Droplet ejector, printer

Abstract

This invention relates to droplet ejection heads and printers. A droplet ejection head is provided that can suppress abnormal ejection even during high-frequency driving. A droplet ejection head includes: a nozzle plate having a nozzle; a pressure chamber forming substrate having a pressure chamber; a vibrating plate; and a piezoelectric element comprising potassium, sodium, and niobium, formed on the vibrating plate. The piezoelectric element has a first electrode and a second electrode, and a piezoelectric layer located between the first and second electrodes. The combined thickness of the piezoelectric layer, the first electrode, and the second electrode is greater than the thickness of the vibrating plate. When a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of expansion of the pressure chamber, the absolute value of the displacement of the vibrating plate is at least twice the absolute value of the displacement of the vibrating plate when a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of contraction of the pressure chamber.

Description

Technical Field

[0001] This invention relates to droplet ejector heads and printers. Background Technology

[0002] It has been known that, for example, as described in Patent Document 1, in an inkjet head, the driving voltage waveform of the piezoelectric element is corrected to suppress undershoot, overshoot, etc., caused by the variation of the driving voltage along with the number of nozzles that are ejected simultaneously.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2011-148287

[0004] However, overshoot is not limited to variations in the number of nozzles. For example, when the drive pulse supplied to the piezoelectric element becomes high-frequency, it cannot keep up with the flexural deformation of the vibrating plate during the transition from the rise phase of the drive waveform to the voltage holding phase, resulting in overshoot.

[0005] Furthermore, droplet ejection anomalies caused by overshoot are prone to occur in droplet ejection heads equipped with piezoelectric elements using piezoelectric materials with low piezoelectric constants. Examples of low piezoelectric materials include potassium sodium niobate (hereinafter sometimes simply referred to as KNN). In piezoelectric elements using KNN as the main material, the displacement of the vibrating plate is smaller than that of piezoelectric elements using lead zirconate titanate (hereinafter sometimes simply referred to as PZT). Therefore, in piezoelectric elements using KNN as the main material, the displacement of the vibrating plate is increased by reducing its thickness and rigidity. However, when the thickness of the vibrating plate is reduced, unexpected displacement of the vibrating plate can easily occur during overshoot, resulting in droplet ejection anomalies. Summary of the Invention

[0006] According to one aspect of the present invention, a droplet ejector head is provided, the droplet ejector head comprising: a nozzle plate having a nozzle for ejecting liquid as droplets; a pressure chamber forming substrate having a pressure chamber connected to the nozzle; a vibrating plate forming a portion of the wall of the pressure chamber; and a piezoelectric element comprising potassium, sodium, and niobium, and formed on the vibrating plate. The piezoelectric element has a first electrode and a second electrode, and a piezoelectric layer located between the first electrode and the second electrode. The combined thickness of the piezoelectric layer, the first electrode, and the second electrode is greater than the thickness of the vibrating plate. When a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of expansion of the pressure chamber, the absolute value of the displacement of the vibrating plate is at least twice the absolute value of the displacement of the vibrating plate when a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of contraction of the pressure chamber. Attached Figure Description

[0007] Figure 1 An exploded perspective view of the droplet ejector head 200 of the embodiment is shown schematically.

[0008] Figure 2 A top view of the droplet ejector head 200 according to the embodiment is shown schematically.

[0009] Figure 3 for Figure 2 Sectional view along line III-III.

[0010] Figure 4 for Figure 2 Sectional view along line IV-IV.

[0011] Figure 5A This is a schematic diagram illustrating an example of the driving voltage waveform input to the piezoelectric element 100.

[0012] Figure 5B To show with Figure 5A A schematic diagram showing the change in position of the vibrating plate 230 corresponding to the driving waveform.

[0013] Figure 5C A schematic diagram illustrating an example of overshoot.

[0014] Figure 5D This is a schematic diagram illustrating the displacement behavior of the vibrating plate 230 under applied voltage.

[0015] Figure 6A A circuit diagram to represent a typical piezoelectric element.

[0016] Figure 6B A circuit diagram representing a piezoelectric element with asymmetry based on the direction of voltage application.

[0017] Figure 7 This is a simplified structural diagram of the piezoelectric actuator fabricated in the embodiment.

[0018] Figure 8 A graph showing the evaluation results of piezoelectric properties.

[0019] Figure 9 A diagram illustrating the displacement behavior when overshoot occurs.

[0020] Figure 10 This is a graph that compares the change in displacement of the vibrating plate under Vlow as the original displacement with the displacement added to correspond to the malfunction.

[0021] Figure 11 A graph comparing the displacement at the stable position when Vlow deviates from the ideal value to the negative side (~-10V) with the displacement of the corresponding malfunction.

[0022] Figure 12 A perspective view of the printer 300 according to the embodiment is shown schematically.

[0023] Explanation of reference numerals in the attached figures

[0024] 10: First electrode; 20: Piezoelectric layer; 30: Second electrode; 100: Piezoelectric element; 200: Droplet ejector; 210: Pressure chamber forming substrate; 211: Pressure chamber; 220: Nozzle plate; 222: Nozzle; 230: Vibrating plate; 300: Printer; Td, Tp: Thickness; Vhigh, Vi, Vlow, Vm: Voltage. Detailed Implementation

[0025] Embodiments of the present invention will now be described with reference to the accompanying drawings. However, the following description illustrates one aspect of the invention and can be modified freely within the scope of the invention. Parts marked with the same reference numerals in the figures represent the same components, and descriptions are suitably omitted. Furthermore, in the figures, X, Y, and Z represent three mutually orthogonal spatial axes. In this specification, the directions along these axes will be described as the X-axis direction, Y-axis direction, and Z-axis direction, respectively. The Z-axis direction represents the thickness direction or stacking direction of the plate, layer, or film. The X-axis and Y-axis directions represent the in-plane directions of the plate, layer, or film.

[0026] The liquid ejector head according to this embodiment will be described with reference to the accompanying drawings.

[0027] Figure 1 An exploded perspective view of the droplet ejector head 200 of this embodiment is shown schematically. Figure 2 A top view of the droplet ejector head 200 according to this embodiment is shown schematically. Figure 3 for Figure 2 Sectional view along line III-III. Figure 4 for Figure 2 A sectional view along line IV-IV. Figure 2 and Figure 3 The piezoelectric element 100 is shown in a simplified diagram.

[0028] like Figures 1-3 As shown, the droplet ejector head 200 includes multiple piezoelectric elements 100, a pressure chamber forming substrate 210, a nozzle plate 220, a vibrating plate 230, a protective substrate 240, a circuit board 250, and a flexible substrate 260. Figure 2 The circuit board 250 is omitted from the illustration. In this embodiment, a plurality of piezoelectric elements 100 are arranged along the Y-axis.

[0029] The pressure chamber forming substrate 210 is, for example, a silicon substrate. A pressure chamber 211 is disposed on the pressure chamber forming substrate 210. The pressure chamber 211 is divided by a plurality of partition walls 212. The volume of the pressure chamber 211 changes due to the movement of the piezoelectric element 100.

[0030] In the pressure chamber forming substrate 210, a first connecting path 213 and a second connecting path 214 are provided at the end of the pressure chamber 211 in the +X axis direction. The first connecting path 213 is configured such that its opening area decreases from the Y axis direction at the end of the pressure chamber 211 in the +X axis direction. The width of the second connecting path 214 in the Y axis direction is, for example, the same as the width of the pressure chamber 211 in the Y axis direction. A third connecting path 215 is provided in the +X axis direction of the second connecting path 214, communicating with multiple second connecting paths 214. The third connecting path 215 constitutes part of a manifold 216. The manifold 216 is a common liquid chamber for each pressure chamber 211. Thus, a supply flow path 217 and a pressure chamber 211, composed of the first connecting path 213, the second connecting path 214, and the third connecting path 215, are provided in the pressure chamber forming substrate 210. The supply flow path 217 communicates with the pressure chamber 211 and supplies liquid to the pressure chamber 211.

[0031] A nozzle plate 220 is mounted on one side of the pressure chamber forming substrate 210. The nozzle plate 220 is made of, for example, SUS (Steel Use Stainless). The nozzle plate 220 is bonded to the pressure chamber forming substrate 210 by, for example, an adhesive or a heat-sealing film. A plurality of nozzles 222 are provided in the nozzle plate 220 arranged along the Y-axis. The nozzles 222 pass through the interior of the pressure chamber 211 and spray liquid.

[0032] A vibrating plate 230 is disposed on the other side of the pressure chamber forming substrate 210. The vibrating plate 230 is, for example, composed of a silicon oxide layer 232 disposed on the pressure chamber forming substrate 210 and a zirconium oxide layer 234 disposed on the silicon oxide layer 232. The vibrating plate 230 may also be a single layer of silicon oxide or a single layer of zirconium oxide. The thickness of the vibrating plate 230 is, for example, 0.5 μm or more and 3 μm or less.

[0033] A piezoelectric element 100 is disposed on the vibrating plate 230. Multiple piezoelectric elements 100 are disposed. The number of piezoelectric elements 100 is not particularly limited. Each piezoelectric element 100 includes a first electrode 10, a piezoelectric layer 20, and a second electrode 30.

[0034] The first electrode 10 is disposed on the vibrating plate 230. The first electrode 10 is disposed between the vibrating plate 230 and the piezoelectric layer 20. The thickness of the first electrode 10 is, for example, 3 nm or more and 300 nm or less. The first electrode 10 is, for example, a metal layer such as a platinum layer, an iridium layer, a titanium layer, a ruthenium layer, a conductive oxide layer of these metals, a lanthanum nickelate (LaNiO3:LNO) layer, a strontium ruthenate (SrRuO3:SRO) layer, etc. The first electrode 10 may also have a structure obtained by stacking multiple layers exemplified above.

[0035] In the droplet ejector head 200, the first electrode 10 is configured as an independent electrode corresponding to each pressure chamber 211. The width of the first electrode 10 in the Y-axis direction is narrower than the width of the pressure chamber 211 in the Y-axis direction. The length of the first electrode 10 in the X-axis direction is longer than the length of the pressure chamber 211 in the X-axis direction. The two ends of the first electrode 10 are located in the X-axis direction with respect to the two ends of the pressure chamber 211. The lead electrode 202 is connected to the X-axis end of the first electrode 10.

[0036] A piezoelectric layer 20 is disposed on the first electrode 10. The piezoelectric layer 20 is disposed between the first electrode 10 and the second electrode 30. In this embodiment, the piezoelectric layer 20 is disposed on both the first electrode 10 and the vibrating plate 230. The thickness of the piezoelectric layer 20 is, for example, 100 nm or more and 3 μm or less. The piezoelectric layer 20 can be deformed by applying a voltage between the first electrode 10 and the second electrode 30.

[0037] The piezoelectric layer 20 is a KNN layer containing potassium (K), sodium (Na), and niobium (Nb). The piezoelectric layer 20 has a perovskite structure. In the piezoelectric layer 20, the ratio of the atomic concentration DA at site A to the atomic concentration DB at site B, DA / DB, is, for example, 1.01 or more and 1.10 or less, preferably 1.02 or more and 1.06 or less. When the piezoelectric layer 20 is a KNN layer, the total number of potassium atoms and sodium atoms in the piezoelectric layer 20 is, for example, more than 1% and less than 10% more than the number of niobium atoms, preferably more than 2% and less than 6%.

[0038] The width of the piezoelectric layer 20 in the Y-axis direction is, for example, wider than the width of the first electrode 10 in the Y-axis direction. The length of the piezoelectric layer 20 in the X-axis direction is longer than the length of the pressure chamber 211 in the X-axis direction. The end of the first electrode 10 in the +X-axis direction is located between the end of the piezoelectric layer 20 in the +X-axis direction and the end of the pressure chamber 211 in the +X-axis direction. The end of the first electrode 10 in the +X-axis direction is covered by the piezoelectric layer 20. On the other hand, the end of the piezoelectric layer 20 in the -X-axis direction is, for example, located between the end of the first electrode 10 in the -X-axis direction and the end of the pressure chamber 211 in the +X-axis direction. The end of the first electrode 10 in the -X-axis direction is not covered by the piezoelectric layer 20.

[0039] The second electrode 30 is disposed on the piezoelectric layer 20. In this embodiment, the second electrode 30 is continuously disposed on the piezoelectric layer 20 and the vibrating plate 230. The second electrode 30 is configured to be a common electrode for multiple piezoelectric elements 100. The thickness of the second electrode 30 is, for example, 3 nm or more and 300 nm or less. The second electrode 30 is, for example, a metal layer such as an iridium layer, a platinum layer, a titanium layer, a ruthenium layer, a conductive oxide layer of these metals, a lanthanum nickelate layer, a strontium ruthenate layer, etc. The second electrode 30 may also have a structure obtained by stacking multiple layers exemplified above.

[0040] In the piezoelectric element 100, by applying a voltage between the first electrode 10, which serves as the lower electrode, and the second electrode 30, which serves as the upper electrode, a voltage can be applied to the piezoelectric layer 20, causing the piezoelectric layer 20 to deform. The piezoelectric element 100 and the vibrating plate 230 function as piezoelectric actuators that change the volume of the pressure chamber 211.

[0041] In the droplet ejector head 200, the vibrating plate 230 and the first electrode 10 are displaced by the deformation of the piezoelectric layer 20, which has electromechanical conversion characteristics. That is, in the droplet ejector head 200, the vibrating plate 230 and the first electrode 10 essentially function as vibrating plates.

[0042] The protective substrate 240 is bonded to the vibrating plate 230 by adhesive 203. A through-hole 242 is provided in the protective substrate 240. In the illustrated example, the through-hole 242 penetrates the protective substrate 240 in the Z-axis direction and communicates with the third communication path 215. The through-hole 242 and the third communication path 215 constitute a manifold 216 that forms a common liquid chamber for each pressure chamber 211. Furthermore, a through-hole 244 penetrating the protective substrate 240 in the Z-axis direction is provided in the protective substrate 240. The end of the lead electrode 202 is located at the through-hole 244.

[0043] An opening 246 is provided in the protective substrate 240. The opening 246 is a space for not obstructing the driving of the piezoelectric element 100. The opening 246 may or may not be sealed.

[0044] A circuit board 250 is disposed on a protective substrate 240. The circuit board 250 includes a semiconductor integrated circuit (IC) for driving the piezoelectric element 100. The circuit board 250 and the lead electrodes 202 are electrically connected via connection wiring 204.

[0045] A flexible substrate 260 is disposed on a protective substrate 240. The flexible substrate 260 has a sealing layer 262 disposed on the protective substrate 240 and a fixing plate 264 disposed on the sealing layer 262. The sealing layer 262 is a layer for sealing the manifold 216. The sealing layer 262 is flexible, for example. A through hole 266 is provided in the fixing plate 264. The through hole 266 penetrates the fixing plate 264 in the Z-axis direction. The through hole 266 is located at a position overlapping the manifold 216 when viewed from the Z-axis direction.

[0046] The piezoelectric element 100 of this embodiment will now be described in more detail.

[0047] In this embodiment, such as Figure 4 As shown, the thickness Tp of the piezoelectric element 100, i.e., the total thickness Tp of the piezoelectric layer 20, the first electrode 10, and the second electrode 30, is greater than the thickness Td of the vibrating plate 230. In this embodiment, the piezoelectric layer 20 is a KNN layer, made of a material with a lower piezoelectric constant than PZT. By setting the thickness Td of the vibrating plate 230 to be smaller than the thickness Tp of the piezoelectric element 100, the rigidity of the vibrating plate 230 can be reduced, and the responsiveness of the vibrating plate 230 to the driving voltage input can be improved.

[0048] Figure 5A This is a diagram illustrating an example of the driving voltage waveform input to the piezoelectric element 100. Figure 5B To show with Figure 5A The graph shows the change in the position of the vibrating plate 230 corresponding to the driving waveform. Figure 5C A diagram illustrating an example of overshoot. Figure 5D A diagram illustrating the displacement behavior of the vibrating plate 230 under applied voltage.

[0049] like Figure 5A As shown, in the initial state, a positive voltage Vm is applied (in standby mode) to maintain a constant electrical state of the piezoelectric layer 20. When liquid is ejected from the nozzle 222, firstly, the volume of the pressure chamber 211 is expanded by reducing the voltage to Vlow to draw liquid into the pressure chamber 211 (pull action). Although Vlow is illustrated as a negative voltage, it can be either 0V or a positive voltage. Next, a positive voltage Vhigh, higher than Vm, is applied to cause the volume of the pressure chamber 211 to contract to eject liquid from the nozzle 222 (push action). Finally, the voltage is returned to Vm.

[0050] In the series of actions described above, the voltage Vlow setting during the pull action is crucial. Figure 5B The diagram shows the variation in the position of the vibrating plate 230 under ideal conditions of Vlow. Figure 5BDuring the pull action, the vibrating plate 230 moves to the uppermost position (the pressure chamber 211 has the largest volume on the side), and during the push action, the vibrating plate 230 moves to the lowermost position (the pressure chamber 211 has the smallest volume on the side).

[0051] Figure 5C The variation in the position of the vibrating plate 230 is shown under conditions where Vlow is undesirable, particularly when Vlow is too low. Figure 5B In contrast, the movement of the vibrating plate 230 during the pull action is different. After the vibrating plate 230 temporarily moves to the uppermost side, it first returns slightly to the lower side before stabilizing. That is, an unexpected positional change occurs in the vibrating plate 230.

[0052] exist Figure 5D The diagram illustrates the displacement behavior of a piezoelectric element and a vibrating plate under an applied voltage. The piezoelectric layer 20 of the piezoelectric element 100 exhibits a property of changing lattice size by extending the crystal in the voltage application direction or having its polarization direction oriented towards the voltage application direction. This property, in principle, is independent of the voltage application direction; for example, it changes in the same direction whether the upper electrode (second electrode 30) is at a positive voltage relative to the lower electrode (first electrode 10) or vice versa. Furthermore, the piezoelectric layer 20 has a voltage at which the lattice size in the voltage application direction is minimized. This voltage varies depending on parameters such as the type of material constituting the piezoelectric layer 20, the film thickness of the piezoelectric layer 20, the polarization direction and amplitude of the piezoelectric layer 20, and the structure of the piezoelectric element 100 (piezoelectric capacitor) including electrodes.

[0053] Ideally, the voltage Vi during the pull action should be the voltage Vi at which the lattice size in the aforementioned voltage application direction is minimized. However, since the voltage Vi varies depending on various parameters, it will change even if a piezoelectric element 100 moves over a long period due to differences among the individual piezoelectric elements 100 constituting a device. Therefore, although the degree varies, it is difficult to avoid unexpected positional changes in the vibrating plate 230 during actuation.

[0054] Furthermore, in this embodiment, in the configuration where the piezoelectric layer 20 is composed of a KNN layer and the thickness Td of the vibrating plate 230 is relatively thin, the vibrating plate 230 is more prone to movement compared to the case where the vibrating plate 230 is relatively thick, and may be more prone to abnormal ejection due to high-frequency vibrations that may cause malfunctions during pull actions.

[0055] Therefore, in the droplet ejector head 200 of this embodiment, a configuration is adopted that can suppress the unexpected displacement of the vibrating plate 230 even when the voltage deviates from the ideal voltage Vi during the pull action.

[0056] Specifically, the configuration is set such that when a voltage of 25V is applied to the piezoelectric element 100 to displace the vibrating plate 230 in the direction of expansion of the pressure chamber 211, the absolute value of the displacement of the vibrating plate 230 is more than 1.5 times the absolute value of the displacement of the vibrating plate 230 when a voltage of 25V is applied to the piezoelectric element 100 to displace the vibrating plate 230 in the direction of contraction of the pressure chamber 211.

[0057] According to the above configuration, as described in the embodiments below, during the pull action, the difference between the displacement of the vibrating plate 230 during overshoot and the displacement when the position of the vibrating plate 230 stabilizes can be reduced. Consequently, the amplitude of the high-frequency vibration generated when the vibrating plate 230 recovers from overshoot also decreases. Therefore, the droplet ejector head 200 according to this embodiment can suppress unexpected abnormal ejection from the nozzle 222.

[0058] The piezoelectric element 100 of this embodiment has an asymmetry in displacement, which varies depending on the direction of the voltage applied between the first electrode 10 and the second electrode 30.

[0059] By giving the piezoelectric element 100 an asymmetry in displacement, the electrical properties of the piezoelectric element 100 are altered. Specifically, conventional (conventional) piezoelectric elements are modified by... Figure 6A In contrast, the piezoelectric element 100 of this embodiment is represented by a parallel circuit of capacitors and resistors. Figure 6B That would be represented as a circuit with diodes connected in series to a resistor.

[0060] Depend on Figure 6B The displacement of the piezoelectric actuator, consisting of the piezoelectric element 100 and the vibrating plate 230, shown changes according to the direction of the applied voltage. Figure 6B In the circuit shown, the combined resistor on the left side of the circuit changes by the amount corresponding to the diode depending on the direction of the applied voltage. Figure 6B In the above, the combined resistance when the lower terminal is set to a high potential and the upper terminal is set to a low potential is greater than the combined resistance when the upper terminal is set to a high potential and the lower terminal is set to a low potential.

[0061] From an electrical perspective, the magnitude of the combined resistance is related to the dielectric loss of the circuit. Figure 6BIn this case, setting the upper terminal to a high potential increases dielectric loss compared to setting the lower terminal to a high potential. Furthermore, the magnitude of dielectric loss is related to the magnitude of piezoelectric displacement. When dielectric loss is low, the increase in displacement is minimal. Thus, as... Figure 6B As shown, by making the combined resistor different depending on the direction of voltage application, it is possible to set it as a piezoelectric element with displacement asymmetrical with respect to the direction of voltage application.

[0062] In this embodiment, when Vlow deviates from the ideal voltage Vi towards the negative side, overshoot occurs in the displacement of the vibrating plate 230, and unexpected movement occurs in the vibrating plate 230. In this case, the amount of overshoot displacement is reduced by decreasing the amount of displacement under a pull action compared to a push action. Therefore, in this embodiment, it is preferable that the resistance of the piezoelectric element 100 when the potential applied to the second electrode 30 is smaller than the potential applied to the first electrode 10 is larger than the resistance when the potential applied to the second electrode 30 is larger than the potential applied to the first electrode 10.

[0063] Several methods can be cited as ways to impart asymmetry to the piezoelectric element 100, that is, to make the displacement of the piezoelectric element 100 different when a positive voltage is applied and when a negative voltage is applied.

[0064] For example, methods such as (asymmetry attribution method 1) changing the material of the interface on the first electrode 10 side or the interface on the second electrode 30 side of the piezoelectric element 100 to change the Schottky barrier on one side, and (asymmetry attribution method 2) forming directional component hierarchies (composition tilt) or electrical hierarchies (electrical tilt) within the piezoelectric layer 20 and creating electrical directionality within the piezoelectric layer 20 can be cited. In this embodiment, since it is only necessary to ultimately achieve the asymmetry of the piezoelectric displacement, either method 1 or method 2 can be used.

[0065] In the case of asymmetry imparting method 1, a layer for changing the Schottky barrier is provided at either the interface between the first electrode 10 and the piezoelectric layer 20 or the interface between the piezoelectric layer 20 and the second electrode 30 of the piezoelectric element 100. Metallic materials, particularly noble metals such as platinum, are often used as electrode materials for the first electrode 10 and the second electrode 30. Therefore, conductive oxide materials are suitable as the materials for the interfaces used to change the Schottky barrier. For example, a configuration in which an SrRuO3 layer or a LaNiO3 layer is formed at the interface between the first electrode 10 and the piezoelectric layer 20 can be configured. Alternatively, an IrOx layer can be formed at the interface between the second electrode 30 and the piezoelectric layer 20.

[0066] In the case of method 2 for imparting asymmetry, methods for creating component classification within the piezoelectric layer 20 include changing the starting materials used to form the piezoelectric layer 20 in the lower and upper layers, and utilizing the different crystallization temperatures of the components of the piezoelectric material composed of a mixture to utilize the difference in the composition of the component that crystallizes earliest in the lower part of the film-forming unit and the component that crystallizes last in the upper part. Methods for creating electrical classification within the piezoelectric layer 20 include adding a gradient to the state of crystal defects by utilizing the differences in crystallinity and internal stress between the upper and lower parts of the piezoelectric layer 20.

[0067] Examples of methods for forming the piezoelectric layer 20 include solution methods such as spin coating to coat liquid precursor materials, and methods such as firing Ar onto solid target materials. + Solid-phase methods include sputtering, where particles such as ions are deposited on the surface of a substrate opposite the target material; and vapor-phase methods, where precursor materials are deposited as gas or vapor on the surface of the substrate. In this embodiment, any one of these methods can be used to form a piezoelectric thin film, or a combination of two or more of these methods can be used.

[0068] In Method 2 described above, when forming component hierarchies within the piezoelectric layer 20, it is preferable to employ an appropriate film-forming method for the piezoelectric layer 20 based on the method of forming the component hierarchies. For example, when forming the piezoelectric layer 20 using a solution method, a solution containing precursor raw materials is coated, and then a series of steps involving drying, degreasing, and calcination to crystallize are repeated multiple times to form a piezoelectric film, resulting in a piezoelectric layer 20 composed of multiple stacked piezoelectric film layers on the substrate. Such a solution method is suitable for the method of forming component hierarchies within the piezoelectric layer 20 in Method 2, which imparts asymmetry, as it allows for relatively easy component hierarchies to be formed by changing the solution material and controlling the calcination conditions.

[0069] In addition, in method 1 above, when a conductive oxide layer is formed at the interface between the piezoelectric layer 20 and either the upper or lower electrode, a film-forming treatment of the layer composed of conductive oxides, etc., is performed before or after the formation of the piezoelectric layer 20 using any of the following methods: solution method, solid phase method, or gas phase method.

[0070] (printer)

[0071] Next, the printer involved in this embodiment will be described with reference to the accompanying drawings. Figure 12 A perspective view of the printer 300 according to this embodiment is shown schematically.

[0072] Printer 300 is an inkjet printer. For example... Figure 12As shown, the printer 300 includes a head unit 310. The head unit 310 has, for example, a droplet ejector head 200. The number of droplet ejector heads 200 is not particularly limited. The housings 312 and 314 of the head unit 310, which constitute the supply unit, are designed to be detachable. The carriage 316, on which the head unit 310 is mounted, is designed to be axially movable on a carriage shaft 322 mounted on the device body 320, and ejects liquid supplied from the liquid supply unit.

[0073] Here, "liquid" refers to any material in its liquid phase, including liquid materials such as sols and gels. Furthermore, not only liquids as a state of matter are included, but also substances obtained by dissolving, dispersing, or mixing functional material particles composed of solid substances such as pigments and metal particles in a solvent. Representative examples of liquids include inks and liquid crystal emulsifiers. Ink is defined as a substance comprising various liquid composites such as general water-based inks, oil-based inks, neutral inks, and hot-melt inks.

[0074] In printer 300, the driving force of drive motor 330 is transmitted to carriage 316 via multiple gears (not shown) and timing belt 332, and carriage 316, which houses head unit 310, moves along carriage shaft 322. On the other hand, a conveyor roller 340, serving as a conveying mechanism, is provided in device body 320. This conveyor roller 340 moves a sheet of paper or other recording medium, such as paper, relative to droplet ejector head 200. The conveying mechanism for conveying the sheet S is not limited to a conveyor roller; it can also be a belt, drum, or the like.

[0075] The printer 300 includes a printer controller 350, which serves as a control unit for controlling the droplet ejector head 200 and the transport roller 340. The printer controller 350 is electrically connected to the circuit board 250 of the droplet ejector head 200. The printer controller 350 includes, for example, RAM (Random Access Memory) for temporary storage of various data, ROM (Read Only Memory) for storing control programs, a CPU (Central Processing Unit), and a drive signal generation circuit for generating drive signals supplied to the droplet ejector head 200.

[0076] It should be noted that the piezoelectric element 100 is not limited to use in liquid ejector heads and printers, but can be used in a wide range of applications. The piezoelectric element 100 is suitable for use as a piezoelectric actuator, such as in ultrasonic motors, vibratory dust collectors, piezoelectric transformers, piezoelectric speakers, piezoelectric pumps, and pressure-to-electric conversion devices. Furthermore, the piezoelectric element 100 is suitable for use as a piezoelectric sensor element, such as in ultrasonic detectors, angular velocity sensors, acceleration sensors, vibration sensors, tilt sensors, pressure sensors, collision sensors, human body sensors, infrared sensors, terahertz sensors, thermal detection sensors, pyroelectric sensors, and piezoelectric sensors. Additionally, the piezoelectric element 100 is suitable for use as a ferroelectric element, such as in ferroelectric RAM (FeRAM), ferroelectric transistor (FeFET), ferroelectric operational circuit (FeLogic), and ferroelectric capacitor. Finally, the piezoelectric element 100 is suitable for use as a voltage-controlled optical element in wavelength converters, optical waveguides, optical modulators, refractive index control elements, and electronic shutter mechanisms.

[0077]

Example

[0078] In this embodiment, an evaluation was conducted. Figure 7 The piezoelectric actuator shown is configured as follows. Regarding the samples, three examples are provided: Example 1, Comparative Example 1, and Comparative Example 2, with the total film thickness of the piezoelectric element (composed of an upper electrode, a piezoelectric layer, and a lower electrode) differing from the total film thickness of the vibrating plate. Apart from the aforementioned total film thickness condition, the common manufacturing process shown below is employed.

[0079] (Manufacturing process)

[0080] First, a SiO2 layer was formed by thermal oxidation of a single-crystal silicon substrate having a (110) facet. Next, a Zr layer was formed on the SiO2 layer by DC (Direct Current) sputtering, followed by a ZrOx layer formed by heat treatment at 850°C. This process formed a ZrOx / SiO2 stacked vibrating plate. The unoxidized portion of the single-crystal silicon substrate became... Figure 7 The portion of the substrate shown.

[0081] Next, a piezoelectric element was formed on the vibrating plate. First, a Ti layer was formed as a bonding layer on the ZrOx layer. Then, a Pt layer and an Ir layer were sequentially deposited on the Ti layer using DC sputtering to form the lower electrode.

[0082] Next, the Ir layer surface was irradiated with ultraviolet light in a vacuum for ten minutes, followed by exposure to a nitrogen atmosphere for one minute to purify the Ir layer surface. Then, a 70 nm film of potassium sodium niobate (KNN) precursor solution was formed by spin coating, followed by lamp annealing at 750 °C for three minutes in an oxygen atmosphere to form the KNN layer. The KNN precursor solution was adjusted to (K+Na):Nb = 104:100 and K:Na = 50:50.

[0083] Next, a pattern was formed on the layer above the ZrOx layer by ion milling. Then, an 11-layer spin-coating method was used to form a KNN precursor solution with the same composition as described above, totaling 400 nm in thickness. Each layer was annealed at 750°C for three minutes in an oxygen atmosphere to crystallize the KNN layer and form a piezoelectric layer. The Ir layer was oxidized during the KNN layer formation process and became the IrOx layer.

[0084] Next, a Pt layer was formed on top of the piezoelectric layer composed of KNN layers by DC sputtering, and the upper electrode was formed.

[0085] Next, the upper electrode, piezoelectric thin film, and lower electrode are sequentially processed into a predetermined pattern using methods such as etching to form a piezoelectric element. The pressure chamber of the piezoelectric actuator is formed by etching the back side of a silicon substrate with KOH, for example, to create a predetermined pattern.

[0086] The film thickness conditions for each sample are as follows.

[0087] [Example]

[0088] The total film thickness of the piezoelectric element was set to 2.2 μm, and the total film thickness of the vibrating plate was set to 1.0 μm.

[0089] [Comparative Example 1]

[0090] The total film thickness of the piezoelectric element was set to 1.2 μm, and the total film thickness of the vibrating plate was set to 2.0 μm. The material used for the piezoelectric layer was the same as in the previous embodiment.

[0091] [Comparative Example 2]

[0092] The total film thickness of the piezoelectric element was set to 2.2 μm, and the total film thickness of the vibrating plate was set to 2.4 μm. The material used for the piezoelectric layer was the same as in the embodiment. Furthermore, for both the embodiment and Comparative Example 1, the dimensions of the pressure chamber were adjusted so that the side with the larger displacement became uniform.

[0093] (Evaluation 1)

[0094] The piezoelectric characteristics of samples from Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated. The measuring apparatus and measuring conditions are described below.

[0095] Measuring device: NLV-2500 laser Doppler vibrometer (manufactured by Polytec)

[0096] Function generator AFG3022C (made by Textronix)

[0097] HDO4024 digital oscilloscope (manufactured by Lecroy Corporation)

[0098] Measurement conditions: Frequency 2kHz, Sin wave

[0099] Vhigh = +25V

[0100] Vlow = -25V

[0101] exist Figure 8 The evaluation results are shown in the figure. The displacement in the driving direction (positive voltage side) is 470-480 nm in both the sample of Example and Comparative Examples 1 and 2, which is the same. On the other hand, the displacement in the opposite direction (negative voltage side) is 400-450 nm in the sample of Comparative Examples 1 and 2, while it is about 260 nm in the sample of Example, which is half the displacement.

[0102] (Evaluation 2)

[0103] The driving waveforms of the piezoelectric actuators in Examples 1 and 2 during the droplet ejection action were analyzed, and the displacement behavior of the vibrating plate was evaluated. The measuring apparatus and measuring conditions are described below.

[0104] The measuring device used was an NLV-2500 laser Doppler vibrometer (manufactured by Polytec).

[0105] Function generator AFG3022C (made by Textronix)

[0106] Digital oscilloscope HDO4024 (manufactured by Lecroy).

[0107] Measurement conditions: Vlow = -10V to 0V (varies)

[0108] Vhigh = Vlow + 25V

[0109] Vm = (Vlow + Vhigh) / 2

[0110] If Vlow is not configured ideally, such as Figure 9 As shown, overshoot occurred during pull, adding the displacement corresponding to the malfunction to the original displacement (the stable displacement position).

[0111] exist Figure 10 The change in the displacement of the vibrating plate under Vlow is shown as a comparison between the original displacement and the displacement with the corresponding malfunction. Figure 11 A graph comparing the displacement at the stable position when Vlow deviates from the ideal value to the negative side (~-10V) with the displacement of the corresponding malfunction. For example... Figure 11 As shown, the greater the deviation of Vlow from the ideal value towards the negative side, the greater the displacement caused by malfunction.

[0112] It should be noted that although the illustrations are omitted, it has been confirmed that when Vlow is ideal or deviates to the positive side, it produces almost no false triggering.

[0113] exist Figure 11 The figure shows a graph comparing the ratio of erroneous actions to actual displacements in the Example and Comparative Example 2. As shown in the figure, it is confirmed that, compared to the sample of Comparative Example 2, the sample of the Example showed a smaller change in displacement when Vlow deviated from the ideal value, and erroneous actions were suppressed.

Claims

1. A droplet ejector head, characterized in that, have: A nozzle plate having nozzles that eject liquid as droplets; A pressure chamber forming substrate has a pressure chamber connected to the nozzle; A vibrating plate forms part of the wall of the pressure chamber; as well as A piezoelectric element, comprising potassium, sodium, and niobium, is formed on the vibrating plate. The piezoelectric element has a first electrode, a second electrode, and a piezoelectric layer located between the first electrode and the second electrode. The piezoelectric element exhibits an asymmetry where the displacement varies depending on the direction of the voltage applied between the first and second electrodes. The combined thickness of the piezoelectric layer, the first electrode, and the second electrode is greater than the thickness of the vibrating plate. When a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of expansion of the pressure chamber, the absolute value of the displacement of the vibrating plate is more than 1.5 times the absolute value of the displacement of the vibrating plate when a voltage of 25V is applied to the piezoelectric element to displace the vibrating plate in the direction of contraction of the pressure chamber.

2. The droplet ejector according to claim 1, characterized in that, The piezoelectric layer is disposed between the vibrating plate and the second electrode, and the first electrode is disposed between the vibrating plate and the piezoelectric layer. In the piezoelectric element, the resistance is greater when the potential applied to the second electrode is smaller than the potential applied to the first electrode than when the potential applied to the second electrode is larger than the potential applied to the first electrode.

3. The droplet ejector according to claim 1 or 2, characterized in that, The piezoelectric layer is disposed between the vibrating plate and the second electrode, and the piezoelectric layer has a plurality of piezoelectric films stacked in a direction from the vibrating plate toward the second electrode.

4. The droplet ejector according to claim 1 or 2, characterized in that, The first electrode or the second electrode contains a conductive oxide material.

5. A printer, characterized in that, include: The droplet ejector head according to any one of claims 1 to 4; A delivery mechanism that moves the recorded medium relative to the droplet ejection head; as well as The control unit controls the droplet ejector head and the conveying mechanism.

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