Patent Publication Number: US-2011049095-A1

Title: Method of forming hydrophobic coating layer on surface of nozzle plate of inkjet printhead

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of prior Application Ser. No. 11/425,204, filed on Jun. 20, 2006 in the U.S. Patent and Trademark Office, which claims priority under 35 U.S.C. §119(a) from Korean Patent Applications Nos. 10-2005-0113498, filed on Nov. 25, 2005, in the Korean Intellectual Property Office, and 10-2005-0124379, filed on Dec. 16, 2005, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to an inkjet printhead having a hydrophobic layer, and more particularly, to a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead. 
     2. Description of the Related Art 
     An inkjet printhead is a device that ejects fine ink droplets onto a desired position of a recording medium to print an image of a predetermined color. The inkjet printhead may be roughly classified into two types of printheads, depending on an ink ejecting method employed: thermally-driven inkjet printheads and piezoelectric inkjet printheads. A thermally-driven inkjet printhead generates a bubble in ink using a heat source and ejects the ink using an expansion force of the bubble. A piezoelectric inkjet printhead deforms a piezoelectric element and ejects ink using a pressure applied to the ink due to the deformation of the piezoelectric element. 
       FIG. 1  is a sectional view illustrating a construction of a conventional piezoelectric inkjet printhead. 
     Referring to  FIG. 1 , a channel plate  10  includes a manifold  13 , a plurality of restrictors  12 , and a plurality of pressure chambers  11 . A nozzle plate  20  includes a plurality of nozzles  22  corresponding to the pressure chambers  11 . Also, a piezoelectric actuator  40  is provided on an upper portion of the channel plate  10 . The manifold  13  is a passage supplying ink flowing from an ink storage (not illustrated) to each of the pressure chambers  11 , and each of the restrictors  12  is a passage through which the ink flows from the manifold  13  into each of the pressure chambers  11 . The plurality of pressure chambers  11 , which are filled with ink to be ejected, are arranged on one side or both sides of the manifold  13 . Each pressure chamber  11  changes its volume as the piezoelectric actuator  40  is driven, thereby creating a pressure change required for an ejection of ink or for an in-flow of ink. A portion that constitutes an upper wall of each of the pressure chambers  11  contained in the channel plate  10  serves as a vibration plate  14  that is deformable by a driving of the piezoelectric actuator  40 . 
     The piezoelectric actuator  40  includes a lower electrode  41 , a piezoelectric layer  42 , and an upper electrode  43  sequentially stacked on the channel plate  10 . A silicon oxide layer  31  is formed as an insulation layer between the lower electrode  41  and the channel plate  10 . The lower electrode  41  is formed on an entire surface of the silicon layer  31  to serve as a common electrode. The piezoelectric layer  42  is formed on the lower electrode  41  such that the piezoelectric layer  42  is positioned on the plurality of pressure chambers  16 . The upper electrode  43  is formed on the piezoelectric layer  42  to serve as a drive electrode, applying a voltage to the piezoelectric layer  42 . 
     In the inkjet printhead having the above construction, water-repellent processing of a surface of the nozzle plate  20  has a direct influence on an ink ejection performance thereof, such as a directionality and an ejection speed of an ink droplet ejected through each of the nozzles  22 . To improve an ink ejection performance, the surface of the nozzle plate  20  outside of the nozzles  22  should have a water-repellent characteristic, i.e., should be hydrophobic, and an inner wall of each of the nozzles  22  should be hydrophilic. In detail, when the surface of the nozzle plate  20  outside of the nozzles  22  is hydrophobic, ink wetting on the surface of the nozzle plate  20  is prevented, so that the directionality of ejected ink may be improved. Also, when the inner wall of each of the nozzles  22  is hydrophilic, a contact angle with respect to an ink droplet decreases and thus capillary force increases, so that a refill time of ink is shortened and an ejection frequency may be increased. Also, since each of the nozzles  22  is filled with ink up to an exit thereof, a uniformity of ink ejection may be improved. 
     A method of forming a hydrophobic coating layer over the entire nozzle plate  20  having the nozzles  22  therein using an electron beam evaporation method has been conventionally-used. According to this conventional method, the hydrophobic coating layer is formed on the inner wall of each of the nozzles  22 , as well as the surface of the nozzle plate  20  outside of the nozzles  22 . The hydrophobic coating layer formed on the inner wall of each of the nozzles  22  reduces refill characteristics of ink and ejection uniformity. 
     To solve these problems, conventional methods of forming a hydrophobic coating layer only on the surface of the nozzle plate  20  are under development. 
       FIG. 2  is a view illustrating a conventional inkjet printhead on which a sulphur compound layer is formed as a hydrophobic coating layer on a surface of a nozzle plate  51  thereof. 
     Referring to  FIG. 2 , after a metal layer  52  is formed on the surface of the nozzle plate  51  including a plurality of nozzles  55 , each nozzle  55  being formed to pass through the nozzle plate  51 , a sulphur compound is coated on the surface of the metal layer  52  to form a sulphur compound layer  53 . The sulphur compound is selectively coated on the surface of the metal layer  52 . However, according to this method, there is a high probability that the metal layer  52  is deposited on an inner wall of each of the nozzles  55  as well as the surface of the nozzle plate  51 . Also, when a number of the nozzles  55  is large, the metal layer  52  may be non-uniformly deposited on different portions of each of the nozzles  55 . In this case, the sulphur compound layer  53  may be formed on the inner wall of each of the nozzles  55  or may be non-uniformly formed. When the sulphur compound layer  53 , which is a hydrophobic coating layer, is not properly formed, areas around each of the nozzles  55  are easily contaminated by ink and an ejection speed of an ink droplet is reduced or an ejection direction of an ink droplet becomes non-uniform, so that an ejection performance is impaired. 
       FIG. 3  is a view illustrating a conventional inkjet printhead on which a water-repellent layer including a fluorine resin is formed on a surface of a nozzle plate  70  thereof. 
     Referring to  FIG. 3 , a water-repellent layer  90  is formed on the surface of the nozzle plate  70  having nozzles  72 . This water-repellent layer  90  includes a fluorine resin particle  94  and a hard body  98  contained in a nickel base  96 . A fluorine resin layer  92  is formed on the surface of the water-repellent layer. However, since nickel is reactive with a portion of ink, nickel is undesirable for commercial use. 
     Japanese Patent Laid-Open Publication No. hei 7-314693 discloses a method of forming a water-repellent layer on a surface of a nozzle plate by blowing a gas through nozzles of the nozzle plate to prevent the water-repellent layer from being formed on an inner surface of each of the nozzles. However, this method requires a complicated apparatus and a difficult process, and thus it is difficult and expensive to use this method. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead to improve ejection directionality and ejection uniformity of the inkjet printhead and to increase an ejection frequency. 
     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 a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead, the method including forming a plurality of nozzles in the nozzle plate, each of the nozzles having an exit and an inner wall, stacking a film on the surface of the nozzle plate such that a portion of the film covers the exit of each of the nozzles, forming a predetermined metal layer on the inner wall of each of the nozzles and the portion of the film covering the exit of each of the nozzles using a plating method, removing the film from the surface of the nozzle plate, forming the hydrophobic coating layer on the surface of the nozzle plate such that the hydrophobic coating layer covers the predetermined metal layer exposed through the exit of each of the nozzles, and removing the predetermined metal layer formed on the inner wall of each of the nozzles and the hydrophobic coating layer formed on the surface of the metal layer. 
     The method may further include forming a seed layer on the inner wall of each of the nozzles and the inner surface of the film covering the exit of each of the nozzles after the stacking of the film and before forming the predetermined metal layer. 
     The method may further include etching the predetermined metal layer exposed through the exit of each of the nozzles to a predetermined depth after the removing of the film. The predetermined metal layer may be etched to a depth of about 1 to about 10 μm. 
     The predetermined metal layer may be formed using a damascening plating method. 
     The hydrophobic coating layer formed on the surface of the predetermined metal layer may be removed by a dry etching method after the predetermined metal layer formed on the inner wall of each of the nozzles is removed. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead, the method including forming a plurality of nozzles in the nozzle plate, each of the nozzles having an exit, stacking a film on the surface of the nozzle plate such that the film covers the exit of each of the nozzles, forming a polymer layer on an inner wall of each of the nozzles and an inner surface of the film covering the exit of each of the nozzles, removing the film from the surface of the nozzle plate, forming a hydrophobic coating layer on the surface of the nozzle plate such that the hydrophobic coating layer covers the polymer layer exposed through the exit of each of the nozzles, and removing the polymer layer formed on the inner wall of each of the nozzles and the hydrophobic coating layer formed on the surface of the polymer layer. 
     The method may further include etching the polymer layer exposed through the exit of each of the nozzles to a predetermined depth after the removing of the film. The polymer layer may be etched using a dry etching method. The polymer layer may be etched to a depth of about 1 to about 10 μm. 
     The forming of the polymer layer may include coating a polymer in a liquid state on the inner wall of each of the nozzles and the inner surface of the film covering the exit of each of the nozzles, and thermally treating the coated polymer to harden the coated polymer. The polymer in the liquid state may be coated using a spray coating method. 
     The polymer layer may be formed of a photoresist. 
     The hydrophobic coating layer formed on the surface of the polymer layer may be removed through a dry etching method after the polymer layer formed on the inner wall of each of the nozzles is removed. 
     The hydrophobic coating layer may include a material that is not damaged by the removing of the polymer layer. The hydrophobic coating layer may include parylene. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of forming a hydrophobic layer on a nozzle plate of an inkjet printhead, the nozzle plate having inner and outer surfaces and a plurality of nozzles having nozzle openings and inner nozzle surfaces, the method including forming a first layer having a predetermined material on the outer surface of the nozzle plate to cover the nozzle openings, forming a second layer having a predetermined material on the inner surface of the nozzles plate to cover the inner nozzle surfaces and the nozzle openings, removing the first layer to uncover the outer surface of the nozzle plate and to expose portions of the second layer through the nozzle openings, forming the hydrophobic layer on the outer surface of the nozzle plate, the nozzle openings, and the exposed portions of the second layer, and removing the second layer and the portion of the hydrophobic layer formed on the exposed portions of the second layer. 
     The second layer may include a metal layer having at least one metal compound. The second layer may include a plurality of the metal layers, each having the at least one metal compound. The second layer may include a polymer layer having at least one polymer material. The at least one polymer material may be a light sensitive polymer material. The second layer may include a plurality of the polymer layers, each having the at least one polymer material. 
     A thickness of a first portion of the second layer formed on upper portions of the inner nozzle surfaces may be greater than a thickness of a second portion of the second layer on remaining portions of the inner nozzle surfaces. The forming of the hydrophobic layer may include forming the hydrophobic layer on upper portions of the inner nozzle surfaces located within a predetermined distance from the nozzle openings. The method may further include etching the second layer to a predetermine depth before forming the hydrophobic layer to uncover the upper portions of the inner nozzle surfaces. 
     The method may further include forming an intermediate layer on the inner surface of the nozzle plate, and forming the second layer on the intermediate layer. The intermediate layer may include at least one metal and the second layer may include at least one metal. The intermediate layer may include a metal and the second layer may also include the metal. The intermediate layer may include a plurality of metal layers. 
     The foregoing and/or other aspects and utilities of the present general inventive concept may also be achieved by providing a method of forming a hydrophobic layer on a nozzle plate of an inkjet printhead, the nozzle plate having first and second surfaces, a plurality of nozzles having nozzle openings and inner nozzle surfaces, and a covering layer formed on the second surface of the nozzle plate to cover the inner nozzle surfaces and the nozzle openings and having exposed portions exposed through the nozzle openings to the first surface of the nozzle plate, the method including forming the hydrophobic layer on the first surface of the nozzle plate, the nozzle openings, and the exposed portions of the covering layer, and removing the covering layer and portions of the hydrophobic layer formed on the exposed portions of the covering 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 sectional view illustrating a construction of a conventional piezoelectric inkjet printhead; 
         FIG. 2  is a sectional view illustrating a conventional inkjet printhead on which a sulphur compound layer is formed as a hydrophobic coating layer on a surface of a nozzle plate thereof; 
         FIG. 3  is a sectional view illustrating a conventional inkjet printhead on which a water-repellent layer including a fluorine resin is formed on a surface of a nozzle plate thereof; 
         FIGS. 4A through 4H  are views illustrating a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an inkjet printhead, according to an embodiment of the present general inventive concept; and 
         FIGS. 5A through 5G  are views illustrating a method of forming a hydrophobic coating layer on a surface of a nozzle plate of an 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. In the drawings, thicknesses of layers and regions may be exaggerated for clarity. A method of forming a hydrophobic coating layer on a surface of a nozzle plate, according to embodiments of the present general inventive concept, may be used on a thermal-driven type inkjet printhead as well as a piezoelectric inkjet printhead. 
       FIGS. 4A through 4H  are views illustrating a method of forming a hydrophobic coating layer on a surface of a nozzle plate  120  of an inkjet printhead, according to an embodiment of the present general inventive concept. In the drawings, a partial portion of the nozzle plate  120  is illustrated with a single nozzle  122  for convenience; however, the nozzle plate  120  includes a plurality of nozzles  122 , such as tens to hundreds of nozzles  122  arranged in a line or a plurality of lines. 
     First, referring to  FIG. 4A , the plurality of nozzles  122 , each having a predetermined shape, are formed in the nozzle plate  120 . The nozzle plate  120  may be, for example, a silicon wafer, which is widely used to manufacture a semiconductor device. Alternatively, the nozzle plate  120  may be, for example, a glass substrate or a metal substrate. Each of the nozzles  122  may have a shape such that a lower portion of each of the nozzles  122  has a decreasing cross-section along a direction from the lower portion to an exit of each of the nozzles  122  (i.e., a decreasing cross-section in an exit direction), and such that an upper portion of each of the nozzles  122  has a constant cross-section along the exit direction. Referring to  FIG. 4B , a predetermined film  130  is stacked on the surface of the nozzle plate  120  to cover the exit of each of the nozzles  122 . 
     Referring to  FIG. 4C , a seed layer  142  is formed on the inner wall of each of the nozzles  122  and an inner surface of the predetermined film  130  covering the exit of each of the nozzles  122 . The seed layer  142  is a layer that allows a predetermined metal layer  144  (see  FIG. 4D ) to be swiftly plated on the inner wall of each of the nozzles  122  and the inner surface of the film  130 . Here, the seed layer  142  may be formed of, for example, Cr and Cu, in which the Cr is formed on the inner wall of each of the nozzles  122  and the inner surface of the film  130  and the Cu is formed on Cr. However, the seed layer  142  may be formed of various metals besides Cr and Cu depending on a material to be plated. 
     Referring to  FIG. 4D , the predetermined metal layer  144  is formed on the seed layer  142  (which is formed on the inner wall of each of the nozzles  122  and the inner surface of the film  130  covering the exit of each of the nozzles  122 ) using a plating method. Here, the metal layer  144  may be formed of, for example, Cu. However, the metal layer  144  may be formed of various metals besides Cu. A variety of plating methods may be used to form the metal layer  144 , such as a damascening plating method. When the damascening plating method is used to form the metal layer  144 , plating can be well performed on an upper portion of each of the nozzles  122 , which is formed narrowly at the exit of each of the nozzles  122 . Accordingly, a portion of the metal layer  144  formed on the upper portion of each of the nozzles  122  has a thickness that is thicker than a thickness of a portion of the metal layer  144  formed on the inner wall of each of the nozzles  122 . 
     Referring to  FIG. 4E , the film  130  stacked on the surface of the nozzle plate  120  is removed. The film  130  may be removed, for example, by using acetone or by manually removing the film  130  from the surface of the nozzle plate  120 . The seed layer  142  and the metal layer  144  exposed through the exit of each of the nozzles  122  may be etched to a predetermined depth. When the seed layer  142  and the metal layer  144  are etched to the predetermined depth, a hydrophobic coating layer  150  (see  FIG. 4F ) may be formed on the inner wall at an upper end of each of the nozzles  122 , as described below, to more effectively prevent ink wetting on the surface of the nozzle plate  120  located on the exit of each of the nozzles  122 . Here, the depth to which the seed layer  142  and the metal layer  144  are etched may be controlled to a desired depth. For example, the metal layer  144  may be etched to a depth of about 1 to about 10 μm. 
     Referring to  FIG. 4F , the hydrophobic coating layer  150  is formed on an entire surface of the nozzle plate  120  to cover the metal layer  144  exposed through the exit of each of the nozzles  122 . Referring to  FIG. 4G , the seed layer  142  and the metal layer  144  formed on the inner wall of each of the nozzles  122  are removed by, for example, using an etching process. Referring to  FIG. 4H , the hydrophobic coating layer  150  covering the exit of each of the nozzles  122  is removed by, for example, using a dry etching process. Alternatively, a portion of the hydrophobic coating layer  150  covering the exit of each of the nozzles  122  may be simultaneously removed during the removing of the seed layer  142  and the metal layer  144 , as opposed to being removed after the seed layer  142  and the metal layer  144  are removed. 
     When the hydrophobic coating layer  150  covering the exit of each of the nozzles  122  is removed, the hydrophobic coating layer  150  is formed on the surface of the nozzle plate  120  outside of the nozzles  122  and on the inner wall at the upper end of each of the nozzles  122  as illustrated in  FIG. 4H . Accordingly, the surface of the nozzle plate  120  outside of the nozzles  122  and the inner wall at the upper end of each of the nozzles  122  are hydrophobic, and an entire inner wall except the inner wall at the upper end of each of the nozzles  122  is hydrophilic. According to another embodiment, an operation of etching the seed layer  142  and the metal layer  144  to a predetermined depth described with reference to  FIG. 4E  may be omitted. In this case, the hydrophobic coating layer  150  is formed only on the surface of the nozzle plate  120  outside the nozzles  122 , and not on the inner wall at the upper end of each of the nozzles  122 . 
       FIGS. 5A through 5G  are views illustrating a method of forming a hydrophobic coating layer on a surface of a nozzle plate  220  of an inkjet printhead, according to another embodiment of the present general inventive concept. 
     Referring to  FIG. 5A , a plurality of nozzles  222  each having a predetermined shape are formed in the nozzle plate  220 . The nozzle plate  220  may be, for example, a silicon wafer, which is widely used to manufacture a semiconductor device. Alternatively, the nozzle plate  220  may be, for example, a glass substrate or a metal substrate. Each of the nozzles  222  may have a shape such that a lower portion of each of the nozzles  222  has a decreasing cross-section along a direction from the lower portion to an exit of each of the nozzles  222  (i.e., a decreasing cross-section in an exit direction), and such that an upper portion of each of the nozzles  222  has a constant cross-section along the exit direction. Referring to  FIG. 5B , a predetermined film  230  is stacked on the surface of the nozzle plate  220  to cover the exit of each of the nozzles  222 . 
     Referring to  FIG. 5C , a polymer layer  240  is formed on an inner wall of each of the nozzles  222  and an inner surface of the film  230  covering the exit of each of the nozzles  222 . Here, the polymer layer  240  may be formed of, for example, a photoresist. Alternatively, the polymer layer  240  may be formed of a material other than the photoresist. The polymer layer  240  may be formed by, for example, coating a polymer in a liquid state on the inner wall of each of the nozzles  222  and the inner surface of the film  230  (covering the exit of each of the nozzles  222 ) at a predetermined thickness, and thermally treating and hardening the coated polymer. The polymer in a liquid state may be coated by, for example, using a spray coating process. 
     Referring to  FIG. 5D , the film  230  stacked on the surface of the nozzle plate  220  is removed. Here, the film  230  may be removed, for example, by using acetone or by manually removing the film  230  from the surface of the nozzle plate  220 . The polymer layer  240  exposed through the exit of each of the nozzles  222  may be etched to a predetermined depth. Here, the polymer layer  240  may be etched, for example, using a dry etching process. When the polymer layer  240  is etched to the predetermined depth, a hydrophobic coating layer  250  (see  FIG. 5G ) may be formed on the inner wall at an upper end of each of the nozzles  122 , as described below, to more effectively prevent ink wetting on the surface of the nozzle plate  220  located on the exit of each of the nozzles  222 . Here, the depth to which the polymer layer  240  is etched may be controlled to a desired value. For example, the polymer layer  240  may be etched to a depth of about 1 to about 10 μm. 
     Referring to  FIG. 5E , the hydrophobic coating layer  250  is formed at a predetermined thickness on an entire surface of the nozzle plate  220  to cover the polymer layer  240  exposed through the exit of each of the nozzles  222 . The hydrophobic coating layer  250  may be formed of a material that is not damaged by the removing the polymer layer  240 . For example, the hydrophilic coating layer  250  may be formed of parylene. 
     Referring to  FIG. 5F , the polymer layer  240  formed on the inner wall of each of the nozzles  222  is removed. The polymer layer  240  may be removed by, for example, a striper, such as acetone. Referring to  FIG. 5G , when the hydrophobic coating layer  250  covering the exit of each of the nozzles  222  is removed (for example, using the dry etching process), the hydrophobic coating layer  250  is formed on the surface of the nozzle plate  220  outside the nozzles  222  and the inner wall at the upper end of each of the nozzles  222 . Accordingly, the surface of the nozzle plate  220  outside the nozzles  222  and on the inner wall at the upper end of each of the nozzles  222  are hydrophobic, and an entire inner wall except the inner wall at the upper end of each of the nozzles  222  has is hydrophilic. According to the present embodiment, an operation of etching the polymer layer  240  to the predetermined depth described with reference to  FIG. 5D  may be omitted. In this case, the hydrophobic coating layer  250  is formed only on the surface of the nozzle plate  220  outside the nozzles  222 , and not on the inner wall at the upper end of each of the nozzles  222 . 
     As described above, according to various embodiments of the present general inventive concept, a surface of a nozzle plate outside of the nozzles is hydrophobic, so that ink wetting on the surface of the nozzle plate is prevented and thus directionality of ejected ink may be secured. Also, an inner wall of each of the nozzles is hydrophilic, so that a refill time of ink is shortened and an ejection frequency is increased. Also, since each of the nozzles is filled with ink up to an exit thereof, a uniformity of ink ejection may be improved. 
     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.