change in the polarization axis direction of a crystal according to Embodiment 1. FIG. It is a graph which shows the result of the first principle electronic state calculation of this embodiment. 1 is a schematic diagram of a recording apparatus according to an embodiment.

Hereinafter, the present invention will be described in detail based on embodiments.
(Embodiment 1)
FIG. 1 is an exploded perspective view showing a schematic configuration of an ink jet recording head which is an example of a liquid jet head according to Embodiment 1 of the present invention. FIG. 2 is a plan view of a flow path forming substrate and its AA. It is a cross-sectional view.

  As shown in the drawing, the flow path forming substrate 10 is made of a silicon single crystal substrate in this embodiment, and an elastic film 50 mainly composed of silicon dioxide is formed on one surface thereof.

  A plurality of pressure generating chambers 12 are arranged in parallel in the width direction of the flow path forming substrate 10. In addition, a communication portion 13 is formed in a region outside the longitudinal direction of the pressure generation chamber 12 of the flow path forming substrate 10, and the communication portion 13 and each pressure generation chamber 12 are provided for each pressure generation chamber 12. Communication is made via a supply path 14 and a communication path 15. The communication part 13 communicates with a reservoir part 31 of a protective substrate, which will be described later, and constitutes a part of a reservoir that becomes a common ink chamber of each pressure generating chamber 12. The ink supply path 14 is formed with a narrower width than the pressure generation chamber 12, and maintains a constant flow path resistance of ink flowing into the pressure generation chamber 12 from the communication portion 13. In this embodiment, the ink supply path 14 is formed by narrowing the width of the flow path from one side. However, the ink supply path may be formed by narrowing the width of the flow path from both sides. Further, the ink supply path may be formed by narrowing from the thickness direction instead of narrowing the width of the flow path.

  Further, on the opening surface side of the flow path forming substrate 10, a nozzle plate 20 having a nozzle opening 21 communicating with the vicinity of the end of each pressure generating chamber 12 on the side opposite to the ink supply path 14 is provided with an adhesive. Or a heat-welded film or the like. The nozzle plate 20 is made of, for example, glass ceramics, a silicon single crystal substrate, or stainless steel.

  On the other hand, the elastic film 50 is formed on the side opposite to the opening surface of the flow path forming substrate 10 as described above, and the insulator film 55 is formed on the elastic film 50. Further, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 are laminated on the insulator film 55 by a process described later to constitute the piezoelectric element 300. Here, the piezoelectric element 300 refers to a portion including the first electrode 60, the piezoelectric layer 70, and the second electrode 80. In general, one electrode of the piezoelectric element 300 is used as a common electrode, and the other electrode and the piezoelectric layer 70 are patterned for each pressure generating chamber 12. In this case, a portion that is configured by any one of the patterned electrodes and the piezoelectric layer 70 and in which piezoelectric distortion is generated by applying a voltage to both electrodes is referred to as a piezoelectric active portion 320. In the present embodiment, the first electrode 60 is a common electrode of the piezoelectric element 300, and the second electrode 80 is an individual electrode of the piezoelectric element 300. However, there is no problem even if this is reversed for the convenience of the drive circuit and wiring. Also, here, the piezoelectric element 300 and the diaphragm that is displaced by driving the piezoelectric element 300 are collectively referred to as an actuator device. In the above-described example, the elastic film 50, the insulator film 55, and the first electrode 60 function as a diaphragm. However, the present invention is not limited to this. For example, the elastic film 50 and the insulator film 55 are provided. Instead, only the first electrode 60 may act as a diaphragm. Further, the piezoelectric element 300 itself may substantially serve as a diaphragm.

The piezoelectric layer 70 is made of a piezoelectric material having a perovskite structure represented by the general formula ABO ₃ having a polarization structure formed on the first electrode 60. As the piezoelectric layer 70, for example, a ferroelectric material such as lead zirconate titanate (PZT) or a material obtained by adding a metal oxide such as niobium oxide, nickel oxide, or magnesium oxide to the ferroelectric material is suitable. Specifically, lead titanate (PbTiO ₃ ), lead zirconate titanate (Pb (Zr, Ti) O ₃ ), lead zirconate (PbZrO ₃ ), lead lanthanum titanate ((Pb, La), TiO ₃ ) ), Lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti) O ₃ ) or lead magnesium titanate zirconate titanate (Pb (Zr, Ti) (Mg, Nb) O ₃ ), etc. Can do. All of these crystals have a pseudo cubic perovskite structure, and a typical lattice constant is about 405 pm to 425 pm.

  In the piezoelectric layer 70, crystals are preferentially oriented in the (100) plane, and the crystal structure thereof is rhombohedral or monoclinic. In the present invention, “crystals are preferentially oriented in the (100) plane” means that all crystals are oriented in the (100) plane and most crystals (for example, 90% or more) are ( 100) oriented in the plane. In the present invention, “the crystal structure is rhombohedral” means that all the crystals are rhombohedral and almost all the crystals (for example, 90% or more). And the case where the remaining crystals that are rhombohedral and are not rhombohedral are monoclinic, tetragonal, and the like. In the present embodiment, the piezoelectric layer 70 has a monoclinic crystal structure.

  Further, in the piezoelectric layer 70, the polarization direction indicating the direction in which the polarization moment is directed is perpendicular to the film surface (the thickness direction of the piezoelectric layer 70, that is, the surface on which the first electrode 60 or the second electrode 80 is provided). It is desirable that the engineered domain arrangement be inclined at a predetermined angle with respect to (perpendicular to the direction). Since the polarization direction of the piezoelectric layer 70 is an engineered domain arrangement, excellent piezoelectric characteristics can be obtained as the piezoelectric layer 70.

Here, the crystal structure of the piezoelectric layer 70 has a perovskite structure represented by the general formula ABO ₃ as described above. Therefore, when Pb (Zr, Ti) O ₃ is used as the piezoelectric layer 70, as shown in FIG. 3, lead (Pb) at the A site, zirconium (Zr) or titanium (Ti) at the B site. ), Oxygen (O) is disposed at the C site. The polarization direction of the piezoelectric layer 70 is an engineered domain arrangement, as shown in FIG. 3, when the crystal constituting the piezoelectric layer 70 is represented by a pseudo-cubic crystal, When the crystal axes in the plane in which the first electrode 60 or the second electrode 80 are provided are the a-axis <100> direction, the b-axis <010> direction, and the film surface vertical direction is the c-axis <001> direction The <111> direction, < 1 11> direction, <1 1 1> direction, < 11 1 direction, in which the polarization direction indicating the direction in which the polarization moment is directed from the substantially central B site is the positive direction of the c-axis. > Direction and the <11 1 > direction, < 1 1 1 > direction, <1 11 > direction, and < 111 > direction, which are negative directions of the c-axis. In addition, the underline which shows the said direction has shown the minus direction in each axis | shaft. Therefore, the positive direction of the c-axis is the <111> direction, the <−111> direction, the <1-11> direction, the <−1-11> direction, and the <11-1> direction that is the negative direction of the c-axis, The <-11-1> direction, <1-1-1> direction, and <-1-1-1> direction can also be rewritten. Incidentally, that the polarization direction of the piezoelectric layer 70 is an engineered domain arrangement means that the polarization direction is completely coincident with the above-described <111> direction or the like in the pseudo cubic notation, and the polarization direction. Is slightly deviated from the above-described <111> direction, but is substantially in the <111> direction. When the polarization direction is substantially the <111> direction, for example, the polarization direction is between the <111> direction and the <100> direction, and the angle between the polarization direction and the <111> direction is For example, it is a case of 10 degrees or less. Thus, when the polarization is deviated from the <111> direction, the piezoelectric layer 70 becomes a monoclinic system, and a higher displacement can be obtained.

  The lattice constant (a-axis, b-axis) in the plane of the piezoelectric layer 70 (surface on which the second electrode 80 is provided) is compared with the lattice constant (c-axis) in the direction perpendicular to this plane, that is, in the thickness direction. The larger one is preferable. That is, it is preferable that the c-axis lattice constant is smaller than the a-axis and b-axis lattice constants. As described above, by using a piezoelectric layer 70 having an in-plane lattice constant (a-axis, b-axis) larger than the c-axis lattice constant, the piezoelectric layer 70 can have a large displacement with a low driving voltage. The piezoelectric layer 70 having so-called high displacement characteristics that can be obtained can be used, and ink (liquid) ejection characteristics can be improved. Here, in the case of a thick film (bulk powder) different from the present embodiment, even if it is a piezoelectric layer 70 (for example, PZT) having a rhombohedral composition, the piezoelectric layer as in the present embodiment. When 70 is a thin film, the a-axis lattice constant can be made larger than the c-axis by utilizing in-plane stress (tensile stress). At this time, the crystal structure is monoclinic.

  The piezoelectric layer 70 is formed thick enough to suppress the thickness so as not to generate cracks in the manufacturing process and to exhibit sufficient displacement characteristics. For example, in the present embodiment, the piezoelectric layer 70 is formed with a thickness of about 0.5 to 2.0 μm. Here, by setting the film thickness of the piezoelectric layer 70 within this range, the ejection amount of ink droplets (droplets) can be improved. For example, when the thickness of the piezoelectric layer 70 is 1.1 μm, the lateral width (shortest width) of the pressure generating chamber 12 is 60 μm, and the driving voltage is 25 V, the direction perpendicular to the film surface of the elastic film 50 (thickness direction) ) Can obtain a large variation of about 300 nm, and as a result, an ink droplet of about 5 picoliter can be ejected.

  Further, each second electrode 80 which is an individual electrode of the piezoelectric element 300 is drawn from the vicinity of the end on the ink supply path 14 side and extended to the insulator film 55, for example, gold (Au) or the like. The lead electrode 90 which consists of is connected.

  On the flow path forming substrate 10 on which such a piezoelectric element 300 is formed, that is, on the first electrode 60, the insulator film 55, and the lead electrode 90, there is a reservoir portion 31 that constitutes at least a part of the reservoir 100. The protective substrate 30 is bonded via an adhesive 35. In the present embodiment, the reservoir portion 31 is formed across the protective substrate 30 in the thickness direction and across the width direction of the pressure generating chamber 12, and as described above, the communication portion 13 of the flow path forming substrate 10 is formed. The reservoir 100 is configured as a common ink chamber for the pressure generating chambers 12. Alternatively, the communication portion 13 of the flow path forming substrate 10 may be divided into a plurality of pressure generation chambers 12 and only the reservoir portion 31 may be used as the reservoir. Further, for example, only the pressure generating chamber 12 is provided in the flow path forming substrate 10, and a reservoir is provided on a member (for example, the elastic film 50, the insulator film 55, etc.) interposed between the flow path forming substrate 10 and the protective substrate 30. An ink supply path 14 that communicates with each pressure generating chamber 12 may be provided.

  A piezoelectric element holding portion 32 having a space that does not hinder the movement of the piezoelectric element 300 is provided in a region of the protective substrate 30 that faces the piezoelectric element 300. The piezoelectric element holding part 32 only needs to have a space that does not hinder the movement of the piezoelectric element 300, and the space may be sealed or unsealed.

  As such a protective substrate 30, it is preferable to use substantially the same material as the coefficient of thermal expansion of the flow path forming substrate 10, for example, glass, ceramic material, etc. In this embodiment, the same material as the flow path forming substrate 10 is used. The silicon single crystal substrate was used.

  The protective substrate 30 is provided with a through hole 33 that penetrates the protective substrate 30 in the thickness direction. The vicinity of the end portion of the lead electrode 90 drawn from each piezoelectric element 300 is provided so as to be exposed in the through hole 33.

  A drive circuit 120 for driving the piezoelectric elements 300 arranged in parallel is fixed on the protective substrate 30. For example, a circuit board or a semiconductor integrated circuit (IC) can be used as the drive circuit 120. The drive circuit 120 and the lead electrode 90 are electrically connected via a connection wiring 121 made of a conductive wire such as a bonding wire.

  In addition, a compliance substrate 40 including a sealing film 41 and a fixing plate 42 is bonded onto the protective substrate 30. Here, the sealing film 41 is made of a material having low rigidity and flexibility, and one surface of the reservoir portion 31 is sealed by the sealing film 41. The fixing plate 42 is formed of a relatively hard material. Since the region of the fixing plate 42 facing the reservoir 100 is an opening 43 that is completely removed in the thickness direction, one surface of the reservoir 100 is sealed only with a flexible sealing film 41. Has been.

  In such an ink jet recording head of this embodiment, ink is taken in from an ink introduction port connected to an external ink supply unit (not shown), and the interior from the reservoir 100 to the nozzle opening 21 is filled with ink, and then the drive circuit 120 is filled. In accordance with the recording signal from the first electrode 60 and the second electrode 80 corresponding to the pressure generating chamber 12, the elastic film 50, the insulator film 55, the first electrode 60, and the piezoelectric layer. By bending and deforming 70, the pressure in each pressure generating chamber 12 is increased, and ink droplets are ejected from the nozzle openings 21.

  Here, a method of manufacturing the ink jet recording head will be described with reference to FIGS. 4 to 7 are cross-sectional views showing a method for manufacturing the ink jet recording head.

First, as shown in FIG. 4A, silicon dioxide (SiO ₂₎ constituting an elastic film 50 on the surface of a flow path forming substrate wafer 110, which is a silicon wafer in which a plurality of flow path forming substrates 10 are integrally formed. ) Is formed. Next, as shown in FIG. 4B, an insulator film 55 made of zirconium oxide is formed on the elastic film 50 (silicon dioxide film 51).

  Next, as shown in FIG. 4C, after the first electrode 60 made of platinum and iridium is formed on the insulator film 55, it is patterned into a predetermined shape. Although the formation method of the 1st electrode 60 is not specifically limited, For example, sputtering method, chemical vapor deposition method (CVD method), etc. are mentioned. In this embodiment, platinum and iridium are used as the material of the first electrode 60. However, the material of the first electrode 60 is not particularly limited to this, and may be only platinum or iridium. Other metal materials may be used.

  Next, as shown in FIG. 5A, for example, a piezoelectric layer 70 made of lead zirconate titanate (PZT) or the like, and a second electrode 80 made of iridium, for example, are used. On the entire surface. In this embodiment, the piezoelectric layer 70 is formed by applying and drying a so-called sol obtained by dissolving and dispersing a metal organic substance in a solvent, gelling it, and baking it at a high temperature to form a piezoelectric layer made of a metal oxide. The piezoelectric layer 70 was formed using a so-called sol-gel method for obtaining 70. The method for forming the piezoelectric layer 70 is not particularly limited. For example, a PVD (Physical Vapor Deposition) method such as a MOD (Metal-Organic Decomposition) method, a sputtering method, or a laser ablation method may be used.

  Next, as shown in FIG. 5B, the second electrode 80 and the piezoelectric layer 70 are simultaneously etched to form the piezoelectric element 300 in a region corresponding to each pressure generating chamber 12. Here, examples of the etching of the second electrode 80 and the piezoelectric layer 70 include dry etching such as reactive ion etching and ion milling.

  Next, as shown in FIG. 5C, a lead electrode 90 made of gold (Au) is formed over the entire surface of the flow path forming substrate wafer 110 and then patterned for each piezoelectric element 300.

  Next, as shown in FIG. 6A, the protective substrate wafer 130 is bonded onto the flow path forming substrate wafer 110 via an adhesive 35. Here, the protective substrate wafer 130 is formed by integrally forming a plurality of protective substrates 30, and the reservoir portion 31 and the piezoelectric element holding portion 32 are formed in advance on the protective substrate wafer 130. By joining the protective substrate wafer 130, the rigidity of the flow path forming substrate wafer 110 is remarkably improved.

  Next, as shown in FIG. 6B, the flow path forming substrate wafer 110 is thinned to a predetermined thickness.

  Next, as shown in FIG. 6C, a mask 52 is newly formed on the flow path forming substrate wafer 110 and patterned into a predetermined shape. Then, as shown in FIG. 7, the flow path forming substrate wafer 110 is anisotropically etched (wet etching) using an alkaline solution such as KOH through a mask 52, thereby generating a pressure corresponding to the piezoelectric element 300. A chamber 12, a communication portion 13, an ink supply path 14, a communication path 15 and the like are formed.

  Thereafter, the mask 52 on the surface of the flow path forming substrate wafer 110 is removed, and unnecessary portions of the outer peripheral edge portions of the flow path forming substrate wafer 110 and the protective substrate wafer 130 are removed by cutting, for example, by dicing. To do. The nozzle plate 20 having the nozzle openings 21 formed on the surface of the flow path forming substrate wafer 110 opposite to the protective substrate wafer 130 is bonded, and the compliance substrate 40 is bonded to the protective substrate wafer 130. Then, the flow path forming substrate wafer 110 or the like is divided into one chip size flow path forming substrate 10 or the like as shown in FIG.

Thereafter, an electric field is applied to the piezoelectric layer 70 to perform polarization processing. Here, the polarization treatment refers to one direction of the piezoelectric layer 70 (the first electrode 60 and the second electrode 80 with respect to the piezoelectric layer 70 in which the polarization direction of the crystal faces an arbitrary direction when the piezoelectric element 300 is manufactured. Is applied in the direction connecting the two, i.e., the film thickness direction of the piezoelectric layer 70, and the direction of the c-axis direction (electric field application direction) component of the polarization moment is aligned. Here, the direction of the electric field E _I during the polarization process is the same as the direction of the actual driving electric field E _R when the ink jet recording head I is used, and the magnitude of the electric field E _I during the polarization process is the ink jet recording head. The absolute value of the actual driving electric field E _R when I is used is made larger. By doing so, the polarization process can be sufficiently performed, and a sufficient piezoelectric displacement can be obtained when the ink jet recording head I is used. For example, the magnitude of the electric field E _I during typical polarization processing is 30V to 60V. In order to sufficiently polarize the piezoelectric layer 70, the value of the electric field E _I at the time of a larger polarization process is required. On the other hand, if the electric field E _I at the time of the polarization process is large, the drive circuit at the time of polarization process Such costs are greatly increased. Further, when a large electric field E _I is applied to the piezoelectric layer 70 during the polarization treatment, cracks may occur in the piezoelectric layer 70 itself, leading to structural destruction. For this reason, it is required to perform sufficient polarization processing by applying a small electric field E _I during the polarization processing.

In the present embodiment, the <001> direction (from the first electrode 60 to the second direction) is a direction perpendicular to the film surface (that is, the surface on which the first electrode 60 or the second electrode 80 is provided) on the piezoelectric layer 70. An electric field is applied (toward the electrode 80). Specifically, for example, as shown in FIG. 8, the polarization direction is <111> direction, < 1 11> direction, <1 1 1> direction, < 11 1> direction, By applying an electric field in the 00 1 > direction, the polarization directions are set to a <11 1 > direction, a < 1 1 1 > direction, a <1 11 > direction, and a < 111 > direction, respectively. That is, for example, the polarization direction of the polarization moment P1 is <111> direction, instead of the polarization moment P5 like a <111> direction, the polarization moment P1 of <111> direction, to move the only c-axis The polarization moment P3 in the <11 1 > direction.

The magnitude of the applied electric field (electric field strength) at this time is such that, when the polarization direction is the <111> direction (polarization moment P1), this polarization direction becomes the <110> direction polarization direction (polarization moment P2). It is larger than the necessary energy and smaller than the energy necessary to change the <111> direction polarization direction (P1) to the <00 1 > direction polarization direction (polarization moment P4). By applying an electric field having such an electric field strength, the <111> direction (P1) can be passed through the <110> direction (P2) to the <11 1 > direction (P3). Similarly, other polarization direction, i.e., <1 11> direction, <1 1 1> direction, <111> direction as each <1 10> direction, <1 1 0> direction, <11 0> direction Can be made to be the < 1 1 1 > direction, <1 11 > direction, and < 111 > direction.

Here, for example, the polarization moment P1 with the <111> direction as the polarization direction, the polarization moment P2 with the <110> direction, the polarization moment P3 with the <11 1 > direction, the polarization moment P4 with the <00 1 > direction, < 111 > The relationship between the path and the energy (meV / cell) when moved so as to have a directional polarization moment P5 was determined by first-principles electronic state calculation. The result is shown in FIG. In FIG. 9, “neutral” indicates a paraelectric state. Further, in FIG. 9, it is obtained by 1 unit cell indicating one unit cell of the piezoelectric layer 70. The piezoelectric layer 70 being in the paraelectric state means a state in which the polarization moment disappears and no polarization moment exists.

As shown in FIG. 9, about 20 meV / cell is required to make the polarization moment P3 having the polarization direction <111> direction passed through the <110> direction to the <11 1 > direction and moved to the <11 1 > direction. against, the direction of polarization <111> direction of the polarization moment P1 <110> direction and <001> by passing and direction to the polarization moment P5 is moved to <111> direction is about 40 meV / cell or more Necessary. In addition, as a path for reversing the polarization direction from the <111> direction to the < 111 > direction, which is the opposite direction, the energy required to pass the <110> direction and the <00 1 > direction is the most. It is considered low.

A line 200 shown in FIG. 9 is a case where the a-axis length and the b-axis length of the crystal are the same length (for example, 420 pm). When the a-axis length (b-axis length) is longer than the c-axis length (for example, 1.01 times), the line 200A shown in FIG. 9 is obtained, and the polarization moment in the <111> direction passes through the <00 1 > direction. It turns out that more energy is needed to make it happen. Here, the first-principles electronic state calculation performed in the present embodiment was performed using the super soft potential method based on the density functional method in the range of Generalized Gradient approximation. The energy cutoff was 40 Hartley, the electron density cutoff was 36 Hartley, and the k-point mesh in the reciprocal lattice space was 4 × 4 × 4.

From the above, when the polarization direction is the <111> direction, the electric field intensity for performing the polarization treatment of the piezoelectric layer 70 is large enough to pass the <110> direction to the <11 1 > direction, that is, the polarization By making the direction larger than the energy required to make the <110> direction polarization direction, and making the <111> direction the polarization direction smaller than the energy necessary to make the <00 1 > direction polarization direction, Polarization processing can be performed with low energy without inverting the polarization direction in the opposite direction.

  Thus, by defining the electric field strength of the applied electric field, it is possible to define a path for reversing the polarization direction. Then, by passing the path that requires the least amount of energy, the electric field strength can be reduced, energy saving can be achieved, and the cost can be reduced. In addition, since it is not necessary to apply a large electric field to the piezoelectric layer 70 to perform the polarization treatment, damage caused by applying an electric field to the piezoelectric layer 70 can be suppressed. In particular, when the piezoelectric layer 70 having a lattice constant larger in the a-axis length (b-axis length) than the c-axis length is used, such an effect appears more remarkably.

In the polarization step, the piezoelectric layer 70 is preferably not in a paraelectric state where the polarization moment disappears. That is, as shown in FIG. 9, in this embodiment, when the polarization direction of the piezoelectric layer 70 is the <111> direction, the electric field strength for performing the polarization treatment of the piezoelectric layer 70 passes the <110> direction and is <11 1 >. Larger than the energy required to change the polarization direction to the <110> direction, and necessary to change the <111> direction to the <00 1 > direction. By making the energy smaller than this energy, it can be said that the energy does not make the piezoelectric layer 70 in the paraelectric state “neutral” (FIG. 9).

Incidentally, as shown in FIG. 9, when the polarization moment is reversed during the polarization process, in order to obtain a paraelectric state, the polarization direction in the <111> direction is changed to the polarization in the <00 1 > direction. Initialization is performed by reversing the polarization moment with a small applied voltage by performing the polarization step with energy that does not cause the piezoelectric layer 70 to be in a paraelectric state. Therefore, the voltage applied to the piezoelectric layer 70 can be lowered to suppress the dielectric breakdown of the piezoelectric layer 70.

In the present embodiment, the electric field intensity for performing the polarization process is larger than the energy required to make the polarization direction in the <110> direction with reference to the polarization direction in the <111> direction, and the polarization in the <111> direction Although it has been described that the direction is smaller than the energy required to make the <00 1 > direction a polarization direction, this can also be said to be a polarization direction based on another direction. That is, for example, the magnitude of the electric field intensity, the polarization directions relative to the <1 11> direction, <1 10> greater than the energy required to the direction of the polarization direction, <1 11> direction of the polarization direction Is the same as that smaller than the energy required to make the polarization direction in the <00 1 > direction. Similarly, even if the polarization direction in the initial state is the <11 1 > direction, it is larger than the energy required to make the <110> direction polarization direction, and the <11 1 > direction polarization direction is < It can also be said that the energy is smaller than the energy required to make the 001> direction of polarization. That is, the applied electric field of the present invention can be said to be the electric field strength (energy) necessary to reverse the polarization direction only in the c-axis direction.

By applying an electric field having such an electric field strength, the polarization moments in the < 1 11> direction, <1 1 1> direction, and < 11 1> direction other than the <111> direction are also < 1. It can be moved so as to be reversed only in the c-axis direction in the 1 1 > direction, the <1 11 > direction, and the < 111 > direction.

(Other embodiments)
Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment. For example, in the first embodiment described above, a silicon single crystal substrate is exemplified as the flow path forming substrate 10, but the present invention is not particularly limited thereto, and the present invention is also effective in, for example, an SOI substrate, a glass substrate, an MgO substrate, and the like. . Further, the elastic film 50 made of silicon dioxide is provided in the lowermost layer of the diaphragm, but the structure of the diaphragm is not particularly limited to this.

  In the first embodiment described above, the actuator device having the thin film type piezoelectric element 300 is described as the pressure generating means for causing the pressure change in the pressure generating chamber 12, but the invention is not particularly limited thereto. It is possible to use a thick film type actuator device formed by a method such as attaching a green sheet or a longitudinal vibration type actuator device in which piezoelectric materials and electrode forming materials are alternately stacked to expand and contract in the axial direction. it can.

  In addition, the ink jet recording head I according to each of the embodiments constitutes a part of a recording head unit including an ink flow path communicating with an ink cartridge and the like, and is mounted on the ink jet recording apparatus. FIG. 10 is a schematic view showing an example of the ink jet recording apparatus.

  In the ink jet recording apparatus II shown in FIG. 10, the recording head units 1A and 1B having the ink jet recording head I are detachably provided with cartridges 2A and 2B constituting the ink supply means, and the recording head units 1A and 1B. Is mounted on a carriage shaft 5 attached to the apparatus main body 4 so as to be movable in the axial direction. The recording head units 1A and 1B, for example, are configured to eject a black ink composition and a color ink composition, respectively.

  The driving force of the driving motor 6 is transmitted to the carriage 3 via a plurality of gears and timing belt 7 (not shown), so that the carriage 3 on which the recording head units 1A and 1B are mounted is moved along the carriage shaft 5. The On the other hand, the apparatus body 4 is provided with a platen 8 along the carriage shaft 5, and a recording sheet S that is a recording medium such as paper fed by a paper feed roller (not shown) is wound around the platen 8. It is designed to be transported.

  In the ink jet recording apparatus II described above, the ink jet recording head I (head units 1A, 1B) is mounted on the carriage 3 and moves in the main scanning direction. However, the present invention is not particularly limited thereto. The present invention can also be applied to a so-called line recording apparatus in which the ink jet recording head I is fixed and printing is performed simply by moving the recording sheet S such as paper in the sub-scanning direction.

  In the first embodiment described above, an ink jet recording head has been described as an example of a liquid ejecting head. However, the present invention is widely intended for all liquid ejecting heads, and is a liquid ejecting a liquid other than ink. Of course, the present invention can also be applied to an ejection head. Other liquid ejecting heads include, for example, various recording heads used in image recording apparatuses such as printers, color material ejecting heads used in the manufacture of color filters such as liquid crystal displays, organic EL displays, and FEDs (field emission displays). Examples thereof include an electrode material ejection head used for electrode formation, a bioorganic matter ejection head used for biochip production, and the like.

  Further, the present invention is not limited to a method for manufacturing a piezoelectric element mounted on a liquid ejecting head typified by an ink jet recording head, and can also be applied to a method for manufacturing a piezoelectric element mounted on another apparatus.

  I ink jet recording head (liquid ejecting head), II ink jet recording apparatus (liquid ejecting apparatus), 10 flow path forming substrate, 12 pressure generating chamber, 13 communicating portion, 14 ink supply path, 15 communicating path, 20 nozzle plate, 21 nozzle opening, 30 protective substrate, 31 reservoir portion, 32 piezoelectric element holding portion, 40 compliance substrate, 60 first electrode, 70 piezoelectric layer, 80 second electrode, 90 lead electrode, 100 reservoir, 120 drive circuit, 121 connection Wiring, 200, 200A line, 300 Piezoelectric element, P1-P5 Polarization moment

Claims (6)

A method of manufacturing a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode, which causes a pressure change in a pressure generation chamber communicating with a nozzle opening,
The piezoelectric layer has a perovskite structure,
The piezoelectric layer is preferentially oriented in the (100) plane,
When the direction of the electric field applied to the piezoelectric layer is the <001> direction perpendicular to the surface on which the second electrode is provided, the polarization direction of the <111> direction is set to the <110> direction. A polarization step of performing polarization treatment of the piezoelectric layer by applying an electric field of energy larger than the required energy and smaller than the energy required to change the polarization direction of the <111> direction to the <001> direction. A method for manufacturing a piezoelectric element.   In the polarization step, when the polarization direction of the piezoelectric layer is changed from the <111> direction to the <111> direction by applying an electric field, the polarization direction in the middle of the change is directed to the <110> direction. The method for manufacturing a piezoelectric element according to claim 1.   3. The method of manufacturing a piezoelectric element according to claim 1, wherein in the polarization step, the piezoelectric layer does not enter a paraelectric state in which a polarization moment disappears.   The method for manufacturing a piezoelectric element according to claim 1, wherein the piezoelectric layer contains lead, zirconium, and titanium.   The lattice constant in the direction perpendicular to the surface on which the second electrode is provided is smaller than the lattice constant in the surface direction on which the second electrode of the piezoelectric layer is provided. The manufacturing method of the piezoelectric element as described in any one.   The method for manufacturing a piezoelectric element according to claim 1, wherein the piezoelectric layer is monoclinic.

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