Patent Publication Number: US-8118403-B2

Title: Inkjet printhead and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from Korean Patent Application No. 10-2008-0078521, filed on Aug. 11, 2008, 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 a thermal inkjet printhead, an image forming apparatus having the same, and a method of manufacturing the thermal inkjet printhead. 
     2. Description of the Related Art 
     Generally, inkjet printers print a color image on a printing medium by ejecting ink droplets onto a desired region of the printing medium. Inkjet printers can be classified into shuttle type inkjet printers that perform printing jobs by moving a printing head in a processing direction of a printing medium and a perpendicular direction to the processing direction, and line printing type inkjet printers including printheads having a size corresponding to the width of a printing medium. Since line printing type inkjet printers perform printing jobs when the printheads are fixed and only the printing medium is processed, line printing type inkjet printers can print at high speed. Line printing type inkjet printers can include a single printhead or a plurality of printheads, having a length substantially corresponding to the width of printing paper. In this case, when the sum of the lengths of the plurality of printhead substantially corresponds to the width of printing paper, the plurality of printheads are referred to as an array type inkjet printhead. 
     Depending on the ink ejecting method, inkjet printheads can be classified into two types: thermal inkjet printheads and piezoelectric inkjet printheads. The thermal inkjet printhead generates bubbles in the ink to be ejected using heat, and ejects the ink using the expansion of the bubbles. On the other hand, the piezoelectric inkjet printhead ejects ink using a pressure generated by deforming a piezoelectric material. 
     The ink droplet ejecting mechanism of the thermal inkjet printhead will now be described in more detail. When a current pulse flows through a heater, the heater generates heat, and thus the ink adjacent to the heater is heated instantly to a temperature of about 300° C. Accordingly, the ink boils and generates bubbles, which expand and thus press the ink in an ink chamber. Therefore, the ink is ejected out of the ink chamber through nozzles in the shape of droplets. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides an inkjet printhead, an image forming apparatus, and a method of manufacturing the inkjet printhead. 
     Additional aspects and utilities 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. 
     In an embodiment and utilities of the present general inventive concept, there is provided an inkjet printhead including a substrate; a chamber layer formed on the substrate and including a plurality of ink chambers; an anti reflective layer formed of a material absorbing light on the chamber layer; and a nozzle layer formed on the anti reflective layer and including a plurality of nozzles. 
     A light transmissivity of the anti reflective layer may be smaller than a light transmissivity of the chamber layer or the nozzle layer. The anti reflective layer may include a plurality of through holes formed therethrough and connected to the nozzles. 
     The nozzle layer may include a photosensitive dry film. The photosensitive dry film may include a negative photoresist. The chamber layer may include a photosensitive polymer. 
     A composite layer of the anti reflective layer and the nozzle layer, which is manufactured in a film form, may be formed on the chamber layer. 
     The inkjet printhead may further include an ink feed hole supplying ink to the ink chamber and formed in the substrate. 
     The inkjet printhead may further include an insulating layer formed on the substrate; a plurality of heaters and a plurality of electrodes, sequentially formed on the insulating layer; and a passivation layer formed so as to cover the heaters and the electrodes. The inkjet printhead may further include an anti-cavitation layer formed on the passivation layer and protecting the heater from a cavitation force generated when bubbles collapse 
     In an embodiment and utilities of the present general inventive concept, there is also provided a method of manufacturing an inkjet printhead, the method including forming a chamber layer having a plurality of ink chambers on a substrate; stacking an anti reflective material layer formed of a material absorbing light and a nozzle material layer on the chamber layer; and forming a nozzle layer including a plurality of nozzles and an anti reflective layer including a plurality of through holes. 
     The chamber layer may be formed by forming a chamber material layer including a liquid photosensitive polymer or a photosensitive dry film and patterning the chamber material layer. 
     The stacking of the anti reflective material layer and the nozzle material layer may include laminating a composite layer of the anti reflective material layer and the nozzle material layer, which is manufactured in a film form, on the chamber layer. 
     The forming of the nozzle layer and the anti reflective layer may include forming the nozzle layer including the nozzles by exposing and developing the nozzle material layer; and forming the anti reflective layer including the through holes connected to the nozzles by removing the anti reflective material layer exposed through the nozzles. 
     The forming of the nozzle layer and the anti reflective material layer may include forming the nozzle layer including the nozzles and the anti reflective layer including the through holes connected to the nozzle by exposing and developing the nozzle material layer. 
     According to the present general inventive concept, a nozzle having a uniform shape can be obtained by forming an anti reflective layer of a material absorbing light between a chamber layer and a nozzle layer, thereby realizing an inkjet printhead having stable ejection properties. 
     In an embodiment and utilities of the present general inventive concept, there is also provided an image forming apparatus including a feeding unit to feed a printing medium along a path, a printing unit including a print head having a substrate, a chamber layer formed on the substrate and including a plurality of ink chambers, an anti reflective layer formed of a material absorbing light on the chamber layer, and a nozzle layer formed on the anti reflective layer and including a plurality of nozzles, and to form an image on the printing medium, and a discharge unit to discharge the printing medium. 
     In an embodiment and utilities of the present general inventive concept, there is also provided an inkjet printhead including a substrate, a chamber layer formed on the substrate to form an ink chamber, a nozzle layer formed on the chamber layer, and an anti reflective layer formed of a material having a light reflecting characteristic between the chamber layer and the nozzle layer. 
     In an embodiment and utilities of the present general inventive concept, there is also provided an inkjet printhead including a nozzle layer having a nozzle, and an anti reflective layer attached to the nozzle layer to reflect light passing the nozzle layer back toward the nozzle layer. 
     In an embodiment and utilities of the present general inventive concept, there is also provided an inkjet printhead including a nozzle layer having a nozzle, and an anti reflective layer formed on the nozzle layer and having a light reflecting characteristic different from a light transmitting characteristic of the nozzle layer. 
     In an embodiment and utilities of the present general inventive concept, there is also provided an inkjet printhead including a chamber layer, a nozzle layer having a nozzle and to define an ink chamber with the nozzle layer, and an anti reflective layer to reflect light such that the light passing the nozzle layer is prevented from being incident into the ink chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and utilities 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 plan view illustrating a thermal inkjet printhead according to an embodiment of the present general inventive concept; 
         FIG. 2  is a cross-sectional view taken along a line II_II′ of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along a line III-III′ of  FIG. 1 ; 
         FIGS. 4 through 9  are cross-sectional views illustrating a method of the inkjet printhead of  FIG. 1 , according to an embodiment of the present general inventive concept; 
         FIG. 10  illustrates a method of exposing a nozzle material layer without an anti reflective layer on a chamber layer; and 
         FIG. 11  is a view illustrating an image forming apparatus having an inkjet printhead according to an 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. Size or thicknesses of constitutional elements may be exaggerated for the sake of clarity of illustration. Meanwhile, the present invention may be in many different forms and should not be construed as being limited to the embodiments set forth herein. For example, when a layer is referred to as being “on” a substrate or another layer, it can be directly on the substrate or the other layer or an intervening layer(s) may also present. 
       FIG. 1  is a schematic plan view illustrating a thermal inkjet printhead  100  according to an embodiment of the present general inventive concept.  FIG. 2  is a cross-sectional view taken along a line II-II′ of  FIG. 1 .  FIG. 3  is a cross-sectional view taken along a line III_III′ of  FIG. 1 . 
     Referring to  FIGS. 1 through 3 , a chamber layer  120 , an anti reflective layer  150 , and a nozzle layer  130  are sequentially formed on a substrate  110 . A plurality of material layers can be formed on the substrate  110 . The substrate  110  and the material layers can be collectively referred to as a substrate. The substrate  110  may be formed of, for example, silicon. An ink feed hole  111 , for supplying ink, is formed through the substrate  110 . A plurality of ink chambers  122 , to be filled with ink supplied via the ink feed hole  111 , are formed in the chamber layer  120 . A plurality of nozzles  132  through which ink is ejected are formed in the nozzle layer  130 . A plurality of through holes  152  are formed through the anti reflective layer  150  formed between the chamber layer  120  and the nozzle layer  130 . 
     An insulating layer  112 , for isolating and insulating the substrate  110  and from a plurality of heaters  114  to be described later, may be formed on the substrate  110 . The insulating layer  112  may be formed of, for example, silicon oxide. The heaters  114 , for heating ink inside the ink chambers  112  so as to generate ink bubbles, are formed on the insulating layer  112 . The heaters  114  may be formed on a bottom surface of the ink chambers  122 . The heater  114  may be formed of, for example, a heating resistor such as a tantalum-aluminum alloy, tantalum-nitride, titanium nitride, tungsten silicide or the like, but the present invention is not limited thereto. A plurality of electrodes  116  are formed on the heaters  114 . The electrode  116  is used to apply a current to the heater  114 , and is formed of a material having good conductivity. The electrode  116  may be formed of aluminum (Al), an aluminum alloy, gold (Au), silver (Ag), etc., but the present invention is not limited thereto. 
     The electrode can be connected to a control unit ( FIG. 11 ) to supply a control signal or a current to the heater  114  through the electrode according to information or data corresponding to an image to be formed on a printing medium in a printing operation. 
     A passivation layer  118  may be formed on the heaters  114  and the electrodes  116 . The passivation layer  118  prevents the heaters  114  and the electrodes  116  from contacting ink that can oxidize or corrode the heaters  114  and the electrodes  116 , and may be formed of, for example, silicon nitride or silicon oxide. An anti-cavitation layer  119  may be formed on portions of the passivation layer  118 , which is formed above the heater  114 . The anti-cavitation layer  119  protects the heater  114  from a cavitation force that is generated when the ink bubbles collapse, and may be formed of, for example, tantalum (Ta). Although not illustrated, a glue layer may be further formed on the passivation layer  118  so that the chamber layer  120  is well attached to the passivation layer  118 . 
     The chamber layer  120  is formed on the passivation layer  118 . The ink chambers  122 , to be filled with the ink supplied via the ink feed hole  111 , are formed in the chamber layer  120 . The ink chamber  122  may be disposed at both sides of the ink feed hole  111  along a longitudinal direction of the ink feed hole  111 . A plurality of restrictors  124  may be formed in the chamber layer  120  to connect the ink feed hole  111  with the ink chambers  122 . The chamber layer  120  may be formed of, for example, a photosensitive polymer. 
     An anti reflective layer  150 , formed of a material absorbing light, may be formed on the chamber layer  120 . The through holes  152  connected to the ink chambers  122  and the nozzles  132  is formed in the anti reflective layer  150 . The light transmissivity of the anti reflective layer  150  may be much smaller than that of the chamber layer  120  or the nozzle layer  130 . The nozzle layer  130  is formed on the anti reflective layer  150 . The nozzles  132  through which ink is ejected are formed in the nozzle layer  130 . The nozzle layer  130  may include a photosensitive dry film. The photosensitive dry film may be formed of, for example, a polymer. The photosensitive dry film may be a negative photoresist. The anti reflective layer  150  can be formed on the chamber layer  120  and then the nozzle layer  130  can be formed on the anti reflective layer  150  as separate layers. In this case, the anti reflective layer  150  and the nozzle layer can be sequentially formed on the chamber layer  120 . However, it is possible that the anti reflective layer  150  and the nozzle layer  130  can be formed as a composite layer of the anti reflective layer  150  and the nozzle layer  130 . That is, the composite layer can be formed in a film form. The composite layer may be formed on the chamber layer  120 . In this case, the anti reflective layer  140  and the nozzle layer  130  can be simultaneously formed on the chamber layer  120  as the composite layer. 
     As described above, in the inkjet printhead according to the present embodiment, by providing the anti reflective layer  150  formed of a material to absorb light between the chamber layer  120  and the nozzle layer  130 , the nozzle  132  having a uniform shape can be formed in the nozzle layer  130 , which will be described later. It is also possible that the nozzle layer  130  can be a uniform thickness since the light is blocked by the anti reflective layer  150  and the light is prevented from affecting the thickness of the nozzle layer  130  during a process to form the inkjet printhead  100 . 
     Hereinafter, a method of manufacturing the inkjet printhead  100  of  FIG. 1  will be described. 
       FIGS. 4 through 9  are cross-sectional views illustrating a method of the inkjet printhead  100  of  FIG. 1 , according to an embodiment of the present general inventive concept. 
     Referring to  FIG. 4 , the substrate  110  is prepared, and then the insulating layer  112  is formed on the substrate  110 . The substrate  110  may be formed of silicon. The insulating layer  112  insulates between the substrate  110  and the heaters  114  to be described later, and may be formed of, for example, silicon oxide. Then, the heaters  114 , which heat ink to generate bubbles, is formed on the insulating layer  112 . The heaters  114  may be formed by depositing a heating resistor (e.g., a tantalum-aluminum alloy, tantalum-nitride, titanium nitride, tungsten silicide, etc.) on the insulating layer  112  and then patterning the heating resistor. A plurality of electrodes  116  for applying a current to the heater  114  are formed on the heaters  114 . The electrodes  116  may be formed by depositing a metal having good conductivity, such as aluminum (Al), an aluminum alloy, gold (Au), silver (Ag), etc. and then patterning the metal. 
     A passivation layer  118  may be formed on the insulating layer  112  so as to cover the heaters  114  and the electrodes  116 . The passivation layer  118  prevents the heaters  114  and the electrodes  116  from contacting ink that can oxidize or corrode the heaters  114  and the electrodes  116 , and may be formed of, for example, silicon nitride or silicon oxide. The anti-cavitation layer  119  may be further formed on portions of the passivation layer  118 , which is formed above the heater  114 . The anti-cavitation layer  119  protects the heater  114  from a cavitation force that is generated when the bubbles collapse, and may be formed of, for example, tantalum (Ta). 
     Referring to  FIG. 5 , the chamber layer  120  having the ink chambers  122  is formed on the passivation layer  118  and at least a portion of the anti-cavitation layer  119 . The chamber layer  120  may be formed by coating a chamber material layer (not illustrated) including, for example, a liquid photosensitive polymer or a photosensitive dry film on the passivation layer  118  and at least a portion of the anti-cavitation layer  119 , and then patterning the chamber material layer. Accordingly, the ink chambers  112 , to be filled with ink to be ejected, are formed in the chamber layer  120 . In addition, the restrictors  124  (see  FIG. 1 ) may be formed in the chamber layer  120  to connect the ink feed hole  111  with the ink chambers  122 . A glue layer (not illustrated) may be further formed on the passivation layer  118  and/or at least a portion of the anti-cavitation layer  119  prior to forming the chamber  120  so that the chamber layer  120  is well attached to the passivation layer  118  and/or at least a portion of the anti-cavitation layer  119 . The glue layer may be formed of, for example, a photosensitive polymer. 
     Referring to  FIG. 6 , an anti reflective material layer  150 ′ and a nozzle material layer  130 ′ are formed on the chamber layer  120 . The anti reflective material layer  150 ′ may be formed of a material absorbing light and having light transmissivity that is much lower than a material of at least one of the chamber layer  120  and the nozzle layer  130 . The nozzle material layer  130 ′ may include a photosensitive dry film. The photosensitive dry film may include a negative photoresist. The anti reflective material layer  150 ′ and the nozzle material layer  130 ′ may be simultaneously formed on the chamber layer  120 . In particular, the anti reflective material layer  150 ′ and the nozzle material layer  130 ′ may be formed by laminating a composite layer, which is formed in a film form by coating the anti reflective material layer  150 ′ on the photosensitive dry film, on the chamber layer  120 . Alternatively, the anti reflective material layer  150 ′ and the nozzle material layer  130 ′ may be sequentially formed on the chamber layer  120 . 
     Referring to  FIG. 7 , the nozzle material layer  130 ′ is exposed and developed by photolithography. In particular, a photomask  170  having a predetermined mask pattern is positioned on the nozzle material layer  130 ′, and then ultra violet (UV) rays are radiated on the photomask  170  so as to expose the nozzle material layer  130 ′. Since the anti reflective material layer  150 ′ is formed of a material absorbing light, the UV rays cannot be transmitted through the anti reflective material layer  150 ′, and accordingly only a desired portion of the nozzle material layer  130 ′ can be exposed. By removing a portion of the nozzle material layer  130 ′, which is not exposed, by a developing solution, the nozzle  132  (see  FIG. 8 ) is formed in a subsequent operation, which will be described later. Likewise, when the anti reflective material layer  150  is formed on the chamber layer  120 , the nozzles  132  having a uniform shape can be formed, as described later. 
       FIG. 10  illustrates the case where a nozzle material layer  130 ′ is exposed when the anti reflective material layer  150 ′ (see  FIG. 6 ) is not formed on a chamber layer  120 . Referring to  FIG. 10 , if the anti reflective material layer  150 ′ is not formed between the chamber layer  120  and the nozzle material layer  130 ′, when the nozzle material layer  130 ′ is exposed, light, such as UV rays transmitted through the nozzle material layer  130 ′ are diffused-reflected on an anti-cavitation layer  119  or a layer having a diffusive and/or reflective characteristic to cause the reflected light to affect another layer, for, example, the nozzle material layer  130 ′. In particular, when an electrode material formed on a heater  114  is patterned when forming an inkjet printhead, an end of an electrode is formed with a step difference. Thus, a step difference  162  is also generated on a portion of the anti-cavitation layer  119 , which corresponds to the end of the electrode  116 . In addition, the electrode  116  is formed of aluminum that might include impurities such as silicon, copper, etc. When the electrode  116  is formed by patterning the electrode material, aluminum is removed by wet etching. At this time, impurities such as silicon, copper, etc., remain on the heater  114 . Since a passivation layer  118  and the anti-cavitation layer  119  are sequentially formed on the heater  114  in subsequent operations, protrusions  161  corresponding to the impurities remaining on the heater  114  are formed on the anti-cavitation layer  119 . 
     Likewise, when the protrusions  161  or the step difference  162  is formed on the anti-cavitation layer  119 , UV rays transmitted through the nozzle material layer  130 ′ are diffused-reflected during the exposing of the nozzle material layer  130 ′ due to the step difference  162  or the protrusions  161 . Since an inappropriate portion of the nozzle material layer  130 ′ is also exposed due to the diffused-reflected UV rays, a nozzle having an uneven shape might be formed. 
     However, according to the present embodiment, as illustrated in  FIGS. 4 through 9 , when the anti reflective material layer  150 ′ is formed of a material absorbing light and disposed on the chamber layer  120 , UV rays transmitted through the nozzle material layer  130 ′ can be blocked by the anti reflective material layer  150 ′ during the exposing of the nozzle material layer  130 ′. Thus, since a desired portion of the nozzle material layer  130 ′ can be exposed, the nozzle  130  having a uniform shape (e.g., a predetermined diameter) can be formed. 
     Referring to  FIG. 8 , the nozzle layer  130  having the nozzles  132  is formed on the anti reflective material layer  150 ′ by exposing the nozzle material layer  130 ′ and then developing the nozzle material layer  130 ′. Referring to  FIG. 9 , the anti reflective layer  150  having a plurality of through holes  152  therethrough is formed by removing the anti reflective material layer  150 ′ formed below the nozzles  132  by dry etching or wet etching. The through holes  152  are connected to the ink chambers  122  and the nozzles  132 . In dry etching, ashing with oxygen plasma may be used, for example. In wet etching, a predetermined developing solution that can develop only the anti reflective material layer  150 ′ may be used. As described so far, only the case of forming the anti reflective layer  150 , including forming the nozzle layer  130  by developing the nozzle material layer  130 ′ and then removing a portion of the anti reflective material layer  150 ′, which is exposed through the nozzles  132 , has been described. However, in the present embodiment, during the developing a portion of the nozzle material layer  130 ′, which is not exposed, a portion of the anti reflective material layer  150 ′, formed below the portion of the nozzle material layer  130 ′, may also be developed. In this case, the nozzle layer  130  and the anti reflective layer  150  can be simultaneously formed by exposing and developing the nozzle material layer  130 ′. 
     In the meantime, the ink feed hole  111  (see  FIG. 1 ), for supplying ink to the ink chambers  122 , may be formed in the substrate  110  in an early stage or a late stage of a process of manufacturing an inkjet printhead. For example, the ink feed hole  111  may be formed through the substrate  110  prior to forming the chamber layer  120  on the substrate  110 , or alternatively the ink feed hole  111  may be formed in the substrate  110  after forming the nozzle layer  130 . 
       FIG. 11  is a view illustrating an image forming apparatus  1100  according to an embodiment of the present general inventive concept. Referring to  FIGS. 1-3  and  11 , the image forming apparatus  1100  includes a feeding unit to feed a printing medium M along a path P, a printing unit  1120  having an inkjet printhead  1130  to form an image on the printing medium M, a discharging unit to discharge the printing medium M, and a control unit to control the above described units to perform a printing operation so that the image can be formed on the printing medium M. It is possible that the control unit  1150  may have an interface to communicate with an external device through a wired or wireless communication line to receive data corresponding to the image. The external device may be another image forming apparatus, a personal computer, a device connected to the control unit  1150  through a network, a scanning device to scan a document to generate the data. The inkjet printhead  100  of  FIG. 1  can be used as the inkjet printhead  1130  of  FIG. 11 . The inkjet printhead  1130  may further include an ink cartridge with an ink storage to supply the ink to the inkjet printhead  110  through the feed hole  111 . 
     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.