Abstract:
A high-density ink-jet printhead, in which a plurality of nozzles, through which ink is ejected, are arrayed on an ink supply manifold in a plurality of rows is provided, wherein the ink-jet printhead includes a substrate; hemispherical ink chambers at a surface of the substrate; a manifold for supplying ink to the ink chambers; ink channels to be in flow communication with the ink chambers and the manifold; a nozzle plate monolithically formed with the substrate; nozzles formed on the nozzle plate, each formed to correspond to a center of each of the ink chambers; heaters formed on the nozzle plate, each having a ring shape and encircling a corresponding nozzle; and electrodes, positioned on the nozzle plate and electrically connected to the heaters, for applying current to the heaters, wherein the nozzles are arrayed on the manifold in at least in three rows, and preferably in five rows.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bubble jet type ink-jet printhead. More particularly, the present invention relates to a high-density ink-jet printhead in which a plurality of nozzles, through which ink is ejected, are arrayed on an ink supply manifold in a plurality of rows, thereby increasing the number of nozzles per unit area. 
     2. Description of the Related Art 
     In general, ink-jet printheads are apparatuses that eject a fine droplet of printer ink on a desired position of a paper to print an image containing one or more predetermined colors. To eject ink onto the paper, an ink-jet printer generally adopts an electro-thermal transducer method that ejects ink onto the paper by generating a bubble in ink using a heat source (this method is called a bubble jet type), or an electromechanical transducer method that ejects ink onto the paper using a change in the volume of ink due to the deformation of a piezoelectric body. 
     In a bubble-jet type ink ejection mechanism, as mentioned above, when power is applied to a heater including a resistance heating element, ink adjacent to the heater is rapidly heated to about 300° C. Heating the ink generates bubbles, which grow and swell, and thus apply pressure in the ink chamber filled with the ink. As a result, ink adjacent to a nozzle is ejected from the ink chamber through the nozzle. 
     There are multiple factors and parameters to consider in making an ink-jet printhead having an ink ejecting unit in a bubble-jet mode. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of undesirable satellite ink droplets that usually accompany an ejected main ink droplet must be avoided during the printing process. Third, cross-talk between adjacent nozzles, from which ink is not ejected, must be avoided, when ink is ejected from one nozzle, or when an ink chamber is refilled with ink after ink is ejected. For this purpose, ink back flow, i.e., when ink flows in a direction opposite to the direction in which ink is ejected, should be prevented. Fourth, for high-speed printing, the refilling period after ink is ejected should be as short a period of time as possible to increase the printing speed. That is, the driving frequency of the printhead should be high. 
     The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely related to and affected by the structure and design, e.g., the relative sizes of ink chamber, ink passage, and heater, etc., as well as by the formation and expansion shape of the bubbles. 
     FIG. 1A illustrates an exploded perspective view of a structure of an ink ejector of a conventional bubble jet type ink-jet printhead according to the prior art. FIG. 1B illustrates a cross-sectional view for explaining a process of ejecting an ink droplet from a conventional bubble jet type ink-jet printhead. FIG. 1C illustrates a plan view of the arrangement of a plurality of nozzles in the conventional inkjet printhead of FIG.  1 A. 
     A conventional bubble jet type ink-jet printhead shown in FIGS. 1A through 1C includes a substrate  10 , barrier walls  38  that are formed on the substrate  10  and that form ink chambers  26 , which are filled with ink  49 , heaters  12  formed in the ink chambers  26 , and a nozzle plate  18  having nozzles  16  from which an ink droplet  49 ′ is ejected. The ink  49  is supplied to the ink chambers  26  via ink channels  24  from ink supply manifolds  14  in flow communication with an ink storage unit (not shown). As a result, the nozzles  16 , which are in flow communication with the ink chambers  26 , are also filled with the ink  49  due to capillary action. In the above ink-jet printhead, a plurality of heaters  12  and a plurality of ink chambers  26  are formed to correspond to the plurality of nozzles  16 , and are arranged in a row, adjacent to each of the ink supply manifolds  14 . 
     In operation of the above ink-jet printhead, the heaters  12  are supplied with current and heated to form bubbles  48  in the ink  49  filled in the ink chambers  26 . Then, the bubbles  48  expand and put pressure on the ink  49  filled in the ink chambers  26 , thereby ejecting an ink droplet  49 ′ to the outside via the nozzles  16 . Then, the ink  49  flows through the ink channels  24  to fill the ink chambers  26 . 
     A process of manufacturing a conventional printhead having the above structure, however, is complicated because the nozzle plate  18  and the substrate  10  are individually made and then bonded together. In particular, the nozzle plate  18  may be misaligned with respect to the substrate  10  during manufacture. 
     Additionally, as previously mentioned, the plurality of nozzles  16 , heaters  12  and ink chambers  26  are arranged on each manifold  14  in a row, but may be arranged at both sides of each manifold  14  in a row. With such a structure, however, there is a limitation in increasing the number of nozzles per unit area, i.e., the density of a nozzle. Accordingly, it is difficult to realize a high-density ink-jet printhead that prints quickly and has high resolution. 
     SUMMARY OF THE INVENTION 
     In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a high-density ink-jet printhead in which hemispherical ink chambers are formed that satisfy the above conditions, and a plurality of nozzles are arranged on each ink supply manifold in a plurality of rows, thereby increasing the density of nozzles. 
     To provide the above feature, there is provided an ink-jet printhead including a substrate; a plurality of ink chambers formed in a hemispherical shape at a surface of the substrate and filled with ink; a manifold formed at a rear surface of the substrate, the manifold for supplying ink to the plurality of ink chambers; a plurality of ink channels each formed at a bottom of each of the plurality of ink chambers to be in flow communication with the manifold; a nozzle plate monolithically formed with the substrate; a plurality of nozzles formed on the nozzle plate, each formed to correspond to a center of each of the plurality of ink chambers; a plurality of heaters formed on the nozzle plate, each of the plurality of heaters having a ring shape and encircling a corresponding one of the plurality of nozzles; and a plurality of electrodes positioned on the nozzle plate and electrically connected to the plurality of heaters, the plurality of electrodes applying current to the heaters. 
     In an embodiment of the present invention, the plurality of nozzles are arrayed on the manifold in at least three rows. In a preferred embodiment of the present invention, the plurality of nozzles are arrayed on the manifold in five rows. 
     Preferably, the substrate is a silicon wafer and the nozzle plate is a silicon oxide layer formed by oxidizing a surface of the silicon wafer. 
     Preferably, each of the plurality of nozzles may have a nozzle guide extending in the depth direction of the ink chamber, at each edge of the plurality of nozzles. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features and advantages of the present invention will become readily apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1A illustrates an exploded perspective view of an ink ejector of a conventional bubble jet type ink-jet printhead; 
     FIG. 1B illustrates a cross-sectional view for explaining a process of ejecting an ink droplet from the ink-jet printhead of FIG. 1; 
     FIG. 1C illustrates a plan view of the conventional ink-jet printhead of FIG. 1A showing an arrangement of a plurality of nozzles; 
     FIG. 2 illustrates a plan view of an ink-jet printhead according to a preferred embodiment of the present invention; 
     FIG. 3 illustrates a cross-sectional view of the ink-jet printhead of FIG. 2, taken along line A-A′; 
     FIG. 4 illustrates a plan view of a unit ink ejector of the ink-jet printhead of FIG. 2; 
     FIG. 5 illustrates a cross-sectional view of the unit ink ejector of FIG. 4, taken along line B-B′; and 
     FIGS. 6A and 6B illustrate cross-sectional views of the mechanism of ejecting ink from an ink ejector having the structure shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 2001-66747, filed Oct. 29, 2001, and entitled: “High-Density Ink-jet Printhead having Multi-Arrayed Structure,” is incorporated by reference herein in its entirety. 
     Hereinafter, the present invention will be described in detail by describing a preferred embodiment of the present invention with reference to the accompanying drawings. Like reference numerals refer to like elements throughout the drawings. In the drawings, the shape and thickness of an element may be exaggerated for clarity and convenience. Further, it will be understood that when a layer is referred to as being on another layer or “on” a substrate, it may be directly on the other layer or on the substrate, or intervening layers may also be present. 
     FIG. 2 illustrates a plan view of an ink-jet printhead according to a preferred embodiment of the present invention. FIG. 3 illustrates a cross-sectional view of the ink-jet printhead of FIG. 2, taken along line A-A′. 
     Referring to FIGS. 2 and 3, in the ink-jet printhead according to a preferred embodiment of the present invention, five rows of ink ejectors  100  are arranged in a zigzag pattern on an ink supply manifold  112 , which is illustrated by dotted lines. Bonding pads  102  that are connected to each ink ejector  100  and are to be bonded with wires are positioned at both sides of each ink ejector  100 . Additionally, the manifold  112  is in flow communication with an ink storage unit (not shown) filled with ink. 
     The manifold  112  is formed at a rear surface of a substrate  110 , and a nozzle plate  120  having a plurality of nozzles  122  is formed on an opposing surface of the substrate  110 . Each one of a plurality of heaters  130  encircles a corresponding one of the plurality of nozzles  122 , which are formed on the nozzle plate  120 . Also, hemispherical ink chambers  114 , each one corresponding to one of the plurality of nozzles  122 , are formed on the substrate  110 . A plurality of ink channels  116  are formed to pass through a bottom of each ink chamber  114 , which are in flow communication with the manifold  112 . 
     The plurality of nozzles  122  are arrayed to be positioned on one manifold  112  in at least three rows, and preferably in five rows, as shown in FIG.  3 . Further, the plurality of nozzles  122  may be freely arranged according to a printing algorithm for realizing an image. Since the plurality of nozzles  122  have a two-dimensional multi-array structure, it is possible to increase the number of nozzles per unit area, thereby enhancing the speed of printing and realizing a high-density ink-jet printhead having high resolution. 
     FIG. 4 illustrates a plan view of a unit ink ejector  100  of FIG.  2 . FIG. 5 illustrates a cross-sectional view of the vertical structure of the unit ink ejector  100  of FIG. 4, taken along line B-B′. Referring to FIGS. 4 and 5, an ink chamber  114 , which is filled with ink, is formed on a substrate  110  of the ink ejector  100 , and a manifold  112 , which supplies ink to the ink chamber  114 , is formed at a rear surface of the substrate  110 . In addition, a manifold  112  and an ink channel  116 , which connects the ink chamber  114  and the manifold  112 , are formed at a center of a bottom of the ink chamber  114 . Preferably, the ink chamber  114  is hemispherical shaped. 
     Also preferably, the substrate  110  is formed of a silicon material that is used in fabricating an integrated circuit. For instance, the substrate  110  may be a silicon substrate of a crystal orientation of (100) and a thickness of about 500 μm. Use of a silicon wafer as the substrate  110  facilitates mass-production of the ink ejectors  100 . The ink chamber  114  may be formed by isotropically etching the surface of the substrate  110  that is exposed via the plurality of nozzles  122 , which are formed on a nozzle plate. Formation of the plurality of nozzles  122  will be explained later. The manifold  112  is formed by anisotropically etching the rear surface of the substrate  110  or by etching the rear surface of the substrate  110  to have a predetermined inclination. Here, the ink chamber  114  is formed in a hemispherical shape having a depth and a radius of about 20 μm. Alternatively, the ink chamber  114  may be formed by anisotropically etching the substrate  110  to a predetermined depth and then, isotropically etching the etched substrate  110 . The ink channel  116  may be formed by anistropically etching a center of a bottom of the ink chamber  114  via the nozzle  122 . The diameter of the ink channel  116  is the same as or slightly smaller than that of the nozzle  122 , thereby preventing ejected ink from flowing back into the ink channel  116 . The diameter of the ink channel  116  affects the speed of refilling ink after the ejecting of the ink, and thus must be precisely controlled. 
     At a surface of the substrate  110 , a nozzle plate  120  having the plurality of nozzles  122  is formed to provide the upper walls of the ink chamber  114 . When the substrate  110  is formed of silicon, the nozzle plate  120  may be a silicon oxide layer that is formed by oxidizing the silicon substrate  110 . More particularly, a silicon wafer is wet or dry-oxidized in an oxidation furnace, thereby forming an oxide layer on the silicon substrate  110 , and thus the nozzle plate  120 . 
     On the nozzle plate  120 , a heater  130  is formed to encircle each nozzle  122 . The heaters  130  are used to generate bubbles in the ink. Preferably, these heaters  130  have a shape of a round-shaped ring and are formed of resistant heating elements, such as a polysilicon layer doped with impurities. Here, the impurity-doped polysilicon layer may be deposited to a predetermined thickness with a source gas such as phosphorous (P) as an impurity by a low-pressure chemical vapor deposition (LPCVD). The thickness of the polysilicon layer deposited is determined so as to have a proper resistance value in consideration of the width and length of the heater  130 . The polysilicon layer, which is deposited on the entire surface of the nozzle plate  120 , is patterned to a round ring shape by a photolithographical process using a photomask and photoresist and an etching process using a photoresist pattern as an etching mask. 
     On the nozzle plate  120  and the heater  130 , a silicon nitride layer may be formed as a first passivation layer  140  that protects the heater  130 . The first passivation layer  140  may also be deposited to a thickness of about 0.5 μm by a LPCVD. 
     Additionally, the heater  130  is connected to metal electrodes  150  so that a pulse current may be applied to the heater  130 . Here, the electrodes  150  are connected to the diameter of the heater  130  to face each other. More specifically, a portion of the first passivation layer  140 , which is formed of a silicon nitride layer, is etched to expose a portion of the heater  130  to which the electrode  150  is connected. Next, the electrode  150  is formed by depositing a metal material, which has excellent conductivity and is easily patterned, e.g., aluminum or an aluminum alloy, to a thickness of about 1 μm by a sputtering method and patterning the same. At the same time, the metal layer constituting the electrode  150  is patterned to form a wiring (not shown) and the bonding pad ( 120  of FIG. 2) on another portion of the substrate  110 . 
     A silicon oxide layer is formed on the first passivation layer  140  and the electrode  150  as a second passivation layer  160 . The second passivation layer  160  may be formed to a thickness of about 1 μm by a chemical vapor deposition at a low temperature, e.g., 400° C., within a range that the electrode  150  and the bonding pad  102  are not deformed. 
     After the second passivation layer  160  is formed, a photoresist pattern is formed on the resultant structure. Then, the first and second passivation layers  140  and  160  and the nozzle plate  120  are sequentially etched with the photoresist pattern as an etching mask to form the nozzle  122  having a diameter of between about 16-20 μm. Next, the ink chamber  114  and the ink channel  116  are formed via the nozzle  112 , as described above. 
     The bottom of the ink chamber  114  conforms to a hemispherical shape, but may additionally include nozzle guides  170 , which extend in the depth direction of the ink chamber  114  from the edges of the nozzle  122 , at an upper portion thereof. The droplet of ink may be precisely ejected in the vertical direction of the substrate  110  via the nozzles  122  due to the nozzle guide  170 . Such a nozzle guide  170  may be formed when the ink chamber  114  is made. That is, an exposed portion of the substrate  110  is anisotropically etched via the nozzle  122  to form a groove to a predetermined depth. Then, a predetermined layer, such as tetraethylortho silicate (TEOS) oxide layer, is deposited along the inner surface of the groove to a thickness of about 1 μm. Thereafter, the TEOS oxide layer formed at the bottom of the groove is etched and removed. As a result, the nozzle guide  170 , which is formed of the TEOS oxide layer, is formed along the inner circumference of the groove. Next, a portion of the substrate  110  that is exposed through the bottom of the groove is isotropically etched to form the ink chamber  114  having the nozzles guides  170  at upper portions thereof. 
     Hereinafter, a mechanism of ejecting an ink droplet from an ink-jet printhead according to the present invention will now be explained with reference to FIGS. 6A and 6B. Referring to FIG. 6A, ink  190  is supplied to an ink chamber  114  via a manifold  112  and an ink channel  116  due to capillary action. When the ink chamber  114  is filled with the ink  190 , a pulse current is applied to the heater  130  through the electrode  150  to generate heat in the heater  130 . The heat generated is transmitted to the ink  190  filled in the ink chamber  114  via a nozzle plate  120  below the heater  130 . As a result, the ink  190  boils to generate a bubble  195  in the ink chamber  114 . The shape of the bubble  195  varies depending on the shape of the heater  130 , but conforms to a doughnut shape in most cases. 
     The bubble  195  of a doughnut shape expands as time elapses. As shown in FIG. 6B, an ink droplet  191  is ejected from the ink chamber  114  via the nozzle  122  due to the pressure of the expanded bubble  196 . At this time, the ejection of the ink droplet  191  can be guided by the nozzle guide  170 , and thus, it is possible to eject the ink droplet  191  precisely in the vertical direction of the substrate  110 . Also, since the ink chamber  114  is formed as a hemisphere, it is possible to prevent backflow of ink, thereby reducing cross talk with adjacent ink ejectors. Furthermore, it is possible to more effectively prevent the back flow of the ink  190  in the case where the diameter of the ink channel  116  is smaller than that of the nozzle  122 . 
     In addition, since the heater  130  has a round ring shape, the heaters have a large surface area. Accordingly, the heaters  130  may be easily heated and cooled, so that a period of time during which the bubble  195  is generated, expands, and collapses, is reduced. Thus, an ink-jet printhead according to the present invention has a high driving frequency and is capable of ejecting ink on paper rapidly. The ink chamber  114  has a hemispherical shaped and thus, the bubble  195  may be more stably generated and expanded as compared to ink chambers of conventional ink-jet printhead having a hexahedron or a pyramid-type shape. Further, the bubbles  195  and  196  can be generated and expanded quickly, which enables rapid ejection of ink. 
     After the ink droplet  191  is ejected from the ink chamber  114 , the ink  190  is cooled and then, the expanded bubble  196  collapses or breaks when a current, which was applied to the heater  130 , is blocked. Next, the ink chamber  114  is filled with the ink  190  again. 
     In conclusion, a high-density ink-jet printhead according to the present invention has the following advantageous. First, a plurality of nozzles are arranged on one ink supply manifold in a plurality of rows, and thus, the density of nozzles may be increased, thereby enhancing the printing speed and providing high resolution printing quality. Second, a substrate having ink chambers and ink channels, a nozzle plate, heaters and electrodes are united on a silicon substrate. Therefore, an ink-jet printhead according to the present invention is easy to manufacture, and further, problems due to misalignment of components may be reduced. Also, such an ink-jet printhead is capable of being mass-produced because a substrate thereof can be a silicon wafer such as are adopted in a process of manufacturing semiconductor devices. Third, in an ink-jet printhead according to the present invention, a heater is formed in a ring shape and an ink chamber is formed in a hemispherical shape. Accordingly, the expansion of bubbles is limited to within the ink chamber, thereby preventing any back flow of ink filled in the ink chamber. Thus, such an ink-jet printhead is free from cross talk resulting from adjacent ink ejectors. Moreover, the direction of ejection of an ink droplet may be guided by nozzle guides, thereby ejecting ink precisely in the vertical direction of a substrate. 
     A preferred embodiment of the present invention has been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. For example, alternate materials may be used as materials for use in elements of the printhead according to the present invention. That is, the substrate may be formed of another material having a good processing property, as well as silicon, and the same applies to the heater, electrodes, the silicon oxide layer, and the silicon nitride layer. In addition, the described method for stacking and forming materials is only for explanatory reasons, and various deposition and etching methods may be used. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.