Piezoelectric element

Abstract

To provide a piezoelectric element that can prevent a reduction in the efficiency of displacement (linearity) of a diaphragm, a head chip, a liquid injection device, and a sensor.SOLUTION: A piezoelectric element of the present invention comprises: a first electrode; a piezoelectric layer formed above the first electrode; and a second electrode formed above the piezoelectric layer. The piezoelectric layer includes potassium, sodium, and niobium. The Young's modulus of the piezoelectric layer measured by the nanoindentation method exceeds 130 GPa.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to piezoelectric elements. to child

Background Art

[0002] A piezoelectric element generally has a substrate, a piezoelectric layer having electro-mechanical conversion characteristics, and two electrodes sandwiching the piezoelectric layer. In recent years, the development of devices using such a piezoelectric element as a drive source (piezoelectric element application devices) has been actively carried out. Examples of piezoelectric element application devices include a liquid ejection head typified by an inkjet recording head, a MEMS element typified by a piezoelectric MEMS element, an ultrasonic measurement device typified by an ultrasonic sensor, and further, a piezoelectric actuator device and the like.

[0003] As an example of a piezoelectric element, for example, Patent Document 1 discloses a piezoelectric element including a piezoelectric layer (PZT layer) containing lead, zirconium, and titanium and having a Young's modulus of 75 GPa, and a first electrode (platinum layer) having a Young's modulus of 200 GPa.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in recent years, from the viewpoint of reducing environmental load, the development of non-lead-based piezoelectric materials with reduced lead (Pb) content has been promoted. As a main material of a piezoelectric element with a low lead content, for example, potassium sodium niobate (KNN; (K,Na)NbO3) has been proposed.

[0006] ​However, as described in Patent Document 1, when an upper electrode with a large Young's modulus is placed on a piezoelectric layer with a small Young's modulus, the piezoelectric layer deforms due to the stress received from the upper electrode, and this causes a deflection (initial deflection) of the diaphragm toward the pressure chamber. Furthermore, piezoelectric layers with a low Young's modulus could not sufficiently bend the diaphragm when the piezoelectric element was driven, resulting in a problem where the amount of displacement decreased (linearity deteriorated), especially when driven at high voltages.

[0007] In the case of a relatively soft piezoelectric layer with a low Young's modulus, the fluctuations during the operation of the piezoelectric element are not sufficiently transmitted to the diaphragm, and some of the drive is consumed by the deformation of the piezoelectric layer itself. Therefore, especially at high voltages, the larger the fluctuation, the greater the proportion of the driving force consumed by the deformation of the piezoelectric layer itself, which leads to a problem of reduced efficiency in diaphragm movement.

[0008] Furthermore, relatively soft piezoelectric layers may deform from the film deposition stage due to their inability to withstand the stress of the upper electrode (second electrode), resulting in a problem of increased initial deflection of the diaphragm. When the diaphragm deflects toward the pressure chamber, the volume of the pressure chamber decreases, which can lead to, for example, a decrease in the droplet discharge volume.

[0009] For these reasons, there is a need for piezoelectric elements that can suppress the decrease in the efficiency (linearity) of diaphragm displacement even when driven at high voltages (e.g., 20-50V).

[0010] Furthermore, this problem is not limited to piezoelectric elements used in piezoelectric actuators mounted on liquid ejection heads, such as those found in inkjet recording heads, but also exists in piezoelectric elements used in other piezoelectric element application devices. [Means for solving the problem]

[0011] To solve the above problems, according to a first aspect of the present invention, a piezoelectric element is provided comprising a first electrode, a piezoelectric layer formed above the first electrode, and a second electrode formed above the piezoelectric layer, wherein the piezoelectric layer contains potassium, sodium, and niobium, and the Young's modulus of the piezoelectric layer, as measured by nanoindentation, exceeds 130 GPa.

[0012] According to a second aspect of the present invention, a head chip is provided comprising: a nozzle plate equipped with a nozzle for discharging droplets; a pressure generating chamber communicating with the nozzle; a flow path forming substrate disposed on the nozzle plate and forming the pressure generating chamber; a diaphragm forming a part of the wall surface of the pressure generating chamber; a piezoelectric element according to the first aspect provided on the diaphragm; and a voltage application unit for applying a voltage to the piezoelectric element.

[0013] According to a third aspect of the present invention, a liquid spraying device is provided which includes a transport means for transporting media and a droplet spraying head for applying droplets to the media, wherein the droplet spraying head is equipped with the head tip of the second aspect described above.

[0014] According to a fourth aspect of the present invention, a sensor is provided comprising a piezoelectric element as described in the first aspect and a voltage detection unit for detecting a voltage output from the piezoelectric element. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing the schematic configuration of the recording device of Embodiment 1. [Figure 2] Figure 1 is an exploded perspective view of the recording head of the recording device. [Figure 3] Figure 1 is a plan view of the recording head of the recording device. [Figure 4] Figure 1 is a cross-sectional view of the recording head of the recording device. [Figure 5] Figure 4 is an enlarged cross-sectional view along the BB' line. [Figure 6A] This figure shows the relationship between the drive voltage and the displacement of the diaphragm in this embodiment. [Figure 6B]This is a diagram showing the relationship between the driving voltage and the efficiency of the displacement of the diaphragm in this embodiment.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows one aspect of the present invention and can be arbitrarily changed within the scope not departing from the gist of the present invention. In each drawing, the same reference numerals are used to indicate the same members, and the description is omitted as appropriate. The numbers after the characters constituting the reference numerals are referred to by the reference numerals including the same characters and are used to distinguish elements having the same configuration. When there is no need to distinguish elements indicated by reference numerals including the same characters from each other, these elements are referred to by reference numerals including only the characters.

[0017] In each drawing, X, Y, and Z represent three mutually orthogonal spatial axes. In this specification, the directions along these axes are respectively referred to as the first direction X (X direction), the second direction Y (Y direction), and the third direction Z (Z direction), and the direction in which the arrow in each figure points is defined as the positive (+) direction, and the opposite direction of the arrow is defined as the negative (-) direction for explanation. The X direction and the Y direction represent the in-plane directions of the plate, layer, and film, and the Z direction represents the thickness direction or the stacking direction of the plate, layer, and film.

[0018] Also, the components shown in each drawing, that is, the shape and size of each part, the thickness of the plate, layer, and film, the relative positional relationship, the repeating unit, etc. may be exaggerated for the purpose of explaining the present invention. Further, the term "above" in this specification does not limit the positional relationship of the components to be "directly above". For example, the expressions "the first electrode on the substrate" and "the piezoelectric layer on the first electrode" described later do not exclude those including other components between the substrate and the first electrode or between the first electrode and the piezoelectric layer.

[0019] (Liquid ejection device) First, an inkjet recording device, which is an example of a liquid injection device according to an embodiment of the present invention, will be described with reference to the drawings. Figure 1 is a perspective view showing the schematic configuration of the inkjet recording device. As shown in Figure 1, in the inkjet recording device (recording device) I, an inkjet recording head unit (droplet ejection head, head unit) II is detachably mounted on cartridges 2A and 2B. Cartridges 2A and 2B constitute the ink supply means. The head unit II has a plurality of inkjet recording heads (head chips, recording heads) 1 (see Figure 2, etc.) and is mounted on a carriage 3. The carriage 3 is mounted on a carriage shaft 5 attached to the main body 4 of the device so as to be movable in the axial direction. These head unit II and carriage 3 are configured to eject, for example, a black ink composition and a color ink composition, respectively.

[0020] The driving force of the drive motor 6 is transmitted to the carriage 3 via a plurality of gears (not shown) and a timing belt 7, causing the carriage 3, on which the head unit II is mounted, to move along the carriage axis 5. Meanwhile, the main body of the device 4 is provided with transport rollers 8 as a transport means, and the recording sheet S, which is a recording medium (media) such as paper, is transported by the transport rollers 8. Note that the transport means for transporting the recording sheet S is not limited to transport rollers, but may also be a belt or drum.

[0021] The recording head (head chip) 1 uses a piezoelectric actuator device, specifically a piezoelectric element 300 (see Figure 2, etc.), which will be described in detail later. By using the piezoelectric element 300, it is possible to avoid a decrease in various characteristics of the recording device I (piezoelectric characteristics, durability, ink ejection characteristics, etc.). In this embodiment, by applying the piezoelectric element 300 described later, the decrease in piezoelectric characteristics (especially displacement) can be sufficiently suppressed.

[0022] Next, a recording head (head chip) 1, which is an example of a head chip mounted on a liquid jetting device, will be described with reference to the drawings. Figure 2 is an exploded perspective view showing the schematic configuration of an inkjet recording head. Figure 3 is a plan view showing the schematic configuration of an inkjet recording head. Figure 4 is a cross-sectional view taken along line AA' of Figure 3. Note that Figures 2 to 4 show only parts of the configuration of the recording head 1 and have been omitted as appropriate.

[0023] As shown in the figure, the recording head (head chip) 1 comprises a nozzle plate 20 equipped with a nozzle 21 for ejecting droplets, a pressure generating chamber 12 communicating with the nozzle 21, a substrate 10 and a partition wall (flow channel forming substrate) 11 provided on the nozzle plate 20 and forming the pressure generating chamber 12, a diaphragm 50 forming a part of the wall surface of the pressure generating chamber 12, a piezoelectric element 300 provided on the diaphragm 50, and a lead electrode (voltage application part) 90 for applying a voltage to the piezoelectric element 300.

[0024] The substrate 10 contains silicon (Si). For example, the substrate 10 is made of a silicon (Si) single crystal substrate.

[0025] Multiple partition walls 11 are formed on the substrate 10. Multiple pressure generating chambers 12 are partitioned by the partition walls 11. Multiple nozzles 21 that eject ink of the same color are arranged side by side along the direction in which they are adjacent (+X direction).

[0026] On one end (+Y direction side) of the pressure generating chamber 12 of the substrate 10, an ink supply passage 13 and a connecting passage 14 are formed. The ink supply passage 13 is configured to reduce the area of ​​the opening on one end of the pressure generating chamber 12. The connecting passage 14 has approximately the same width as the pressure generating chamber 12 in the +X direction. A connecting section 15 is formed on the outside (+Y direction side) of the connecting passage 14. The connecting section 15 constitutes part of the manifold 100. The manifold 100 is a common ink chamber for each pressure generating chamber 12. In this way, the substrate 10 has a liquid flow path formed therein, consisting of the pressure generating chamber 12, the ink supply passage 13, the connecting passage 14, and the connecting section 15.

[0027] A nozzle plate 20, for example made of SUS (stainless steel), is bonded to one side of the substrate 10 (the side facing the -Z direction). Nozzles 21 are arranged in parallel on the nozzle plate 20 along the +X direction. The nozzles 21 communicate with each pressure generating chamber 12. The nozzle plate 20 can be bonded to the substrate 10 by adhesive, heat-sealing film, or the like.

[0028] A diaphragm 50 is formed on the other side (the side in the +Z direction) of the substrate 10. The diaphragm 50 is composed of, for example, an elastic film 51 formed on the substrate 10 and an insulating film 52 formed on the elastic film 51. The elastic film 51 is made of, for example, silicon dioxide (SiO2), and the insulating film 52 is made of, for example, zirconium oxide (ZrO2). The elastic film 51 does not have to be a separate component from the substrate 10. A part of the substrate 10 may be thinned and used as the elastic film 51. The elastic film 51 is not limited to SiO2, and may be a film made of, for example, aluminum oxide (Al2O3), tantalum oxide (V) (Ta2O5), silicon nitride (SiN), etc.

[0029] A piezoelectric element 300, including a first electrode 60, a piezoelectric layer 70, and a second electrode 80, is formed on the insulating film 52 via an adhesion layer 56. The adhesion layer 56 is made of, for example, titanium oxide (TiOX), titanium (Ti), SiN, etc., and has the function of improving the adhesion between the piezoelectric layer 70 and the diaphragm 50. The adhesion layer 56 is optional.

[0030] The piezoelectric layer 70 is composed of a so-called KKK-based material containing potassium, sodium, and niobium. However, during the formation process of the piezoelectric layer 70, these alkali metals may diffuse into the first electrode 60. Therefore, by providing an insulating film 52 between the first electrode 60 and the substrate 10, and having the insulating film 52 function as a stopper, it is possible to suppress the arrival of the alkali metals constituting the piezoelectric layer 70 into the substrate 10.

[0031] A first electrode 60 is provided for each pressure generating chamber 12. In other words, the first electrode 60 is configured as an independent individual electrode for each pressure generating chamber 12. The first electrode 60 is formed to be smaller than the width of the pressure generating chamber 12 in the ±X direction. Also, the first electrode 60 is formed to be wider than the width of the pressure generating chamber 12 in the ±Y direction. That is, in the ±Y direction, both ends of the first electrode 60 are formed to extend beyond the region on the diaphragm 50 that faces the pressure generating chamber 12. A lead electrode (voltage application part) 90 for applying voltage to the piezoelectric element 300 is connected to one end of the first electrode 60 (opposite the communication passage 14).

[0032] The piezoelectric layer 70 is provided between the first electrode 60 and the second electrode 80. The piezoelectric layer 70 is a thin film piezoelectric material. The piezoelectric layer 70 is formed with a width wider than the width of the first electrode 60 in the ±X direction. Also, the piezoelectric layer 70 is formed with a width wider than the ±Y length of the pressure generation chamber 12 in the ±Y direction. The end of the piezoelectric layer 70 on the ink supply path 13 side (+Y direction side) extends outward beyond the +Y direction end of the first electrode 60. In other words, the +Y direction end of the first electrode 60 is covered by the piezoelectric layer 70. On the other hand, the end of the piezoelectric layer 70 on the lead electrode 90 side (-Y direction side) is inward (+Y direction side) beyond the -Y direction end of the first electrode 60. In other words, the -Y direction end of the first electrode 60 is not covered by the piezoelectric layer 70.

[0033] The second electrode 80 is continuously provided on the piezoelectric layer 70 and the diaphragm 50 in the +X direction. In other words, the second electrode 80 is configured as a common electrode common to multiple piezoelectric layers 70. In this embodiment, the first electrode 60 is configured as an individual electrode independently provided corresponding to the pressure generating chamber 12, and the second electrode 80 is configured as a common electrode continuously provided in the direction in which the pressure generating chambers 12 are arranged side by side. However, the first electrode 60 may be configured as a common electrode and the second electrode 80 as an individual electrode.

[0034] In this embodiment, the diaphragm 50 and the first electrode 60 are displaced by the displacement of the piezoelectric layer 70, which has electromechanical conversion characteristics. That is, the diaphragm 50 and the first electrode 60 substantially function as a diaphragm. However, in reality, the second electrode 80 is also displaced by the displacement of the piezoelectric layer 70, so the region in which the diaphragm 50, the first electrode 60, the piezoelectric layer 70, and the second electrode 80 are sequentially stacked functions as the movable part (also called the vibrating part) of the piezoelectric element 300.

[0035] In this embodiment, either the elastic membrane 51 or the insulating membrane 52 may be omitted to allow it to function as a diaphragm, or both the elastic membrane 51 and the insulating membrane 52 may be omitted so that only the first electrode 60 functions as a diaphragm.

[0036] A protective substrate 30 is bonded to the substrate 10 (diaphragm 50) on which the piezoelectric element 300 is formed, using an adhesive 35. The protective substrate 30 has a manifold portion 32. The manifold portion 32 constitutes at least a part of the manifold 100. In this embodiment, the manifold portion 32 penetrates the protective substrate 30 in the thickness direction (Z direction) and is further formed over the width direction (+X direction) of the pressure generating chamber 12. The manifold portion 32 is in communication with the communication portion 15 of the substrate 10. With these configurations, a manifold 100 is formed which serves as a common ink chamber for each pressure generating chamber 12.

[0037] A piezoelectric element holding portion 31 is formed in the region containing the piezoelectric element 300 on the protective substrate 30. The piezoelectric element holding portion 31 has a space that does not hinder the movement of the piezoelectric element 300. This space may or may not be sealed. The protective substrate 30 is provided with a through hole 33 that penetrates the protective substrate 30 in the thickness direction (Z direction). The end of the lead electrode 90 is exposed inside the through hole 33.

[0038] Examples of materials for the protective substrate 30 include Si, SOI, glass, ceramic materials, metals, and resins, but it is more preferable that it be made of a material with a thermal expansion coefficient approximately the same as that of the substrate 10.

[0039] A drive circuit 120, which functions as a signal processing unit, is fixed to the protective substrate 30. The drive circuit 120 can be, for example, a circuit board or a semiconductor integrated circuit (IC). The drive circuit 120 and the lead electrodes 90 are electrically connected via connecting wiring 121, which consists of conductive wires such as bonding wires inserted through through holes 33. The drive circuit 120 can be electrically connected to a printer controller 200 (see Figure 1). Such a drive circuit 120 functions as a control means for a piezoelectric actuator device (piezoelectric element 300).

[0040] Furthermore, a compliance substrate 40, consisting of a sealing film 41 and a fixing plate 42, is bonded to the protective substrate 30. The sealing film 41 is made of a material with low rigidity, and the fixing plate 42 can be made of a hard material such as metal. The region of the fixing plate 42 facing the manifold 100 is an opening 43 that is completely removed in the thickness direction (Z direction). One side of the manifold 100 (the side in the +Z direction) is sealed only with the flexible sealing film 41.

[0041] Such a recording head 1 ejects ink droplets in the following manner. First, ink is drawn in through an ink inlet connected to an external ink supply means (not shown), filling the manifold 100 and the nozzle 21 with ink. Then, according to a recording signal from the drive circuit 120, a voltage is applied between the first electrode 60 and the second electrode 80 corresponding to the pressure generating chamber 12, causing the piezoelectric element 300 to bend and deform. This increases the pressure in each pressure generating chamber 12, causing ink droplets to be ejected from the nozzle 21.

[0042] (Piezoelectric element) Next, the configuration of the piezoelectric element 300 will be described with reference to the drawings. Figure 5 is an enlarged cross-sectional view taken along the BB' line in Figure 4. As shown in the figure, the piezoelectric element 300 comprises a substrate 10, a first electrode 60 formed on the substrate 10, a piezoelectric layer 70 formed on the first electrode 60 and containing potassium, sodium, and niobium, and a second electrode 80 formed on the piezoelectric layer 70.

[0043] The substrate 10 is provided with a pressure generating chamber 12 partitioned by a plurality of partition walls 11. This configuration forms the movable part of the piezoelectric element 300. The thicknesses of each element listed here are examples and can be changed without altering the essence of the present invention.

[0044] The materials for the first electrode 60 and the second electrode 80 are preferably noble metals such as platinum (Pt) or iridium (Ir), or their oxides. The materials for the first electrode 60 and the second electrode 80 can be any conductive material. The materials for the first electrode 60 and the second electrode 80 may be the same or different.

[0045] The substrate 10 is, for example, a flat plate made of a semiconductor or an insulator. The substrate 10 may be a single layer or a structure in which multiple layers are laminated. The substrate 10 may include a diaphragm that is flexible and can be deformed (bent) by fluctuations in the piezoelectric layer 70. Examples of materials for the diaphragm include silicon oxide, zirconium oxide, or laminates thereof.

[0046] On the other side of the substrate 10 (the side in the +Z direction), a diaphragm 50 is formed, composed of an elastic film 51 and an insulating film 52, as described above. The elastic film 51 is preferably made of silicon dioxide (SiO2), and the insulating film 52 preferably contains zirconium oxide (ZrO2), for example. By using zirconium oxide as the insulating film 52, the Young's modulus of the diaphragm 50 itself can be increased. As a result, deflection of the diaphragm 50 due to stress from the piezoelectric layer 70 or the second electrode 80 when no voltage is applied can be suppressed. From this viewpoint, it is preferable that the insulating film 52 is made of zirconium oxide.

[0047] The first electrode 60 is formed on the substrate 10 (diaphragm 50 in Figure 5). The shape of the first electrode 60 is, for example, layered or thin film. The thickness (length in the Z-axis direction) of the first electrode 60 is, for example, 50 nm or more and 300 nm or less. The planar shape of the first electrode 60 (shape viewed from the Z-axis direction) is not particularly limited as long as it is a shape that allows the piezoelectric layer 70 to be placed between the two when the second electrode 80 is placed opposite it.

[0048] Examples of materials for the first electrode 60 include various metals such as nickel, iridium, and platinum, their conductive oxides (e.g., iridium oxide), a composite oxide of strontium and ruthenium (SrRuOx:SRO), and a composite oxide of lanthanum and nickel (LaNiOx:LNO). The first electrode 60 may be a single-layer structure of the materials exemplified above, or it may be a structure in which multiple materials are stacked.

[0049] The first electrode 60, together with the second electrode 80, can form one of the electrodes (for example, a lower electrode formed below the piezoelectric layer 70) for applying a voltage to the piezoelectric layer 70.

[0050] Furthermore, the diaphragm 50 may be omitted, and the first electrode 60 may also function as a diaphragm. That is, the first electrode 60 may have the function of one electrode for applying voltage to the piezoelectric layer 70, and the function of a diaphragm that can be deformed by fluctuations in the piezoelectric layer 70.

[0051] Furthermore, a layer that provides adhesion between the first electrode 60 and the substrate 10 (for example, an adhesion layer 56), or a layer that provides strength or conductivity, may be formed between the two. Examples of such layers include layers of various metals such as titanium, nickel, iridium, and platinum, or their oxides.

[0052] Furthermore, it is preferable to provide, for example, a seed layer (also called an orientation control layer) between the first electrode 60 and the piezoelectric layer 70. The seed layer has the function of controlling the orientation of the piezoelectric crystals constituting the piezoelectric layer 70. That is, by providing a seed layer, the piezoelectric crystals constituting the piezoelectric layer 70 can be preferentially oriented to a predetermined plane orientation, and as a result, the hardness of the piezoelectric layer 70 can be sufficiently increased.

[0053] The piezoelectric layer 70 is formed on the first electrode 60. The thickness of the piezoelectric layer 70 is, for example, 50 nm to 2000 nm.

[0054] The piezoelectric layer 70 is formed by a solution method (also called a liquid-phase method or wet method) such as the MOD method or the sol-gel method, or by a gas-phase method such as the sputtering method. In this embodiment, it is formed by a solution method and is a perovskite-type composite oxide represented by the general formula ABO3, containing potassium (K), sodium (Na), and niobium (Nb). That is, the piezoelectric layer 70 contains a piezoelectric material consisting of a KNN-based composite oxide represented by the following formula (1).

[0055] (K X Na 1-X )NbO3··· (1) (0.1 ≤ X ≤ 0.9)

[0056] The piezoelectric material constituting the piezoelectric layer 70 may be any KNN-based composite oxide and is not limited to the composition represented by formula (1) above. For example, other metal elements (additives) may be included in the A site or B site of potassium sodium niobate. Examples of such additives include manganese (Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), and copper (Cu).

[0057] This type of additive may contain one or more elements. Generally, the amount of additives is 20% or less, preferably 15% or less, and more preferably 10% or less, relative to the total amount of the main constituent elements. By using additives, it is easier to improve various properties and diversify the composition and function, but it is preferable that KNN is present in a proportion of more than 80% from the viewpoint of exhibiting properties derived from KNN. Furthermore, even in the case of a composite oxide containing these other elements, it is preferable that it is configured to have an ABO3 type perovskite structure.

[0058] Furthermore, in this specification, "a perovskite-type composite oxide containing K, Na, and Nb" refers to "a composite oxide with an ABO3-type perovskite structure containing K, Na, and Nb," and is not limited to composite oxides with an ABO3-type perovskite structure containing K, Na, and Nb. That is, in this specification, "a perovskite-type composite oxide containing K, Na, and Nb" includes piezoelectric materials represented as a mixed crystal containing a composite oxide with an ABO3-type perovskite structure containing K, Na, and Nb (for example, the KNN-based composite oxide exemplified above) and other composite oxides having an ABO3-type perovskite structure.

[0059] Other composite oxides are not limited to the scope of this embodiment, but preferably lead-free piezoelectric materials that do not contain lead (Pb). This results in a piezoelectric element 300 that is highly biocompatible and has a low environmental impact.

[0060] The piezoelectric layer 70 according to this embodiment is a KNN-type piezoelectric thin film with a Young's modulus of 130 GPa or higher. By setting the Young's modulus of the piezoelectric layer 70 to 130 GPa or higher, it is possible to suppress a decrease in piezoelectric properties that are significantly superior compared to conventional KNN thin films. Specifically, even when driven at high voltage (e.g., 20-50 V), it is possible to suppress a decrease in the efficiency (linearity) of the diaphragm displacement. Preferably, the Young's modulus of the piezoelectric layer 70 is 150 GPa or higher. On the other hand, there is no particular upper limit to the Young's modulus of the piezoelectric layer 70, but if the Young's modulus of the piezoelectric layer 70 is too high, the displacement itself will be hindered, so it may be set to 200 GPa or less.

[0061] The Young's modulus of the piezoelectric layer 70 according to this embodiment is at a high level of 130 GPa or more. By increasing the Young's modulus in this way, the piezoelectric layer 70 can be made sufficiently rigid, and as a result, deformation of the piezoelectric layer 70 itself can be avoided even when a high voltage is applied, and a decrease in the efficiency of the diaphragm displacement can be suppressed. Furthermore, by making the piezoelectric layer 70 sufficiently rigid, deformation due to stress on the second electrode 80 can be suppressed, and the initial deflection of the diaphragm 50 can be reduced.

[0062] From this perspective, it is preferable that the ratio of the Young's modulus of the piezoelectric layer 70 to the Young's modulus of the second electrode 80 be 0.8 or more and 1.0 or less. By providing a second electrode 80 and piezoelectric layer 70 that satisfy this ratio range, it becomes possible to further suppress deformation of the piezoelectric layer 70 due to the stress of the second electrode 80.

[0063] Here, the Young's modulus of the piezoelectric layer 70 is measured by the following method. The Young's modulus was measured based on nanoindentator measurement. In this embodiment, nanoindentator measurement is performed using a UMIS-2000 manufactured by CSIRO. Specifically, the Young's modulus is calculated based on the load applied to the indenter and the projected area below the indenter when the indenter with a spherical tip is pressed into the surface of the piezoelectric layer 70.

[0064] Furthermore, as mentioned above, in order to suppress the decrease in the efficiency (linearity) of the diaphragm displacement, it is effective to make the piezoelectric layer 70 sufficiently hard. To increase the hardness of the piezoelectric layer 70, it is effective to increase its density. Specifically, the density of the piezoelectric layer 70 should be 4.41 g / cm³. 3 It is preferable to have the above. More preferably 4.50 g / cm³ 3 That concludes the explanation. On the other hand, there is no particular upper limit to the density of the piezoelectric layer 70, but from the viewpoint of not including non-piezoelectric foreign matter, 4.77 g / cm³ is appropriate. 3 The following is acceptable.

[0065] A preferred method for controlling the Young's modulus and density of the piezoelectric layer 70 will be described later.

[0066] The second electrode 80 is formed on the piezoelectric layer 70. The second electrode 80 is positioned opposite the first electrode 60 via the piezoelectric layer 70. The shape of the second electrode 80 is, for example, layered or thin film. The thickness of the second electrode 80 is, for example, 10 nm to 500 nm. The planar shape of the second electrode 80 is not particularly limited, as long as it is a shape that allows the piezoelectric layer 70 to be placed between the first electrode 60 and the second electrode 60 when the second electrode 80 is positioned opposite the first electrode 60.

[0067] For example, the materials listed above for the first electrode 60 can be used as the material for the second electrode 80. However, in order for the ratio of the Young's modulus of the piezoelectric layer 70 to the Young's modulus of the second electrode 80 to satisfy the above range, it is preferable to use platinum (Pt) as the material for the second electrode 80.

[0068] One of the functions of the second electrode 80 is to work in conjunction with the first electrode 60 to act as the other electrode (for example, an upper electrode formed above the piezoelectric layer 20) for applying a voltage to the piezoelectric layer 70.

[0069] According to the piezoelectric element 300 of Embodiment 1 described above, the efficiency of displacement during high-voltage (e.g., 20-50V) driving can be improved by sufficiently increasing the Young's modulus of the piezoelectric layer 70.

[0070] Furthermore, although the above embodiment described an inkjet recording head as an example of a liquid ejection head, the present invention is applicable to liquid ejection heads in general, and can also be applied to liquid ejection heads that eject liquids other than ink. Other examples of liquid ejection heads include various recording heads used in image recording devices such as printers, colorant ejection heads used in the manufacture of color filters for liquid crystal displays, electrode material ejection heads used in electrode formation for organic EL displays and FEDs (field emission displays), and bio-organic material ejection heads used in biochip manufacturing.

[0071] Furthermore, the present invention is not limited to piezoelectric elements mounted on liquid injection heads, but can also be applied to piezoelectric elements mounted on other piezoelectric element application devices. Examples of piezoelectric element application devices include ultrasonic devices, motors, pressure sensors, pyroelectric elements, and ferroelectric elements. In addition, complete systems utilizing these piezoelectric element application devices, such as liquid injection devices using the above-mentioned liquid injection head, ultrasonic sensors using the above-mentioned ultrasonic devices, robots using the above-mentioned motors as a driving source, IR sensors using the above-mentioned pyroelectric elements, and ferroelectric memories using ferroelectric elements, are also included in the category of piezoelectric element application devices.

[0072] In particular, the piezoelectric element of the present invention is suitable as a piezoelectric element mounted in a sensor. Examples of sensors include gyro sensors, ultrasonic sensors, pressure sensors, and speed / acceleration sensors. When the piezoelectric element of the present invention is applied to a sensor, for example, a sensor can be created by providing a voltage detection unit that detects the voltage output from the piezoelectric element 300 between the first electrode 60 and the second electrode 80. In such a sensor, when the piezoelectric element 300 is deformed due to some external change (change in physical quantity), a voltage is generated in conjunction with the deformation. Various physical quantities can be detected by detecting this voltage with the voltage detection unit.

[0073] Next, an example of a method for manufacturing the piezoelectric element 300 will be described. First, a substrate (silicon substrate) 10 is prepared, and an elastic film 51 made of silicon dioxide (SiO2) is formed on its surface by thermal oxidation of the substrate 10. Next, a zirconium film is formed on the elastic film 51 by sputtering or vapor deposition, and an insulating film 52 made of zirconium oxide (ZrO2) is obtained by thermal oxidation. In this way, a diaphragm 50 consisting of the elastic film 51 and the insulating film 52 is formed on the substrate 10.

[0074] Next, TiO XAn adhesion layer 56 is formed. The adhesion layer 56 can be formed by sputtering or thermal oxidation of the Ti film. Next, a first electrode 60 made of Pt is formed on the adhesion layer 56. The first electrode 60 can be appropriately selected depending on the electrode material, and can be formed by vapor phase deposition such as sputtering, vacuum deposition (PVD), or laser ablation, or liquid phase deposition such as spin coating.

[0075] Next, a resist of a predetermined shape is formed on the first electrode 60 as a mask, and the adhesion layer 56 and the first electrode 60 are patterned simultaneously. The patterning of the adhesion layer 56 and the first electrode 60 can be performed, for example, by dry etching such as reactive ion etching (RIE) or ion milling, or by wet etching using an etching solution. The shape of the patterned adhesion layer 56 and the first electrode 60 is not particularly limited.

[0076] Next, multiple piezoelectric films are formed on the first electrode 60. The piezoelectric layer 70 is composed of these multiple piezoelectric films. The piezoelectric layer 70 can be formed, for example, by a chemical solution method (wet method) in which a solution containing a metal complex (precursor solution) is applied and dried, and then fired at a high temperature to obtain a metal oxide. It can also be formed by other methods such as laser ablation, sputtering, pulsed laser deposition (PLD), chemical vapor deposition (CVD), and aerosol deposition. In this embodiment, it is preferable to use a wet method (liquid phase method) from the viewpoint of orienting the surface orientation of the piezoelectric layer 70 in the (100) direction and increasing the Young's modulus of the piezoelectric layer 70.

[0077] Here, the wet method (liquid phase method) refers to a method of forming a film using chemical solution methods such as the MOD method or the sol-gel method, and is a concept distinct from gas phase methods such as the sputtering method. In this embodiment, a gas phase method may be used as long as it can form a piezoelectric layer 70 with a surface orientation oriented in the (100) direction.

[0078] For example, a piezoelectric layer 70 formed by a wet method (liquid phase method) has multiple piezoelectric films 74 formed by a series of steps including a step of applying a precursor solution to form a precursor film (coating step), a step of drying the precursor film (drying step), a step of heating and degreasing the dried precursor film (degreasing step), and a step of firing the degreasing precursor film (firing step). That is, the piezoelectric layer 70 is formed by repeating the series of steps from the coating step to the firing step multiple times. In addition, in the series of steps described above, the firing step may be performed after repeating the steps from the coating step to the degreasing step multiple times.

[0079] Layers and films formed by wet processes have interfaces. These layers and films retain traces of coating or firing, and these traces become interfaces that can be confirmed by observing their cross-section or by analyzing the elemental concentration distribution within the layer (or film). Strictly speaking, an interface refers to the boundary between layers or films, but here it refers to the area near the boundary of a layer or film. When a cross-section of a layer or film formed by a wet process is observed with an electron microscope, such interfaces can be identified as areas with a darker or lighter color near the boundary with an adjacent layer or film. Furthermore, when the elemental concentration distribution is analyzed, such interfaces can be identified as areas with a higher or lower concentration of an element near the boundary with an adjacent layer or film. The piezoelectric layer 70 is formed by repeating a series of steps from the coating step to the firing step multiple times, or by repeating the steps from the coating step to the degreasing step multiple times before performing the firing step (it is composed of multiple piezoelectric films 74), and therefore has multiple interfaces corresponding to each piezoelectric film 74.

[0080] The specific procedure for forming the piezoelectric layer 70 using a wet method (liquid phase method) is as follows: First, a precursor solution containing a predetermined metal complex is prepared. The precursor solution is obtained by dissolving or dispersing a metal complex, which can form a composite oxide containing K, Na, and Nb upon calcination, in an organic solvent. At this time, a metal complex containing additives such as Mn may be further mixed in. By mixing a metal complex containing Mn into the precursor solution, the Young's modulus of the resulting piezoelectric layer 70 can be further increased.

[0081] Examples of metal complexes containing potassium (K) include potassium 2-ethylhexanoate and potassium acetate. Examples of metal complexes containing sodium (Na) include sodium 2-ethylhexanoate and sodium acetate. Examples of metal complexes containing niobium (Nb) include niobium 2-ethylhexanoate and pentaethoxyniobium. When manganese (Mn) is added as an additive, examples of metal complexes containing Mn include manganese 2-ethylhexanoate. In this case, two or more metal complexes may be used in combination. For example, potassium 2-ethylhexanoate and potassium acetate may be used in combination as metal complexes containing potassium (K). Examples of solvents include 2-n-butoxyethanol, n-octane, or a mixture thereof. The precursor solution may contain additives that stabilize the dispersion of the metal complexes containing K, Na, and Nb. Examples of such additives include 2-ethylhexanoic acid.

[0082] Then, the above-mentioned precursor solution is applied to the substrate 10 on which the elastic film 51, the insulating film 52, and the first electrode 60 are formed, to form a precursor film (coating step). Next, this precursor film is heated to a predetermined temperature, for example, around 130°C to 250°C, and dried for a certain period of time (drying step).

[0083] The heating rate during the drying process is preferably 30°C to 350°C / sec. By firing the piezoelectric film at such a heating rate using the solution method, a piezoelectric layer 70 that is not pseudocubic can be realized. Here, "heating rate" refers to the rate of change in temperature over time from 350°C to the target firing temperature.

[0084] Next, the dried precursor film is heated to a predetermined temperature, for example, 350°C to 500°C, and degreased by holding it at this temperature for a certain period of time (degreasing step).

[0085] In the degreasing process, the heating temperature is preferably 350°C or higher, from the viewpoint of increasing the Young's modulus of the piezoelectric layer 70. More preferably, it is 370°C or higher. On the other hand, if the heating temperature in the degreasing process is excessively high, there is a risk that foreign matter will be formed due to undesirable reactions. Therefore, the heating temperature is preferably 420°C or lower.

[0086] The heating time in the degreasing process is preferably 2 minutes or more, from the viewpoint of increasing the Young's modulus of the piezoelectric layer 70. More preferably, it is 3 minutes or more. On the other hand, if the heating time in the degreasing process is excessively long, there is a risk that the carbon components removed by degreasing will reattach. For this reason, the heating time is preferably 7 minutes or less.

[0087] Finally, the degreased precursor film is heated to a high temperature, for example, around 650°C to 800°C, and held at this temperature for a certain period of time to crystallize. This completes the piezoelectric film (sintering process).

[0088] In the firing process, it is preferable to crystallize the precursor film while applying pressure. Performing the firing process while applying pressure improves the hardness of the piezoelectric layer 70 and further increases the Young's modulus. The pressurized condition is preferably 0.005 MPa or higher relative to atmospheric pressure. On the other hand, if the pressure during firing is excessively high, too much process gas may be incorporated into the film, potentially causing unexpected reactions. Therefore, it is preferable to keep the pressurized pressure at 0.9 MPa or lower relative to atmospheric pressure.

[0089] In the firing process, the heating temperature is preferably 650°C or higher, from the viewpoint of increasing the Young's modulus of the piezoelectric layer 70. More preferably, it is 700°C or higher. On the other hand, if the heating temperature in the firing process is excessively high, there is a risk of diffusion of alkali metal components to the lower electrode and dissolution of the metal material constituting the lower electrode. For this reason, the heating temperature is preferably 760°C or lower.

[0090] The heating time in the firing process is preferably 1 minute or more, from the viewpoint of increasing the Young's modulus of the piezoelectric layer 70. More preferably, it is 2 minutes or more. On the other hand, if the heating time in the firing process is excessively long, alkali metal components may diffuse to the lower electrode. For this reason, the heating time is preferably 8 minutes or less.

[0091] Examples of heating devices used in the drying, degreasing, and firing processes include RTA (Rapid Thermal Annealing) devices that heat by irradiation with infrared lamps, and hot plates. The above process is repeated multiple times to form a piezoelectric layer 70 consisting of multiple piezoelectric films. In addition, in the series of processes from the coating process to the firing process, the firing process may be performed after repeating the coating process to the degreasing process multiple times.

[0092] Furthermore, before and after forming the second electrode 80 on the piezoelectric layer 70, a reheating treatment (post-annealing) may be performed in a temperature range of 600°C to 800°C as needed. By performing post-annealing in this manner, a good interface can be formed between the piezoelectric layer 70 and the first electrode, and between the piezoelectric layer 70 and the second electrode 80. In addition, the crystallinity of the piezoelectric layer 70 can be improved, and the Young's modulus can be further increased.

[0093] After the firing process, the piezoelectric layer 70, which consists of multiple piezoelectric films, is patterned into the shape shown in Figure 5. Patterning can be performed by dry etching such as reactive ion etching or ion milling, or by wet etching using an etching solution.

[0094] Subsequently, a second electrode 80 is formed on the piezoelectric layer 70. The second electrode 80 can be formed in the same manner as the first electrode 60.

[0095] Through the above process, a piezoelectric element 300 comprising a first electrode 60, a piezoelectric layer 70, and a second electrode 80 is manufactured. [Examples]

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to these examples.

[0097] (Example 1) First, the surface of a 6-inch silicon substrate was thermally oxidized to form an elastic film (1370 nm) made of silicon dioxide on the substrate. Furthermore, a zirconium film was formed on the elastic film by sputtering, and this was thermally oxidized to form an insulating film (400 nm) made of zirconium oxide (ZrO2). In this way, a diaphragm consisting of the elastic film and the insulating film was formed on the substrate.

[0098] Next, a first electrode (135 nm) made of platinum (Pt) was formed on the diaphragm by sputtering, a resist of a predetermined shape was formed as a mask, and the first electrode 60 was patterned by RIE.

[0099] Next, a piezoelectric layer was formed on the first electrode using the following procedure. First, a precursor solution consisting of potassium 2-ethylhexanoate, sodium 2-ethylhexanoate, lithium 2-ethylhexanoate, niobium 2-ethylhexanoate, and manganese 2-ethylhexanoate was applied to the substrate by spin coating to form a precursor film (coating step). Subsequently, the precursor film was dried at 180°C (drying step), and then degreased at 380°C for 3 minutes (degreasing step). Next, the degreased precursor film was subjected to a heat treatment at 750°C for 3 minutes using RTA (Rapid Thermal Annealing) under a pressurized atmosphere of 0.01 MPa relative to atmospheric pressure to form a piezoelectric film (sintering process). This process from coating to interintering was repeated multiple times to fabricate a piezoelectric layer consisting of multiple piezoelectric films with a total thickness of 1060 nm and a Young's modulus of 155 GPa. The Young's modulus was measured by nanoindentation, as described above.

[0100] Finally, a second electrode made of platinum (Pt), similar to the first electrode, was formed on the piezoelectric layer to obtain a piezoelectric element.

[0101] (Comparative Example 1) The same procedure as in Example 1 was followed, except that the Young's modulus of the piezoelectric layer was set to 125 GPa and the total film thickness to 1200 nm.

[0102] For each of the above-described examples and comparative examples, the initial deflection of the diaphragm and the displacement of the diaphragm when voltage is applied were investigated. The results are shown in Table 1, Figure 6A, and Figure 6B. The initial deflection was determined as follows.

[0103] <Initial Deflection> For the piezoelectric elements of Example 1 and Comparative Example 1, the displacement (initial deflection) when voltage was applied was determined. Here, a displacement measuring device (laser Doppler displacement meter) was used to determine the displacement at room temperature (25°C).

[0104] [Table 1]

[0105] (Test results) As shown in Table 1, Example 1 was able to reduce the initial deflection by about 13% compared to Comparative Example 1.

[0106] Figure 6A shows the displacement of the diaphragm when voltage is applied to Example 1 and Comparative Example 1, respectively. Figure 6B shows the efficiency (linearity) of the diaphragm displacement when voltage is applied to Example 1 and Comparative Example 1, respectively. Note that the vertical axis in Figure 6B shows "displacement / voltage," but the displacement at a driving voltage of 10V is normalized to 1.

[0107] As shown in Figure 6A, in the region of 20V or higher, Example 1 obtained a larger displacement than Comparative Example 1, but no significant difference was observed between Example 1 and Comparative Example 1. On the other hand, as shown in Figure 6B, the efficiency (linearity) of the displacement at high voltage was suppressed better in Example 1 than in Comparative Example 1, indicating that Example 1 is a piezoelectric element with better efficiency even at high voltages. [Explanation of Symbols]

[0108] I... Inkjet recording device (liquid ejection device), II... Inkjet recording head unit (head unit), 1... Inkjet recording head (liquid ejection head), 10... Substrate, 12... Pressure generating chamber, 13... Ink supply path, 14... Communication passage, 15... Communication section, 20... Nozzle plate, 21... Nozzle, 30... Protective substrate, 31... Piezoelectric element holder, 32... Manifold section, 40... Compliance substrate, 50... Diaphragm, 51... Elastic film, 52... Insulator film, 60... First electrode, 70... Piezoelectric layer, 80... Second electrode, 90... Lead electrode, 100... Manifold, 300... Piezoelectric element

Claims

1. First electrode and, A piezoelectric layer formed above the first electrode, A second electrode formed above the piezoelectric layer, A piezoelectric element comprising, The piezoelectric layer contains potassium, sodium, and niobium. The Young's modulus of the piezoelectric layer, as measured by nanoindentation, exceeds 130 GPa. The density of the piezoelectric layer is 4.41 g / cm³. ３ A piezoelectric element characterized by the above.

2. The piezoelectric element according to claim 1, characterized in that the ratio of the Young's modulus of the piezoelectric layer to the Young's modulus of the second electrode is 0.8 or more and 1 or less.

3. Furthermore, the system includes a substrate positioned on the opposite side of the piezoelectric layer from the first electrode, The piezoelectric element according to claim 1 or 2, characterized in that the substrate contains zirconium oxide.

4. The density of the piezoelectric layer is 4.50 g / cm³. ３ The piezoelectric element according to any one of claims 1 to 3, characterized in that it is as described above.

5. The density of the piezoelectric layer is 4.77 g / cm³. ３ The piezoelectric element according to any one of claims 1 to 4, characterized in that it is as follows:

6. The piezoelectric element according to any one of claims 1 to 5, characterized in that the Young's modulus of the piezoelectric layer is 150 GPa or more.

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