Patent Publication Number: US-7585053-B2

Title: Thermal inkjet printhead

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(a) from Korean Patent Application No. 10-2005-0093055, filed on Oct. 4, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to an inkjet printhead, and more particularly, to a thermal inkjet printhead to enhance ink ejection characteristics thereof by preventing and/or dissipating heat accumulation around a heater thereof. 
     2. Description of the Related Art 
     An inkjet printhead ejects ink droplets on desired positions of recording paper in order to print predetermined color images. Inkjet printers are classified into two categories: a shuttle type inkjet printer having a printhead that is shuttled in a direction perpendicular to a transporting direction of a print medium, and a line printing type inkjet printer having a page-wide array printhead corresponding to a width of a print medium. The latter has been developed for realizing high-speed printing. The array printhead has a plurality of inkjet printheads arranged in a predetermined configuration. In the line printing type inkjet printer, during printing, the array printhead is fixed and a print medium is transported, thereby allowing the high-speed printing. 
     The inkjet printhead is categorized into two types according to the ink droplet ejection mechanism thereof: a thermal inkjet printhead and a piezoelectric inkjet printhead. The thermal inkjet printhead ejects ink droplets due to an expansion force of ink bubbles generated by thermal energy. The piezoelectric inkjet printhead ejects ink droplets by a pressure applied to ink due to a deformation of a piezoelectric body. 
     The ink droplet ejection mechanism of the thermal inkjet printhead is as follows. When a current flows through a heater made of a heating resistor, the heater is heated and ink near the heater in an ink chamber is instantaneously heated up to about 300° C. Accordingly, ink bubbles are generated by ink evaporation and the generated bubbles are expanded to exert a pressure on the ink filled in the ink chamber. Thereafter, an ink droplet is ejected through a nozzle out of the ink chamber. 
       FIG. 1  is a schematic cross-sectional view illustrating a conventional thermal inkjet printhead. Referring to  FIG. 1 , the conventional inkjet printhead includes a substrate  11  on which a plurality of material layers are stacked, a chamber layer  20  stacked on the substrate  11  and defining an ink chamber  22 , and a nozzle layer  30  stacked on the chamber layer  20 . Ink is filled in the ink chamber  22  and a heater  13  to heat the ink to generate bubbles therein is installed under the ink chamber  22 . In addition, the nozzle layer  30  has a nozzle  32  to eject the ink. 
     The substrate  11  is generally a silicon substrate. An insulation layer  12  to provide insulation between the heater  13  and the substrate  11  is formed on the substrate  11 . The insulation layer  12  is generally made of silicon oxide. The heater  13  to heat the ink in the ink chamber  22  to generate bubbles therein is disposed on the insulation layer  12 . Conductors  14  to supply an electric current to the heater  13  are disposed on the heater  13 . 
     A passivation layer  15  is formed on the heater  13  and the conductors  14  to protect the heater  13  and the conductors  14 . The passivation layer  15  prevents the heater  13  and the conductors  14  from oxidizing or directly contacting the ink, and is generally formed of silicon oxide or silicon nitride. An anti-cavitation layer  16  is formed on the passivation layer  15 . The anti-cavitation layer  16  protects the heater  13  from a cavitation pressure induced by bubble extinction, and is generally made of tantalum (Ta). 
     In this structure, some heat generated by the heater  13  is used to form bubbles and the rest of the heat (i.e., residual heat) should be dissipated through the insulation layer  12  formed under the heater  13  toward the substrate  11 . However, because the insulation layer  12  is made of silicon oxide having low thermal conductivity, the residual heat generated by the heater  13  may not be dissipated toward the substrate  11 , but instead may be accumulated in the insulation layer  12  near the heater  13 . When the heat is accumulated in the insulation layer  12 , the temperature of the ink filled in the ink chamber  22  increases, and thus a viscosity of the ink decreases, thereby degrading ink ejection characteristics, such as ink ejection frequency and ink ejection velocity. 
     Recently, line printing type inkjet printers have been actively developed to satisfy demands of high integration and high speed. Since an array printhead used in the line printing type inkjet printer includes many heaters, a large quantity of heat is generated from the heaters. Accordingly, if the conventional thermal inkjet printhead is employed in the array printhead, ink ejection characteristics thereof may degrade. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides a thermal inkjet printhead to enhance an ink ejecting ability thereof by preventing and/or dissipating heat accumulation around a heater thereof. 
     Additional aspects and advantages of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an inkjet printhead, including a substrate, an insulation layer formed on the substrate, a heater formed on the insulation layer, a conductor formed on the heater to supply a current to the heater, a chamber layer stacked on the insulation layer having the heater and the conductor therebetween, and having an ink chamber formed therein to be filled with ink to be ejected, a nozzle layer stacked on the chamber layer and having a nozzle through which the ink in the ink chamber is ejected, and a plurality of thermal plugs formed in a lower portion of the insulation layer to contact the insulation layer and the substrate and to dissipate heat generated by the heater toward the substrate. The plurality of thermal plugs may include tungsten or silver. 
     The inkjet printhead may further include a metal layer formed on a top surface of the plurality of thermal plugs. The metal layer may include at least one metal selected from the group consisting of aluminum, aluminum alloy, gold, and silver. 
     The substrate may be a silicon substrate. The insulation layer may include silicon oxide. 
     The inkjet printhead may further include a passivation layer formed on surfaces of the heater and the conductor. The passivation layer may include silicon oxide or silicon nitride. The inkjet printhead may further include an anti-cavitation layer formed on the passivation layer which forms the bottom of the ink chamber. The anti-cavitation layer may include Tantalum. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a thermal printhead, including a substrate, a chamber layer disposed on the substrate and including an ink chamber to contain ink, a nozzle layer disposed on the chamber layer and including a nozzle to eject the ink, a heating unit to heat the ink and to eject the ink through the nozzle by forming bubbles therein, an insulating layer disposed between the substrate and the heating unit to provide insulation between the substrate and the heating unit, and at least one thermal plug contacting the insulating layer and the substrate to dissipate residual heat generated by the heating unit to the substrate. 
     The at least one thermal plug may extend in a direction perpendicular to the insulating layer. The at least one thermal plug may extend in a direction parallel to an ink ejecting direction. The at least one thermal plug may have a height that is substantially-equal to one half of a width of the insulating layer. The at least one thermal plug may have a height that is less than one half of a width of the insulating layer. The at least one thermal plug may have a height that is greater than one half of a width of the insulating layer. 
     The at least one thermal plug may include a plurality of thermal plugs. Each of the plurality of thermal plugs may have an identical shape. At least one plug of the plurality of thermal plugs may have a shape that is different from at least one other plug of the plurality of thermal plugs. Each of the plurality of thermal plugs may have an identical height. At least one plug of the plurality of thermal plugs may have a height that is different from at least one other plug of the plurality of thermal plugs. The plurality of thermal plugs may be disposed at substantially-regular intervals along at least a portion of the insulating layer. The plurality of thermal plugs may be disposed at a position corresponding to a position of the heating unit. 
     The printhead may further include at least one metal layer contacting the insulating layer and the at least one thermal plug to further dissipate the residual heat generated by the heating unit. The at least one metal layer may be a continuous layer. The at least one metal layer may include a first portion extending in a first direction, and a second portion extending in a second direction having an angle with the first direction. The at least one metal layer may contact a portion of the at least one thermal plug facing the nozzle. The at least one metal layer may contact a second portion of the at least one thermal plug substantially-perpendicular to the first portion. A length of the at least one metal layer may substantially-correspond to a length of the insulating layer. A width of the at least one metal layer is smaller than a height of the at least one thermal plug. The width of the at least one metal layer is less than a width of the insulating layer. 
     The at least one metal layer may extend in a direction substantially-parallel to the substrate. The at least one metal layer may have a width corresponding to a size of the heating unit. The at least one metal layer may extend in a direction substantially-perpendicular to the at least one thermal plug. The at least one metal layer may include at least one conductive metal. The at least one thermal plug may include the at least one conductive metal. The printhead may further include a conducting layer to supply a current to the heating unit. The conducting layer may include the at least one metal. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing an inkjet print head, including a substrate, a ink chamber region disposed on the substrate to contain ink therein, a nozzle layer disposed on the ink chamber region to eject the ink therefrom, a heating layer disposed below the ink chamber region to heat the ink in the ink chamber region, an insulating layer disposed between the substrate and the heating layer to provide insulation between the substrate and the heating unit, and a heat dissipation layer formed within the insulation layer and extending therethrough to a heat sink region to dissipate heat from the heating layer and the insulation layer. 
     The heat sink region may be the substrate. The heat dissipation layer may include a metal layer extending along a length of the insulating layer, and at least one projection extending from the metal layer through the insulating layer to the heat sink region. The heat dissipation layer may include a plurality of intermittent projections extending from within the insulating layer to the heat sink region. The plurality of intermittent projections may be disposed at regular intervals within the insulating layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic cross-sectional view illustrating a conventional thermal inkjet printhead; 
         FIG. 2  is a schematic cross-sectional view illustrating a thermal inkjet printhead, according to an embodiment of the present general inventive concept; and 
         FIG. 3  is a schematic cross-sectional view illustrating a thermal inkjet printhead, according to another embodiment of the present general inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
       FIG. 2  is a schematic cross-sectional view illustrating a thermal inkjet printhead, according to an embodiment of the present general inventive concept. Referring to  FIG. 2 , an inkjet printhead according to this embodiment includes a substrate  111  on which a plurality of materials layers are formed, a chamber layer  120  stacked on the substrate  111 , and a nozzle layer  130  stacked on the chamber layer  120 . An ink chamber  122  to be filled with ink to be ejected is formed in the chamber layer  120 . A nozzle  132  to eject ink filled in the ink chamber  122  is formed through the nozzle layer  130  on an upper portion of the ink chamber  122 . Although the nozzle  132  is illustrated on the upper portion of the ink chamber  122  in  FIG. 2 , the present general inventive concept is not so limited. 
     The substrate  111  may be a silicon substrate, but the present general inventive concept is not limited to the substrate  111  being a silicon substrate. An insulation layer  112  having a predetermined thickness is formed on an upper side of the substrate  111  to provide heat and electronic insulation between the substrate  111  and a heater  113 , which will be described later. The insulation layer  112  may include silicon oxide, but the present general inventive concept is not limited to the insulation layer  112  including silicon oxide. The heater  113  to heat the ink filled in the ink chamber  122  to generate bubbles is formed on the insulation layer  112 . The heater  113  may include a heating resistor made of, for example, a tantalum-aluminum alloy, tantalum nitride, titanium nitride, or tungsten silicide. A conductor  114  to supply a current to the heater  113  is formed on the heater  113 . The conductor  114  may include at least one metal having excellent electric conductivity, such as a metal selected from the group consisting of aluminum (Al), an aluminum alloy, gold (Au), and silver (Ag). 
     A passivation layer  115  to protect the heater  113  and the conductor  114  may be formed on the surfaces of the heater  113  and the conductor  114 . The passivation layer  115  prevents the heater  113  and the conductor  114  from oxidizing or directly contacting the ink, and may be formed of silicon oxide or silicon nitride. An anti-cavitation layer  116  may be formed on the passivation layer  115  and forms a bottom of the ink chamber  122 . The anti-cavitation layer  116  protects the heater  113  from a cavitation pressure induced by bubble extinction, and may primarily include tantalum (Ta). 
     A plurality of thermal plugs  140  may be formed in a lower portion of the insulation layer  112  to contact the insulation layer  112  and the substrate  111 . The thermal plugs  140  dissipate residual heat from the heater  113  toward the substrate  111 . The term “residual heat” refers to heat generated by the heater  113  that does not contribute to the formation of the bubbles in the ink. The residual heat (which does not contribute to the bubble formation by the heater  113 ) may be accumulated in the insulation layer  112  near the heater  113 . Thus, the heat accumulation in the insulation layer  112  can be prevented and/or dissipated by the thermal plugs  140 . The thermal plugs  140  may include a high thermal conductive material, such as tungsten (W), silver (Ag), and the like. 
     The thermal plugs  140  may have a substantially-rectangular shape, as illustrated in  FIG. 2 . However, the present general inventive concept is not so limited. For example, the thermal plugs  140  may have other shapes suitable to prevent and/or dissipate heat accumulation in the insulation layer  112 . In addition, each of the thermal plugs  140  may have the same shape, as illustrated in  FIG. 2 , one or more of the thermal plugs  140  may have a different shape from others of the thermal plugs  140 , or all of the thermal plugs  140  may have different shapes with respect to each other. 
     The thermal plugs  140  may have a height corresponding to approximately one half of a width of the insulation layer  112 , as illustrated in  FIG. 2 . However, the present general inventive concept is not so limited. For example, the height of the thermal plugs  140  may be less than approximately one half of the width of the insulation layer  112 . Alternatively, the height of the thermal plugs  140  may be greater than approximately one half of the width of the insulation layer  112 , such as approximately the width of the insulation layer  112 . Moreover, although each of the thermal plugs  140  illustrated in  FIG. 2  has substantially the same height, the present general inventive concept is not so limited. For example, one or more of the thermal plugs  140  may have a different height from others of the thermal plugs  140 , or all of the thermal plugs  140  may have different heights with respect to each other. 
     The thermal plugs  140  may be disposed at regular intervals along an entire length of the insulation layer  112 , as illustrated in  FIG. 2 . However, the present general inventive concept is not so limited. For example, the thermal plugs  140  may be arranged at irregular intervals along the entire length of the insulation layer  112 , or along only a portion of the length of the insulation layer  112 . Alternatively, the thermal plugs  140  may be arranged at regular intervals along only a portion of the length of the insulation layer  112 , such as only on a left portion thereof, a right portion thereof, a middle portion thereof, or two such portions thereof. Moreover, the thermal plugs  140  may be disposed with respect to a position of the heater  113 . For example, if the heater  113  is positioned only on a portion of the insulation layer  112  (in contrast to  FIG. 2 , where the heater  113  is positioned along an entire length of the insulation layer  112 ), the thermal plugs  140  may be disposed at a corresponding position. 
     In the inkjet printhead of the present embodiment, when the current flows through the heater  113  via the conductor  114 , the heater  113  generates the heat, and thus the ink in the ink chamber  122  is heated. Accordingly, the bubbles are generated by a portion of the heat and expand in the ink chamber  122 . Due to the expansion force of the bubbles, the ink in the ink chamber  122  is ejected from the nozzle  132 . The residual heat does not contribute to the bubble formation and often accumulates in the insulation layer  112  near the heater  113 . However, the residual heat is rapidly dissipated through the thermal plugs  140 , having a high thermal conductivity, toward the substrate  111 . Thus, the inkjet printhead according to the present embodiment can prevent and/or dissipate heat accumulation in the insulation layer  112  near the heater  113  after ink ejection, thereby enhancing ink ejection characteristics, such as ink ejection frequency and ink ejection velocity. 
       FIG. 3  is a schematic cross-sectional view illustrating a thermal inkjet printhead, according to another embodiment of the present general inventive concept. Hereinafter, differences between the present embodiment and the previous embodiment illustrated in  FIG. 2  will be mainly described. 
     Referring to  FIG. 3 , an inkjet printhead according to the present embodiment includes a substrate  211  on which a plurality of materials layers are formed, a chamber layer  220  stacked on the substrate  111  and having an ink chamber  222  formed therein, and a nozzle layer  230  stacked on the chamber layer  220  and including a nozzle  232 . 
     The substrate  211  may be a silicon substrate, but the present general inventive concept is not limited to the substrate being a silicon substrate. An insulation layer  212  having a predetermined thickness is formed on an upper side of the substrate  211  to provide heat and electronic insulation between the substrate  211  and a heater  213 , which will be described later. The insulation layer  212  may include silicon oxide, but the present general inventive concept is not limited to the insulation layer  212  including silicon oxide. A heater  213  is formed on the insulation layer  212 , and a conductor  214  is formed on the heater  213 . A passivation layer  215 , which may include silicon oxide or silicon nitride) to protect the heater  213  and the conductor  214 , may be formed on surfaces of the heater  213  and the conductor  214 . An anti-cavitation layer  216 , which may include tantalum (Ta), may be formed on the passivation layer  215  to form a bottom of the ink chamber  222 . 
     A plurality of thermal plugs  240  may be formed in a lower portion of the insulation layer  212  to contact the insulation layer  212  and the substrate  211 . A metal layer  250  may be formed on upper sides of the thermal plugs  240 . The metal layer  250  and the thermal plugs  240  dissipate residual heat from the heater  213  toward the substrate  211 . The residual heat does not contribute to the bubble formation (i.e., the bubbles formed due to the heat generated by the heater  213 ) and can accumulate in the insulation layer  212  near the heater  213 . However, due to the thermal plugs  240  and the metal layer  250 , heat accumulation in the insulation layer  212  is prevented and/or discharged. The thermal plugs  240  may include a high thermal conductive material, such as tungsten (W), silver (Ag), and the like. The metal layer  250  may include the same material as the conductor  214 , for example, at least one metal selected from the group consisting of aluminum (Al), aluminum alloy, gold (Au), and silver (Ag). 
     The thermal plugs  240  may have a substantially-rectangular shape, as illustrated in  FIG. 3 . However, the present general inventive concept is not so limited. For example, the thermal plugs  240  may have other shapes suitable to prevent and/or dissipate heat accumulation in the insulation layer  212 . In addition, each of the thermal plugs  240  may have the same shape, as illustrated in  FIG. 3 , one or more of the thermal plugs  240  may have a different shape from others of the thermal plugs  240 , or all of the thermal plugs  240  may have different shapes with respect to each other. 
     The thermal plugs  240  may be disposed at regular intervals along an entire length of the insulation layer  212 , as illustrated in  FIG. 3 . However, the present general inventive concept is not so limited. For example, the thermal plugs  240  may be arranged at irregular intervals along the entire length of the insulation layer  212 , or along only a portion of the length of the insulation layer  212 . Alternatively, the thermal plugs  240  may be arranged at regular intervals along only a portion of the length of the insulation layer  212 , such as only on a left portion thereof, a right portion thereof, a middle portion thereof, or two such portions thereof. Moreover, the thermal plugs  240  may be disposed with respect to a position of the heater  213 . For example, if the heater  213  is positioned only on a portion of the insulation layer  212  (in contrast to  FIG. 3 , where the heater  213  is positioned along an entire length of the insulation layer  212 ), the thermal plugs  240  may be disposed at a corresponding position. 
     The thermal plugs  240  may have a height corresponding to approximately one half of a width of the insulation layer  212 , as illustrated in  FIG. 3 . However, the present general inventive concept is not so limited. For example, the height of the thermal plugs  240  may be less than approximately one half of the width of the insulation layer  212 . Alternatively, the height of the thermal plugs  240  may be greater than approximately one half of the width of the insulation layer  212 . Moreover, although each of the thermal plugs  240  illustrated in  FIG. 3  has substantially the same height, the present general inventive concept is not so limited. For example, one or more of the thermal plugs  240  may have a different height with respect to others of the thermal plugs  240 , or all of the thermal plugs  240  may have different heights with respect to each other. 
     The metal layer  250  may be a continuous layer and a substantially flat layer, as illustrated in  FIG. 3 . However, the present general inventive concept is not so limited. For example, the metal layer  250  may be a broken layer having one or more portions that are discontinuous with other portions thereof. Moreover, the metal layer may have portions that extend in a particular direction, and other portions that extend in another direction having an angle with the particular direction. 
     As discussed above, the metal layer  250  may contact upper sides of the thermal plugs  240 , as illustrated in  FIG. 3 . However, the present general inventive concept is not so limited. For example, the metal layer  250  may contact at least one other side of the thermal plugs  240  in addition to, or instead of, the upper sides thereof. Furthermore, the metal layer  250  may contact identical sides of the thermal plugs  240 , as illustrated in  FIG. 3 , where the metal layer  250  contacts the upper sides of each of the thermal plugs  240 . Alternatively, the metal layer  250  may contact different sides of the thermal plugs  240 , such as an upper side of one thermal plug  240  and a right side of anther thermal plug  240 . 
     The metal layer  250  may have a length corresponding to a length of the insulation layer  212 . However, the present general inventive concept is not so limited. For example, the metal layer  250  may have a length that is shorter than a length of the insulation layer. Furthermore, a width of the metal layer  250  may vary. For example, the width of the metal layer  250  may be less than half of a width of the insulation layer  212 , as illustrated in  FIG. 3 . Alternatively, the width of the metal layer  250  may be greater than half of the width of the insulation layer  212 . In addition, the width of the metal layer  250  may vary with respect to a width of one or more other layers of the printhead, such as a width of the heater  213  or a width of the conductor  214 . 
     In the inkjet printhead of the present embodiment, the residual heat generated by the heater  213  and accumulated in the insulation layer  212  is dissipated through the metal layer  250  and the thermal plug  240  toward the substrate  211 , thereby preventing the heat accumulation in the insulation layer  212 . In addition, the heat accumulated in the insulation layer  212  may be directly dissipated through the thermal plug  240  toward the substrate  211 . 
     As described above, an inkjet printhead according to various embodiments of the present general inventive concept may include a plurality of thermal plugs, which include an excellent thermal conductive material, formed in a lower portion of an insulation layer formed on a substrate to contact the insulation layer and the substrate, thereby effectively dissipating residual heat accumulation in the insulation layer after ink ejection. Accordingly, the inkjet printhead can prevent and/or dissipate residual heat accumulation in the insulation layer, thereby enhancing ink ejection characteristics, such as ink ejection frequency and ink ejection velocity. 
     The general inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. For example, it will also be understood that when a layer is referred to as being “on” another layer or a substrate, the layer can be directly on the other layer or the substrate, or the layer can be indirectly on the other layer or the substrate, such as through intervening layers. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.