Method of manufacturing ink jet head and ink jet head

Abstract

To provide a method of manufacturing an inkjet head which can more properly reduce variations in characteristics of a piezoelectric element, and to provide the inkjet head.SOLUTION: A method for manufacturing an inkjet head includes a plurality of piezoelectric elements each having two electrodes and a piezoelectric layer located between the two electrodes, and a plurality of nozzles corresponding to the plurality of piezoelectric elements, respectively, and is capable of ejecting ink by applying a voltage between the two electrodes to apply a pressure fluctuation to the ink in the nozzle corresponding to the piezoelectric element. For each of the plurality of piezoelectric elements, adjustment is performed so that the variation in the value obtained by dividing the change rate of the capacitance of the piezoelectric element between two applied voltages by the facing area of the electrodes falls within a predetermined reference range.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an inkjet manufacturing method and an inkjet head. [Background technology]

[0002] In inkjet heads that eject ink from nozzles, variations in the characteristics among multiple nozzles significantly affect the quality of the output. In piezo-type inkjet heads, it is important to address variations in the polarization characteristics of the piezoelectric element. Piezoelectric elements are capacitive and are directly affected by the thickness of the piezoelectric element. Patent Document 1 discloses a technology that corrects variations in the thickness of the piezoelectric layer by adjusting the width of the electrodes that apply voltage to the piezoelectric layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-156987 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the characteristics of a piezoelectric element do not depend only on its thickness. However, directly measuring the polarization characteristics is time-consuming, and there is also the problem that the measurement operation itself may change the polarization characteristics of the piezoelectric element.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide an inkjet head and a method for manufacturing the same that can more appropriately reduce variations in the characteristics of the piezoelectric elements. [Means for solving the problem]

[0006] In order to achieve the above object, one aspect of the present disclosure is to A method for manufacturing an inkjet head comprising: a plurality of piezoelectric elements each having two electrodes and a piezoelectric layer located between the two electrodes; and a plurality of nozzles respectively corresponding to the plurality of piezoelectric elements, wherein ink can be ejected by applying a pressure fluctuation to ink in the nozzles corresponding to the piezoelectric elements by applying a voltage between the two electrodes, the method comprising: For each of the plurality of piezoelectric elements, an adjustment is made so that the variation in the value obtained by dividing the rate of change in capacitance of the piezoelectric element between two applied voltages by the opposing area of ​​the electrodes falls within a predetermined reference range.

[0007] Another aspect of the present disclosure is forming a plurality of piezoelectric elements on a substrate using an exposure mask to form the second electrodes, the plurality of piezoelectric elements including a piezoelectric layer, a first electrode located on a first surface of the piezoelectric layer, and a plurality of second electrodes located on the opposite side of the piezoelectric layer from the first surface, the plurality of piezoelectric elements corresponding to the number of the second electrodes; applying two different voltages to each of the piezoelectric elements and measuring the rate of change in capacitance of the piezoelectric elements; A distribution of a first variable obtained by dividing the rate of change by an opposing area of ​​the first electrode and the second electrode with respect to the position of the piezoelectric element is obtained; selecting, from a group of exposure masks that are set in advance and are different from one another, exposure mask patterns for obtaining a plurality of second electrodes each having an area corrected in accordance with a correction amount of the facing area that makes the distribution closer to flat and brings the variation within a reference range; determining that the selected exposure mask pattern is used for forming the plurality of second electrodes; This is a method for manufacturing an inkjet head.

[0008] Another aspect of the present disclosure is a plurality of piezoelectric elements each having two electrodes and a piezoelectric layer located between the two electrodes; a plurality of nozzles respectively corresponding to the plurality of piezoelectric elements; a driving unit that applies a voltage between the two electrodes to apply a pressure fluctuation to ink in the nozzle corresponding to the piezoelectric element, thereby causing ink to be ejected from the nozzle; and Equipped with For each of the plurality of piezoelectric elements, the variation in the value obtained by dividing the rate of change in capacitance of the piezoelectric element between two applied voltages by the opposing area of ​​the electrodes is ±6.8% or less. It is an inkjet head. [Effects of the Invention]

[0009] According to the present invention, it is possible to more appropriately reduce variations in the characteristics of the piezoelectric elements in the inkjet head. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram schematically illustrating a cross-sectional structure near a nozzle in a head chip of an inkjet head. [Figure 2] 10A and 10B are diagrams illustrating a configuration for causing a vibrating section to perform a deformation operation. [Figure 3] 10A and 10B are diagrams illustrating the arrangement of downstream supply paths in a head chip. [Figure 4] FIG. 10 is a graph showing the experimental results of measuring the relationship between the ejection speed and parameters. [Figure 5] FIG. 10 is a diagram schematically illustrating an example of the distribution of parameters on a wafer. [Figure 6] 10A and 10B are diagrams illustrating adjustment of the opposing area. [Figure 7] 10 is a flowchart showing an adjustment procedure for the vibration unit. [Figure 8] 10A and 10B are diagrams illustrating other structures of the vibration section. [Figure 9] 10A and 10B are diagrams illustrating other structures of the vibration section. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating the cross-sectional structure near a nozzle N in a head chip 10 of an inkjet head 1 of this embodiment. In reality, the head chip 10 has multiple nozzles N. The openings of the multiple nozzles N are arranged on the bottom surface of the head chip 10 at intervals according to the resolution, etc. Here, the bottom side of the head chip 10 is defined as the -Z side. In the cross section shown, the direction perpendicular to the Z direction is defined as the X direction. The Y direction is defined as perpendicular to the X and Z directions. The bottom surface may be a flat surface parallel to the XY plane, or may have irregularities as necessary. The arrangement of the nozzles N may be two-dimensional. This XZ cross section is a cross section parallel to the ink ejection direction of the head chip 10.

[0012] The head chip 10 has a flow path member 11, a vibration section 12 (piezoelectric element), and a nozzle plate 13. The nozzle plate 13 is located on the most negative side in the Z direction on the head chip 10. Here, the opening surface of the nozzle N is defined as the bottom surface. The nozzle plate 13 has the nozzle N. The flow path member 11 is located on the +Z side of the nozzle plate 13. The flow path member 11 has multiple overlapping layers and has hollow pressure chambers 111 inside. A common supply channel 115 extends in the Y direction on the -Z side of the pressure chambers 111. Ink is supplied to each pressure chamber 111 by an upstream supply channel 113 that branches off from the common supply channel 115 and extends in the Z direction. The pressure chambers 111 and the nozzles N are connected by a downstream supply channel 114. The top side (+Z side) of the pressure chambers 111 is covered by a vibration plate 112. The pressure chamber 111, the upstream supply channel 113, and the downstream supply channel 114 are collectively referred to as the ink flow channel of each nozzle N.

[0013] The ink flow paths are not limited to the above-described positional relationship. For example, the common supply path 115 and the upstream supply path 113 may be located above (on the +Z side of) the pressure chamber 111, and the nozzle N may be directly connected to the bottom surface (on the -Z side) of the pressure chamber 111. The flow path member 11 is insulating and can be precisely machined. For example, the flow path member 11 may be a glass substrate, a Si substrate, or a resin substrate such as polyimide. The multiple layer members may be different from each other. Note that, as long as the conductive layer is separated from the vibration section 12, a conductive layer may be included in, for example, the nozzle plate 13. The conductive layer may be made of, for example, SUS. The vibration plate 112 may also be used in combination with the lower electrode 122 of the vibration section 12. In this case, the material of the vibration plate 112 is the same as that of the lower electrode 122.

[0014] The vibration section 12 is located above the pressure chamber 111 with the vibration plate 112 sandwiched therebetween, in a range where at least a portion of the vibration section 12 overlaps with the pressure chamber 111 in a plan view perspective. The vibration section 12 has a lower electrode 122, a piezoelectric member 121, and an upper electrode 123 bonded together in this order. That is, the piezoelectric member 121 (piezoelectric layer) is located between two electrodes, the lower electrode 122 and the upper electrode 123. The piezoelectric member 121 has a thin-film layered structure. The lower electrode 122 and the upper electrode 123 also have thin plate-like structures. Therefore, the vibration section 12 has a structure in which the lower electrode 122, the piezoelectric member 121, and the upper electrode 123 are layered together in this order. The lower electrode 122 is bonded to the vibration plate 112. A voltage is applied between the lower electrode 122 and the upper electrode 123 by operation of the drive section of the inkjet head 1, and deformation corresponding to the voltage occurs in the piezoelectric member 121. The vibration plate 112 deforms in response to this deformation, which changes the size (volume) of the pressure chamber 111, and the vibration unit 12 applies a pressure fluctuation to the ink inside the pressure chamber 111. The ink that has been subjected to the pressure fluctuation with an appropriate waveform and amplitude is ejected from the nozzle N.

[0015] The head chip 10 has a plurality of vibration units 12 corresponding to the plurality of nozzles N, respectively. The lower electrode 122 may be a common electrode for the plurality of vibration units 12. For example, the lower electrode 122 may extend in the Y direction and be positioned across the plurality of sets of pressure chambers 111 and the piezoelectric members 121. This allows a common potential, such as a ground potential, to be applied to the lower surface of each piezoelectric member 121. The upper electrodes 123 are individual electrodes, and each may be set to an individually set potential. A potential difference between the upper electrode 123 and the lower electrode 122, i.e., a voltage, is applied to the piezoelectric member 121, causing the piezoelectric member 121 to deform. By appropriately determining the pattern of change in this voltage, the presence or absence of ink ejection from each nozzle N and the amount of ink ejection can be determined according to the amount of deformation of the piezoelectric member 121 and the frequency of the periodic deformation.

[0016] The upper electrode 123 may be quadrangular, particularly rectangular, in plan view when viewed along the Z direction, which is the stacking direction of the vibrating section 12. Alternatively, the upper electrode 123 may be elliptical or circular in plan view.

[0017] The piezoelectric member 121 is mainly a ferroelectric material, and may be, for example, lead zirconate titanate (PZT). The lower electrode 122 and the upper electrode 123 may be made of any metal with high electrical conductivity. For example, the lower electrode 122 and the upper electrode 123 may be made of titanium, iridium, platinum, chromium, gold, or a combination thereof. In the case of a combination of multiple metals, the multiple metals may be stacked in different layers. Alternatively, the lower electrode 122 and the upper electrode 123 may be made of an alloy of multiple metals. The upper electrode 123 and the lower electrode 122 may be made of different materials.

[0018] The diaphragm 112 is, for example, a thin Si substrate that is capable of elastic deformation. A portion of the diaphragm 112 faces the pressure chamber 111 and is vibrable, and the other portion is joined and fixed to the flow path member 11 or the like.

[0019] The lower electrode 122 is connected to a conductor that is connected to the upper surface side, such as a via (not shown) that penetrates the flow path member 11, for example.

[0020] FIG. 2 is a diagram illustrating a configuration for causing the vibration section 12 to deform. The head chip 10 has an electric circuit 22, i.e., a circuit member (not shown) having conductor wiring or a conductor surface on its upper surface, above the flow path member 11. Each signal line of the electric circuit 22 connects each of the upper electrodes 123 and the vias to a connection terminal located on the circuit member. The connection terminal is connected to a circuit board 21 (drive unit) including a drive IC and the like that outputs the change pattern of the potential difference, such as a flexible printed circuit (FPC). This connection portion may be obtained using an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), a silver paste, or the like. The circuit board 21 generates and outputs a drive voltage signal having a waveform corresponding to input image data and other data related to the presence or absence of ink ejection and the amount of ink ejection at each timing for each nozzle N. The waveform of the drive voltage signal may be trapezoidal or rectangular. The circuit board 21 may convert a predetermined digital waveform to an analog signal, amplify it, and output it. Alternatively, the circuit board 21 may generate the drive voltage signal by switching between multiple input voltages.

[0021] The circuit member may also have an ink supply path that communicates with the common supply path 115 and an ink reservoir located further above the circuit member.

[0022] In addition to the head chip 10, the inkjet head 1 of this embodiment has a circuit member, an ink storage section, and a circuit board 21. Note that the inkjet head 1 may have a common circuit board 21 for a plurality of head chips 10, circuit members, and ink storage sections. The inkjet head 1 may also have components other than those described above, such as a heating section (heater) for heating and keeping ink warm, and a temperature measuring section (thermistor, etc.).

[0023] 3 is a diagram illustrating the arrangement of downstream supply channels 114 in head chip 10. When viewed from above in the Z direction, downstream supply channels 114 may be arranged two-dimensionally. Ink may be supplied from a common supply channel 115 to pressure chambers 111 that communicate with different downstream supply channels 114 in the Y direction. Furthermore, flow channel member 11 may have multiple common supply channels 115 extending in the Y direction.

[0024] In this way, the multiple downstream supply channels 114 and nozzles N, as well as the multiple vibration units 12 that apply pressure fluctuations to the ink in the pressure chambers 111 that communicate with them, can be formed together on a wafer substrate with high precision using semiconductor processes, particularly MEMS (Micro Electro Mechanical System) technology. The film of the piezoelectric member 121 can be formed using, for example, a sputtering method or a sol-gel method. The size of each upper electrode 123 may be determined by the opening area of ​​a photomask used during formation. The manufacturing process will be described later.

[0025] The characteristics of the multiple vibration parts 12 of the head chip 10 obtained in this way are prone to variation. It has been known that the variation depends on the variation in capacitance between the vibration parts 12. It is also known that the capacitance C between the parallel plates via the piezoelectric member depends on the applied voltage.

[0026] Furthermore, when forming the vibration part 12 using the above-mentioned MEMS technology, the characteristics of the piezoelectric member 121 formed on the wafer substrate tend to have a spatially non-uniform distribution with a specific tendency. That is, the characteristics tend to vary structurally between the center and the periphery of the wafer substrate. A technique for reducing the non-uniformity by correcting the facing area S in accordance with such variations is known.

[0027] However, experiments by the inventors have shown that this technique leaves behind non-uniformity. Meanwhile, in one embodiment, it has been found that the ink ejection velocity v is proportional to a parameter P = ΔC / S (first variable) obtained by dividing the rate of change ΔC = (C(V2) - C(V1)) / C(V1) of capacitance C between two predetermined applied voltages V1 and V2 by the opposing area S of the parallel plates that serve as electrodes. In other words, the opposing area S here is the smaller area of ​​the upper electrode 123 and the lower electrode 122, i.e., the area of ​​the upper electrode 123 in a plan view.

[0028] The applied voltage V2 may be set to, for example, a value at which the capacitance C reaches a maximum value relative to the voltage. That is, the tendency of the capacitance C relative to the applied voltage V is determined, and the applied voltage V2 at which the capacitance C reaches a maximum or maximum value is identified. The capacitance C can be obtained, for example, from the waveform obtained when a target voltage is applied as a bias voltage and then an AC voltage with a small voltage amplitude is applied. The small voltage amplitude may be, for example, 0.5 V, or 1.0 V peak-to-peak. The target voltage may be varied at appropriate intervals to sequentially determine the capacitance C. Alternatively, the correspondence between the applied voltage V and the capacitance C may be automatically obtained using a programmable measuring instrument. This avoids the apparent underestimation of the rate of change by determining the rate of change between the capacitance C on both sides of the maximum value of the capacitance C. Furthermore, since the rate of change is large near the maximum value of the capacitance C, it is easy to accurately evaluate the variation in the rate of change ΔC.

[0029] The applied voltage V1 may be lower than the applied voltage V2. The applied voltage V1 may be a value used in normal capacitance measurement, i.e., in measuring the impedance Z. This value may vary depending on the manufacturer and the model of the inkjet head 1. The applied voltage V1 may be, for example, in a range where the minimum value of the AC voltage according to the voltage amplitude is a positive voltage, for example, 1.0 V for an amplitude of 0.5 V.

[0030] The applied voltages V1 and V2 are not limited to those described above. For example, the applied voltage V2 may be the maximum voltage expected to be applied to the inkjet head 1. However, it is preferable that the applied voltages V1 and V2 be values ​​or voltage differences that are unlikely to be underestimated, as described above.

[0031] Figure 4 is a graph showing the experimental results of measuring the relationship between the parameter P and the ejection velocity v. It can be seen that the ejection velocity v shows a high linear correlation with the parameter P obtained by measurements at the applied voltages V1 and V2. The coefficient of determination is 0.99. In other words, by determining the opposing area S in accordance with the spatial change in the rate of change ΔC, the ejection velocity v can be kept within the desired range.

[0032] In this embodiment, in manufacturing the inkjet head 1, the multiple individual upper electrodes 123 are formed using a photomask that defines their area. The rate of change ΔC of each vibration part 12 that includes the upper electrode 123 is measured. Based on the obtained rate of change ΔC, the distribution of the parameter P when the size of the upper electrodes 123 is uniform is obtained. Then, a photomask (exposure mask) is determined in which the facing area S, i.e., the area of ​​the upper electrodes 123, is adjusted to flatten the distribution of the parameter P. This reduces the variation in the parameter P depending on the position on the wafer, and reduces the variation in the ink ejection speed v from each nozzle N in the inkjet head 1.

[0033] The allowable range of variation Δv in the ejection velocity v can be determined based on the distance between the bottom surface and the recording medium and the quality standards for the content recorded on the recording medium. For example, assume that the distance h between the bottom surface and the recording medium is 14 mm and the recording medium transport speed vc is 1.0 m / sec. In this case, the parameter P may be limited to a variation of ±6.8% or less, so that the variation is within a range of approximately 5-12% of the reference speed, for example, ±0.25 m / s of a reference speed of 8.50 m / s. When the ejection velocity v is 8.25 m / sec, the ink lands at a position that has traveled vc × h / v = 1697 μm from the point where the ink overlaps the recording medium in a planar view. On the other hand, when the ejection velocity is 8.75 m / sec, the ink lands at a position that has traveled 1600 μm. In other words, the difference between these landing positions is 97 μm. In normal image quality, a deviation of about 100 μm does not cause a significant degradation in image quality. Therefore, the range of parameter P within ±6.8% of the reference value is the reference adjustment range in which no significant degradation in image quality occurs.

[0034] Alternatively, consider a case where the distance h between the bottom surface and the recording medium is 7 mm and the recording medium transport speed vc is 1.0 m / sec. In this case, the parameter P may be limited to ±3.4% or less to fall within a ±0.50 m / s variation range from the reference speed. When the ejection speed is 8.00 m / sec, the ink lands at a position after moving 875 μm. When the ejection speed is 9.00 m / sec, the ink lands at a position after moving 778 μm. In other words, the difference between these landing positions is 97 μm, which is less than 100 μm. Therefore, under these conditions, a range of ±3.4% or less of the reference value for parameter P is the reference range for adjustment that does not cause a significant degradation in image quality.

[0035] The reference speed may be a speed that can be set when the inkjet head 1 is used. If there are multiple settable speeds, it may be any one of them. Alternatively, the reference speed may be determined by the median or average of the obtained speeds. Furthermore, the reference value of the parameter P may be determined by the average value or the like without specifying the reference speed.

[0036] FIG. 5 is a diagram schematically showing an example of the distribution of the parameter P on a wafer. As described above, this distribution on the wafer exhibits a specific tendency, typically a tendency for the value of the parameter P to decrease toward the wafer's center and outer edge. Therefore, a distribution (exposure mask pattern) of photomasks (exposure masks) is set in which the amount of correction for the upper electrode area gradually increases from the center to the outer edge, i.e., the facing area S decreases. As indicated by the thin, thick, and dotted lines, the magnitude of this tendency varies depending on the characteristics of the manufacturing equipment and its aging. In this embodiment, a pattern list (exposure mask group) including multiple types of photomask patterns with different trends in the facing area S is prepared (set) in advance, depending on the magnitude of the tendency. The rate of change ΔC of capacitance is measured for each vibrating unit 12, and the distribution of the parameter P with respect to the position of the vibrating unit 12 is obtained. Then, a photomask pattern is selected in which the change tendency of this distribution approaches flatness and the variation falls within a standard range.

[0037] FIG. 6 is a diagram illustrating the adjustment of the facing area S. In FIG. The facing area S of the upper electrode 123, i.e., the opening size of the photomask, may be changed according to a predetermined standard. For example, as shown by the solid line in FIG. 6( a), if the upper electrode 123 is rectangular in plan view, the facing area S may be reduced by changing, typically reducing, the length along the short side as shown by the dashed line. In particular, the upper electrode 123 may be rectangular in plan view. Also, as shown in FIG. 6( b), if the upper electrode 123 is elliptical in plan view, the facing area S may be reduced by changing, typically reducing, the length of the minor axis. Also, as shown in FIG. 6( c), if the upper electrode 123 is circular in plan view, the diameter of the circle may be changed, typically reducing, to maintain the circular shape and reduce the facing area S.

[0038] 7 is a flowchart showing the procedure for adjusting vibration unit 12. This adjustment is performed at the beginning of the manufacture of head chip 10. In addition, it may be performed repeatedly at appropriate intervals during mass production of head chip 10. Since the characteristics of piezoelectric member 121 may change over time, the adjustment may be performed repeatedly at appropriate intervals depending on the rate of change over time. Alternatively, the adjustment may be performed again at the discretion of a user or the like, and the user may issue a command through an input operation or the like.

[0039] First, a plurality of vibration sections 12 including individual second electrodes are formed on a wafer substrate on which the head chip 10 is formed using a reference photomask pattern (P1). That is, a lower electrode 122, which is a common first electrode, may be formed, a piezoelectric layer as a piezoelectric member 121 may be formed at each position of the vibration section 12, and an upper electrode 123, which is an individual second electrode, may be formed on the piezoelectric member 121. Alternatively, the order of forming the individual electrodes and the common electrode may be reversed. That is, individual first electrodes may be formed on a certain substrate using a photomask pattern, and then a piezoelectric film and a common second electrode may be formed. In this case, the substrate is peeled off from the first electrode after the second electrode is formed. The substrate may be used as the vibration plate 112 as it is.

[0040] For the plurality of vibration parts 12 on the wafer, the capacitance at applied voltages V1 and V2 and the area of ​​each second electrode are measured (P2). The plurality of vibration parts 12 to be measured here do not have to be all of the vibration parts 12 on the wafer. The plurality of vibration parts 12 to be measured may be selected, for example, every predetermined number from one end of the array. Alternatively, the plurality of vibration parts 12 to be selected may be determined in advance so as to include, for example, both ends and the center of the array.

[0041] Based on the measurement results, a parameter P of the target vibration part 12 is calculated and its distribution on the wafer is obtained (P3). Based on the distribution of the parameter P, a photomask pattern is selected that makes the distribution close to a constant and the variation falls within a standard range (P4).

[0042] In this way, a plurality of vibration parts 12 each having an upper electrode 123 formed using the selected photomask pattern are obtained on the wafer (P5).

[0043] 8 and 9 are diagrams illustrating other structures of the vibration section 12. FIG. 8, in addition to the piezoelectric member 121, a layer of dielectric 124 may be positioned between the upper electrode 123 and the lower electrode 122 so as to overlap the piezoelectric member 121. In this case, the capacitance Ct of the vibrating part 12 is the combined capacitance of the piezoelectric member 121 and the dielectric 124. In other words, the parameter Pt that should be made uniform is the value obtained by dividing the capacitance Ct including the influence of the dielectric 124 by the area of ​​the upper electrode 123. As described above, by adjusting the size of the upper electrode 123, the variation in capacitance corresponding to the variation in the characteristics of the piezoelectric member 121 and the dielectric 124 can be easily reduced.

[0044] 9, the dielectric 124b may not have a uniform thickness. The dielectric 124b may be located only partially between the lower electrode 122b and the piezoelectric member 121. In other words, the dielectric 124b may be located in a specific shape only partially within the range that overlaps with the upper electrode 123 in a plan view. In this case, the thickness of the lower electrode 122b may be thicker in the portion where the dielectric 124b is not present than in the portion where the dielectric 124b is present. The sum of the thickness of the dielectric 124b and the thickness of the lower electrode 122b may be constant.

[0045] The dielectric 124 may extend outside the range of the upper electrode 123 and the piezoelectric member 121 in plan view. For example, the dielectric 124 may be an interlayer insulating film located between the vibration parts 12, and a part of the dielectric 124 may extend between the lower electrode 122b and the piezoelectric member 121.

[0046] In this case, the capacitance Cs is the combined capacitance of the piezoelectric member 121 and the dielectric material 124b. Furthermore, since the lower electrode 122b is not flat, the capacitance Cs becomes more complicated.

[0047] As described above, the manufacturing method of the inkjet head 1 of this embodiment relates to an inkjet head 1 including multiple vibration units 12 and multiple nozzles N corresponding to the multiple vibration units 12. In the inkjet head 1, the vibration unit 12 includes two electrodes, an upper electrode 123 and a lower electrode 122, and a piezoelectric member 121 located between the two electrodes. The inkjet head 1 can eject ink by applying a pressure fluctuation to ink in the nozzles N corresponding to the vibration units 12 by applying a voltage between the upper electrode 123 and the lower electrode 122. This manufacturing method adjusts the variation in the value obtained by dividing the rate of change ΔC of the capacitance C of each vibration unit 12 between two applied voltages V1 and V2 by the opposing area S of the electrodes within a predetermined reference range for each vibration unit 12. This manufacturing method can more easily and appropriately reduce the variation in the characteristics of the multiple vibration units 12 compared to conventional methods. Therefore, this manufacturing method can standardize the ink ejection speed among the multiple nozzles N and reduce degradation in output quality.

[0048] Furthermore, the predetermined reference range may be ±6.8% or less of the reference value of parameter P. This ensures that, given a generally expected distance between the ink ejection surface and the ink landing surface and a generally expected recording medium transport speed, variations in the ink landing position can be kept within a range that does not significantly deteriorate output quality.

[0049] Alternatively, the predetermined reference range may be ±3.4% or less with respect to the reference value of the parameter P. This makes it possible to more stably reduce degradation in output quality.

[0050] Furthermore, a dielectric 124 may be positioned at least either between the piezoelectric member 121 and the upper electrode 123 or between the piezoelectric member 121 and the lower electrode 122. In this case, the rate of change ΔC in the capacitance of the vibrating section 12 is determined taking into account the effect of the dielectric 124. The dielectric 124 may be used to adjust the capacitance C of the vibrating section 12, or may have a structure inserted therein for other purposes, such as insulation. This makes it easier to design the vibrating section 12, including the structure required for the head chip 10.

[0051] Furthermore, the dielectric 124 may have a specific shape in a part of the range where it overlaps with the vibrating part 12 in a plan view of the vibrating part 12 in the direction in which the upper electrode 123 and the lower electrode 122 overlap, i.e., in the Z direction. That is, the dielectric 124 having a structure specific to the other applications described above may be positioned between the upper electrode 123 and the lower electrode 122. The vibrating part 12 may have the structure of the dielectric 124 sandwiched therebetween as needed, thereby improving the degree of freedom in the structure.

[0052] The applied voltages V1 and V2 may also include the maximum voltage set for the inkjet head 1. Since the rate of change ΔC is determined from a voltage that corresponds to the expected voltage during operation of the inkjet head 1, it is easy to obtain a value that corresponds to the actual change in capacitance.

[0053] Alternatively, the applied voltages V1 and V2 may include the value of the applied voltage at which the capacitance C reaches its maximum value relative to the voltage applied to the vibration unit 12. The voltage dependency of capacitance reaches its maximum value at a certain voltage, and the capacitance is small before and after that. Calculating the rate of change ΔC of capacitance using two voltages that sandwich the voltage corresponding to the maximum value of capacitance results in an underestimate. Therefore, by including the voltage corresponding to the maximum value of capacitance in the applied voltages V1 and V2, the rate of change ΔC can be obtained with high accuracy. This makes it possible to more appropriately reduce variations in the ink ejection speed.

[0054] Furthermore, at least one of the upper electrode 123 and the lower electrode 122 may be rectangular in plan view. In this case, the length along the short side of one of the at least one electrodes may be changed to adjust the variation in the parameter P. Alternatively, the at least one electrode may be elliptical in plan view. In this case, the length along the short side of one of the at least one electrodes may be changed to adjust the variation in the parameter P. Alternatively, the at least one electrode may be circular in plan view. In this case, the diameter of one of the at least one electrodes may be changed to adjust the variation in the parameter P. By uniquely defining the size adjustment method in this way, the spacing between the second electrodes is likely to be maintained uniform. Furthermore, in a typical reduction size, adjusting the shorter side further does not result in the short side or short axis being interchanged with the long side or long axis, thereby enabling uniform size adjustment.

[0055] Alternatively, the manufacturing method of the inkjet head 1 of this embodiment includes the following steps: (1) forming a plurality of vibration sections 12, each including a layer of a piezoelectric member 121, a lower electrode 122 located on a first surface of the piezoelectric member 121, and a plurality of upper electrodes 123 located on the opposite side of the first surface of the piezoelectric member 121, on a substrate using an exposure mask to form the upper electrodes 123; (2) applying two different voltages V1 and V2 to each of the vibration sections 12 and measuring the rate of change ΔC in the capacitance C of the vibration section 12; (3) obtaining a distribution of a parameter P, which is the rate of change ΔC divided by the planar area of ​​the second electrode, i.e., the opposing area S with respect to the first electrode, with respect to the position of the vibration section 12; (4) selecting, from a list of different patterns set in advance, photomask patterns for obtaining a plurality of second electrodes each having an area corrected according to the amount of correction of the opposing area S to flatten the obtained distribution and bring the variation within a reference range; and then determining to use the selected photomask patterns for forming the plurality of second electrodes. According to a manufacturing method including such steps, an inkjet head 1 in which variations in each vibrating portion 12 are reduced can be easily obtained by manufacturing the inkjet head 1 only once on a trial basis.

[0056] The inkjet head 1 of this embodiment also includes a plurality of vibration units 12, a plurality of nozzles N respectively corresponding to the plurality of vibration units 12, and a circuit board 21. Each vibration unit 12 has two electrodes, an upper electrode 123 and a lower electrode 122, and a piezoelectric member 121 located between these two electrodes. The circuit board 21 is capable of applying a voltage between the two electrodes to impart pressure fluctuations to ink in the nozzles N respectively corresponding to the vibration units 12, thereby causing the ink to be ejected from the nozzles N. For each of the plurality of vibration units 12, the variation in the value obtained by dividing the rate of change ΔC in the capacitance C of the vibration unit 12 between two applied voltages V1 and V2 by the opposing area S of the upper electrode 123 and the lower electrode 122 is within ±6.8% of a reference value. By keeping the variation in this parameter P=ΔC / S within an appropriate range, the variation in ink ejection characteristics of the inkjet head 1 is more appropriately reduced. This allows the ink ejection speed of the inkjet head 1 to be more uniform. Therefore, degradation in the quality of the output content from the inkjet head 1 is reduced.

[0057] Alternatively, the inkjet head 1 may have a variation of ±3.4% or less with respect to a reference value in the parameter P. This allows the inkjet head 1 to be more stable and reduce degradation in output quality.

[0058] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above description, the reference range of the parameter P is determined based on the absolute value of the variation in the ejection velocity v, but this is not limiting. It may also be determined based on the relative variation width of the ejection velocity v.

[0059] In the above description, the upper electrode 123 is an individual electrode and the lower electrode 122 is a common electrode, but this is not limiting. The opposite is also possible. Furthermore, the lower electrode 122, which is at a common potential, may be separated for each vibration section 12.

[0060] Furthermore, the shape of the upper electrode 123 is not limited to the above-mentioned rectangle, ellipse, or circle. For example, it may be a rectangle with rounded corners, a polygon with five or more corners, etc. Furthermore, even if the shape of the upper electrode 123 is a rectangle, it may be a parallelogram, a rhombus, a trapezoid, or any other shape other than a rectangle with right-angled corners.

[0061] Furthermore, the size of the photomask pattern does not have to be changed by changing the short side or the short axis, but may be changed by changing the long side or the long axis, or by changing both the short side and the long side, or the short axis and the long axis.

[0062] Furthermore, the applied voltages V1 and V2 may be determined to values ​​other than those described above.

[0063] Although a pattern list of multiple photomask patterns is set in advance in the above example, this is not limiting and photomask patterns may be individually designed and generated each time depending on the required accuracy and the effort and cost required to generate the photomask patterns.

[0064] Furthermore, the number and arrangement of the nozzles N and vibration parts 12 in the inkjet head 1 may be determined arbitrarily. On the other hand, the way in which the upper electrode 123 is deformed may be changed and set depending on the arrangement of the nozzles N.

[0065] Furthermore, the positions and shapes of the pressure chambers 111 and ink flow paths in the inkjet head 1 are not limited to the examples shown above, but may be any shape suitable for ink ejection.

[0066] Furthermore, in the above description, the bend mode in which the vibration plate 112 is bent and deformed to impart pressure fluctuations to the ink has been described, but this is not limiting. For example, the pressure fluctuations imparted to the ink may be a shear mode caused by shear stress.

[0067] In the above description, the upper electrode 123, which is an individual electrode, is formed first, and then the layer of the piezoelectric member 121 and the lower electrode 122, which is a common electrode, are formed in this order, but the formation of the vibration part 12 is not limited to this order. The lower electrode 122 may be formed first, and then the piezoelectric layer and the upper electrode 123 may be formed in this order.

[0068] In addition, the specific configurations, contents and procedures of the processing operations, etc. shown in the above embodiments can be modified as appropriate without departing from the spirit of the present invention. The scope of the present invention includes the scope of the invention described in the claims and its equivalents. [Explanation of symbols]

[0069] 1 Inkjet head 10 Head Chip 11 Flow path member 111 Pressure Chamber 112 Diaphragm 113 Upstream supply route 114 Downstream supply channel 115 Common supply route 12 Vibration unit 121 Piezoelectric material 122, 122b bottom electrode 123 Upper electrode 124, 124b Dielectric 13 Nozzle plate 21 Circuit Board 22 Electrical Circuits N nozzle S facing area v Discharge speed ΔC rate of change

Claims

1. A method for manufacturing an inkjet head comprising: a plurality of piezoelectric elements each having two electrodes and a piezoelectric layer located between the two electrodes; and a plurality of nozzles respectively corresponding to the plurality of piezoelectric elements, wherein ink can be ejected by applying a voltage between the two electrodes to impart a pressure fluctuation to ink in the nozzles corresponding to the piezoelectric elements, the method comprising: For each of the plurality of piezoelectric elements, an adjustment is performed so that the variation in the value obtained by dividing the rate of change in capacitance of the piezoelectric element between two applied voltages by the opposing area of ​​the electrodes falls within a predetermined reference range. A method for manufacturing an inkjet head.

2. 2. The method for manufacturing an ink jet head according to claim 1, wherein the predetermined reference range is within ±6.8% of the reference value of the value.

3. 2. The method for manufacturing an ink jet head according to claim 1, wherein the predetermined reference range is within ±3.4% of the reference value of the value.

4. a dielectric is located between at least one of the piezoelectric layer and the two electrodes; The rate of change in capacitance of the piezoelectric element is determined taking into account the influence of the dielectric. The method for manufacturing the ink jet head according to claim 1.

5. The method for manufacturing an ink jet head according to claim 4 , wherein the dielectric has a specific shape in a part of the area overlapping the piezoelectric element in a plan view of the piezoelectric element seen from the overlapping direction of the two electrodes.

6. The method for manufacturing an inkjet head according to claim 1 , wherein the two applied voltages include a maximum voltage set for the inkjet head.

7. 2. The method for manufacturing an ink jet head according to claim 1, wherein the two applied voltages include values ​​of applied voltages at which the electrostatic capacitance of the piezoelectric element takes a maximum value.

8. At least one of the electrodes is rectangular in plan view, In the adjustment of the variation, a length of any one of the at least one electrodes along a short side thereof is changed. The method for manufacturing the ink jet head according to claim 1.

9. At least one of the electrodes is elliptical in plan view; In the adjustment of the variation, a minor axis length of any one of the at least one electrodes is changed. The method for manufacturing the ink jet head according to claim 1.

10. At least one of the electrodes is circular in plan view; In the adjustment of the variation, a diameter of any one of the at least one electrodes is changed. The method for manufacturing the ink jet head according to claim 1.

11. forming a plurality of piezoelectric elements on a substrate using an exposure mask to form the second electrodes, the plurality of piezoelectric elements including a piezoelectric layer, a first electrode located on a first surface of the piezoelectric layer, and a plurality of second electrodes located on the opposite side of the piezoelectric layer from the first surface, the plurality of piezoelectric elements corresponding to the number of the second electrodes; applying two different voltages to each of the piezoelectric elements and measuring the rate of change in capacitance of the piezoelectric elements; a distribution of a first variable obtained by dividing the rate of change by an opposing area of ​​the first electrode and the second electrode with respect to the position of the piezoelectric element; selecting, from a group of exposure masks that are set in advance and are different from one another, exposure mask patterns for obtaining a plurality of second electrodes each having an area corrected in accordance with a correction amount of the facing area that makes the distribution closer to flat and brings the variation within a reference range; determining whether the selected exposure mask pattern is used to form the plurality of second electrodes; A method for manufacturing an inkjet head.

12. a plurality of piezoelectric elements each having two electrodes and a piezoelectric layer located between the two electrodes; a plurality of nozzles respectively corresponding to the plurality of piezoelectric elements; a driving unit that applies a voltage between the two electrodes to apply a pressure fluctuation to ink in the nozzle corresponding to the piezoelectric element, thereby causing ink to be ejected from the nozzle; and Equipped with For each of the plurality of piezoelectric elements, the variation in the value obtained by dividing the rate of change in capacitance of the piezoelectric element between two applied voltages by the opposing area of ​​the electrodes is ±6.8% or less with respect to a reference value. Inkjet head.

13. 13. The ink jet head according to claim 12, wherein the variation is within ±3.4% of the reference value.

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