Abstract:
A method of manufacturing a bubble-jet type ink jet printhead. The method includes forming resistive heater elements on a substrate, forming a patterned electrode layer on the resultant structure, forming an insulating layer over the resultant structure, forming barrier walls on the resultant structure and attaching a nozzle plate on the resultant structure. The method may further include etching a hole in the insulating layer, forming a second electrode layer over the etched insulating layer to contact the resistive heater elements and forming a second insulating layer thereon, where the barrier walls and then the nozzle plate are formed on top of the second insulating layer. The barrier walls group together resistive heater elements in pairs and form barriers between different pairs of resistive heater elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 09/798,954 filed on 6 Mar. 2001 now U.S. Pat. No. 6,726,308. This related application is relied on and incorporated herein by references in its entirety. 
    
    
     CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application entitled BUBBLE-JET TYPE INK-JET PRINTHEAD filed with the Korean Industrial Property Office on Jul. 24, 2000 and there duly assigned Ser. No. 2000/42365. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet printhead, and more particularly, to a bubble-jet type ink-jet printhead. 
     2. Description of the Related Art 
     The ink ejection mechanisms of an ink-jet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form a bubble in ink causing ink droplets to be ejected, and an electromechanical transducer type in which a piezoelectric crystal bends to change the volume of ink causing ink droplets to be expelled. 
     Meanwhile, a bubble-jet type ink-jet printhead having an ink ejector needs to meet the following conditions. First, a simplified manufacturing process, the low manufacturing cost, and high volume production must be allowed. Second, to produce high quality color images, creation of small and minute satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle or ink refills an ink chamber after ink ejection, cross-talk with adjacent nozzles from which no ink is ejected must be prevented. Fourth, for a high speed print, a cycle beginning with ink ejection and ending with ink refill must be as short as possible. 
     However, the above conditions tend to conflict with one another, and furthermore, the performance of an ink-jet printhead is closely related to the structures of an ink chamber, an ink channel, and a heater, the type of formation and expansion of bubbles associated therewith, and the relative size of each component. 
     In efforts to overcome problems related to the above requirements, ink-jet print heads having a variety of structures have been proposed in U.S. Pat. Nos. 4,339,762; 4,882,595; 5,760,804; 4,847,630; and 5,850,241, European Patent No. 317,171, and Fan-Gang Tseng, Chang-Jin Kim, and Chih-Ming Ho, “A Novel Micoinjector with Virtual Chamber Neck”, IEEE MEMS &#39;98, pp.57-62. However, ink-jet printheads proposed in the above patents and literature may only satisfy some of the aforementioned requirements but do not completely provide an improved ink-jet printing approach. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an objective of the present invention to provide a bubble-jet type ink-jet printhead having a structure for effectively preventing a back flow of ink. 
     It is another objective of the present invention to provide a bubble-jet type ink-jet printhead in which an ink channel, along which ink flows, has a simple structure and ink is supplied smoothly. 
     It is still another objective of the present invention to provide a bubble-jet type ink-jet printhead that allows for minute adjustment in an ink ejection amount and ejection of a fixed amount. 
     It is yet still another objective of the present invention to provide a bubble-jet type ink-jet printhead that allows for high-speed operation by shortening an ink refill time. 
     It is further an object of the present invention to provide an inkjet printhead that produces uniform droplet size. 
     It is still further an object of the present invention to provide an ink jet ejection mechanism that has two heater units for each nozzle hole; 
     It is also an object of the present invention to provide an ink chamber that can be filled from two directions. 
     Accordingly, to achieve the above objectives, the present invention provides a bubble-jet type ink jet printhead including a substrate, a plurality of chamber walls arranged parallel to one another on the substrate for dividing a chamber into a plurality of unit chambers having a predetermined height, which are ink flow areas, a bubble generating means, provided for each unit chamber, which includes two unit heaters spaced apart by a predetermined distance on the substrate, and a nozzle plate, combined above the substrate, in which a plurality of nozzles are formed, each nozzle corresponding to a region between the two unit heaters of each bubble generating means. In the ink-jet printhead, ink is supplied from both sides of the unit chamber. 
     Furthermore, the two unit heaters of each bubble generating means are electrically coupled to each other. The two unit heaters may be integrated or spaced apart by a predetermined distance, between which an electrical connection member is disposed. 
     The opposite portions of the two unit heaters of the bubble generating means may be coupled to a common signal line and the exterior ends of the two unit heaters may be commonly coupled to one parallel connection member. Alternatively, the ends of one side of each bubble generating means are coupled to a serial connection member while the ends of the other side are coupled to electrical signal lines, respectively. The exterior ends of the two unit heaters of the bubble generating means may be connected to the parallel connection member integrated therewith, and the common signal line may be commonly coupled to the middle portions of a plurality of bubble generating means. 
     A first insulating layer may be disposed between the common signal line and the bubble generating means, and a contact hole for contacting the common signal line and a connection portion of both unit heaters of the bubble generating means may be formed in the first insulating layer. A second insulating layer may be formed on the uppermost surface of a stack structure including the bubble generating means and the chamber wall is formed on the second insulating layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIGS. 1A and 1B  are cross-sectional views showing the structure of a conventional bubble-jet type ink-jet printhead along with ink ejection mechanism; 
         FIG. 2  is a schematic top view of a bubble-jet type ink-jet printhead according to an embodiment of the present invention; 
         FIG. 3  is a cross-sectional view taken along line A-A of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along line B-B of  FIG. 2 ; 
         FIG. 5  is an extracted view showing the portion C of  FIG. 2 ; 
         FIGS. 6-9B  show an ink ejection process for a bubble-jet type ink-jet printhead according to the present invention; 
         FIG. 10  is a top view showing the structure of a region around one unit chamber in the bubble-jet type ink-jet printhead according to the present invention; 
         FIG. 11  is a cross-sectional view taken along line D-D of  FIG. 10 ; 
         FIG. 12  is a cross-sectional view taken along line E-E of  FIG. 10 ; 
         FIG. 13  illustrates a view of the electrical connections of a single bubble generator according to a first embodiment of the present invention; 
         FIG. 14  illustrates a second embodiment of the present invention having a serial electrical connection structure; and 
         FIGS. 15A-15H  show a process of forming a bubble generator applied to the bubble-jet type ink-jet printhead according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1A and 1B , a bubble-jet type ink ejection mechanism will now be described. When a current pulse is applied to a heater  12  consisting of resistive heating elements located at an ink channel  10  where a nozzle  11  is formed, heat generated by the heater  12  boils ink  14  forming a bubble  15  within the ink channel  10 , which causes an ink droplet  14 ′ to be ejected. A back flow of ink in the opposite direction of a nozzle must be avoided during ink ejection. Another heater  13  in  FIGS. 1A and 1B  is provided for this purpose. 
     A heater is mainly shown in  FIGS. 2 and 3 , and components related thereto are omitted to aid in the understanding, and the detailed structure of the heater will be described separately.  FIGS. 2 and 3  schematically show an ink-jet printhead having a structure in which nozzles  201  are arranged in two rows. Referring to  FIGS. 2 and 3 , a plurality of electrode pads  101  are arranged at predetermined intervals along both edges in the longitudinal direction of the substrate  100 . A nozzle plate  200 , in which the nozzles  200  are arranged in two rows, is disposed at the upper portion of the substrate  100 . An isolation wall  102   a  extending from the middle portion of the substrate  100  in a longitudinal direction is disposed between the substrate  100  and the nozzle plate  200 , and outer walls  102   b  are disposed along both edges in the longitudinal direction of the nozzle plate  200 . Thus, an ink chamber  300  disposed between the substrate  100  and the nozzle plate  200  is partitioned into two, and ink is supplied to the ink chamber  300  through ink feed grooves  103  formed at both short sides of the substrate  100 . 
     Meanwhile, a plurality of chamber walls  102   c  extending in a direction vertical to both outer walls  102   b  and the isolation wall  102   a  are arranged parallel to one another between each of the outer walls  102   b  and the isolation wall  102   a  in a direction in which the outer walls  102   b  and the isolation wall  102   a  extend. Both ends of the chamber wall  102   c  are separated from the outer wall  102   b  and the isolation wall  102   a  by a predetermined space. A unit chamber  300   a  isolated by the chamber wall  102   c  is provided for each nozzle, and the unit chambers  300   a  are connected to one another through openings between the ends of the chamber walls  102   c . Unit heaters  400   a  and  400   b  constituting a symmetrical bubble generator  400  are disposed at the lower portion of the unit chamber  300   a . As will be described later, the two unit heaters  400   a  and  400   b  of the bubble generator  400  for each nozzle  201  or unit chamber  300   a  are electrically coupled to each other, and the heaters  400   a  and  400   b  may have either parallel or serial connection structure. Also, both unit to heaters  400   a  and  400   b  are arranged in a straight line parallel to the chamber walls between the chamber walls  102   c , and the heaters  400   a  and  400   b  generate the same thermal energy, which causes bubbles of the same size to be formed. 
     As shown in  FIGS. 3 and 5  in detail, the nozzle  201  of the nozzle plate  200  is located at the upper center between the unit heaters  400   a  and  400   b . Referring to  FIG. 4 , which is a cross-sectional view taken along line B-B of  FIG. 2 , the ink feed grooves  103  are disposed at both ends of the substrate  100 . Reference numerals  500  and  501  denote a portion of an ink cartridge for storing ink and a sealing material for sealing the gap between the ink cartridge  500  and the nozzle plate  200 . 
     An ink ejection process in the ink-jet printhead according to the present invention having a distinctive structure as described above will now be described.  FIG. 6  shows a state in which ink fills the unit chamber  300   a . Ink  600  is introduced from both sides of the unit chamber  300   a . In this case, the ink  600  is filled by capillary action and gravity.  FIG. 7  shows an early stage at which bubbles are formed at a region in contact with the unit heaters  400   a  and  400   b  upon application of a voltage pulse to the unit heaters  400   a  and  400   b  of the bubble generator  400 . In this case, bubbles  600   b  are generated by the unit heaters  400   a  and  400   b  disposed on both sides of a central axis that passes through the nozzle  201 . As the bubbles  600   b  expand, pressure is applied to the ink  600  present between the bubbles  600   b  and the ink  600  on the outside thereof, causing a back flow of a small amount of ink  600 . 
       FIG. 8  shows a state in which the bubbles  600   b  formed by the unit heaters  400   a  and  400   b  expand so that a region between the bubbles  600   b  is closed as a voltage pulse continues to be applied to the unit heaters  400   a  and  400   b  of the bubble generator  400 . Thus, the ink  600  present in the closed region by the bubbles  600   b , that is, a region below the nozzle  201 , begins to be ejected through the nozzle  201  by force applied by the expansion of the bubbles  600   b.    
       FIG. 9A  is a top view showing a state in which the bubbles  600   b  generated by the unit heaters  400   a  and  400   b  reach their maximum growth as application of a voltage pulse to the unit heaters  400   a  and  400   b  of the bubble generator  400  continues to complete ejection of the ink  600  present in the closed region between the bubbles  600   b  through the nozzle  201 , and  FIG. 9B  is a side view showing the same state. 
     As shown in  FIGS. 9A and 9B , the bubbles  600   b  fully expanded by the unit heaters  400   a  and  400   b  cause the ink  600  between the bubbles  600   b  to be ejected in droplets  600   a . At the same time that ejection of the droplet  600   a  is complete in this way, a voltage ceases to be applied to the unit heaters  400   a  and  400   b  of the bubble generator  400  and hence the bubbles  600   b  that have reached maximum growth collapse and the ink  600  begins to refill. Thus, the process returns to an initial state shown in  FIG. 5 . 
     The structural features of the ink-jet printhead according to the present invention that ejects ink droplet through the above process are to include an isolated unit chamber provided for each nozzle and a bubble generator consisting of unit heaters disposed on both sides of the nozzle. Due to the structural features, as both bubbles generated by both unit heaters grow, ink below the nozzle is separated or isolated from the ink on the outside of the bubbles, thus preventing a back flow of the ink present below the nozzle. Furthermore, the ink below the nozzle is isolated by both bubbles and sufficient pressure is exerted on the ink, so as to generate a droplet which will be ejected with high pressure. Further, due to the structural features, it is possible to minutely adjust the size of a droplet ejected depending on the amount of heat generated by the bubble generator. The ink-jet printhead according to the present invention includes an ink channel having a simple structure unlike a conventional printhead, thereby effectively preventing the clogging of an ink channel due to foreign materials or the occurrence of cross-talk with adjacent regions. 
     The detailed structure of the heaters  400   a  and  400   b  will now be described.  FIG. 10  is a top view showing the arrangement structure of a portion around the unit chamber  300   a .  601  and  602  denote insulating layers for insulating signal lines  101   a  and  101   a ′ connected to the bubble generator  400  from each other. First, referring to  FIGS. 10 and 11 , the two unit heaters  400   a  and  400   b  of the bubble generator  400  unite into a single body, the middle portion of which is in contact with the common signal line  101   a ′ coupled to the common electrode pad  101 ′. Thus, a resistance component at the portion in contact with the common signal line  101   a ′ is shorted out of the circuit by the common signal line  101   a ′ and hence both unit heaters  400   a  and  400   b  are connected in series by the common signal line  101   a ′. The common signal line  101   a ′ is coupled to another bubble generator  400  as well. Further, the first insulating layer  601  is formed at a portion excluding the common signal line  101   a ′ in the middle portion of the bubble generator  400 , while the second insulating layer  602  is formed over the common signal line  101   a ′ and the bubble generator  400 . 
       FIG. 13  illustrates a view of the electrical connections of a single bubble generator according to the first embodiment of the present invention. Meanwhile, as shown in  FIG. 13 , a parallel connector  401 , which is integrated with the bubble generator  400  and electrically connected to both ends of the bubble generator  400 , is formed on one side of the bubble generator  400 , on top of which an individual signal line  101   a  is formed. The individual signal line  101   a  extends longitudinally to be connected to the electrode pad  101 . The individual signal line  101   a  and the electrode pad  101  are integrated with each other and formed on the parallel connector  401  consisting of resistors thus removing resistance component of the parallel connector  401  by an electrical short. 
     As shown in  FIG. 12 , the first insulating layer  601  is interposed between the parallel connector  401  and the common signal line  101   a ′, thereby electrically separating the parallel connector  401  and individual signal line  101   a  from the common signal line  101   a ′. The second insulating layer  602  is positioned on the uppermost surface of the stack structure thereby protecting the unit heaters  400   a  and  400   b  of the bubble generator  400  from ink. The chamber wall  102   c , the top surface of which contacts the bottom of the nozzle plate  200 , is formed on the second insulating layer  602  with a predetermined height. 
     In the bubble generator  400  and a peripheral structure associated therewith, the unit heaters  400   a  and  400   b  of the bubble generator  400  are electrically coupled to each other in parallel between the common signal line  101   a ′ and the individual signal line  101   a  formed on the parallel connector  401 . The parallel connection structure may be modified to a serial connection structure by appropriate arrangement of the signal lines.  FIG. 14  illustrates a second embodiment of the present invention having this serial connection structure. In this case, as shown in  FIG. 14 , both unit heaters  400   a  and  400   b  of the bubble generator  400  are separated from each other, between which a serial connection unit  101   b  is interposed. Also, the outer portions of the unit heaters  400   a  and  400   b  may be coupled to a common signal line  101 ′ and an individual signal line  101 , respectively. In this case, the unit heaters  400   a  and  400   b  may be integrally connected and the serial connector  101   b  stacked on the middle portion of the integrated unit heater  400   a  and  400   b  corresponding to a nozzle, thereby obtaining the same serial connection effect. 
     The serial connector  101   b  can be applied to the bubble generator  400  shown in  FIGS. 10-13 . In this case, the unit heaters  400   a  and  400   b  integrally formed are separated and the serial connector  101   b  is interposed between the unit heaters  400   a  and  400   b . The common signal line  101   a ′ is connected to the serial connector  101   b.    
     To aid in the understanding on the structures of the bubble generator  400  shown in  FIGS. 10-13  and the bubble generator shown in  FIG. 14 , which is an applied example of the bubble generator shown in  FIGS. 10-13 , a process of forming the bubble generator  400  shown in  FIGS. 10-13  will now be described. As shown in  FIG. 15A , after having deposited a resistive material such as TaAl over the silicon substrate  100 , the resistive material is etched by photolithography to form the bubble generator  400  and the parallel connector  401 . 
     As shown in  FIG. 15B , the individual signal line  101   a  is formed of a material having a high conductivity such as Al on the parallel connector  401  by means of deposition and etching. As shown in  FIG. 15C , the first insulating layer  601  is formed over the substrate  100 . As shown in  FIG. 15D , a contact hole  603  is formed at the middle portion of the bubble generator  400  by photolithography. 
     As shown in  FIG. 15E , a material having a high conductivity such as Al is deposited over the first insulating layer  601  and then etched to form the common signal line  101   a ′ which intersects the bubble generator  400  and overlaps the contact hole  603 . 
     As shown in  FIG. 15F , SiN or SiO 2  is deposited over the substrate  100  to form the second insulating layer  602 , As shown in  FIG. 15G , partial etching is performed on the second insulating layer  602  and the underlying first insulating layer  601  by photolithography so that a portion of the end of the individual signal line  101   a  may be exposed. Here, the exposed portion is the electrode pad  101 . 
     As shown in  FIG. 15H , after having formed a film on the second insulating layer  602  by a thick-film forming process, the film is etched by photolithography to form the chamber walls  102   c  which extend parallel to the bubble generator  400  on either side of the bubble generator  400 . 
     Etching techniques and film forming methods used in the above process are not described in detail. Of course, thin film growth and stacking and etching thereof, which are well known in the art, can be applied to the above process. In the ink-jet printhead according to the present invention as illustrated above, arrangement of a nozzle and a droplet generating structure associated therewith may be modified in various ways using the unit chambers and the bubble generator. 
     The ink-jet printhead according to the present invention can freely adjust the maximum amount of droplet ejected at one time within allowable range by controlling the interval between both heaters of the bubble generator, while ejecting droplets having a stable and uniform size. 
     Meanwhile, according to the ink-jet printhead shown in  FIGS. 2-4 , ink is supplied to the ink chamber on both short sides of the substrate. In addition to the structure, ink may be supplied to the chamber by forming a through hole that extends parallel to the isolation wall at the middle portion of two rows of the nozzles, that is, the portion adjacent to the isolation wall, or by removing the isolation wall and forming a long through hole instead. 
     As described above, the ink-jet printhead according to the present invention is constructed such that a unit chamber is provided for each nozzle and bubbles are generated chamber on both sides of a nozzle within the unit chamber, thereby effectively preventing a back flow of ink while facilitating adjustment of the size of ink droplet ejected through the nozzle. Furthermore, the ink-jet printhead according to the present invention allows for high-speed and high-pressure ink ejection with relatively low pressure compared to a conventional printhead. In particular, an ink channel having a simple structure is provided, thereby avoiding the clogging of the ink channel due to foreign materials while effectively preventing defectiveness of the printhead. Accordingly, the ink-jet printhead according to the present invention allows ink droplets to be ejected with a quick response rate and high driving frequency by virtue of the unit chamber and the ink feed channel.