JP6221409B2 - Liquid ejection head, polarization treatment method for liquid ejection head, and liquid ejection apparatus - Google Patents

Description

  The present invention relates to a liquid discharge head that discharges liquid stored in a liquid chamber as droplets from a nozzle by pressurization of a piezoelectric element, a polarization processing method for the liquid discharge head, and a liquid discharge apparatus.

  2. Description of the Related Art Conventionally, there are liquid discharge heads and liquid discharge apparatuses that discharge liquid stored in a liquid chamber as droplets from nozzles by pressurization of piezoelectric elements, as in image forming apparatuses using inkjet technology.

  As such a liquid ejecting apparatus, as a basic structure, a plurality of liquid chambers storing liquid, nozzles that eject liquid droplets in communication with each liquid chamber, and piezoelectric elements that pressurize the liquid are used. An energy generating means such as a mechanical conversion element, an electrothermal conversion element such as a heater, or a diaphragm that forms the wall surface of the ink flow path and an electrode facing the diaphragm, and a liquid with the energy generated by the energy generation means Liquid droplets are ejected from the nozzles by pressurizing the liquid in the room.

  In addition, the recording head in the image forming apparatus using the ink jet technology uses a piezoelectric actuator that is a piezoelectric element as an energy generating means, and uses a piezoelectric actuator in a longitudinal vibration mode that extends and contracts in the axial direction. Two types, one using a mode piezoelectric actuator, have been put into practical use.

  As an example of using an actuator in a flexural vibration mode, for example, a uniform piezoelectric material layer is formed over the entire surface of the diaphragm by a film forming technique, and this piezoelectric material layer has a shape corresponding to a liquid chamber by a lithography method. A piezoelectric element is known that is divided into two liquid chambers and is independent of each liquid chamber (see, for example, Patent Document 1).

  In addition, the piezoelectric element used for the actuator in the flexural vibration mode includes, for example, a lower electrode that is a common electrode, a PZT film (piezoelectric layer) formed on the upper layer of the lower electrode, and an individual electrode formed on the upper layer of the PZT film. The upper electrode and the upper electrode are formed with an interlayer insulating film on the upper layer to insulate the lower electrode from the upper electrode, and electrically connected to the upper electrode through a contact hole opened in the interlayer insulating film A structure having such a wiring is known (see, for example, Patent Document 2).

  However, most of the lower electrodes use metal electrodes mainly based on lead (Pt), and there is concern about the guarantee of the fatigue characteristics of the PZT film. In general, it is considered that characteristic deterioration due to Pb diffusion contained in PZT is a factor of fatigue characteristics. For example, fatigue characteristics are improved by using an oxide electrode (see, for example, Patent Document 3). .

  In general, PZT is in a state where the polarization direction of the piezoelectric crystal is random immediately before the voltage is applied, and may be an aggregate of domains in which the polarization direction of the piezoelectric crystal is aligned by repeating the voltage application. Are known. For this reason, it is desirable to align the direction of polarization before voltage application.

  Therefore, a high voltage exceeding the drive pulse voltage is applied to the piezoelectric element, or a voltage is applied between the electrode and the charge supply means to generate a corona discharge, thereby supplying electric charge to generate an electric field in the piezoelectric body. Various techniques for stabilizing the amount of displacement with respect to a predetermined drive voltage, such as generation, have been considered (see, for example, Patent Document 4).

  However, for example, in the case of processing by corona discharge as in the method described in Patent Document 4, since the corona discharge processing is performed after the piezoelectric film is formed, for example, subsequent formation such as interlayer film formation or lead wiring formation is performed. There was a risk of depolarization due to the thermal history or the like in this step. Specifically, when a thermal history exceeding 300 ° C. is given after the corona discharge treatment, there has been a problem of returning to the state before the corona discharge treatment.

  As a result, it becomes difficult to maintain good droplet discharge characteristics, and stable droplet discharge cannot be performed, and it is difficult to arrange piezoelectric elements at high density. The problem that it ends up has arisen.

  Therefore, the inventor of the present application considers that the step of performing the polarization process by injecting the electric charge generated by the corona discharge or the glow discharge is preferably performed in a later process than the process of forming the interlayer film or the lead wiring. It came to.

  Here, when performing polarization processing by charge injection such as corona discharge, charge concentrates on the drive channel individual electrode portion, which is the end of the electrode in the same column, and therefore, in-column characteristics vary due to excessive progress of polarization processing. It has been newly found that dielectric breakdown is likely to occur between the upper and lower electrodes due to excessive charge injection.

  The present invention has been made in order to solve the above-described conventional problems, and can inject a uniform amount of charge into the pad at the end of each individual electrode. A liquid discharge head capable of maintaining good discharge, ensuring stable discharge characteristics of liquid droplets, and capable of arranging piezoelectric elements at high density, a polarization processing method for the liquid discharge head, and liquid discharge An object is to provide an apparatus.

In order to achieve the above object, a liquid discharge head according to the present invention pressurizes a liquid chamber that stores liquid, a plurality of nozzles that communicate with the liquid chamber and discharges liquid, and a liquid stored in the liquid chamber. An actuator substrate that forms a piezoelectric element as an actuator that discharges liquid from the nozzle, and the actuator substrate has individual electrodes of the piezoelectric element formed in a row and ends of the individual electrodes Short-circuit electrodes that are mutually short-circuited in the same row are formed in the vicinity of the electrode pads arranged in the section, and the short-circuit electrodes that are short-circuited to each other in the same row are formed with respect to the liquid chamber forming surface of the actuator substrate 1E7 to 1E10 [Ω] resistance .

  According to the present invention, it is possible to inject a uniform amount of charge into the pad at the end of the individual electrode, thereby maintaining good droplet discharge characteristics and stable droplet discharge. It is possible to provide a liquid discharge head, a liquid discharge head polarization processing method, and a liquid discharge apparatus that can secure characteristics and can arrange piezoelectric elements at high density.

1 is a schematic side view illustrating an example of an image forming apparatus including a droplet discharge head according to an embodiment of the present invention. 1 is a schematic plan view illustrating an example of an image forming apparatus including a droplet discharge head according to an embodiment of the present invention. It is a schematic block diagram which shows the example of 1 structure of the droplet discharge part which is the basic composition part of the droplet discharge head concerning embodiment of this invention. FIG. 6 is a cross-sectional view of the periphery of the piezoelectric element taken along the line AA in FIG. 5, showing a configuration example of a droplet discharge unit that is a basic component of the droplet discharge head according to the embodiment of the present invention. FIG. 3 is a plan view of the periphery of a piezoelectric element showing a configuration example of a droplet discharge unit that is a basic component of the droplet discharge head according to the embodiment of the present invention. It is explanatory drawing which shows typically the mode of the charge injection to the pad electrode for common electrodes and the pad electrode for individual electrodes by the discharge process in the droplet discharge head which concerns on embodiment of this invention. FIG. 3 is an electrode arrangement diagram illustrating the principle of polarization of a piezoelectric element by charge injection in a droplet discharge head according to an embodiment of the present invention. FIG. 5 is an equivalent circuit diagram illustrating the principle of polarization of a piezoelectric element by photocharge injection in a droplet discharge head according to an embodiment of the present invention. (A) And (b) is a graph which shows the example of a measurement of the PE hysteresis loop characteristic of the piezoelectric element before and after the polarization process in the droplet discharge head which concerns on embodiment of this invention. It is a graph which shows (theta) -2 (theta) measurement data of the X-ray measured about SRO which comprises the oxide electrode film in the droplet discharge head which concerns on embodiment of this invention. It is explanatory drawing which shows an example of the polarization process of the actuator board | substrate in the droplet discharge head which concerns on embodiment of this invention. FIG. 3 is a plan view showing an example of an actuator substrate in which a plurality of droplet discharge portions in the droplet discharge head according to the embodiment of the present invention are formed in two rows facing each other. It is explanatory drawing which shows the other example of the polarization process of the actuator board | substrate in the droplet discharge head which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

(Configuration of image forming apparatus 1)
First, the configuration of an example of an image forming apparatus 1 equipped with a liquid discharge head, a liquid discharge head polarization processing method, and a liquid discharge apparatus according to the present invention will be described with reference to FIGS. 1 and 2.

  The image forming apparatus 1 includes a paper feeding cassette 3 that stores recording materials P in a stacked state on a stacking unit 2 and a half-moon roller-like shape that separates and feeds the top recording material P from the stacking unit 2 one by one. The sheet feeding roller 4 and the separation pad 5 made of a material having a large friction coefficient facing the sheet feeding roller 4 are provided.

  The paper feed roller 4 contacts the surface of the uppermost recording material P, and feeds the recording material P downstream (left side in FIG. 1) by rotating clockwise in FIG. The separation pad 5 is urged toward the paper feed roller 4, and the uppermost recording material P and the other recording material P are recorded so that the lower recording material P is not overlapped and fed downstream. The material P is separated.

  The image forming apparatus 1 includes a regulation guide 6, a leading edge detection sensor 7, a conveyance belt 8, a counter roller 9, a conveyance guide 10, an upstream pressure roller 11, and a downstream pressure roller 12 from the upstream side in the conveyance direction of the recording paper P. The pressing member 13, the paper discharge roller 14, and the paper discharge roller 15 are arranged in the order of conveyance.

  The regulation guide 6 regulates the conveyance direction of the recording material P fed by the paper feed roller 4 from the lower side to the upper side in FIG.

  The leading edge detection sensor 7 detects the leading edge and the trailing edge of the recording material P, and uses the detection signals as trigger signals for the registration function, the printing start timing, the feeding timing of the next recording paper P, and the like.

  The conveyor belt 8 is an endless belt member that is stretched between the conveyor roller 16 and the tension roller 17 and rotates in the clockwise direction in FIG. The surface of the conveying belt 8 is charged by the charging roller 18 and conveys the recording material P by electrostatic adsorption. The conveyance belt 8 is rotated in the sub-scanning direction by the rotation of the conveyance roller 16 via the timing belt 20, the timing roller 21, and the drive shaft 22 by the driving of the sub-scanning motor 19. An underlay member 23 is arranged on the inner surface on the upper surface side of the conveyor belt 8 corresponding to the image forming area.

  The charging roller 18 is disposed so as to come into contact with the surface layer of the conveyor belt 8 and rotate following the rotation of the conveyor belt 8, and 2.5 N is applied to both ends of the drive shaft 22 as a pressing force. .

  The counter roller 9 nips and conveys the recording material P between the upstream ends of the conveying belt 8.

  The conveyance guide 10 is configured to follow the conveyance belt 8 by changing the conveyance direction of the recording material P by about 90 ° from the upward direction to the horizontal direction.

  The upstream pressure roller 11 and the downstream pressure roller 12 are urged toward the upper surface side of the transport belt 8 by the pressing member 13, and the recording material P is nipped and transported between the upper surfaces of the transport belt 8.

  The paper discharge roller 14 and the paper discharge roller 15 have, for example, the paper discharge roller 14 as a driving roller and the paper discharge roller 15 as a driven roller. The paper discharge roller 14 and the paper discharge roller 15 take over the recording material P from the downstream end of the transport belt 8 and nip transport the paper to a paper discharge tray 24 for paper discharge. The paper discharge roller 14 and the paper discharge roller 15 switch back the recording material P after single-sided printing in the direction opposite to the paper discharge direction together with the rotational movement direction of the conveyor belt 8 during double-sided printing. To 25.

  The double-sided paper feeding unit 25 takes in the recording material P switched back by the reverse rotation of the conveying belt 8, reverses the front and back, and feeds the recording material P to the upstream side of the leading edge detection sensor 7 again.

  The image forming apparatus 1 includes, as a printing unit, a carriage 31, a guide rod 32 and a guide rail 33 that hold the carriage 31 so as to be movable and scanned in the main scanning direction, a main scanning motor 34, a drive pulley 35, and a driven pulley 36. And a timing belt 37 that spans the belt.

  For example, the carriage 31 has liquid ejection heads 38K, 38C, 38M, and 38Y that eject ink droplets of black (K), cyan (C), magenta (M), and yellow (Y) in the main scanning direction. A recording head 38 is disposed along the direction. The carriage 31 is equipped with a sub tank 39 for each color for supplying each color ink to the recording head 38. The sub tank 39 is supplementarily supplied with ink from a main tank (not shown) via an ink supply tube 40 for each color.

  The liquid discharge heads 38K, 38C, 38M, and 38Y are mounted on the carriage 31 with the droplet discharge direction facing downward. In addition, although the independent liquid discharge heads 38K, 38C, 38M, and 38Y are used here, it may be configured to use one or a plurality of print heads having a plurality of nozzle rows that discharge ink droplets of each color. it can. Further, the number of colors and the arrangement order are not limited to this.

  The main scanning motor 34 moves and scans the carriage 31 in the main scanning direction by reciprocating the timing belt 37 spanned between the driving pulley 35 and the driven pulley 36 along the main scanning direction.

  On the other hand, in the non-printing area on one side of the carriage 31 in the scanning direction, a maintenance / recovery mechanism 41 is disposed that is the home position of the carriage 31 and maintains and recovers the state of the nozzles of the recording head 38. .

  The maintenance / recovery mechanism 41 includes caps 42 for capping each nozzle surface of the recording head 38, a wiper blade 43 that is a blade member for wiping the nozzle surface, and an idle discharge receiver 44. The idle discharge receptacle 44 is adapted to receive droplets when performing idle discharge in which droplets that do not contribute to recording in order to discharge the thickened ink.

  Next, the overall operation of the image forming apparatus 1 having such a configuration will be described. In the image forming apparatus 1, the uppermost recording material P is separated and fed one by one from the stacking unit 2 and detected by the leading edge detection sensor 7. The recording material P is regulated in a substantially vertical upward direction by the regulation guide 6, conveyed while being sandwiched between the conveyance belt 8 and the counter roller 9, and further guided by the conveyance guide 10 to approximately 90 °. The transport direction is changed. The recording material P is pressed against the upper surface of the transport belt 8 by the upstream pressure roller 11 and the downstream pressure roller 12 and is transported below the recording head 38.

  At this time, an alternating voltage is applied to the charging roller 18 so that a positive output and a negative output are alternately repeated from an AC bias supply unit by a control circuit (not shown). Thereby, plus and minus are alternately charged in a band shape with a predetermined width in the charging voltage pattern in which the conveyor belt 8 alternates, that is, in the sub-scanning direction that is the circumferential direction.

  The recording material P is adsorbed by the electrostatic force on the positively and negatively charged conveying belt 8 and is conveyed in the sub-scanning direction by the circumferential movement of the conveying belt 8.

  Therefore, by driving the recording head 38 according to the image signal while moving the carriage 31 in the forward and backward directions along the main scanning direction, ink droplets are ejected onto the stopped recording material P. The line is recorded, the recording material P is conveyed by a predetermined amount, and then the next line is recorded. Upon receiving a recording end signal or a signal indicating that the trailing edge of the recording material P has reached the recording area, the recording operation is terminated and the recording material P is discharged onto the discharge tray 24.

  In the case of double-sided printing, when recording of the first printed surface is completed, the recording roller P and the transport belt 8 are rotated in the reverse direction to switch back the recorded recording material P so that both sides are printed. The paper is fed into the paper feeding unit 25. Further, the recording material P is turned upside down and fed again to the upstream side from the leading edge detection sensor 7, the timing is controlled, and the recording material P is conveyed to the conveying belt 8 and recorded on the back surface as described above. Thereafter, the paper is discharged onto the paper discharge tray 24.

  During printing (recording) standby, the carriage 31 is moved to the maintenance / recovery mechanism 41 that is the home position, and the nozzle surface of the recording head 38 is capped by the cap 42 to keep the nozzle in a wet state. Prevents ejection failures due to drying. Further, a recovery operation is performed in which ink is sucked from the nozzles while the recording head 38 is capped by the cap 42, and the thickened ink and bubbles are discharged. The ink adhering to the nozzle surface of the recording head 38 by this recovery operation is wiped by the wiper blade 43 and removed by cleaning. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. Thereby, the stable ejection performance of the recording head 38 can be maintained.

  Next, the basic configuration of each liquid discharge head 38K, 38C, 38M, 38Y of the recording head 38 will be described. In the following description, since the liquid ejection heads 38K, 38C, 38M, and 38Y have the same configuration, the configuration of the recording head 38 will be described for convenience of explanation.

  As shown in FIG. 3, the recording head 38 includes a substrate 52 having a liquid chamber 51 in which a liquid 50 is stored, and a nozzle substrate 54 in which nozzles 53 that communicate with the liquid chamber 51 and discharge the liquid 50 as droplets 50A are formed. And a diaphragm 55 that covers the liquid chamber 51 and a piezoelectric element 56. As the substrate 52, a silicon substrate or the like is used.

  The piezoelectric element 56 uses an actuator that pressurizes the liquid 50 stored in the liquid chamber 51 and discharges the droplet 50 </ b> A from the nozzle 53, that is, an electro-mechanical conversion element as energy generating means. The piezoelectric element 56 includes a first electrode 56A as a lower electrode, a piezoelectric film 56B as an electro-mechanical conversion film, and a second electrode 56C as an upper electrode in order from the lower layer on the diaphragm 55 side. It has a layer structure.

  Further, as shown in FIGS. 4 and 5, the upper layer of the piezoelectric element 56 is covered with a first insulating protective film 57. Contact holes 57a and 57b are formed in the first insulating protective film 57, and the third electrode 58 and the fourth electrode so as to enter the upper layer of the first insulating protective film 57 and the contact holes 57a and 57b. 59 is provided. A second insulating protective film 60 is provided on the first insulating protective film 57 including the third electrode 58 and the fourth electrode 59. In FIG. 5, the first insulating protective film 57 and the second insulating protective film 60 are not shown.

  The third electrode 58 is electrically connected to the first electrode 56A through the contact hole 57a, and the fourth electrode 59 is electrically connected to the second electrode 56C through the contact hole 57b. At this time, the first electrode 56A and the third electrode 58 are used as a common electrode, and the second electrode 56C and the fourth electrode 59 are used as individual electrodes. A common electrode pad 61 and an individual electrode pad 62 are provided in the contact hole 60a.

  The piezoelectric element 56 manufactured so far is subjected to corona discharge or glow discharge, and the generated charges are injected through the electrode pads 61 and 62 to perform polarization processing.

  As shown in FIG. 6, when corona discharge is performed using the corona wire 63, cations are generated by ionizing molecules in the atmosphere, and positive ions are generated via the electrode pads 61 and 62 of the piezoelectric element 56. Charges are accumulated in the piezoelectric element 56 by the flow of ions.

  Here, as shown in FIG. 7, it is assumed that the number of individual electrodes is A (1 in FIGS. 5 and 7) and the number of common electrodes is B (2 in FIGS. 5 and 7). Here, it is assumed that the areas of the individual electrode and the common electrode are the same.

  Here, as shown in FIG. 8, if charge Q is generated, how much charge is accumulated in one piezoelectric element 56 will be examined. For example, while the charge Q is generated on the upper electrode side, only the charge Q (B / A) is generated on the lower electrode side, and an internal potential difference is generated due to the charge difference between the upper electrode and the lower electrode. I think that the polarization process is being performed.

  The common electrode has a predetermined resistance value with respect to the back surface of the substrate 52, and is about 1E7 [Ω] in the present embodiment. Therefore, it is considered that the charge at the time of the polarization process almost flows to the GND, and a potential difference is generated by the charge charged to the individual electrode, and the polarization process is performed.

  Here, the state of the polarization process is determined from the PE hysteresis loop. For example, as shown in FIG. 9, when a hysteresis loop is measured with an electric field strength of ± 150 kV / cm and the polarization at the first 0 kV / cm is returned to 0 kV / cm after applying a voltage of Pini, +150 kV / cm The polarization at 0 kV / cm is Pr. At this time, the value of Pr−Pini is defined as a difference in polarization amount, and whether the polarization state is good or bad is determined from the difference in polarization amount.

Here, the polarization amount difference Pr-Pini is preferably has a 10 [mu] C / cm ² or less, further preferably has a 5 [mu] C / cm ² or less. That is, if this value is not satisfied, sufficient characteristics cannot be obtained for displacement deterioration after continuous driving of the piezoelectric element 56 as a PZT actuator.

Below, the material of each structure of this invention and a construction method are demonstrated concretely.

〔substrate〕
As the substrate 52, it is preferable to use a silicon single crystal substrate, and it is preferable to have a thickness in the range of 100 [μm] to 600 [μm]. There are three types of crystal orientation in the cubic lattice of crystal, (100), (110), and (111), but (100) and (111) are generally widely used in the semiconductor industry. Therefore, in this embodiment, a single crystal substrate mainly having a (100) plane orientation is mainly used. Further, when the liquid chamber 51 as shown in FIG. 3 is manufactured, the silicon single crystal substrate is processed by using etching.

  As an etching method in this case, it is common to use anisotropic etching. Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure. For example, in anisotropic etching immersed in an alkaline solution such as potassium hydroxide (KOH), the (111) plane has an etching rate of about 1/400 compared to the (100) plane.

Therefore, a structure having an inclination of about 54 ° can be produced in the plane orientation (100), whereas a deep groove can be produced in the plane orientation (110), so that the arrangement density can be maintained while maintaining rigidity. It is known that can be raised. In this embodiment, it is possible to use a single crystal substrate having a (110) plane orientation. In this case, silicon dioxide (SiO ₂ ), which is a mask material, is also etched, so it is preferable to use this point with attention.

[Vibration plate 55]
The vibration plate 55 is deformed by receiving the force generated by the piezoelectric element 56, and discharges a droplet 50 </ b> A of a liquid 50 such as ink in the liquid chamber 51 from the nozzle 53. Therefore, it is preferable that the diaphragm 55 has a predetermined strength.

Examples of the material include silicon (Si), SiO ₂ , silicon nitride (Si ₃ N ₄ ), and the like produced by, for example, a CVD method. Furthermore, it is preferable to select a material close to the linear expansion coefficient of the first electrode 56A and the piezoelectric film 56B which are lower electrodes as shown in FIG. In particular, in general, PZT is often used as the material for the piezoelectric film 56B.

Therefore, the material of the diaphragm 55 is in the range of 5 × 10 ⁻⁶ (1 / K) to 10 × 10 ⁻⁶ (1 / K), which is close to the linear expansion coefficient 8 × 10 ⁻⁶ (1 / K) of PZT. A material having a linear expansion coefficient of is preferable. Furthermore, a material having a linear expansion coefficient in the range of 7 × 10 ⁻⁶ (1 / K) to 9 × 10 ⁻⁶ (1 / K) is more preferable.

  Specific examples of the material include aluminum oxide, zirconium oxide, iridium oxide, ruthenium oxide, tantalum oxide, hafnium oxide, osmium oxide, rhenium oxide, rhodium oxide, palladium oxide, and compounds thereof. These materials can be manufactured by a spin coater using, for example, a sputtering method or a sol-gel method. The film thickness is preferably in the range of 0.1 [μm] to 10 [μm], and more preferably in the range of 0.5 [μm] to 3 [μm]. If it is smaller than this range, it becomes difficult to process the liquid chamber 51 as shown in FIG. On the other hand, if it is larger than the above range, the diaphragm 55 becomes difficult to deform, and it becomes unstable to eject the droplet 50A such as an ink droplet from the nozzle 53.

[First electrode 56A]
The first electrode 56A is preferably made of a metal or a metal and an oxide. Here, both materials are devised so as to suppress peeling and the like by putting an adhesion layer between the diaphragm 55 and the metal film constituting the first electrode 56A. The details of the metal electrode film and the oxide electrode film including the adhesion layer are described below.

[Adhesion layer 65]
For example, after forming titanium (Ti) by sputtering, the adhesion layer is thermally oxidized using a RTA (Rapid Thermal Annealing) apparatus to form a titanium oxide film. The thermal oxidation conditions are, for example, a temperature in the range of 650 [° C.] to 800 [° C.], a treatment time in the range of 1 [min] to 30 [min], and an O 2 atmosphere.

  Reactive sputtering may be used to form the titanium oxide film, but a thermal oxidation method at a high temperature of the titanium film is desirable. The production of the adhesion layer by reactive sputtering requires a special sputtering chamber configuration because the substrate 52 needs to be heated at a high temperature. Furthermore, the crystallinity of the titanium oxide film is better in the oxidation by the RTA apparatus than in the oxidation by a general furnace. This is because in an ordinary oxidation in a heating furnace, an easily oxidizable titanium film forms several crystal structures at a low temperature, so that it is necessary to break it once. Therefore, oxidation by RTA having a high temperature rising rate is advantageous in order to form better crystals.

  Moreover, as materials other than titanium, materials such as tantalum (Ta), iridium (Ir), and ruthenium (Ru) can be used. The thickness of the adhesion layer is preferably in the range of 10 [nm] to 50 [nm], and more preferably in the range of 15 [nm] to 30 [nm]. If the thickness is less than this range, there is a concern about the adhesion, and if it exceeds this range, the quality of the crystal of the electrode film produced on the adhesion layer is affected.

[Metal electrode film]
Platinum (Pt), which has high heat resistance and low reactivity, is used as the metal material for the metal electrode film, but it may not be said that it has sufficient barrier properties against lead (Pb). Yes, a platinum group element such as iridium or platinum-rhodium (Rh), or an alloy film thereof may be used. The base in the case of use of platinum (in particular, SiO ₂₎ due to poor adhesion to a, it is preferable to laminate the previously adhesion layer described above.

  As a manufacturing method, vacuum film formation such as sputtering or vacuum deposition is generally used. The film thickness is preferably in the range of 80 [nm] to 200 [nm], and more preferably in the range of 100 [nm] to 150 [nm]. If the thickness is smaller than this range, a sufficient current cannot be supplied as the first electrode 56 </ b> A, and a problem may occur when the droplet 50 </ b> A is ejected from the nozzle 53. Furthermore, in the case where the thickness is larger than this range, an expensive material of a platinum group element is used, so that the material cost increases.

  Further, in the case of using platinum as a material, the surface roughness increases as the film thickness is increased, and the surface roughness and crystal orientation are affected with respect to the first oxide electrode film 57 and PZT formed thereon. It becomes easy to exert. Along with this, there is a risk that it may be difficult to secure a sufficient displacement amount as an actuator for discharging the droplet 50A from the nozzle 53.

[Oxide electrode film]
As a material for the oxide electrode film, SrRuO ₃ (hereinafter, abbreviated as “SRO” as appropriate) is preferably used. In addition to SrRuO ₃ , Srx (A) (1-x) Ruy (1-y), A = Ba, Ca, B = Co, Ni, x, y = 0 to 0.5 But you can. The oxide electrode film can be produced by a film formation method such as sputtering. The film quality of the SrRuO ₃ thin film varies depending on the sputtering conditions. Therefore, in order to place the SrRuO ₃ film in the (111) orientation in accordance with the Pt (111) of the first electrode 55 with particular emphasis on the crystal orientation, the film forming temperature is 500 [° C.] or higher. It is preferable to form a film by heating the substrate. For example, regarding SRO film formation conditions, after room temperature film formation, thermal oxidation is performed at a crystallization temperature (650 ° C.) by RTA treatment. In this case, the SRO film is sufficiently crystallized and a sufficient value is obtained as a specific resistance as an electrode. However, as the crystal orientation of the film, (110) is easily preferentially oriented and formed thereon. (110) is also easily oriented in the PZT film.

  As for the crystallinity of SRO produced on Pt (111), since the lattice constants of Pt and SRO are close to each other, the 2θ positions of SRO (111) and Pt (111) are measured in the normal X-ray θ-2θ measurement. Are difficult to distinguish. With respect to Pt, diffraction lines cancel each other at a position where 2θ inclined by Psi = 35 ° is about 32 ° due to the disappearance rule, and no diffraction intensity is observed. Therefore, it is possible to confirm whether the SRO is preferentially oriented to (111) by inclining the Psi direction by about 35 ° and judging from the peak intensity where 2θ is about 32 °.

  FIG. 10 is a graph showing X-ray θ-2θ measurement data obtained by measuring the crystallinity of SRO constituting such an oxide electrode film while fixing 2θ = 32 ° and shaking Psi. When Psi = 0 °, almost no diffraction intensity is observed with SRO (110), but near Psi = 35 °, diffraction intensity is observed. I was able to confirm. In addition, regarding the SRO produced by the room temperature film formation + RTA process described above, the diffraction intensity of SRO (110) is observed when Psi = 0 °.

  Further, when the amount of displacement after being driven when the piezoelectric element 56 was continuously operated as an actuator was estimated as compared with the initial displacement, the orientation of the PZT had a great influence. 110) is insufficient in suppressing displacement deterioration.

  Further, when the surface roughness of the SRO film is observed, the film formation temperature is affected, and the surface roughness is very small from room temperature to 300 ° C. and becomes 2 [nm] or less. As for the roughness, the surface roughness (average roughness) measured by AFM is used as an index.

  Although the surface roughness is very flat, the crystallinity is not sufficient, and sufficient characteristics cannot be obtained with respect to initial displacement as a PZT actuator formed thereafter and displacement deterioration after continuous driving. . The surface roughness is preferably in the range of 4 [nm] to 15 [nm], and more preferably in the range of 6 [nm] to 10 [nm]. If this range is exceeded, the dielectric breakdown voltage of the PZT film formed thereafter is very poor and leaks easily. Therefore, in order to obtain crystallinity and surface roughness as described above, the film forming temperature is 500 [° C.] or higher and 700 [° C.], preferably 520 [° C.] or higher and 600 [° C.]. Implement the membrane.

  Regarding the composition ratio between strontium (Sr) and ruthenium after film formation, Sr / Ru is preferably 0.82 or more and 1.22 or less. If it is out of this range, the specific resistance increases, and sufficient conductivity as an electrode cannot be obtained. The thickness of the SRO film is preferably in the range of 40 [nm] to 150 [nm], and more preferably in the range of 50 [nm] to 80 [nm]. If the thickness is smaller than this range, sufficient characteristics cannot be obtained for initial displacement and displacement deterioration after continuous driving, and a function as a stop etching layer for suppressing over-etching of the piezoelectric film (PZT film) can also be obtained. Because it becomes difficult. If the thickness is exceeded, the dielectric strength of the piezoelectric film (PZT film) formed thereafter is very poor and leaks easily.

Further, the specific resistance is preferably 5 × 10 ⁻³ [Ω · cm] or less, and more preferably 1 × 10 ⁻³ [Ω · cm] or less. If it is larger than this range, a sufficient contact resistance cannot be obtained at the interface between the first electrode 56A and the third electrode 58, and a sufficient current cannot be supplied as the first electrode 56A. This is because a problem may occur when the nozzle 53 is discharged.

[Piezoelectric film (electro-mechanical conversion film) 56B]
PZT was mainly used as the material for the piezoelectric film 56B. PZT is a solid solution of lead zirconate (PbTiO ₃ ) and titanic acid (PbTiO ₃ ), and the characteristics differ depending on the ratio. In general, the composition exhibiting excellent piezoelectric characteristics has a ratio of PbZrO ₃ and PbTiO ₃ of 53:47. In terms of chemical formula, Pb (Zr0.53, Ti0.47) O ₃ is generally used. (53/47).

Examples of complex oxides other than PZT include barium titanate (BaTiO ₃ ). In this case, it is also possible to prepare a barium titanate precursor solution by using a barium alkoxide as a barium source and a compound of titanium alkoxide as a titanium source as starting materials and dissolving them in a common solvent. These materials are described by the general formula ABO ₃
A = Pb, Ba, Sr
B = Ti, Zr, Sn, Ni, Zn, Mg, Nb
This corresponds to a composite oxide containing as a main component.

Specifically, (Pb1-x, Ba) (Zr, Ti) O ₃ , (Pb1-x, Sr) (Zr, Ti) O ₃ , which partially replaces Pb of the A site with Ba or Sr. This is the case. Such substitution is possible with a divalent element, and the effect thereof has an effect of reducing characteristic deterioration due to evaporation of lead during heat treatment.

  The piezoelectric film 56B can be manufactured by a spin coater using a sputtering method or a sol-gel method. In that case, since patterning is required, a desired pattern is obtained by photolithography etching or the like. When PZT is produced by the sol-gel method, a PZT precursor solution can be produced by using a compound such as lead acetate, zirconium alkoxide, titanium alkoxide as a starting material and dissolving it in methoxyethanol as a common solvent to obtain a uniform solution. . Since the metal alkoxide compound is easily hydrolyzed by moisture in the atmosphere, an appropriate amount of a stabilizer such as acetylacetone, acetic acid or diethanolamine may be added to the precursor solution as a stabilizer.

  When the piezoelectric film 56B is obtained on the entire surface of the substrate 52, it is obtained by forming a coating film by a solution coating method such as spin coating and performing heat treatments such as solvent drying, thermal decomposition, and crystallization. Since the transformation from the coating film to the crystallized film involves volume shrinkage, it is necessary to adjust the precursor concentration so that a film thickness of 100 nm or less can be obtained in one step in order to obtain a crack-free film. Become.

  The film thickness of the piezoelectric film 56B is preferably in the range of 0.5 [μm] to 5 [μm], and more preferably in the range of 1 [μm] to 2 [μm]. If the thickness is smaller than this range, sufficient deformation (displacement) cannot be generated. If the thickness is larger than this range, many layers are stacked, so that the number of steps increases and the process time becomes longer.

  The relative dielectric constant of the piezoelectric film 56B is preferably in the range of 600 to 2000, and more preferably in the range of 1200 to 1600. At this time, if it is smaller than this range, sufficient deformation (displacement) characteristics cannot be obtained, or if it exceeds this range, polarization processing is not performed sufficiently, and sufficient characteristics cannot be obtained for displacement deterioration after continuous driving. This is because there is a possibility that such a problem may occur.

[Second electrode 56C]
The second electrode 56C is preferably made of a metal or an oxide and a metal. Details of the oxide electrode film and the metal electrode film are described below.

[Oxide electrode film]
As the material or the like of the oxide electrode film, the same materials as those described for the oxide electrode film used in the first electrode 56A can be used. The thickness of the oxide electrode film (SRO film) is preferably in the range of 20 [nm] to 80 [nm], and more preferably in the range of 40 [nm] to 60 [nm]. This is because if the thickness is smaller than this film thickness range, sufficient characteristics cannot be obtained for the initial deformation (displacement) and the deterioration characteristics of the deformation (displacement). On the other hand, if it exceeds this range, the dielectric breakdown voltage of the piezoelectric film (PZT film) formed thereafter is very bad and it is easy to leak.

[Metal electrode film]
As the material for the metal electrode film, the same materials as those described for the metal electrode film used in the first electrode 56A can be used. The film thickness is preferably in the range of 30 [nm] to 200 [nm], and more preferably in the range of 50 [nm] to 120 [nm]. If the thickness is smaller than this range, a sufficient current cannot be supplied as the second electrode 56C, and a problem may occur when the droplet 50A is ejected from the nozzle 53. Further, when the thickness is larger than this range, an expensive material of a platinum group element is used, so that the material cost increases.

  Further, when platinum is used as a material, the surface roughness increases when the film thickness is increased, and a process failure such as film peeling occurs when a wiring or the like is manufactured through the first insulating protective film 57. Is likely to occur.

[First insulating protective film 57]
For the first insulating protective film 57, it is necessary to select a material that prevents damage to the piezoelectric element 56 due to the film forming / etching process and is difficult to transmit moisture in the atmosphere. For this reason, the material of the first insulating protective film 57 needs to be a dense inorganic material. In addition, when an organic material is used as the first insulating protective film 57, it is not suitable because it is necessary to increase the film thickness in order to obtain sufficient protection performance.

  If the first insulating protective film 57 is a thick film, the vibration of the diaphragm 55 is remarkably hindered, resulting in the recording heads 38 of the liquid discharge heads 38K, 38C, 38M, and 38Y having low discharge performance. In order to obtain high protection performance with a thin film, it is preferable to use an oxide, nitride, or carbide film, but adhesion to the electrode material, the piezoelectric material, and the diaphragm material serving as the base of the first insulating protective film 57. It is necessary to select a material with a high value.

  In addition, it is necessary to select a film formation method that does not damage the piezoelectric element 56 as the film formation method of the first insulating protective film 57. That is, a plasma CVD method in which a reactive gas is turned into plasma and deposited on a substrate, or a sputtering method in which a film is formed by causing a plasma to collide with a target material and flying away is not preferable.

Examples of a preferable film formation method for the first insulating protective film 57 include a vapor deposition method and an ALD method, but an ALD method with a wide range of materials that can be used is preferable. As a preferable material, an oxide film used for a ceramic material such as Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , Ta ₂ O ₃ , TiO ₂ is exemplified. In particular, by using the ALD method, a thin film having a very high film density can be produced and damage in the process can be suppressed.

  The film thickness of the first insulating protective film 57 needs to be a thin film enough to ensure the protection performance of the piezoelectric element 56, and at the same time as thin as possible so as not to inhibit the deformation (displacement) of the diaphragm 55. There is a need. The thickness of the first insulating protective film 57 is preferably in the range of 20 [nm] to 100 [nm]. This is because if the thickness is greater than 100 [nm], the deformation (displacement) amount of the diaphragm 55 is reduced, resulting in the recording heads 38 of the liquid ejection heads 38K, 38C, 38M, and 38Y having low ejection efficiency. On the other hand, when the thickness is smaller than 20 [nm], the function of the piezoelectric element 56 as a protective layer is insufficient, so that the performance of the piezoelectric element 56 is deteriorated as described above.

  At this time, a configuration in which the first insulating protective film 57 has two layers is also conceivable. In this case, in order to increase the thickness of the second insulating protective film, a configuration in which the second insulating protective film is opened in the vicinity of the second electrode 56C so as not to significantly disturb the vibration of the diaphragm 55 can be cited. .

In this case, as the second insulating protective film, any oxide, nitride, carbide or a composite compound thereof can be used, and SiO ₂ generally used in semiconductor devices can also be used. .

  Arbitrary methods can be used for forming the two-layer first insulating protective film 57, and examples thereof include a CVD method and a sputtering method. It is preferable to use a CVD method capable of forming an isotropic film in consideration of the step coverage of the pattern forming portion such as the electrode forming portion. The film thickness of the second insulating protective film needs to be a film thickness that does not cause dielectric breakdown by the voltage applied between the first electrode 56A and the third electrode 58. That is, it is necessary to set the electric field strength applied to the first insulating protective film 57 within a range not causing dielectric breakdown. Furthermore, in consideration of the surface properties of the base of the first insulating protective film 57 and the formation of the contact holes 57a and 57b, the thickness of the first insulating protective film 57 needs to be 200 [nm] or more. Preferably it is 500 [nm] or more.

[Third electrode 58, fourth electrode 59, and electrode pads 61, 62]
The material of the third electrode 58 and the fourth electrode 59 and the electrode pads 61 and 62 is any of silver (Ag) alloy, copper (Cu), aluminum (Al), gold (Au), Pt, and Ir. It is preferable that it is the metal electrode material which consists of these. As a method for manufacturing these electrodes, a sputtering method or a spin coating method is used, and then a desired pattern is obtained by photolithography etching or the like.

  The film thickness is preferably in the range of 0.1 [μm] to 20 [μm], and more preferably in the range of 0.2 [μm] to 10 [μm]. If the thickness is smaller than this range, the resistance increases, and it becomes impossible to flow a sufficient current to the electrode, and the ejection of the droplet 50A from the nozzle 53 becomes unstable. If it is larger than this range, the process time becomes longer.

  Further, for example, the contact resistance of the contact holes 57a and 57b in the case of forming 10 [μm] × 10 [μm] is 10 [Ω] or less with respect to the first electrode 56A, and with respect to the second electrode 56C. 1 [Ω] or less is preferable. More preferably, it is 5 [Ω] or less for the first electrode 56A and 0.5 [Ω] or less for the second electrode 56C. This is because if it exceeds this range, a sufficient current cannot be supplied, and a malfunction may occur when the droplet 50A is ejected from the nozzle 53.

[Second insulating protective film 60]
The function as the second insulating protective film 60 is a passivation layer that functions as a protective layer for the third electrode 58 for the common electrode and the fourth electrode 59 for the individual electrodes. As shown in FIGS. 4 and 5, the second electrode 56C and the first electrode 56A are removed except for the contact hole 60a serving as a lead portion for the second electrode 56C and the lead portion for the first electrode 56A (not shown). Coating. Thereby, an inexpensive Al or an alloy material containing Al as a main component can be used as the electrode material. As a result, the recording head 38 with low cost and high reliability can be obtained.

  As the material of the second insulating protective film 60, any inorganic material or organic material can be used, but it is necessary to use a material with low moisture permeability. Examples of the inorganic material include oxides, nitrides, and carbides, and examples of the organic material include polyimide, acrylic resin, and urethane resin.

However, an organic material is not suitable for patterning because it needs to be a thick film. Therefore, it is preferable to use an inorganic material that can exhibit a wiring protection function with a thin film. In particular, it is preferable to use Si ₃ N ₄ on the Al wiring because it is a proven technology for semiconductor devices. The film thickness is preferably 200 [nm] or more, and more preferably 500 [nm] or more. This is because, when the film thickness is thin, a sufficient passivation function cannot be exhibited, and thus disconnection due to corrosion of the wiring material occurs, thereby reducing the reliability of the ink jet.

Further, a structure having openings in the piezoelectric element 56 and the surrounding diaphragm 55 is preferable. This is the same reason that the region corresponding to the individual liquid chamber of the first insulating protective film 57 is thinned. As a result, the recording head 38 with high efficiency and high reliability can be obtained. Since the piezoelectric element 56 is protected by the insulating protective films 57 and 60, when the contact hole 60a of the second insulating protective film 60 is formed, a photolithography method and dry etching can be used. In addition, the area of each electrode pad 61, 62 is preferably 50 × 50 [μm ² ] or more, and more preferably 100 × 300 [μm ² ] or more. If it is less than this value, sufficient polarization processing cannot be performed, and there is a possibility that problems such as failure to obtain sufficient characteristics for deformation (displacement) deterioration after continuous driving may occur.

  Next, a more specific example of the present embodiment will be described.

<Example 1>
First, Example 1 is demonstrated based on above-mentioned FIG.4 and FIG.5.
In Example 1, a thermal oxide film (film thickness: 1 [μm]) was formed on a 6-inch silicon wafer as the substrate 52, and the first electrode 56A was formed.

  First, as an adhesion film for the first electrode 56A, a titanium film (film thickness 30 [nm]) was formed by a sputtering apparatus, and then thermally oxidized at 750 [° C.] using RTA. Subsequently, a platinum film (film thickness 100 [nm]) as a metal film and an SrRuO film (film thickness 60 [nm]) as an oxide film were formed by sputtering. Film formation was performed at a substrate heating temperature of 550 [° C.] during the sputtering film formation.

  Next, a piezoelectric film 55 was formed on the upper layer of the substrate 52. First, a solution adjusted to Pb: Zr: Ti = 114: 53: 47 was prepared, and a film was formed by spin coating.

  For the synthesis of a specific precursor coating solution, lead acetate trihydrate, isopropoxide titanium and isopropoxide zirconium were used as starting materials. Crystal water of lead acetate was dissolved in methoxyethanol and then dehydrated. The lead amount is excessive with respect to the stoichiometric composition. This is to prevent crystallinity deterioration due to so-called lead loss during heat treatment. Then, isopropoxide titanium and isopropoxide zirconium are dissolved in methoxyethanol, the alcohol exchange reaction and the esterification reaction are advanced, and the PZT precursor solution is synthesized by mixing with the methoxyethanol solution in which the lead acetate is dissolved. did.

  The PZT concentration of this PZT precursor solution was 0.5 mol / liter. Using this PZT precursor solution, a film was formed by spin coating, and after the film formation, drying at 120 [° C.] and thermal decomposition at 500 [° C.] were performed. After thermal decomposition treatment of the third layer, crystallization heat treatment (temperature 750 [° C.]) was performed by RTA (rapid heat treatment). At this time, the film thickness of PZT was 240 [nm]. This process was performed a total of 8 times (24 layers) to obtain a PZT film thickness of about 2 [μm].

  Next, the second electrode 56C was formed. First, as the oxide film of the second electrode 56C, a SrRuO film (film thickness 40 [nm]) and a metal film Pt film (film thickness 125 [nm]) were formed by sputtering. Thereafter, a photoresist (TSMR8800) manufactured by Tokyo Ohka Kogyo Co., Ltd. was used to form a film by spin coating, a resist pattern was formed by a normal photolithography method, and then an ICP etching apparatus manufactured by Samco Co., Ltd. was used. A pattern as shown was prepared.

Next, as the first insulating protective film 57, an Al ₂ O ₃ film having a thickness of 50 [nm] was formed using an ALD method. At this time, TMA (Sigma Aldrich) was used as the Al raw material, and O ₃ generated by an ozone generator was used as the O raw material, and the film formation was advanced by alternately laminating Al and O. Thereafter, as shown in FIGS. 3 and 4, contact hole portions 57a and 57b were formed by etching.

  Thereafter, Al was sputtered as the third electrode 58, the fourth electrode 59, and the electrode pads 61 and 62, and was patterned by etching.

Then, as the second insulating protective film 60, Si ₃ N ₄ was formed to a thickness of 500 [nm] by plasma CVD, and the piezoelectric element 56 was manufactured. At this time, 25 areas of 30 [mm] × 10 [mm] in a 6-inch silicon wafer were arranged.

  In the present embodiment, the piezoelectric element driving is performed on the actuator substrate 70 formed of the entire composite laminated substrate having various electrodes including the substrate 25 and the piezoelectric element 56 after the second insulating protective film 60 is formed. An IC (not shown) is mounted.

  Since the mounting space can be reduced by directly mounting the piezoelectric element driving IC on the actuator substrate 70, the number of actuator substrates 70 that can be taken from a 6-inch silicon wafer can be increased, and the cost can be reduced. It becomes possible.

  Conventionally, when performing polarization processing by corona discharge on the actuator substrate 70, the periphery of the individual electrode pad 62 at the end of the actuator substrate 70 is covered with the second insulating protective film 60 or another insulating film. It has been broken. For this reason, the electric field is concentrated on the end of the second electrode 56 </ b> C that is an individual electrode constituting the drive channel of the piezoelectric element 56, that is, on the individual electrode pad 62. As a result, the potential difference between the individual electrode pads 62 is increased, causing a dielectric breakdown between the upper and lower electrodes, and causing a problem that the polarization process proceeds too much locally.

  On the other hand, the actuator substrate 70 of the first embodiment has a configuration as shown in FIG. That is, short-circuited in the same row in the vicinity of the individual electrode pad 62 at the end of the second electrode 56C, which is an individual electrode for connecting the terminals of the piezoelectric element driving IC (both not shown). A Vcom wiring 71 is integrally formed as an electrode.

  On the actuator substrate 70, dummy electrodes 72 are formed on the same row of second electrodes 56C as individual electrodes. The dummy electrode 72 is connected to the Com wiring 73.

  The Com wiring 73 is a wiring connected to the first electrode 56 </ b> A that is a common electrode of the piezoelectric element 56. The Com wiring 73 is formed on the actuator substrate 70 via the diaphragm 55 and has a resistance of 1E7 to 1E10 [Ω] with respect to the liquid chamber forming surface. As a result, charge concentration on the individual electrode pad 62 can be suppressed, and dielectric breakdown in the piezoelectric element 56 of the droplet discharge portion (drive channel) can be prevented.

  The Vcom wiring 71 has a resistance of 1E7 to 1E10 [Ω] with respect to the liquid chamber forming surface of the actuator substrate 70. If the shorted Vcom wiring 71 is formed in the periphery of the individual electrode pad 62, the effect can be exhibited. At this time, the Vcom wiring 71 is formed in the same row as the individual electrode pads 62 at a pitch equal to or less than twice the pitch of the individual electrode pads 62, that is, at a position not exceeding twice the individual electrode pads 62. desirable.

  Here, if the shorted Vcom wiring 71 is formed at a position more than twice the individual electrode pad 62, charge concentration on the individual electrode pad 62 occurs, and the effect of forming the shorted Vcom wiring 71 is diminished. End up.

  In such a configuration, when performing polarization processing by corona discharge on the actuator substrate 70, the stage 74 on which the actuator substrate 70 is set is connected to the GND 75 as shown in FIG. The electric charge flowing into the Vcom wiring 71 due to the corona discharge leaks to the GND 75 with a predetermined time constant through the resistor 76 of 1E7 to 1E10 [Ω]. As a result, electric field concentration on the individual electrode pad 62 can be prevented. The resistor 76 can apply a predetermined voltage waveform as long as it is 1E7 [Ω] or more in actual driving. On the other hand, if the high resistance side of the resistor 76 is set to 1E10 [Ω] or more, the injected charge does not leak to the GND 75, so that the potential of the electrode having the same potential increases, and the charge of the corona discharge becomes the individual electrode pad 62. Therefore, the specifications are as described above.

  In the first embodiment, the shorted electrodes short-circuited in the same column are formed by the Vcom wiring 71. The Vcom wiring 71 is a wiring for supplying a driving waveform for driving the piezoelectric element 56 to the piezoelectric element driving IC. Further, a short electrode pad 77 is formed in the Vcom wiring 71 by providing a pad opening. In this way, by forming the short-circuited electrodes short-circuited in the same column with the Vcom wiring 71, the actuator substrate 70 can be effectively used. In addition, coupled with the fact that the Vcom wiring 71 can be reduced in resistance, the chip size of the piezoelectric element 56 can be reduced, and a great effect can be obtained in terms of actuator characteristics and cost.

  Note that bumps (not shown) are formed on the second electrode 56 </ b> C and the dummy electrode 72, which are individual electrodes constituting the drive channel of the piezoelectric element 56. The bump is preferably a gold bump, and the cost can be reduced by using a gold stud bump. The reason why the gold stud bump is used is that the bump formation area is smaller than the area of the actuator substrate 70, and the gold plating bump by the plating method increases the cost of process and material loss.

  In addition, the effect of forming bumps on the second electrode 56C, which is an individual electrode, before polarization processing by corona charging or the like will be described. As the piezoelectric element driving IC is mounted at a high density, the area of the second electrode 56C, which is an individual electrode, becomes very small.

  On the other hand, in the polarization process by corona charging or the like, it is necessary to inject a predetermined charge into the second electrode 56C that is an individual electrode and the first electrode 56A that is a common electrode. Therefore, bumps are formed on the second electrode 56C, which is an individual electrode, so that the surface area of the second electrode 56C can be increased and stable polarization processing can be performed.

In order to compare the effects of the above-described configurations, as shown in Table 1, polarization treatment experiments with three configurations were performed. The structure of the charging apparatus using corona discharge used in this experiment employs a scorotron method, a voltage of 9 [kV] is applied to a corona wire of φ50 [μm], and 2.5 to the grid electrode. A voltage of [kV] was applied and the treatment was performed for 30 seconds. Evaluation items are
(1) Presence or absence of dielectric breakdown between the upper and lower electrodes of the piezoelectric element 56 by corona discharge polarization treatment (2) Polarization amount difference (Pr-Pini)
It is.

  In this way, the Vcom wiring 71 is continuously formed as a short-circuit electrode on the same row of the individual electrode pads 62 at the same pitch as the individual electrode pads 62. In the polarization process, the electric charge charged in the short-circuit electrode pad 77 formed on the Vcom wiring 71 leaks to the GND 75 while being controlled by the predetermined resistance 76. Therefore, the individual electrode pad 62 can be held at a predetermined potential, and the electric field can be prevented from concentrating on the individual electrode pad 62.

  By this polarization processing, the positive and negative coercive electric field in the polarization amount-electric field characteristic of the piezoelectric element 56 has a characteristic of shifting to the negative side with respect to the center of 0 (V), and the change in the polarization characteristic in actual driving can be reduced. it can.

<Example 2>
In recent years, with the aim of improving the printing speed and the like, the increase in the number of nozzles has been demanded, and accordingly, the length of the head has been increasing.

  In order to realize this increase in the number of nozzles and the length of the head, it is necessary to mount the piezoelectric element driving ICs on the same row. Therefore, in order to secure the mounting accuracy and mounting area of the piezoelectric element driving IC, the distance between the second electrodes 56C, which are the individual electrodes of the connecting portion of the piezoelectric element driving IC, is increased. For this reason, it is known that electric charges concentrate on the second electrode 56C, which is an individual electrode of the connecting portion that becomes the discontinuous portion, during the polarization treatment by corona charging or the like, and thus dielectric breakdown is likely to occur.

  Also in the present configuration shown in FIG. 11, in the vicinity of the second electrode 56C, which is an individual electrode between drive channels to which individual piezoelectric element driving ICs are connected, specifically, on the same line, in the same column. The Vcom wiring 71 short-circuited to the other is formed. The electrode having the same potential is connected between the chips of the piezoelectric element 56 that is imposed on the wafer, and has a resistance of 1E10 [Ω] or more with respect to the liquid chamber forming surface of the actuator substrate 70. Yes.

  Therefore, the Vcom wiring 71 short-circuited in the same column is subjected to polarization processing by corona discharge in a state where the Vcom wiring 71 is connected to the GND 75 by a resistor 76 of 1E10 [Ω] or less, thereby Charge concentration on the individual electrode pads 62 can be prevented. After the polarization process, the short circuit part is cut by chip division or the like.

<Example 3>
As shown in FIG. 13, the Vcom wiring 71 and the Com wiring 73 that are short-circuited to each other in the same column have the same potential.

  The Com wiring 73 is formed on the actuator substrate 70 via the diaphragm 55 and has a resistance of 1E7 to 1E10 [Ω] with respect to the liquid chamber forming surface. Then, by setting the Vcom wiring 71 to the same potential as the Com wiring 73, the charge injected during the polarization process by corona discharge is leaked to the GND 75, so that the charge is concentrated on the individual electrode pad 62 at the end. Can be prevented.

  Specifically, mutually short-circuited short-circuit electrodes in the same column are formed by the Vcom wiring 71, and at the time of polarization processing, they are short-circuited by connecting with the Com wiring 73 and the short-circuiting wire 78. After the polarization processing, the short-circuiting wire 78 is connected. The same effect as described above can be obtained by cutting.

  Note that the method for separating the short-circuited states of both the Vcom wiring 71 and the Com wiring 73 is not limited to the above. For example, it is short-circuited in a state where it is impositioned on a wafer which is the same substrate, and by adopting a configuration that can cut wiring on the chip dividing surface etc. when dividing processing by a dicing process etc., there is no cost increase realizable.

  Further, the Vcom wiring 71 and the Com wiring 73 are formed adjacent to each other, and at the time of cutting, the short circuit portion is cut by laser processing, so that the degree of freedom in wiring design can be increased, the chip can be downsized, and the number of impositions As the number of actuators increases, the cost of the actuator chip can be reduced.

  As described above, in the present embodiment, the step of performing the polarization process by injecting the electric charge generated by the corona discharge into the Vcom wiring 71 which is the short-circuited electrodes short-circuited in the same column, Processing is performed in a later process than processes such as interlayer film formation and lead wiring formation.

  Specifically, after a thermal history process exceeding 300 ° C., polarization processing is performed by injecting electric charges generated by corona discharge into the Vcom wirings 71 short-circuited in the same column. .

  At this time, the polarization process is performed by injecting charges generated by corona discharge through the individual electrode pads 62 so that the processes can be performed collectively at the wafer level. Therefore, it is possible to manufacture the piezoelectric element 56 that changes in displacement with respect to the drive pulse voltage, and it is possible to discharge the droplet 50A of the liquid 50 such as ink liquid from the nozzle 53 satisfactorily. Furthermore, stable droplets 50A can be ejected from the nozzles 53, and the piezoelectric elements 56 can be arranged with high density.

  As described above, the image forming apparatus 1 includes the recording head 38 including the liquid discharge heads 38K, 38C, 38M, and 38Y according to the present invention. As a result, the size and cost can be reduced, and the number of nozzles 53 that can be ejected with the same size of the liquid ejection heads 38K, 38C, 38M, and 38Y can be increased, so that further high-speed printing is possible.

  Further, the liquid discharge heads 38K, 38C, 38M, and 38Y according to the present embodiment can inject a uniform charge amount into the individual electrode pads 62 at the end. As a result, the discharge characteristics of the droplets 50A from the nozzles 53 can be satisfactorily maintained, the stable discharge characteristics of the droplets 50A can be secured, and the piezoelectric elements 56 can be arranged at high density. it can.

  As described above, the liquid discharge heads 38 </ b> K, 38 </ b> C, 38 </ b> M, and 38 </ b> Y are stored in the liquid chamber 51 that stores the liquid 50, the plurality of nozzles 53 that communicate with the liquid chamber 51 and discharge the liquid 50, and the liquid chamber 51. An actuator substrate 70 that forms a piezoelectric element 56 as an actuator that pressurizes the liquid 50 and discharges the droplet 50A from the nozzle 53, and the actuator substrate 70 has individual electrodes of the piezoelectric element 56 arranged in a row. In addition, the Vcom wiring 71 is formed as a short-circuited electrode short-circuited in the same column in the vicinity of the individual electrode pad 62 disposed at the end of the second electrode 56C, which is an individual electrode. Therefore, it is possible to inject a uniform charge amount into the individual electrode pad 62 at the end of the second electrode 56C, which is an individual electrode, and thereby the ejection characteristics of the droplet 50A. It is possible to satisfactorily hold, it is possible to ensure the discharge characteristics stable droplets, moreover, it is possible to arrange the piezoelectric elements in high density.

  As described above, the image forming apparatus according to the present invention can inject a uniform charge amount into the individual electrode pad at the end of the second electrode, which is an individual electrode. The discharge characteristics can be maintained well, the stable discharge characteristics of the droplets can be secured, and the piezoelectric elements can be arranged at high density. It is also useful for general image forming apparatuses.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 38K Liquid discharge head 38C Liquid discharge head 38M Liquid discharge head 38Y Liquid discharge head 38 Recording head 50 Liquid 50A Droplet 53 Nozzle 56 Piezoelectric element 56A 1st electrode (common electrode)
56C Second electrode (individual electrode)
58 Third electrode (common electrode)
59 Fourth electrode (individual electrode)
62 Individual electrode pad 70 Actuator substrate 77 Short-circuit electrode pad

Japanese Patent No. 3365485 Japanese Patent No. 4218309 Japanese Patent No. 3019845 JP 2004-202849 A

Claims (9)

A liquid chamber storing liquid;
A plurality of nozzles communicating with the liquid chamber and discharging liquid;
An actuator substrate forming a piezoelectric element as an actuator for pressurizing the liquid stored in the liquid chamber and discharging the liquid from the nozzle;
With
The actuator substrate has individual electrodes of the piezoelectric elements formed in a row, and short-circuit electrodes short-circuited to each other in the same row in the vicinity of the electrode pads for individual electrodes arranged at the end portions of the individual electrodes. Formed ,
The liquid discharge head according to claim 1, wherein the short-circuited electrodes short-circuited in the same row have a resistance of 1E7 to 1E10 [Ω] with respect to the liquid chamber forming surface of the actuator substrate . A liquid chamber storing liquid;
A plurality of nozzles communicating with the liquid chamber and discharging liquid;
An actuator substrate forming a piezoelectric element as an actuator for pressurizing the liquid stored in the liquid chamber and discharging the liquid from the nozzle;
With
The actuator substrate has individual electrodes of the piezoelectric elements formed in a row, and short-circuit electrodes short-circuited to each other in the same row in the vicinity of the electrode pads for individual electrodes arranged at the end portions of the individual electrodes. Formed,
The liquid discharge head according to claim 1, wherein the short-circuited electrodes short-circuited in the same row are part of the Vcom wiring. Claim 1 or the mutual short-circuit electrode pads shorted to within the same column in the vicinity of the individual electrode pads at the end of each column, characterized in that it is arranged below 2 times the pitch of the individual electrode pads The liquid discharge head according to claim 2 . The polarization of the piezoelectric element - liquid of any one of claims 1 to 3 coercive field of positive and negative in an electric field characteristics characterized in that it shifts to the negative side with respect to 0 (V) center Discharge head. The shorted electrodes that are short-circuited to each other in the same column are Vcom wires, and are short-circuited to the Com wires during the polarization treatment by corona discharge, and the short-circuit state between the Vcom wires and the Com wires is released after the polarization treatment. The liquid ejection head according to claim 2 , wherein the liquid ejection head is provided. 6. The liquid ejection head according to claim 5 , wherein a wiring for short-circuiting both the Vcom wiring and the Com wiring on the chip dividing surface is cut. Wherein a Vcom line are adjacent and the Com wiring, the liquid discharge head according to claim 5 or claim 6 characterized in that it has a cut surface by laser processing. Comprising a liquid discharge head according to any one of claims 1 to 7, a plurality of actuators are formed on the same substrate, mutually shorted the short-circuit electrode in the same column are short-circuited on the wafer, the actuator Polarizing treatment is performed by corona discharge in a state where an electrode having a resistance of 1E10 [Ω] or more with respect to the liquid chamber forming surface of the substrate is connected to GND with a resistance of 1E9 [Ω] or less. A method for polarization treatment of a liquid discharge head. A liquid ejection apparatus comprising the liquid ejection head according to any one of claims 1 to 7.

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