JP5207546B2 - Liquid discharge head, liquid discharge head manufacturing method, and image forming apparatus - Google Patents

Description

  The present invention relates to a liquid discharge head, a method for manufacturing a liquid discharge head, and an image forming apparatus, and in particular, a liquid discharge head in which a piezoelectric film is provided between two electrode films, a method for manufacturing a liquid discharge head, and the liquid discharge head The present invention relates to an image forming apparatus including

  Patent Document 1 discloses a piezoelectric actuator that has an annular shape and includes an individual electrode that is formed so as to surround the central portion of the pressure chamber in a region that overlaps with an edge other than the central portion of the pressure chamber in plan view. Has been. Furthermore, Patent Document 1 discloses a piezoelectric actuator in which the piezoelectric layer is not formed in a region overlapping the central portion of the pressure chamber in plan view, and is formed in a region other than the region overlapping the central portion. . In patent document 1, while using a cyclic | annular individual electrode (upper electrode) and making it the structure which does not provide a piezoelectric layer in the area | region which overlaps with the center part of a pressure chamber, the displacement amount of a diaphragm is enlarged. .

JP 2006-150948 A (for example, paragraphs [0008] to [0010], [0028], [0038])

  In recent years, the density of nozzles in liquid discharge heads has been increasing, and it has been required to simultaneously increase the density of nozzle arrangement (reducing the area of the piezoelectric actuator) and increase the displacement of the diaphragm by the piezoelectric actuator. It has been.

  As shown in FIG. 10, in the piezoelectric actuator 200 having the annular individual electrode (upper electrode) 210, the vibration chamber 204 (also used as the common electrode (lower electrode)) of the pressure chamber 206 formed in the pressure chamber plate 202. If the piezoelectric layer 208 is not provided in the region overlapping with the central portion (the entire layer is removed), the common electrode (lower electrode) 204 is exposed to the atmosphere. In the case of the piezoelectric layer 208 made of a thin film PZT having a thickness of several microns to several tens of microns, the upper electrode 210 and the lower electrode 204 are in contact with each other through the atmosphere, so that the electrode is formed by creeping discharge or ion migration that travels along the side surface of the piezoelectric layer 208. Problems such as short circuit are likely to occur. In order to avoid the above problem, it is conceivable to increase the distance between the upper electrode 210 and the lower electrode 204 by retracting the upper electrode 210 from the center of the pressure chamber 206 toward the edge. However, unlike the piezoelectric actuator in the normal flexural vibration (lateral vibration) mode, in the piezoelectric actuator using the annular upper electrode 210, when the upper electrode 210 is retracted from the center of the pressure chamber 206, the voltage of the piezoelectric layer 208 is increased. The area of the portion to which is applied is reduced, and the displacement amount of the diaphragm 204 is reduced.

  Further, if the entire piezoelectric layer 208 covering the diaphragm 204 is scraped, the displacement amount of the diaphragm 204 can be increased, but the rigidity of the diaphragm 204 is lowered.

  The present invention has been made in view of such circumstances, and provides a liquid ejection head having a large displacement amount and high reliability, a method for manufacturing the liquid ejection head, and an image forming apparatus including the liquid ejection head. The purpose is to do. Another object of the present invention is to realize the rigidity of the diaphragm together with the above object.

  In order to solve the above problems, a liquid discharge head according to a first aspect of the present invention includes a flow path unit having a plurality of pressure chambers arranged along a plane, and a pressure by changing the volume of the pressure chamber. A piezoelectric actuator that applies pressure to the liquid in the chamber, and the piezoelectric actuator includes at least the pressure on the diaphragm when viewed from a direction perpendicular to the plane and a diaphragm that forms one wall surface of the pressure chamber. A common electrode formed in a region other than a region overlapping the central portion of the chamber, the common electrode having a hole formed in each of the regions overlapping with the central portion of the plurality of pressure chambers, and formed on the common electrode A piezoelectric layer, which is formed in a region overlapping each of the central portions of the plurality of pressure chambers when viewed from a direction orthogonal to the plane, and has a recess that fits in a hole formed in the common electrode. Electric A piezoelectric layer covering an edge of the pressure chamber on the center side, and an edge formed on the piezoelectric layer and being a region other than the center of the plurality of pressure chambers when viewed from a direction orthogonal to the plane And a plurality of annular individual electrodes arranged in overlapping regions.

  According to the first aspect, the lower electrode is covered with the piezoelectric film so as not to be in direct contact with the atmosphere, thereby increasing the displacement amount of the diaphragm (for example, by creeping discharge or ion migration). A short circuit between the upper electrode and the lower electrode can be prevented, and the reliability of the liquid discharge head can be improved.

  The liquid ejection head according to a second aspect of the present invention is the liquid ejection head according to the first aspect, wherein the bottom surface of the concave portion of the piezoelectric layer is constituted by the diaphragm.

  According to the said 2nd aspect, the displacement amount of a diaphragm can be enlarged more by arrange | positioning a piezoelectric layer only to the area | region which respectively overlaps with the edge part which is areas other than the center part of a pressure chamber.

  A liquid discharge head according to a third aspect of the present invention is the liquid discharge head according to the first aspect, wherein the piezoelectric layer is formed in a region overlapping with the center of the plurality of pressure chambers when viewed from a direction orthogonal to the plane. A thin portion, and the thin portion is thinner than a region other than a region overlapping the central portion of the plurality of pressure chambers of the piezoelectric layer when viewed from a direction orthogonal to the plane, and constitutes the recess. It is a thing.

  According to the third aspect, in addition to the effects described above, the piezoelectric layer thinner than the edge is left in the region overlapping the center of the pressure chamber, thereby increasing the displacement of the diaphragm and increasing the rigidity of the diaphragm. Can be increased.

In the liquid ejection head according to the fourth aspect of the present invention, in the first to third aspects, the hole of the common electrode and the edge of the individual electrode on the pressure chamber side are orthogonal to the plane. The planar shapes when viewed from the direction in which they are made are substantially similar to each other.

The liquid ejection head according to a fifth aspect of the present invention is the liquid ejection head according to the fourth aspect, wherein the concave portion of the piezoelectric layer and the edge of the individual electrode on the pressure chamber side are perpendicular to the plane. The planar shapes when viewed are substantially similar to each other.

The liquid ejection head according to a sixth aspect of the present invention is the liquid ejection head according to the fourth or fifth aspect, wherein the pressure chamber and the edge of the individual electrode on the pressure chamber side are perpendicular to the plane. The planar shapes when viewed are substantially similar to each other.

  According to the fourth to sixth aspects, since the electric field can be applied substantially evenly to the region of the piezoelectric layer on the central portion side of the pressure chamber, the piezoelectric layer can be effectively displaced.

  A liquid ejection head according to a seventh aspect of the present invention is the liquid ejection head according to any one of the first to sixth aspects, wherein the individual electrode extends to a region overlapping the pressure chamber partition of the pressure chamber.

  According to the seventh aspect, the area of the active portion of the piezoelectric layer that is displaced by the electric field generated between the individual electrode and the common electrode can be increased, and the displacement of the diaphragm can be further increased.

An image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus including the liquid ejection head according to the first to seventh aspects, wherein the individual electrode is on the opposite side of the piezoelectric layer from the diaphragm. Disposed on a surface, the common electrode is grounded, the piezoelectric layer is polarized in a direction from the diaphragm toward the individual electrode, and the individual electrode is only in the liquid (ink) ejection operation. And a voltage applying means for applying a negative driving voltage waveform to the piezoelectric layer so that an electric field in the same direction as the polarization direction of the piezoelectric layer is applied to the piezoelectric layer.

  According to the eighth aspect, since the drive voltage is applied to the individual electrodes only when the ink ejection operation is performed, an electric field does not act on the piezoelectric layer during normal times. For this reason, deterioration of the piezoelectric layer can be prevented, and the reliability of the liquid discharge head can be further improved.

  A method for manufacturing a liquid ejection head according to a ninth aspect of the present invention includes: (a) a flow path unit having a plurality of pressure chambers arranged along a plane, and the pressure as viewed from a direction orthogonal to the plane. A common electrode formed in a region other than a region overlapping at least a central portion of the pressure chamber on a diaphragm constituting one wall surface of the chamber, wherein the common electrode is formed in a region overlapping each of the central portions of the plurality of pressure chambers. A step of forming a common electrode having a hole; and (b) formed on the common electrode in regions overlapping with central portions of the plurality of pressure chambers when viewed from a direction orthogonal to the plane, Forming a piezoelectric layer having a recess that fits in the formed hole, and covering the edge of the common electrode on the central portion side of the pressure chamber with the piezoelectric layer; and (c) on the piezoelectric layer in the plane. View from orthogonal direction , And forming a plurality of annular individual electrodes disposed in the plurality of overlapping each pressure chamber which is a region other than the center portion edge region.

  According to a tenth aspect of the present invention, in the ninth aspect, the bottom surface of the concave portion of the piezoelectric layer is configured by the diaphragm.

  In the method for manufacturing a liquid discharge head according to the eleventh aspect of the present invention, the step (b) of the ninth aspect includes the plurality of pressure chambers as viewed from a direction perpendicular to the plane of the piezoelectric layer. Forming a thin-walled portion in a region overlapping with the central portion of the piezoelectric layer that is thinner than a region other than the region overlapping with the central portion of the plurality of pressure chambers of the piezoelectric layer, and forming the concave portion.

According to a twelfth aspect of the present invention, in the ninth to eleventh aspects, the method for manufacturing a liquid ejection head includes the holes of the common electrode and the edge of the individual electrode on the pressure chamber side. planar shape when viewed from a direction perpendicular to the plane formed to be substantially similar in shape to each other.

According to a thirteenth aspect of the present invention, in the twelfth aspect, the method for manufacturing a liquid ejection head is perpendicular to the plane of the concave portion of the piezoelectric layer and the edge of the individual electrode on the pressure chamber side. planar shape when viewed from a direction is formed so that the shape similar to each other.

According to a fourteenth aspect of the present invention, in the twelfth to thirteenth aspect, the method for manufacturing a liquid ejection head is orthogonal to the plane of the pressure chamber and the edge of the individual electrode on the pressure chamber side. planar shape when viewed from a direction is formed so that the shape similar to each other.

  In the method for manufacturing a liquid ejection head according to the fifteenth aspect of the present invention, in the steps (c) of the ninth to fourteenth aspects, the individual electrode extends to a region overlapping the pressure chamber partition of the pressure chamber. Is formed.

  According to a sixteenth aspect of the present invention, there is provided a method for manufacturing a liquid discharge head, wherein the piezoelectric layer is formed by a sputtering method in steps (b) of the ninth to fifteenth aspects.

According to the present invention, the common electrode ( lower electrode ) is covered with the piezoelectric film so as not to be directly in contact with the atmosphere, thereby increasing the displacement of the diaphragm (for example, by creeping discharge or ion migration). ) A short circuit between the individual electrode ( upper electrode ) and the lower electrode can be prevented, and the reliability of the liquid discharge head can be improved.

The figure which shows typically the inkjet recording device which concerns on one Embodiment of this invention. Top view showing the periphery of the printing unit of an ink jet recording apparatus Block diagram showing control system of inkjet recording apparatus The figure which shows the liquid discharge head which concerns on the 1st Embodiment of this invention. The figure which shows the liquid discharge head which concerns on the 1st Embodiment of this invention. Sectional drawing which shows the manufacturing method of the liquid discharge head which concerns on the 1st Embodiment of this invention. Sectional drawing which shows the manufacturing method of the liquid discharge head which concerns on the 1st Embodiment of this invention (continuation of FIG. 5). Sectional drawing which shows the manufacturing method of the liquid discharge head which concerns on the 2nd Embodiment of this invention. The graph which shows the waveform of the drive voltage when driving the liquid discharge head which concerns on this invention Sectional view showing a piezoelectric actuator with annular individual electrodes

  Hereinafter, preferred embodiments of a liquid discharge head, a method of manufacturing a liquid discharge head, and an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

[Configuration of Image Forming Apparatus]
First, the configuration of an image forming apparatus (inkjet recording apparatus) including a liquid ejection head according to the present invention will be described with reference to FIG. FIG. 1 is a diagram schematically illustrating an ink jet recording apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view illustrating the periphery of a printing unit of the ink jet recording apparatus.

  As shown in FIG. 1, the ink jet recording apparatus 1 according to this embodiment includes a liquid ejection head 12K that ejects four colors of ink of black (K), cyan (C), magenta (M), and yellow (Y). , 12C, 12M, and 12Y, and based on image data input from the host computer (reference numeral 60 in FIG. 3), four colors of ink are printed on the printing surface of the recording paper 16 from the printing unit 10. Is a device that forms a color image by ejecting water.

  As shown in FIG. 2, in the printing unit 10, line-type liquid ejection heads 12 </ b> K, 12 </ b> C, 12 </ b> M, and 12 </ b> Y having a length corresponding to the maximum paper width of the recording paper 16 are orthogonal to the paper transport direction (sub-scanning direction). This is a so-called full line type head arranged in the direction (main scanning direction).

  The ink storage / loading unit 14 stores four colors of inks of KCMY. The ink stored in the ink storage / loading unit 14 is supplied to the liquid ejection head 12 via the ink supply path.

  The ink color and the number of colors are not limited to the above KCMY standard colors (four colors). For example, a liquid discharge head that discharges light ink and dark ink may be added. For example, a liquid discharge head that discharges light ink such as light cyan and light magenta may be added.

  The paper feeding unit 18 supplies the recording paper 16 to the printing unit 10. It has a magazine for rolled paper (continuous paper). A plurality of magazines having different paper widths, paper quality, etc. may be provided. Further, a cassette loaded with cut sheets may be provided.

  The decurling unit 20 heats the recording paper 16 delivered from the paper supply unit 18 by the heating drum 22 to remove curl from the recording paper 16. In the decurling process, it is preferable to control the heating temperature so that the print surface is slightly curled outward.

  The cutter 24 includes a fixed blade 24A disposed on the back side of the printing surface of the recording paper 16, and a round blade 24B disposed on the printing surface side. The recording paper 16 delivered from the paper supply unit 18 is cut into a desired size by the cutter 24. The decurling unit 20 performs the decurling process, and the cut recording paper 16 is sent to the suction belt conveyance unit 26.

  The suction belt conveyance unit 26 includes two rollers 28 and 30 and an endless belt 32 wound between the rollers 28 and 30. The power of the motor is transmitted to at least one of the rollers 28 and 30, and the belt 32 is driven in the clockwise direction in FIG. As a result, the recording paper 16 held on the surface of the belt 32 is conveyed from left to right in FIG.

  The rollers 28 and 30 and the belt 32 are arranged such that portions facing the nozzle surfaces of the liquid ejection heads 12K, 12C, 12M, and 12Y of the printing unit 10 and the sensor surface of the printing detection unit 34 are flat.

  The width of the belt 32 is wider than the width of the recording paper 16 (see FIG. 2). A number of suction holes (not shown) are formed on the surface of the belt 32. An adsorption chamber 36 is provided at a position facing the nozzle surface of the print unit 10 and the sensor surface of the print detection unit 34 inside the belt 32. The suction chamber 36 is set to a negative pressure by a fan 38. As a result, the recording paper 16 is attracted and held on the surface of the belt 32.

  The heating unit 40 heats the recording paper 16 before printing in order to shorten the time from the ink landing on the recording paper 16 to the drying. As the heating unit 40, for example, a heating fan that heats the recording paper 16 by blowing heated air is used.

  The print detection unit 34 includes an image sensor for imaging the ink droplet ejection result by the print unit 10. As shown in FIG. 2, the print detection unit 34 is configured by a line sensor having a light receiving element array wider than the ink ejection width (image recording width) by the liquid ejection heads 12K, 12C, 12M, and 12Y. As the print detection unit 34, for example, an area sensor may be used.

  The post-drying unit 42 is a device that dries the printing surface of the recording paper 16. For example, a heating fan is used as the post-drying unit 42.

  The belt cleaning unit 44 removes ink attached to the belt 32. As a method of cleaning the belt 32, for example, a method of niping a brush roll, a water absorbing roll, or the like, or an air blow method of blowing clean air can be applied.

  The heating / pressurizing unit 46 is a device for controlling the glossiness of the surface of the image printed on the recording paper 16. The heating / pressurizing unit 46 is disposed at the subsequent stage of the post-drying unit 42, presses with a pressure roller 48 having a predetermined surface uneven shape while heating the printing surface, and transfers the uneven shape to the image surface.

  The recording paper 16 (printed material) on which an image is printed as described above is discharged from the paper discharge unit 52. The ink jet recording apparatus 1 according to the present embodiment sorts a printed matter on which an image to be printed is printed and a printed matter on which a test pattern for detecting a printing result is printed, and outputs the selected printed matter to each of the paper discharge units 52A and 52B. Sorting means (not shown) for switching the paper discharge path for feeding is provided.

  When the main image and the test print are simultaneously formed on the recording paper 16 in parallel, the test print portion is separated by the cutter 50. As with the cutter 24, the cutter 50 includes a fixed blade 50A and a round blade 50B.

  FIG. 3 is a block diagram showing a control system of the inkjet recording apparatus 1.

  The system controller 64 is a control unit that controls each unit of the inkjet recording apparatus 1. The system controller 64 includes a central processing unit (CPU) and its peripheral circuits, and performs control of communication with the host computer 60, control of reading and writing of the memory 68, and control for controlling the motor 72 and the heater 76. Generate a signal.

The program storage unit 66 is a storage area for storing various control programs. As the program storage unit 66, for example, a semiconductor memory such as a ROM or an EEPROM (registered trademark) , or a magnetic medium such as a hard disk can be used.

  The memory 68 is a storage device including a storage area for various data and a work area when the system controller 64 performs calculations. As the memory 68, for example, a semiconductor memory such as a RAM or a magnetic medium such as a hard disk can be used.

  The communication interface 62 is an interface for performing communication connection with the host computer 60. As the communication interface 62, for example, a serial interface such as USB or IEEE1394, a parallel interface such as Centronics, a wireless network, or Ethernet (registered trademark) can be applied. Image data input via the communication interface 62 is temporarily stored in the memory 68.

  The print control unit 78 performs predetermined signal processing on the image data temporarily stored in the memory 68 in accordance with a control signal input from the system controller 64 to generate a print control signal (dot data). The print controller 78 controls the head driver 82 based on the print control signal, and controls the discharge amount and discharge timing of the ink discharged from each liquid discharge head 12K, 12C, 12M, 12Y of the print unit 10. Do. The print control unit 78 corrects the print control signal based on the ink droplet ejection result obtained from the print detection unit 34. Thereby, a desired dot size and dot arrangement are realized.

  The buffer memory 80 is a storage device including a work area when the print control unit 78 processes image data.

  The head driver 82 generates drive signals for driving the liquid discharge heads 12K, 12C, 12M, and 12Y based on the dot data input from the print control unit 78, and the liquid discharge heads 12K, 12C, 12M, 12Y.

  The motor driver 70 drives the motor 72 in accordance with a control signal input from the system controller 64, transmits power to the rollers 28 and 30 of the suction belt transport unit 26, and controls transport of the recording paper 16.

  The heater driver 74 controls the heating of various heating means (heater 76) included in the decurling unit 20, the heating unit 40, the post-drying unit 42, the heating / pressurizing unit 46, and the like according to a control signal input from the system controller 64. I do.

[First Embodiment]
Next, the liquid discharge head 12 according to the first embodiment of the present invention will be described. 4 and 5 are diagrams showing the liquid discharge head according to the first embodiment of the present invention. 4A and 5A are plan views showing the top surface of the liquid discharge head, and FIGS. 4B and 5B are cross-sectional views of the liquid discharge head.

  As shown in FIG. 4B, the liquid ejection head 12 according to the present embodiment includes a flow path unit 126 in which the pressure chamber 106 is formed, and a piezoelectric actuator 124 that changes the volume of the pressure chamber 106. .

The flow path unit 126 is configured by stacking the pressure chamber plate 102, the spacer plate 128, the manifold plate 130, and the nozzle plate 132. As a material of the pressure chamber plate 102, the spacer plate 128, and the manifold plate 130, for example, a silicon-based material such as Si, SiO ₂ , SiN, or quartz glass, or a metal-based material such as stainless steel can be used. Moreover, as a material of the nozzle plate 132, for example, a resin material such as polyimide, a metal material such as stainless steel, or Si can be used.

  A plurality of pressure chambers (pressure chamber holes) 106 are formed in the pressure chamber plate 102. The pressure chamber 106 has a substantially oval shape (substantially elliptical shape) long in the main scanning direction in plan view. The size (length in the longitudinal direction) of the pressure chamber 106 is, for example, φ300 μm.

  As shown in FIG. 4A, communication holes 134 and 140 are formed in the spacer plate 128 at positions overlapping with both longitudinal ends of each pressure chamber 106. The manifold plate 130 has a communication hole 136 and a common flow path 142. The common flow path 142 communicates with the communication hole 140 of the spacer plate 128. The communication holes 136 of the manifold plate 130 have the same shape as the communication holes 134 of the spacer plate 128 and are formed at positions that overlap each other in plan view.

  A nozzle 138 is formed in the nozzle plate 132 at a position overlapping the communication holes 134 and 136. Although not shown, a plurality of nozzles 138 are provided in a two-dimensional shape (matrix shape) on the ejection surface (nozzle surface) of the liquid ejection head 12. The nozzle 138 is formed by performing, for example, excimer laser processing.

  As shown in FIG. 4, the common flow path 142 communicates with the pressure chamber 106 through the communication hole 140, and the pressure chamber 106 communicates with the nozzle 138 through the communication holes 134 and 136. Thus, an ink flow path is formed in which the ink supplied from the ink storage / loading unit 14 via the common flow path 142 reaches the nozzle 138 through the pressure chamber 106.

  Next, the piezoelectric actuator 124 will be described. The piezoelectric actuator 124 includes a lower electrode 112 formed on the vibration plate 122 (surface silicon layer 104, silicon oxide layer 108) serving as a wall surface of the pressure chamber 106, a piezoelectric film 116, and an upper electrode formed on the piezoelectric film 116. 120 is included. Here, the thickness of the diaphragm 122 is 10 μm as an example.

  The piezoelectric actuator 124 according to this embodiment has a structure (upper address structure) in which the lower electrode 112 is a common electrode and the upper electrode 120 is an individual electrode. The upper electrode 120 is connected to an external wiring (not shown) (for example, a flexible cable). The lower electrodes 112 are electrically connected to each other at a position (not shown) and are grounded.

  As shown in FIGS. 4A and 5A, the upper electrode 120 is formed in an annular shape surrounding the central portion of the pressure chamber 106, and an area other than the central portion of the pressure chamber 106 (pressure chamber plate 102). (Region in the vicinity of (pressure chamber partition wall)).

  In addition, the lower electrode 112 and the piezoelectric film 116 are formed with a hole in a region overlapping the central portion of the pressure chamber 106. The diameter of the hole (reference numeral 112H in FIG. 6) formed in the lower electrode 112 is larger than the diameter of the hole (reference numeral 116H in FIG. 7) formed in the piezoelectric film 116, and the hole 116H of the piezoelectric film 116 has a lower electrode. The hole 112 </ b> H is formed in the hole 112 </ b> H. Therefore, as shown in FIGS. 4B and 5B, the end portion of the lower electrode 112 on the center side of the pressure chamber 106 is covered with the piezoelectric film 116. Thereby, it is possible to prevent the occurrence of creeping discharge and ion migration between the upper electrode 120 and the lower electrode 112.

  In the present embodiment, the upper electrode 120 and the holes 112H and 116H have an oval shape, but may have other shapes (for example, a polygon). The planar shape of the hole 112H of the lower electrode 112 is substantially similar to the inner peripheral shape of the upper electrode 120 (planar shape of the edge of the upper electrode 120 on the center portion side of the pressure chamber 106), and the hole 112H and the upper electrode 120 are formed. Are preferably arranged so as to share the center of each other. Further, it is preferable that the hole 116H of the piezoelectric film 116 has a shape substantially similar to the inner peripheral shape of the upper electrode 120, and the hole 116H and the upper electrode 120 are arranged so as to share the center of each other. Further, the planar shape of the pressure chamber 106 is preferably substantially similar to the inner peripheral shape of the upper electrode 120, and the pressure chamber 106 and the upper electrode 120 are preferably disposed so as to share the center of each other. As a result, an electric field can be applied to the region of the piezoelectric film 116 on the central portion side of the pressure chamber 106 substantially uniformly to apply pressure to the pressure chamber 106 substantially evenly.

  In the example shown in FIGS. 4B and 5B, the piezoelectric film 116 is formed so as to overlap the pressure chamber plate 102 (pressure chamber partition wall) in the outer peripheral region of the pressure chamber 106. In addition, the piezoelectric film 116 and the upper electrode 120 are arranged so that the edge portion on the central portion side of the pressure chamber 106 overlaps in plan view. Thereby, the area of the active portion of the piezoelectric film 116 that is displaced by the electric field generated between the upper electrode 120 and the lower electrode 112 can be increased, and the displacement amount of the diaphragm 122 can be further increased.

  In the example shown in FIGS. 4B and 5B, the upper electrode 120 extends toward the center of the pressure chamber 106 relative to the lower electrode 112. When a voltage is applied to the upper electrode 120, an electric field generated between the upper electrode 120 and the lower electrode 112 is applied to the portion of the piezoelectric film 116 where the lower electrode 112 is not formed in the lower layer (leaks out). Therefore, the displacement of the diaphragm 122 can be further increased.

  Hereinafter, an outline of the operation of the liquid discharge head 12 will be described. When a drive signal is supplied to the upper electrode 120 from the head driver (reference numeral 82 in FIG. 3) and an electric field is applied to the piezoelectric film 116 disposed between the lower electrode 112 and the upper electrode 120, the piezoelectric film 116 is displaced ( The diaphragm 122 is deformed so as to be convex toward the pressure chamber 106 side. As a result, the ink in the pressure chamber 106 is pressurized, and ink droplets are ejected from the nozzles 138 communicating with the pressure chamber 106.

  After the ink is ejected, when the diaphragm 122 returns to the original state, new ink is supplied from the common flow path 142 to the pressure chamber 106 through the communication hole 140.

[Method of Manufacturing Liquid Discharge Head According to First Embodiment]
Next, a method for manufacturing a liquid discharge head according to the first embodiment of the present invention will be described. 6 and 7 are cross-sectional views illustrating the method of manufacturing the liquid ejection head according to the first embodiment of the present invention.

First, a pressure chamber 106 was formed, and a pressure chamber plate 102 made of a silicon substrate (Si substrate), a surface silicon layer 104 constituting one wall surface of the pressure chamber 106, and a pressure chamber 106 for the surface silicon layer 104 were formed. A substrate structure 100 including an insulating layer (for example, a silicon oxide layer (SiO ₂ )) 108 formed on the surface opposite to the surface is created (FIG. 6A). Here, the dimension of the pressure chamber 106 is, for example, φ300 μm.

  Next, the lower electrode film 110 is formed on the surface of the silicon oxide layer 108 (FIG. 6B). The material of the lower electrode film 110 is, for example, Ir, Pt, Ti, Ti—Ir, TiW—Ir, Ti—Pt, or TiW—Pt. A method for forming the lower electrode film 110 is, for example, a sputtering method, a vapor deposition method, or a CVD method. The thickness of the lower electrode film 110 is, for example, 100 to 300 nm.

  Next, the lower electrode film 110 is etched, a hole 112H is formed at a position corresponding to the center of the pressure chamber 106, and the lower electrode 112 is formed (FIG. 6C). Note that the lower electrode 112 may be formed by lift-off film formation using a resist instead of forming a solid film of the lower electrode film 110 over the silicon oxide layer 108 and etching it.

Next, a piezoelectric film (PZT film) 114 is formed by sputtering on the surface of the silicon oxide layer 108 exposed from the lower electrode 112 and the hole 112H of the lower electrode 112 (FIG. 6D). The material of the piezoelectric film 114 is, for example, lead zirconate titanate (PZT; Pb (Zr, Ti) O ₃ ) or barium titanate (BaTiO ₃ ). The film thickness of the piezoelectric film 114 is 3 μm to 4 μm, for example.

  Next, the piezoelectric film 114 is dry etched to form a hole 116H at a position corresponding to the center of the pressure chamber 106 (FIG. 7A). 7A, the piezoelectric film 114 is patterned by dry etching (RIE) using a fluorine-based gas or a chlorine-based gas using an organic film or a metal film as a mask. The diameter of the hole 116H of the piezoelectric film 116 after the hole 116H is formed is smaller than the diameter of the hole 112H of the lower electrode 112, and the piezoelectric film 116 covers the lower electrode 112. The diameter difference D1 between the hole 116H of the piezoelectric film 116 and the hole 112H of the lower electrode 112 is, for example, several μm to 5 μm.

  Next, after the piezoelectric film 116 is formed, the piezoelectric film 116 is annealed at a predetermined heating temperature (annealing temperature) in an oxygen atmosphere.

  Next, the upper electrode film 118 is formed on the surfaces of the piezoelectric film 116 and the silicon oxide layer 108 (FIG. 7B). The material of the upper electrode film 118 is, for example, an alloy material such as TiW—Au, Ti—Au, TiW—Cu, or Ti—Cu. Moreover, the thickness of the upper electrode film 118 is 100 to 300 nm, for example.

  Next, the upper electrode film 118 is etched (dry etching or wet etching) to form the annular upper electrode 120 (FIG. 7C). Here, the upper electrode 120 is formed so as to partially overlap the pressure chamber plate 102 (pressure chamber partition wall). The radial width D2 of the upper electrode 120 is 60 μm as an example, the dimension D3 of the portion overlapping the pressure chamber plate 102 of the upper electrode 120 is 10 μm as an example, and the size D4 of the portion overlapping the pressure chamber 106 is 50 μm as an example. . In the step of FIG. 7C, for example, the upper electrode film 118 is patterned by dry etching (RIE) or wet etching using a fluorine-based gas or a chlorine-based gas using an organic film or a metal film as a mask. The upper electrode 120 may be formed by lift-off film formation using a resist, for example.

  According to the present embodiment, the lower electrode 112 is formed only at the edge portion other than the central portion of the pressure chamber 106 and is covered with the piezoelectric film 116 so as not to directly touch the atmosphere. While realizing the increase, a short circuit between the upper electrode 120 and the lower electrode 112 (for example, due to creeping discharge or ion migration) can be prevented, and the reliability of the liquid discharge head can be improved.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the following description, the description of the same configuration as in the first embodiment is omitted.

  In the present embodiment, a thin layer of piezoelectric material is formed in a region of the diaphragm 122 that overlaps the pressure chamber 106 to ensure the rigidity of the diaphragm 104.

  FIG. 8 is a cross-sectional view illustrating a method of manufacturing a liquid discharge head according to the second embodiment of the present invention. The steps up to the formation of the piezoelectric film 114 are the same as those shown in FIGS. 6 (a) to 6 (d).

  After the piezoelectric film 114 is formed as shown in FIG. 8A, the piezoelectric film 114 formed on the surfaces of the lower electrode 112 and the silicon oxide layer 108 is etched as shown in FIG. 8B. . In the step of FIG. 8B, a thin portion 114B thinner than the region 114A immediately above the lower electrode 112 is formed in a region overlapping the central portion of the pressure chamber 106 of the piezoelectric film 114. Here, the film thickness of the piezoelectric film 114 in the region 114A is 3 μm to 4 μm, for example, and the film thickness of the piezoelectric film 114 in the region 114B is 1 μm, for example.

  The thin-walled portion 114B has a shape that is substantially similar to the inner peripheral shape of the upper electrode 120 (planar shape of the edge on the center side of the pressure chamber 106), the hole 112H of the lower electrode 112, and the planar shape of the pressure chamber 106, It is preferable to form these so as to share the mutual center. As a result, an electric field can be applied to the region of the piezoelectric film 116 on the central portion side of the pressure chamber 106 substantially uniformly to apply pressure to the pressure chamber 106 substantially evenly.

  Next, the upper electrode film 118 is formed on the surfaces of the piezoelectric film 116 and the silicon oxide layer 108 (FIG. 8C).

  Next, the upper electrode film 118 is etched (dry etching or wet etching) to form the annular upper electrode 120 (FIG. 8D). The planar shape of the upper electrode 120 and the positional relationship with the pressure chamber 106 are the same as those in the first embodiment.

  According to the present embodiment, the lower electrode 112 is covered with the piezoelectric film 116 so as not to directly touch the atmosphere, thereby increasing the displacement amount of the diaphragm 122 (for example, by creeping discharge or ion migration). ) The short-circuit between the upper electrode 120 and the lower electrode 112 can be prevented, and the reliability of the liquid discharge head can be improved.

  Furthermore, according to the present embodiment, since the thin portion 114B is formed in the region overlapping the central portion of the pressure chamber 106, the rigidity of the diaphragm 122 can be increased.

[Driving method of liquid discharge head]
In the above embodiment, since the piezoelectric film 114 is formed by sputtering, the following effects can also be obtained. The polarization direction of the piezoelectric film 114 formed by the sputtering method is opposite to the normal direction, that is, the direction from the diaphragm 122 toward the upper electrode 120 (upward in FIG. 4 and the like). Therefore, in order to apply an electric field in the same direction as the polarization direction of the piezoelectric film 114, when the lower electrode 112 is grounded to a potential of 0 [V], the upper electrode 120 is set to a negative potential. It is necessary to apply a driving voltage.

  As shown in FIG. 9, the potential of the upper electrode 120 is 0 [V] in normal times other than when the ink ejection operation is performed, and the diaphragm 122 is not deformed. After the ink discharge operation starts, the potential of the upper electrode 120 is changed from 0 [V] to −V1 [V] (where V1> 0) to deform the diaphragm 122 and expand the volume of the pressure chamber 106. Ink is drawn into the pressure chamber 106 via the common flow path 142. Then, at the timing when the pressure wave generated in the pressure chamber 106 turns positive, the potential of the upper electrode 120 is changed from −V1 [V] to 0 [V] to return the diaphragm 122 to the state before deformation. As a result, the ink in the pressure chamber 106 is pressurized and ink droplets are ejected from the nozzle 138.

  According to the present embodiment, since the drive voltage is not applied to the upper electrode 120 and the electric field does not act on the piezoelectric film 114 at normal times other than when the ink ejection operation is performed, deterioration of the piezoelectric film 114 can be prevented. . Thereby, the reliability of the liquid discharge head 12 can be further improved.

  In the present invention, a liquid discharge head other than the liquid discharge head that discharges the ink (for example, a liquid discharge head for discharging a conductive paste to form a fine wiring pattern on a substrate, or an organic light emitter is used as a substrate. It can also be applied to liquid discharge heads for forming high-definition displays by discharging upwards, and liquid discharge heads for forming microelectronic devices such as optical waveguides by discharging optical resin onto substrates. is there.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet recording apparatus, 10 ... Printing part, 12 ... Liquid discharge head, 14 ... Ink storage / loading part, 16 ... Recording paper, 18 ... Paper feed part, 20 ... Decal processing part, 22 ... Heating drum, 24 ... Cutter , 26 ... Adsorption belt conveyance unit, 28, 30 ... Roller, 32 ... Belt, 34 ... Print detection unit, 36 ... Adsorption chamber, 38 ... Fan, 40 ... Heating unit, 42 ... Post-drying unit, 44 ... Belt cleaning unit, 46 ... Heating / pressurizing unit, 48 ... Pressure roller, 50 ... Cutter, 52 ... Paper discharge unit, 60 ... Host computer, 62 ... Communication interface, 64 ... System controller, 66 ... Program storage unit, 68 ... Memory, 70 ... motor driver, 72 ... motor, 74 ... heater driver, 76 ... heater, 78 ... print control unit, 80 ... buffer memory, 82 ... head driver, DESCRIPTION OF SYMBOLS 00 ... Substrate structure, 102 ... Pressure chamber plate, 104 ... Surface silicon layer, 106 ... Pressure chamber, 108 ... Insulating layer (silicon oxide layer), 110 ... Lower electrode film, 112 ... Lower electrode, 114, 116 ... Piezoelectric film 118 ... Upper electrode film, 120 ... Upper electrode, 122 ... Vibration plate, 124 ... Piezoelectric actuator, 126 ... Flow path unit, 128 ... Spacer plate, 130 ... Manifold plate, 132 ... Nozzle plate

Claims (10)

A flow path unit having a plurality of pressure chambers arranged along a plane;
A piezoelectric actuator that changes the volume of the pressure chamber to apply pressure to the liquid in the pressure chamber;
The piezoelectric actuator is
A diaphragm constituting one wall surface of the pressure chamber;
A common electrode formed in a region other than a region overlapping at least the central portion of the pressure chamber on the diaphragm, as viewed from a direction orthogonal to the plane, and a region overlapping each of the central portions of the plurality of pressure chambers A common electrode having a hole formed in
A piezoelectric layer formed on the common electrode, which is formed in a region overlapping each of the central portions of the plurality of pressure chambers when viewed from a direction orthogonal to the plane, and fits in a hole formed in the common electrode. A piezoelectric layer having a recess and covering the edge of the common electrode on the center side of the pressure chamber;
Wherein formed on the piezoelectric layer, when viewed from the direction perpendicular to the plane, and a separate electrode of a plurality of annular arranged in said plurality of edge and overlapping each area which is an area other than the center portion of the pressure chamber ,
When viewed from a direction orthogonal to the plane, the planar shapes of the hole of the common electrode, the recess of the piezoelectric layer, the pressure chamber, and the edge of the individual electrode on the pressure chamber side are mutually The hole of the common electrode, the recess of the piezoelectric layer, the pressure chamber, and the planar shape of the individual electrode are formed so as to be substantially similar, and share the center of each other. Liquid discharge head to be arranged .   The liquid discharge head according to claim 1, wherein the bottom surface of the concave portion of the piezoelectric layer is configured by the vibration plate. The piezoelectric layer includes a thin portion formed in a region overlapping with a central portion of the plurality of pressure chambers when viewed from a direction orthogonal to the plane,
2. The liquid discharge head according to claim 1, wherein the thin-walled portion is thinner than a region other than a region overlapping the central portion of the plurality of pressure chambers of the piezoelectric layer when viewed from a direction orthogonal to the plane, and constitutes the concave portion. . The individual electrodes, any one liquid discharge head according to 3 from which claim 1 extends to a region overlapping with the pressure chamber bulkhead of the pressure chamber. In an image forming apparatus provided with the liquid discharge head of any one of Claim 1 to 4 ,
The individual electrodes are disposed on a surface of the piezoelectric layer opposite to the diaphragm;
The common electrode is grounded;
The piezoelectric layer is polarized in a direction from the diaphragm toward the individual electrode;
An image forming apparatus further comprising a voltage applying unit that applies a driving voltage waveform having a negative potential to the individual electrodes only during the liquid discharging operation and causes an electric field in the same direction as the polarization direction of the piezoelectric layer to act on the piezoelectric layer. . (A) In a flow path unit having a plurality of pressure chambers arranged along a plane, when viewed from a direction orthogonal to the plane, at least the center of the pressure chamber on a diaphragm constituting one wall surface of the pressure chamber Forming a common electrode formed in a region other than a region overlapping with a portion, the common electrode having a hole formed in each of the regions overlapping with a central portion of the plurality of pressure chambers;
(B) A piezoelectric layer formed on the common electrode in a region overlapping with the central portion of each of the plurality of pressure chambers when viewed from a direction orthogonal to the plane, and having a recess that fits into a hole formed in the common electrode. Covering the edge of the common electrode on the center side of the pressure chamber with the piezoelectric layer; and
(C) On the piezoelectric layer, a plurality of annular individual electrodes disposed in regions overlapping with edges that are regions other than the central portion of the plurality of pressure chambers when viewed from a direction orthogonal to the plane are formed. and a step of,
When viewed from a direction orthogonal to the plane, the planar shapes of the hole of the common electrode, the recess of the piezoelectric layer, the pressure chamber, and the edge of the individual electrode on the pressure chamber side are mutually The hole of the common electrode, the recess of the piezoelectric layer, the pressure chamber, and the planar shape of the individual electrode share a center with each other. A method of manufacturing a liquid discharge head to be arranged . The method of manufacturing a liquid ejection head according to claim 6, wherein a bottom surface of the concave portion of the piezoelectric layer is configured by the vibration plate. A region in which the step (b) overlaps with a central portion of the plurality of pressure chambers of the piezoelectric layer in a region overlapping with a central portion of the plurality of pressure chambers when viewed from a direction orthogonal to the plane of the piezoelectric layer. The method of manufacturing a liquid discharge head according to claim 6 , further comprising a step of forming a thin portion thinner than a region other than the region and forming the concave portion. In step (c), the individual electrodes, any one method of manufacturing a liquid discharge head according to claim 6 to 8 which extends up to a region that overlaps with the pressure chamber bulkhead of the pressure chamber. In the step (b), a method for manufacturing a liquid discharge head according to any one of claims 6 to 9 formed by sputtering the piezoelectric layer.

Images