An ink-jet head, a substrate for an ink-jet head, and an ink-jet apparatus

Abstract: A substrate for an ink-jet head provides a protective layer which can assuredly cover electrothermal transducers even if the thickness of the layer is small. A thin intermediate layer (4) is provided between a heating resistive layer (2) and electrodes (3). The thin intermediate layer is an insulator on heating portions of the heating resistive layer. According to such a configuration, the life of the heating resistive layer becomes long, and occurrence of burnt deposits is suppressed. Since steps at portions where the thin intermediate layer is provided are small, an excellent film quality can be obtained even if the thickness of the protective layer is relatively small, and an excellent protective property is obtained.

Description: This invention relates to an ink-jet head for performing printing by forming a very small droplet by discharging a printing liquid, such as ink or the like, utilizing thermal energy, and causing the droplet to adhere to a printing material, such as paper or the like. The invention also relates to a substrate for such an ink-jet head, and to an ink-jet apparatus. An ink-jet head used in an ink-jet printing method of utilizing thermal energy for forming a very small droplet to be discharged generally includes a heating resistive layer provided on a substrate, respective pairs of electrodes provided on the heating resistive layer and electrically connected thereto, and respective heating portions of the heating resistive layer provided between the pairs of electrodes. Thermal energy is generated from selected ones of the heating portions by passing current through the heating resistive layer from the corresponding pairs of electrodes. The state of ink in an ink channel is changed by the thermal energy, and printing is performed by discharging the ink onto a printing material by the pressure caused by volume expansion of bubbles in this changed state. The configurations of such ink-jet heads are disclosed, for example, in Japanese Patent Laid-Open Application (Kokai) Nos. 55-128467 (1980) and 59-194866 (1984). FIGS. 7(A) and 7(B) are schematic diagrams illustrating the general configuration of such an ink-jet head. In FIGS. 7(A) and 7(B), reference numeral 1 represents a substrate for an ink-jet head on which a heating resistive layer 2 and pairs of electrodes 3 are provided. The heating resistive layer 2 for converting electric energy into thermal energy is provided on the surface of the insulating ink-jet-head substrate 1, and the pairs of electrodes 3 for passing current through the heating resistive layer 2 are provided on the heating resistive layer 2. The pairs of electrodes 3 comprise individual electrode portions for selectively driving segments of the heating resistive layer 2, and a common electrode portion for distributing current. The thermal energy is generated from a heating portion 9 provided between the corresponding pair of electrodes. A protective layer 6, for preventing the heating resistive layer 2 and the electrodes 3 from galvanic corrosion, and destruction due to cavitation, is provided on the heating resistive layer 2 including the heating portion 9 and the electrodes 3. Reference numeral 8 represents discharging ports for discharging ink. The heating portions 9 are provided in an ink channel 7 communicating with the discharging ports 8. Reference numeral 10 represents an ink chamber, communicating with the ink channel 7, for supplying the ink channel 7 with ink. The ink channel 7 and the ink chamber 10 are configured by recesses provided in a top plate 11, and the ink-jet-head substrate 1. An ink supply port 12 for supplying the ink chamber 10 with ink is formed in the top plate 11. In such a conventional ink-jet head, the thickness of the protective layer is about 1 - 3 µm in order to maintain its covering property in steps produced by the electrodes in the vicinity of the heating portions. However, when such a thick protective layer is present on the heating portions, loss of thermal energy due to the protective layer is unnegligible. Hence, in order to obtain a temperature necessary for bubbling ink on the surface of the protective layer, the temperature at the heating portion must be higher than the temperature on the surface of the protective layer. This is one of the reasons for accelerating degradation of the heating resistive layer. Furthermore, when the temperature at the heating portion is increased, bubbling of ink occurs in the midst of application of thermal energy. Hence, energy supplied after the bubbling causes a rapid increase in the surface temperature of the protective layer, to decompose organic components of the ink, thereby producing burnt deposits on the protective layer. In order to solve such problems, ink-jet heads in which a thinner protective layer is provided on heating portions have been devised. For example, in Japanese Patent Laid-Open Application (Kokai) No. 62-103148 (1987), a configuration is disclosed in which only portions of a protective layer, provided on electrothermal transducers, present on heating portions are thinned by performing half etching in dry etching. In Japanese Patent Laid-Open Application (Kokai) No. 63-191646 (1988), a configuration is disclosed in which an oxide film is formed by performing anodic oxidation of heating portions of a heating resistive layer, and an organic insulating film is formed on electrodes so that at least a part of the oxide film is exposed. However, in the first configuration, since the thickness of the protective layer on the heating portions is determined by the state of the etching, it is difficult to strictly control the thickness of the protective layer on the heating portions. As a result, discharging characteristics of respective ink-jet heads may slightly differ from one another. In the second configuration, in addition to the fact that it is difficult to control the thickness of the oxide film on the heating portions as in the first configuration, only materials having an excellent protective property obtained by performing anodic oxidation of the heating resistive layer can be used. Document EP-A-0 396 315 shows a substrate for an ink-jet head comprising the features of the preamble of the attached claim 1. Particularly, this document discloses in its fig. 3 an ink jet head substrate with a cavitation protecting layer and an insulative layer. That is, this document shows two layers with the purpose of protecting and insulating the heating resistive layer. Further, document US-A-4 951 063 shows a thermal ink jet head with a specific heating element structure comprising a resistive layer, an isolation layer of silicon nitride and a cavitational stress protecting layer of tantalum. Furthermore, document EP-A-0 596 705 shows a heater element for a thermal ink jet head comprising a resistive layer on top of a substrate. The resistive layer in turn is covered by a dielectric isolation layer and a tantalum layer. Finally, document "Patent Abstracts of Japan, vol. 004, No. 125 (M-030), September 3, 1980 & JP 55 082 678 A" discloses a thermal head with a heater layer on a substrate, whereon a stress relieving layer consisting of an oxide or nitride and a wear resistant layer are provided. The present invention has been made in consideration of the above-described problems. It is an object of the present invention to provide a substrate for an ink-jet head in which the thickness of a protective layer on heating portions can be strictly controlled to a desired value, and a desired material can be used as a heating resistive layer. Further, according to the present invention a substrate for an ink-jet head is provided which has an excellent protective property even if the thickness of a protective layer on heating portions is small. Still further, according to the present invention a substrate for an ink-jet head is provided in which the life of a heating resistive layer is long, and few burnt deposits are produced on a protective layer. The solutions to achieve these objectives are as set out in the appended independend claims. Advantageous modifications are as set forth in tha appended dependend claims. Details of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. FIG. 1 is a schematic diagram illustrating the surrounding structure of a heating portion of an ink-jet head according to a first embodiment of the present invention; FIGS. 2(A) and 2(B) are schematic diagrams illustrating a substrate for an ink-jet head according to a second embodiment of the present invention; FIG. 3 is a schematic diagram illustrating a substrate for an ink-jet head according to a third embodiment of the present invention; FIG. 4 is a schematic diagram illustrating a substrate for an ink-jet head according to a fourth embodiment of the present invention; FIGS. 5(A) through 5(C) are schematic diagrams illustrating production processes of the substrate for an ink-jet head according to the fourth embodiment; FIG. 6 is an external perspective view illustrating an ink-jet apparatus (IJA) which mounts an ink-jet head obtained according to the present invention as an ink-jet-head cartridge (IJC); and FIGS. 7(A) and 7(B) are schematic diagrams illustrating the configuration of a general ink-jet head. Preferred embodiments of the present invention will now be described in detail with reference to the drawings. First Embodiment FIG. 1 is a schematic diagram illustrating the surrounding structure of an ink-jet head according to a first embodiment of the present invention. The present invention provides the configuration of a protective layer which can assuredly cover electrothermal transducers even if the thickness of the layer is small. That is, a thin intermediate layer is provided between a heating resistive layer and electrodes, and the thin intermediate layer on heating portions comprises an insulator. According to this configuration, the life of the heating resistive layer is increased, and occurrence of burnt deposits is suppressed. Since steps at portions where the thin intermediate layer is provided are small, an excellent film quality is obtained even if the thickness of the layer is small, and therefore an excellent protective property is obtained. In FIG. 1, reference numeral 2 represents a heating resistive layer for generating thermal energy utilized for discharging ink. Reference numeral 3 represents interconnection conductors, serving as electrodes, provided on the heating resistive layer 2 and electrically connected thereto, for passing current through the heating resistive layer 2. Reference numeral 9 represents a heating portion where the interconnection conductor 3 is not provided on the heating resistive layer 2. Thermal energy is generated from the heating portion 9. An thin intermediate layer 4 is provided between the heating resistive layer 2 and the interconnection conductor 3. In the present embodiment, Si 3 N 4 is used for the thin intermediate layer 4. The important point in the present embodiment is that the portion of the thin intermediate layer 4 present on the heating portion 9 is an insulator. The thin intermediate layer 4 covers the heating portion 9 and contacts both of the heating resistive layer 2 and the interconnection conductors 3. Hence, if the portion of the thin intermediate layer 4 present on the heating portion 9 is a conductor, current flows through the thin intermediate layer 4, and therefore the heating portion 9 does not operate. The thin intermediate layer 4 may comprise an insulator, or a metal or the like whose portion on the heating portion 9 is processed to be an insulator. When using an insulator for the thin intermediate layer 4, it is necessary to provide throughholes 5 for electrically connecting the heating resistive layer 2 to the interconnection conductors 3. Any insulating or metallic materials having cavitation-resistive property may be used for the thin intermediate layer 4. For example, insulators, such as Si 3 N 4 and SiC, and metals, such as Ta and Fe, may be used. Since the thin intermediate layer 4 is provided on the heating resistive layer 2, it can be formed in a state in which substantially no steps are produced. Accordingly, a layer having an excellent film property can be formed even if the thickness of the layer is small. In consideration of the covering property and the effect of provision of a thin film, the thickness of the thin intermediate layer 4 is preferably 200 - 700 nm. When using a metal for the thin intermediate layer 4, it is preferable to perform heat treatment in an oxygen or nitrogen atmosphere for making a portion on the heating portion 9 an insulator. That is, particularly when using Al for the electrodes 3, the growth of an oxide or nitride layer is prevented by Al 2 O 3 or AlN formed on Al by the heat treatment, and nitriding or oxidation stops at a thickness of about 100 nm. On the other hand, the portion of the thin intermediate layer 4 on the heating portion 9 is completely subjected to nitriding or oxidized. Accordingly, by performing insulating processing by heat treatment in an oxygen or nitrogen atmosphere, a conductive portion having a substantially constant thickness can be obtained in an electrode portion even if the time period of the heat treatment is not controlled. It is, of course, possible to perform insulating processing according to anodic oxidation or the like by controlling the time period of the insulating processing. When using an insulator for the thin intermediate layer 4, a protective layer 6 is provided on the interconnection conductors 3. The protective layer 6 is formed, for example, by coating an organic resin. At that time, the protective layer 6 is provided except on the heating portion 9. However, since no problem arises even if the resin is coated on a boundary portion between the interconnection conductors 3 and the heating portion 9 because the temperature of the boundary portion is lower than the temperature at a central portion, it is preferable, from the viewpoint of reliability, to coat the resin on portions of the heating portion 9 in the proximity of the interconnection conductors 3 (boundary portions) in order to assuredly protect the interconnection conductor 3. It is also possible to perform insulating processing only for the interconnection conductor 3 as when using a metal for the thin intermediate layer 4. Next, a description will be provided of a method of manufacturing an ink-jet head according to the first embodiment. A Ta/Ir layer having a thickness of 100 nm was formed on a Si substrate 1 having a thermally oxidized film, serving as a heat storage layer, by sputtering. The formed layer was etched to a desired pattern, as shown in FIG. 1, to form the heating resistive layer 2. Thereafter, a Si 3 N 4 film, serving as the thin intermediate layer 4, having a thickness of 300 nm was formed on the heating resistive layer 2 by sputtering, and through-holes 5 for electrically connecting the interconnection conductors 3, serving as the electrodes, to the heating resistive layer 2 were formed by etching. Then, an Al film having a thickness of 500 nm was formed on the thin intermediate layer 4 by sputtering. The formed layer was etched to a desired pattern, as shown in FIG. 1, to form the interconnection conductors 3. Then, the protective layer 6 was formed by coating Photoneece (trade name: made by Toray Industries, Inc.), serving as an organic resin, on the interconnection conductor 3 to a thickness of 1 µm followed by provisional curing at 80 - 90 °C, patterning the cured film to a desired shape, and performing complete curing of the film at 350 - 450 °C. A top plate having recesses for an ink channel and an ink chamber was connected onto the ink-jet-head substrate obtained in the above-described manner, and thus the ink-jet head of the present embodiment was obtained. Printing was performed using the ink-jet head of the present embodiment. No disconnection due to galvanic corrosion or the like of the heating resistive layer was observed. The same degree of reliability as in conventinal heads was obtained, and occurrence of burnt deposits on the heating portions could be reduced. Second Embodiment In the first embodiment, the heating resistive layer 2 is provided also under the interconnection conductor 3, serving as the electrodes. In a second embodiment of the present invention, however, a heating resistive layer is provided only at portions which serve as heating portions. FIGS. 2(A) and 2(B) are schematic diagrams illustrating a substrate for an ink-jet head according to the second embodiment. The ink-jet head is formed as in the first embodiment except that the pattern of the heating resistive layer is changed as shown in FIGS. 2(A) and 2(B). A thin intermediate layer may be provided only on a heating portion, as shown in FIG. 2(B). In this case, it is unnecessary to provide throughholes. Printing was performed using the ink-jet head of the present embodiment. No disconnection due to galvanic corrosion or the like of the heating resistive layer was observed. The same degree of reliability as in conventinal heads was obtained, and occurrence of burnt deposits on the heating portions could be reduced. Third Embodiment A description will now be provided of a method for manufacturing an ink-jet head, in which a thin intermediate layer 4 comprises two layers made of an insulator and a metal, according to a third embodiment of the present invention. FIG. 3 is a schematic diagram illustrating the ink-jet head according to the third embodiment. A HfB 2 film having a thickness of 100 nm was formed on an Si substrate 1 having a thermally oxided film, serving as a heat storage layer, by sputtering. The formed film was etched to a desired pattern, as shown in FIG. 3, to form a heating resistive layer 2. Thereafter, a Si 3 N 4 film having a thickness of 300 nm was formed on the heating resistive layer 2 by sputtering as a first thin intermediate layer 4a. Then, throughholes 5 for electrically connecting the interconnection conductors 3, serving as electrodes, to the heating resistive layer 2 were formed by etching. Then, a Ta film having a thickness of 200 nm was formed on the Si 3 N 4 layer 4a by sputtering, and portions in the vicinity of boundaries between the formed film and the interconnection conductors 3, and portions between the patterns of the heating resistive layer 2 were etched, to form a second thin intermediate layer 4b. Then, an Al film having a thickness of 500 nm was formed on the second thin intermediate layer 4b by sputtering. The formed film was etched to a desired pattern, as shown in FIG. 3, to form the interconnection conductors 3. Then, a protective layer 6 made of an organic resin was coated on the interconnection conductors 3 to a thickness of 1 µm, and the organic resin present on the heating portions was removed. A top plate having recesses for an ink channel and an ink chamber was connected onto the ink-jet-head substrate obtained in the above-described manner, and thus the ink-jet head of the present embodiment was obtained. Printing was performed using the ink-jet head of the present embodiment. No disconnection due to galvanic corrosion or the like of the heating resistive layer was observed. The same degree of reliability as in conventinal heads was obtained, and occurrence of burnt deposits on the heating portions could be reduced. Fourth Embodiment Next, a description will be provided of a method for forming an ink-jet head, in which a metal is used for a thin intermediate layer, according to a fourth embodiment of the present invention. FIG. 4 is a schematic diagram illustrating a substrate for an ink-jet head according to the fourth embodiment. FIGS. 5(A) through 5(C) are diagrams illustrating production processes of the substrate for an ink-jet head according to the fourth embodiment. A Ta/Ir film having a thickness of 100 nm was formed on a Si substrate 1 having a thermally oxided film, serving as a heat storage layer, by sputtering. The formed film was etched to a desired pattern to form a heating resistive layer 2 (FIG. 5(A)). Then, a Ta film having a thickness of 200 nm was formed on the heating resistive layer 2 by sputtering, to form a thin intermediate layer 4. Thereafter, an Al film having a thickness of 500 nm was formed by sputtering on the thin intermediate layer 4. The formed film was etched to a desired pattern to form interconnection conductors 3 (FIG. 5(B)). Then, the substrate was left in the atmosphere at 500 °C for 10 - 30 hours. The surface of the Ta film between the patterns of the interconnection conductors 3 on the heating portions 9 and the surface of the Al film were oxidized to form oxide films (FIG. 5(C)). The Ta film, serving as the thin intermediate layer 4, is completely converted into a Ta 2 O 5 film. However, since the growth of an oxide layer is prevented by an Al 2 O 3 film formed on the Al film, serving as the interconnection conductors 3, the oxidation stops when the thickness of the Al film becomes about 100 nm. Thus, the Ta film between the patterns of the interconnection conductors 3 on the heating portions 9 is oxidized. Hence, the Ta/Ir film of the heating resistive layer 2 is not dissolved even if it is immersed in ink. A top plate having recesses for an ink channel and an ink chamber was connected onto the ink-jet-head substrate obtained in the above-described manner, and thus the ink-jet head of the present embodiment was obtained. Printing was performed using the ink-jet head of the present embodiment. No disconnection due to galvanic corrosion or the like of the heating resistive layer was observed. The same degree of reliability as in conventinal heads was obtained, and occurrence of burnt deposits on the heating portions could be reduced. Fifth Embodiment An ink-jet head was manufactured in the same manner as in the fourth embodiment except that the heating resistive layer and the thin intermediate layer were changed from the Ta/Ir film and the Ta film to a HfB 2 film and a Fe film, respectively, and insulating processing was performed in a nitrogen atomsphere. Printing was performed using the ink-jet head of the present embodiment. No disconnection due to galvanic corrosion or the like of the heating resistive layer was observed. The same degree of reliability as in conventinal heads was obtained, and occurrence of burnt deposits on the heating portions could be reduced. A description will now be provided of an example of an ink-jet apparatus which can mount an ink-jet head according to the present invention. FIG. 6 is an external perspective view illustrating an example of an ink-jet apparatus (IJA) which mounts an ink-jet head obtained according to the present invention as an ink-jet-head cartridge (IJC). In FIG. 6, reference number 20 represents an ink-jet-head cartridge including nozzles for discharging ink while facing a printing surface of printing paper, serving as a printing medium, fed onto a platen 24. Reference numeral 16 represents a carriage 16 for holding the IJC 20. The carriage 16 is connected to a part of a driving belt 18 for transmitting the driving force of a driving motor 17, and is slidable along two guide shafts 19A and 19B disposed in parallel with each other. Hence, the IJC 20 can reciprocate over the entire width of the printing paper. A head recovery device 26 is disposed at one end of a moving path of the IJC 20, for example, at a position facing a home position. Capping of the IJC 20 is performed by the driving force of a motor 22 via a transmission mechanism 23. By performing capping when, for example, terminating printing, the IJC 20 is protected. A blade 30 made of a silicone rubber, serving as a wiping member, is disposed at a side of the head recovery device 26. The blade 30 is held by a blade holding member 30A in the form of a cantilever, and operates by the motor 22 and the transmission mechanism 23, as the head recovery device 26, so as to be engageable with a discharging surface of the IJC 20. At an appropriate timing during a printing operation of the IJC 20, or after discharge recovery processing using the head recovery device 26, the blade 30 is protruded in the moving path of the IJC 20. Dew condensation, wetting, dust or the like on the discharging surface of the IJC 20 is wiped in accordance with the moving operation of the IJC 20. The individual components shown in outline in the drawings are all well known in the ink-jet head, ink-jet-head substrate and ink-jet apparatus arts and their specific construction and operation are not critical to the operation or the best mode for carrying out the invention.

Claims: A substrate for an ink-jet head, said substrate comprising: a protected heating resistive layer (2) for generating thermal energy utilized for discharging a liquid; respective pairs of electrodes (3) electrically connected to said heating resistive layer (2) thereon; and heating portions (9) of said heating resistive layer (2) provided between corresponding pairs of electrodes (3), thermal energy being generated from said heating portions (9) by passing current through said heating resistive layer (2) from the electrodes; characterized in that said heating resistive layer (2) is protected by a single insulative and thin intermediate layer (4) having a cavitation-resistive property. A substrate according to claim 1, wherein the electrodes (3) are electrically connected to said heating resistive layer (2) through throughholes (5) provided in said thin intermediate layer (4). A substrate according to claim 2, wherein said thin intermediate layer (4) comprises Si 3 N 4 . A substrate according to claim 1, wherein the surfaces of the electrodes (3) are insulated. A substrate according to claim 1, wherein a protective layer (6) is provided on the electrodes (3) except said heating portions (9). An ink-jet head comprising: a substrate according to claim 1; discharging ports for discharging the liquid; an ink channel communicating with said discharging ports; an ink chamber for supplying said ink channel with ink. An ink-jet head according to claim 6, wherein the electrodes (3) are electrically connected to said heating resistive layer (2) through throughholes (5) provided in said thin intermediate layer (4). An ink-jet head according to claim 7, wherein said thin intermediate layer (4) comprises Si 3 N 4 . An ink-jet head according to claim 6, wherein the surfaces of the electrodes (3) are insulated. An ink-jet head according to claim 6, wherein a protective layer (6) is provided on the electrodes (3) except said heating portions (9). An ink-jet apparatus comprising: an ink-jet head according to claim 6; and conveying means (22, 23) for conveying a printing material onto which the liquid is discharged.

Inventors: SUZUKI TAKUMI, SUZUKI, TAKUMI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1996
Main classification: B41J2
IPC codes: B41J2