Patent Publication Number: US-6709089-B2

Title: Ink-jet head, method of manufacture thereof, and ink-jet printer

Description:
This application is a continuation of application Ser. No. 09/367,926 filed on Aug. 20, 1999, which is International Application PCT/JP99/00025 filed on Jan. 8, 1999, which designated the U.S., claims the benefit thereof and incorporates the same by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an ink-jet head for ejecting ink drops to paper or the like to perform printing, a method of manufacturing the same, and an ink-jet recording apparatus on which the ink-jet head is mounted. 
     BACKGROUND ART 
     Recently, a very small actuator has been demanded for use in an ink-jet recording apparatus for the purpose of high-speed and high-precision printing with the development of a multi-nozzle structure and for the purpose of miniaturization of the apparatus. To this end, there is an ink-jet recording apparatus using static electricity for an actuator (for example, JP-A-6-71882). The ink-jet head is characterized in that an electrostatic actuator is formed of parallel plate electrodes, so that the actuator can be miniaturized and a multi-nozzle structure can be realized. 
     FIGS. 10 and 11 are a sectional view and a plan view, respectively, of a conventional ink-jet head driven by an electrostatic actuator. The ink-jet head shown in FIG.  10  and FIG. 11 has a lamination structure in which an electrode glass substrate  100 , a diaphragm substrate  200 , and a nozzle plate  300  are laid on the top of one another and bonded with each other. An ink supply port  104  is formed in the electrode glass substrate  100 , and ink  400  is supplied from the ink supply port  104  to a reservoir  204  formed in the diaphragm substrate  200 . The ink  400  is equally distributed to a plurality of cavities  203  through orifices  302  defined by the nozzle plate  300  and recess portions of the diaphragm substrate  200 . The lower surface of each of the cavities  203  is constituted by a transformable diaphragm  201 . This diaphragm  201  faces an individual electrode  101  through an air gap and an insulating film  200  for preventing short-circuit so as to constitute an electrostatic actuator. A common electrode  205  is disposed on the diaphragm substrate  200 . An voltage is applied between the diaphragm  201  and the individual electrode  101  through this common electrode  205 , so that an electrostatic attractive force is generated to transform the diaphragm  201  downward. After that, an ink drop  401  is ejected from a nozzle  301  by the pressure due to the spring force of the diaphragm  201  which is generated when the applied voltage is removed. 
     In the above-mentioned electrostatically driven ink-jet head, it is regarded as being preferable, from the point of practical view, to drive the electrostatic actuator by a driving voltage of 100 V or less. In order to drive the electrostatic actuator by a driving voltage of 100 V or less, the distance between the insulating film  202  of the electrostatic actuator and the individual electrode  101  is formed accurately to be in a range of from 2,000 to 3,000 angstroms. To this end, a diaphragm substrate constituted by a silicon single-crystal substrate having a bonded surface mirror-finished with high precision was required to be bonded, by anode-bonding, directly with an electrode glass substrate constituted by a borosilicate glass substrate and provided with a step by etching. In this case, however, there is a problem that such a silicon substrate mirror-finished with high precision is expensive and hard to obtain. In addition, in order to obtain required strength, it is necessary to use a thin silicon single-crystal substrate and reduce the height of partitions between respective cavities because the thickness of the partitions are reduced in accordance with the high density of nozzles. However, it is extremely difficult to handle such a thin silicon single-crystal substrate, and particularly there is another problem that it is difficult to increase the size of the substrate. 
     By the way, there is a method in which etching of a sacrificial layer is used to produce such a narrow gap as described above. For example, a method in which a sacrificial layer is. formed and then the sacrificial layer is removed by etching so as to form air gaps is proposed in JP-A-10-510374, page 8 and U.S. Pat. No. 54,596, in FIG. 2. However, all the air gaps are provided for electrostatically modulating positions of the reflecting surface of a light valve. In addition, all the air gaps are made open, unlike closed air gaps formed between insulating film and individual electrodes of an electrostatic actuator of an ink-jet head. It is therefore impossible to apply the technique disclosed in the above-mentioned publications or the like as it is to the manufacturing of an ink-jet head. 
     DISCLOSURE OF THE INVENTION 
     It is an object of the present invention to provide an ink-jet head and a manufacturing method thereof, in which a substrate low in cost, easy to handle and large in size can be used to improve the productivity. 
     It is another object of the present invention to provide an ink-jet recording apparatus mounted with an ink-jet head manufactured by the above-mentioned manufacturing method. 
     (1) One aspect of the present invention is an ink jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein the air gaps are formed by sacrificial layer etching. In the present invention, since the air gaps are formed by sacrificial layer etching, the air gaps can be formed with high precision, for example, in a range of from 2,000 to 3,000 angstroms, so that it is possible to drive the ink-jet head by a driving voltage of 100 V or less. In addition, it is not necessary to use a silicon single-crystal substrate, so that the substrate can be made layer in size. Therefore, the ink-jet head can be suitably adapted for a line printer or the like having a multi-nozzle. 
     (2) Another aspect of the present invention is a method of manufacturing an ink-jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein the air gaps are formed by sacrificial layer etching. In the present invention, since a sacrificial layer can be formed in a thin film process such as vapor deposition, CVD, or the like, a silicon single-crystal substrate mirror-finished with high precision is not required and electrostatic actuators can be formed only in such a thin film process. It is therefore possible to use a large-sized glass substrate, and thereby improve the productivity. 
     (3) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the individual electrodes are formed on a substrate; an insulating film, a sacrificial layer and a diaphragm layer are subsequently formed so as to cover the individual electrodes; and window portions are formed in the diaphragm layer in part of predetermined positions where support portions of the diaphragms are to be located to perform the sacrificial layer etching through the window portions. Since the window portions are formed at places corresponding to the support portions of the diaphragms in such a manner and no aperture portion is formed in the diaphragms themselves, there is no deterioration in the properties of the diaphragms. In addition, it will go well if etching liquid permeates the sacrificial layer in its short-side direction through the window portions. Therefore, there is an advantage that it is easy for the etching liquid to permeate the sacrificial layer. The insulating layer, the sacrificial layer and the diaphragm layer may be formed in the order of the insulating layer, the sacrificial layer and the diaphragm layer, or in the order of the sacrificial layer, the insulating layer and the diaphragm layer. 
     (4) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (3), wherein slit portions are formed in the sacrificial layer and the diaphragm layer in positions where the window portions in the predetermined positions are not formed. Since the support portions are formed in the slit portions as they are, the support portions become so firm that the diaphragms can be supported stably. 
     (5) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (3), wherein a plurality of window portions are dispersively formed for each of the air gaps. Since the window portions are dispersively formed, the sacrificial layer etching is performed uniformly. In addition, although the portions where the window portions are located are weak and apt to lift in the manufacturing process, the strength is increased by dispersively forming the window portions, so that the ink-jet head can be manufactured easily. 
     (6) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the window portions are closed to form cavity partitions after the sacrificial layer etching. As a result, it is possible to obtain a closed structure efficiently, and it is possible to prevent ink from soaking into the electrostatic actuators. 
     (7) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the diaphragms are formed of a laminated film constituted by a conductive film and a film having a tensile force. which is a film-forming stress. It is therefore possible to prevent the diaphragms from sagging. It is possible to prevent the diaphragms from touching the lower layer (individual electrodes) when the sacrificial layer etching is finished. 
     (8) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (7), wherein the diaphragms are formed by laminating, for example, an Ni layer and a silicon nitride layer on each other. The diaphragms come in contact with the electrodes when the electrostatic actuators are driven. However, there is no fear of abrasion since it is the Ni layer with high hardness that comes in contact with the electrodes. In addition, the silicon nitride layer has enough tension so as not to produce sagging in the diaphragms. 
     (9) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the diaphragms are formed of a conductive film having a tensile force which is a film-forming stress. It is therefore possible to prevent the diaphragms from sagging even if the diaphragms are of a single layer. It is possible to prevent the diaphragms from touching the lower layer (individual electrodes) when the sacrificial layer etching is finished. 
     (10) A still further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (9), wherein the diaphragms are formed by depositing, for example, Pt. Since the diaphragms can be formed of a single layer which is a Pt layer with high hardness and high tension, it is possible to simplify the manufacturing process. 
     (11) Another aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the sacrificial layer is formed of an organic film, and the sacrificial layer etching is performed by dry etching. By the dry etching, the management of the manufacturing becomes not difficult, unlike wet etching, so that it is possible to simplify the process. 
     (12) A further aspect of the present invention is a method of manufacturing an ink-jet head based on the above-mentioned manufacturing method (2), wherein the independent electrodes are formed on an electrode glass substrate; the independent electrodes are covered with an insulating film; a sacrificial layer is formed on the insulating film; a diaphragm layer is formed on the sacrificial layer; window portions are formed in the diaphragm layer in predetermined positions where support portions of the diaphragms are to be located between the individual electrodes; the sacrificial layer is etched through the window portions to thereby form an electrostatic actuator structure; Ni is subsequently deposited all over the surface and thereafter patterned to thereby form partition base portions to close the window portions; cavity partitions are formed on the partition base portions by Ni electrocasting; and then a nozzle plate is bonded on the cavity partitions. In the present invention, since the sacrificial layer can be formed in a thin film process such as vapor deposition, CVD, or the like, a silicon single-crystal substrate mirror-finished with high precision is not required, and electrostatic actuators can be formed only in such a thin film process. It is therefore possible to use a large-sized glass substrate and thereby improve the productivity. Further, it is possible to obtain a closed structure efficiently, and there is such an advantage that it is possible to prevent ink from soaking into the electrostatic actuators, etc. 
     (13) A still further aspect of the present invention is an ink-jet recording apparatus equipped with an ink-jet manufactured by any one of the above-mentioned ink-jet head manufacturing methods (2) to (12). Since the ink-jet head manufactured by any one of the ink-jet head manufacturing methods (2) to (12) has no limitation in the material of a substrate, a glass substrate may be used. It is therefore possible to use a large-sized glass substrate, so that it is possible to manufacture a high-performance printer at a low price. 
     (14) Another aspect of the present invention is an ink-jet recording apparatus equipped with an ink-jet head for a line printer manufactured by any one of the above-mentioned ink-jet head manufacturing methods (2) to (12). Since the ink-jet head manufactured by any one of the ink-jet head manufacturing methods (2) to (12) has no limitation in the material of a substrate, a glass substrate may be used. It is therefore possible to use a large-size glass substrate, so that it is possible to form a multi-nozzle. As a result, it is possible to manufacture a line printer at a low price. 
     (15) A further aspect of the present invention is an ink-jet head comprising a plurality of nozzle holes, ejection chambers independent of each other and communicating with the nozzle holes respectively, electrically conductive diaphragms constituting parts of the respective ejection chambers, and individual electrodes facing the diaphragms through air gaps respectively, and ejecting ink in the ejection chambers toward recording paper through the respective nozzle holes by applying voltages between the diaphragms and the individual electrodes to thereby transform the diaphragms, wherein an insulating film is formed on the individual electrodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an ink-jet head manufactured by a manufacturing method according to Embodiment 1 of the present invention. 
     FIG. 2 is a sectional view of the ink-jet head taken on line  2 — 2  in FIG.  1 . 
     FIG. 3 is a manufacturing process diagram of the ink-jet head according to Embodiment 1 of the present invention. 
     FIG. 4 is a perspective view of the ink-jet head in the manufacturing process of FIG.  3 . 
     FIG. 5 is a manufacturing process diagram of an ink-jet head according to Embodiment 2 of the present invention. 
     FIG. 6 is an explanatory diagram showing an example of peripheral mechanism of the ink-jet head manufactured through the manufacturing process of FIG. 3 or FIG.  5 . 
     FIG. 7 is an outline view of an ink-jet recording apparatus in which the mechanism of FIG. 6 is incorporated. 
     FIG. 8 is an explanatory diagram showing another example of peripheral mechanism of the ink-jet head manufactured through the manufacturing process of FIG. 3 or FIG.  5 . 
     FIG. 9 is an outline view of an ink-jet recording apparatus (line printer) in which the mechanism in FIG. 8 is incorporated. 
     FIG. 10 is a plan view of an ink-jet head driven by a conventional electrostatic actuator. 
     FIG. 11 is a sectional view of the ink-jet head driven by the conventional electrostatic actuator. 
    
    
     THE BEST MODE FOR CARRYING-OUT THE INVENTION 
     Embodiment 1 
     FIG. 1 is a plan view of an ink-jet head manufactured by a manufacturing method according to Embodiment 1 of the present invention, and FIG. 2 is a sectional view of the same ink-jet head taken on line  2 — 2 . This ink-jet head has a basic structure substantially the same as that of the ink-jet head shown in FIGS. 10 and 11. Therefore, the structure will be described below while paying attention to portions directly concerned with the present invention. This ink-jet head has an electrode glass substrate  100 , individual electrodes  101  disposed on this electrode glass substrate  100  and covered with an insulating film  202  of silicon dioxide, diaphragms  201  facing the individual electrodes  101  through air gaps  250  respectively, ink cavities  203 , cavity partition base portions  213 , cavity partitions  214 , and a nozzle plate  300 . Although window portions  212  for sacrificial layer etching are shown in FIG. 1, these window portions  212  are formed in the manufacturing process but they are not present after manufacturing. Accordingly, the window portions  212  in FIG. 1 are illustrated merely to indicate their positions which are located at predetermined intervals in the longitudinal direction of the cavity partition base portions  213  and the cavity partitions  214 . 
     FIG. 3 is a diagram showing a manufacturing process of the ink-jet head shown in FIGS. 1 and 2. 
     (a) First, Cr and Au are deposited to a thickness of 50 angstroms and a thickness of 1,000 angstroms, respectively, on the electrode glass substrate  100  by sputtering, and Cr and Au are then patterned by photolithography to thereby form the individual electrodes  101 . 
     (b) Next, silicon dioxide is deposited to a thickness of 1,000 angstroms by CVD so as to form the insulating film  202  which covers the individual electrodes  101 . Thereafter, Al is vapor-deposited to a thickness of 2,000 angstroms on the insulating film  202  so as to form the sacrificial layer  110 . 
     (C) Here, slits  211  are provided in the sacrificial layer  110  so as to be located between the individual electrodes  101 . With these slits  211 , in the step which will be described later, one of the widthwise end portions of each diaphragm  201  can be formed directly on the electrode glass substrate  100  so as to form a support portion of the diaphragm  201 . The above-mentioned process is not given to positions corresponding to the window portions  212  for sacrificial layer etching (see FIG. 1) so that the slits  211  are not formed there. 
     (d) Next, Ni which will form a common electrode  205  of the electrostatic actuators is sputtered to a thickness of 1,000 angstroms on the sacrificial layer  110 . After that, a silicon nitride film  210  is deposited to a thickness of 7,000 angstroms by CVD so as to produce the diaphragms  201  constituted by the common electrode  205  and the silicon nitride film  210 . At this time, the end portions (on the side where the slits  211  are provided) of the diaphragms  201  are formed directly on the electrode glass substrate  100  so as to cover the sacrificial layer  110 . After the diaphragms  201  are produced, the silicon nitride film  210  and the Ni film (common electrode)  205  are etched corresponding to the slit portions  211  and the window portions  212  for sacrificial layer etching. Here, the reason why the silicon nitride film  210  is used is to prevent the diaphragms  201  from sagging by using the fact that the tensile force of the silicon nitride film is its film-forming stress. 
     (e) After the window portions  212  are opened, an aqueous solution of 32% HCl and 30% hydrogen peroxide is circulated from these window portions  212  at room temperature so as to etch the Al sacrificial layer  110 . Here, if transparent electrode material such as ITO is used for the individual electrodes  101  instead of Cr/Au, the conditions of etching the sacrificial layer  110  can be observed. In the stage where this sacrificial layer etching has been finished, air gaps  250  formed by the sacrificial layer etching are made to communicate with the outside only through the window portions  212 . 
     (f) After the sacrificial layer etching, Ni is again deposited all over the surface to a thickness of 3,000 angstroms in order to close the window portions  212 , and a Ni film  213   a  is formed. The air gaps  250  are closed in this step. 
     (g) After the Ni film is formed, the partition base portions  213  are formed by patterning. The air gaps  250  are enclosed in this process. That is, each air gap  250  is enclosed with the corresponding partition base portion  213  at the window portion  212  and with the corresponding diaphragm  201  over the rest portion. Therefore, each air gap  250  is closed out. 
     (h) Next, resist  410  is applied to a thickness of 100 microns. After that, the resist  410  is cut out like slits perpendicularly to reach the partition base portions  213  by anisotropic dry etching. 
     (i) The cavity partitions  214  are formed respectively on the partition base portions  213  by Ni electrocasting, and the resist  410  is removed. The conditions at this time are as shown in FIG.  4 . The positions corresponding to the window portions  212  are located at predetermined intervals in the longitudinal direction of the diaphragms  201 , and formed in such a state that the leading edge portions of the diaphragms  201  are cut out partially. 
     (j) The nozzle plate  300  of stainless steel in which nozzles  301  are provided is bonded onto the cavity partitions  214  by epoxy resin adhesive so as to form an ink-jet head in FIG.  1  and FIG.  2 . 
     Embodiment 2 
     FIG. 5 is a manufacturing process diagram of an ink-jet head according to Embodiment 2 of the present invention. Embodiment 2 differs from Embodiment 1 in that each diaphragm  201  is constituted by a single layer having electrical conductivity. 
     (a) to (c) The steps up to forming of a sacrificial layer  110  are the same as those in Embodiment 1 (the same as (a) to (c) of FIG.  3 ). 
     (d) After the sacrificial layer  110  is formed, Pt having film-forming stress which is a tensile force is deposited to a thickness of 5,000 angstroms so as to form diaphragms  201 . 
     (e) After Pt is deposited, slit portions  211  and window portions  212  are formed by dry etching with carbon tetrafluoride. 
     (f) The Al sacrificial layer  110  is etched. 
     (g) After the Al sacrificial layer  110  is etched and removed, Ni is deposited to a thickness of 3,000 angstroms to close the window portions  212 . After that, partition base portions  213  are formed by patterning. 
     (h) Subsequently, cavity partitions  214  may be formed by Ni electrocasting in the same manner as that in Embodiment 1. However, a nozzle plate  300  constituted by a silicon single-crystal substrate and provided with cavity partitions  214  formed integrally by anisotropic dry etching is bonded to the partition base portions  213  with epoxy resin adhesive, in this Embodiment 2. 
     Embodiment 3 
     A manufacturing method in Embodiment 3 of the present invention will be described. In this Embodiment 3, the sacrificial layer  110  in Embodiment 2 is changed from an Al film to an organic film, and removed by oxygen plasma. Since oxygen plasma is used, there appears no sagging in diaphragms  201  due to the surface tension of etching liquid, unlike wet etching. Accordingly, there are no etching leftovers caused by the failure in circulating the etching liquid. In addition, cleansing and drying after etching becomes unnecessary, so that it is possible to simplify the process. 
     Embodiment 4 
     FIG. 6 is an explanatory diagram showing an example of a peripheral mechanism of an ink-jet head manufactured in the manufacturing process in any one of Embodiments 1 to 3. This ink-jet head  50  is attached to a carriage  51 , and this carriage  51  is attached to guide rails  52  movably. The position of the carriage  51  is controlled in the width direction of paper  54  fed out by a roller  53 . This mechanism in FIG. 6 is incorporated in an ink-jet recording apparatus  55  shown in FIG.  7 . 
     Embodiment 5 
     FIG. 8 is an explanatory diagram showing another example of a peripheral mechanism of an ink-jet head manufactured through the manufacturing process in any one of Embodiments 1 to 3. In this Embodiment 5, an ink-jet head  60  for a line printer is constituted. Since a glass substrate is used for a substrate so that necessary constituent parts can be piled up thereon as described above, it is possible to manufacture a line printer ink-jet head having a multi-nozzle arrangement with 1,000 nozzles or more if a large-sized glass substrate is used. In FIG. 8, data lines  61  and ink pipes  62  are led to the ink-jet head  60 . Rollers  63  are disposed on front and rear sides of the ink-jet head  60 . By the ink-jet head  60 , one-line&#39;s printing is performed simultaneously on paper  54  fed out by the rollers  53 . This mechanism of FIG. 8 is incorporated in an ink-jet recording apparatus  65  shown in FIG.  9 .