Patent Publication Number: US-2005134643-A1

Title: Ink-jet printhead and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the priority of Korean Patent Application No. 2003-94416, filed on Dec. 22, 2003, 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 ink-jet printhead and a method of manufacturing the same. More particularly, the present general inventive concept relates to an ink-jet printhead that has a high ink ejecting efficiency, and the method of manufacturing the ink-jet printhead.  
      2. Description of the Related Art  
      Generally, ink-jet printheads are devices that print a predetermined image in color or black and white by ejecting a small volume droplet of printing ink at a desired position on a recording sheet. Ink-jet printheads are usually categorized into two types according to an ink droplet ejection mechanism used. One type is a thermally driven ink-jet printhead in which a heat source is employed to form and expand bubbles in the ink to cause ink droplets to be ejected. The other type is a piezoelectrically driven ink-jet printhead in which a piezoelectric material is deformed to exert pressure on the ink to cause ink droplets to be ejected.  
      Hereinafter, the ink ejection mechanism in the thermally driven ink-jet printhead will be described in greater detail. When a pulse current flows through a heater composed of an electric resistance heating material, the heater generates heat and ink adjacent to the heater is heated to about 300° C., thereby boiling the ink. As the ink is boiled, bubbles are generated in the ink, and the bubbles expand and apply pressure to the ink in an ink chamber. As a result, the ink near a nozzle is ejected out of the ink chamber in droplets through the nozzle.  
      The thermal driving method includes a top-shooting method, a side-shooting method, and a back-shooting method depending on a growth direction of bubbles and an ejection direction of ink the droplets. In the top-shooting method, the bubble growth direction is the same as the direction in which the ink droplets are ejected. In the side-shooting method, the bubble growth direction is at a right angle to the direction in which the ink droplets are ejected. In the back-shooting method, the bubble growth direction is opposite to the direction in which the ink droplets are ejected.  
      An ink-jet printhead using the thermal driving method as described above should satisfy the following requirements. First, the manufacturing of the ink-jet printheads should be as simple as possible, costs of the manufacture of the ink-jet printheads should be low, and mass production of the ink-jet printheads should be easy. Second, in order to obtain a high-quality image, cross talks between adjacent nozzles should be suppressed while a distance between adjacent nozzles should be small. That is, in order to increase dots per inch DPI, a plurality of nozzles should be arranged with a high density. Third, in order to perform a high-speed printing operation, a period in which the ink chamber is refilled with ink after the ink is ejected out of the ink chamber should be as short as possible and the cooling of heated ink and a heater should be performed quickly to increase a driving frequency.  
       FIG. 1  is a partial perspective view illustrating a conventional ink-jet printhead using the top-shooting method, and  FIG. 2  is a cross-sectional view illustrating the ink-jet printhead of  FIG. 1 .  
      Referring to  FIG. 1 , the ink-jet printhead includes a base plate  10  on which a plurality of material layers are deposited, a chamber layer  20  deposited on the base plate and defining an ink chamber  22 , and a nozzle plate  30  deposited on the chamber layer  20 . The ink chamber  22  is filled with ink, and a heater  13  ( FIG. 2 ) to heat the ink and generate bubbles in the ink is installed under the ink chamber  22 . Ink feedholes  24  form paths to supply the ink into the ink chamber  22 , and are connected to an ink reservoir (not shown). A plurality of nozzles  32  through which the ink is ejected are formed in positions corresponding to each ink chamber  22 .  
      Referring to  FIG. 2 , an insulating layer  12  to insulate a substrate  11  from the heater  13  is formed on the substrate  11  composed of silicon. The heater  13  is formed on the insulating layer  12  and heats ink in the ink chamber  22 , thereby generating bubbles in the ink. The heater  13  is formed by vapor-depositing a thin film of tantalum nitride TaN or tantalum-aluminum TaAl on the insulating layer  12 . A conductor  14  through which a current is supplied to the heater  13  is installed on the heater  13 . The conductor  14  is formed of a metallic material having good conductivity.  
      A passivation layer  15  to passivate the heater  13  and the conductor  14  is formed on the heater  13  and the conductor  14 . The passivation layer  15  prevents the heater  13  and conductor  14  from oxidizing and directly contacting the ink, and is composed of silicon nitride. An anti-cavitation layer  16 , on which the ink chamber  22  is formed, is formed on the passivation layer  15 .  
      The chamber layer  20  defining the ink chamber  22  is deposited on the base plate  10 . The chamber layer  20  is generally composed of a material from the polyacrylate group. The nozzle plate  30  in which the nozzles  32  are formed is deposited on the chamber layer  20 . A polyimide PI film processed by laser or a nickel Ni plate plated with gold Au is used as the nozzle plate  30 .  
      In the configuration as described above, when heat is generated by the heater  13  and the ink chamber  22  is filled with the ink, bubbles are generated in the ink and expand near the heater  13 , and the generated bubbles apply pressure to the ink in the ink chamber  22 , thereby forcing the ink in the ink chamber  22  to be ejected in droplets through the nozzles  32 .  
      However, in the ink-jet printhead as described above, the chamber layer  20  is constantly in contact with high temperature ink. Therefore, the material forming the chamber layer  20  may swell and the chamber layer  20  may be separated from the substrate  11  or the nozzle plate  30 . When the separation between the layers occurs, ink ejection is largely effected, and the quality of printing decreases.  
     SUMMARY OF THE INVENTION  
      The present general inventive concept provides an ink-jet printhead that has a high ink ejecting efficiency, and a method of manufacturing the ink-jet printhead.  
      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 advantages of the present general inventive concept are achieved by providing an ink-jet printhead comprising: a substrate on which a heater to boil ink and a conductor to supply current to the heater are formed, a chamber layer disposed on the substrate, the chamber layer defining an ink chamber containing the ink and at least part of the chamber layer being composed of polyimide, and a nozzle plate disposed on the chamber layer, the nozzle plate having nozzles through which the ink is ejected.  
      The polyimide may be formed by imidizing polyamic acid at a predetermined temperature.  
      The predetermined temperature may be 240° C. to 400° C.  
      The polyimide may be formed when the nozzle plate is attached to an upper surface of the chamber layer.  
      A thickness of the chamber layer may be 10 μm to 100 μm.  
      An ink feedhole to supply the ink to the ink chamber may be formed in the substrate.  
      An insulating layer to insulate the substrate from the heater may be further included, the insulating layer being formed on the substrate.  
      A passivation layer to passivate the heater and the conductor may be further included, the passivation layer being formed above the heater and the conductor.  
      An anti-cavitation layer may be further included, the anti-cavitation being formed above the passivation layer.  
      The nozzle plate may be composed of one of polyimide and nickel Ni.  
      The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by providing a method of manufacturing an ink-jet printhead comprising forming a heater and a conductor on a substrate, forming a chamber layer defining an ink chamber by coating polyamic acid on the substrate and patterning the polyamic acid, and attaching a nozzle plate having nozzles to an upper surface of the chamber layer at a predetermined temperature and converting at least part of the polyamic acid into polyimide.  
      The forming of the chamber layer may include forming a polyamic acid film by coating the polyamic acid on the substrate to a predetermined thickness and baking the polyamic acid, and patterning the polyamic acid film.  
      The polyamic acid may be coated on the upper surface of the substrate by spin coating.  
      The thickness of polyamic acid film may be 10 μm to 100 μm.  
      The polyamic acid film may be patterned using a photolithography process.  
      The polyamic acid film may be patterned using dry etching.  
      The nozzle plate may be attached to the upper surface of the chamber layer at a temperature of 240° C. to 400° C.  
      Forming an ink feedhole may be further included to supply the ink into the ink chamber in the substrate. 
    
    
     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 partial perspective view illustrating a conventional ink-jet printhead;  
       FIG. 2  is a cross-sectional view illustrating the ink-jet printhead of  FIG. 1 ;  
       FIG. 3  is a top view schematically illustrating an ink-jet printhead according to an embodiment of the present general inventive concept;  
       FIG. 4  is a vertical cross-sectional view illustrating the ink-jet printhead of  FIG. 3  taken along the line IV-IV′;  
       FIGS. 5A through 5F  are cross-sectional views illustrating a method of manufacturing an ink-jet printhead according an the embodiment of the present general inventive concept;  
       FIG. 6A  is a top view illustrating a sample to test adhesive strength; and  
       FIG. 6B  is a side view illustrating a sample to test adhesive strength. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the embodiment of the present general inventive concept, examples of which are illustrating in the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are described below in order to explain the present general inventive concept, referring to the figures. In the figures, the thicknesses of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present.  
       FIG. 3  is a top view schematically illustrating an ink-jet printhead using a top-shooting method according to an embodiment of the present general inventive concept. Referring to  FIG. 3 , nozzles  132  can be disposed in two rows on the surface of the ink-jet printhead, and bonding pads  101 , on each of which a conductor can be bonded, can be disposed at both sides of the nozzles  132 . The nozzles  132  may be disposed in one row, or in three or more rows to improve printing resolution.  
       FIG. 4  is a cross-sectional view illustrating the ink-jet printhead of  FIG. 3  taken along the line IV-IV′. Referring to  FIG. 4 , a chamber layer  120 , and nozzle plate  130  can be sequentially deposited on a substrate  111 . An ink feedhole  102  to supply ink to an ink chamber  122  can be formed in the substrate  111 . The ink feedhole  102  can be connected to an ink reservoir (not shown). The chamber layer  120  defines the ink chamber  122  by forming sidewalls of the ink chamber  122 . The nozzles  132 , through which the ink is ejected out of the ink chamber  122 , can be formed in the nozzle plate  130 .  
      A silicon wafer generally used in the manufacturing of integrated circuits may be used as the substrate  111 . An insulating layer  112  can be formed on the substrate  111 . The insulating layer  112  functions not only as an insulation between the substrate  111  and a heater  113 , but also as an adiabatic layer to prevent heat generated by the heater  113  from flowing toward the substrate  111 . The insulating layer  112  may be a silicon oxide layer or a silicon nitride layer.  
      The heater  113  to boil the ink in the ink chamber  122  generates bubbles  135  in the ink and can be formed on the insulating layer  112 . The heater  113  may be composed of an electric resistance heating material such as tantalum nitride TaN, tantalum-aluminium alloy TaAI, titanium nitride TiN, or tungsten silicide.  
      A conductor  114  to supply a current to the heater  113  can be formed on the heater  113 . The conductor  114  can be patterned to expose part of the heater  113 . The conductor may be composed of a metal having high conductivity such as aluminium, aluminium alloy, or tungsten.  
      A passivation layer  115  to passivate the heater  113  and the conductor  114  can be formed on the heater  113  and the conductor  114 . The passivation layer prevents the heater  113  and conductor  114  from oxidizing and directly contacting the ink, and may be a silicon nitride layer.  
      An anti-cavitation layer  116 , on which the ink chamber  122  can be formed, can be formed on the passivation layer  115 . The anti-cavitation layer  116  prevents the heater  113  from damages due to a high pressure generated by the shrinking of the bubbles  135  in the ink in the ink chamber  122 . The anti-cavitation layer  116  may be composed of tantalum Ta.  
      The chamber layer  120  can be formed on the above-described structure. The chamber layer  120  defines the ink chamber  122 , in which the ink is filled. The chamber layer  120  forms sidewalls of the ink chamber  122 . The thickness of the chamber layer  120  may be approximately 10 μm to 100 μm. The chamber layer  120  can be completely or partially composed of polyimide, which has a good swelling characteristic against ink. The polyimide can be formed by imidization of polyamic acid when the nozzle plate  130  is attached to an upper surface of the chamber layer  120  at a temperature of about 240° C. to 400° C.  
      The nozzle plate  130 , on which the nozzles  132  can be formed, can be installed on the chamber layer  120 . The nozzle plate  130  can be attached to the upper surface of the chamber layer  120  at a temperature of about 240° C. to 400° C., at which point the polyamic acid is imidized. At this time, the polyamic acid is imidized to form polyimide on the chamber layer  120 . The nozzle plate  130  may be formed of a polyimide PI film processed by a laser or a nickel Ni plate plated with gold Au.  
      Hereinafter, a method of manufacturing the inkjet printhead according to an embodiment of the present general inventive concept will be described while referring to  FIGS. 5A through 5F .  
      Referring to  FIG. 5A , the insulating layer  112  can be formed on the substrate  111  and the heater  113  can be formed on the insulating layer  112 . The substrate  111  can be formed by processing a silicon wafer to a thickness of about 400 μm to 650 μm. The silicon wafer, of which mass production is possible, is one of a type generally used in semiconductor devices.  FIG. 5A  illustrates a small portion of the silicon wafer, and several tens to hundreds of the ink-jet printheads according to an embodiment of the present general inventive concept may be manufactured on a single wafer.  
      The insulating layer  112  can be formed on a surface of the prepared silicon substrate  111 . The insulating layer  112  may be formed by vapor depositing silicon oxide or silicon nitride on the surface of the substrate  111 . The insulating layer  112  prevents heat energy generated by the heater  113  from flowing to the substrate  111 .  
      Next, the heater  113  to boil the ink and generate bubbles  135  in the ink can be formed on the insulating layer  12 . The heater  113  may be formed by vapor depositing an electric resistance heating material such as tantalum nitride TaN, tantalum-aluminium alloy TaAI, titanium nitride TiN, or tungsten silicide to a predetermined thickness.  
      Referring to  FIG. 5B , the conductor  114  to apply the current to the heater  113  can be formed on the heater  113 . The conductor  114  may be formed by vapor depositing a metal having high conductivity such as aluminium, an aluminium alloy, or tungsten on the heater  113  and patterning the deposited metal to expose a portion of the heater  113 .  
      Referring to  FIG. 5C , the passivation layer  115  can be formed on the heater  113  and the conductor  114 , and the anti-cavitation layer  116  can be formed on the passivation layer  115 . The passivation layer  115  may be formed by vapor depositing silicon nitride on the conductor  114  and the exposed portion of the heater  113 . The passivation layer  115  prevents the heater  113  and the conductor  114  from oxidizing and directly contacting the ink. The anti-cavitation layer  116  may be formed by vapor depositing tantalum Ta on the surface of the passivation layer  115  and patterning the tantalum Ta. The anti-cavitation layer  116  prevents the heater  113  from damage due to the high pressure generated by the shrinking of the bubbles in the ink in the ink chamber  122 .  
      Referring to  FIG. 5D , the chamber layer  120  defining the ink chamber  122  can be formed on the passivation layer  115  and the anti-cavitation layer  116 .  
      First, polyamic acid can be spin coated on the surface of the structure illustrated in  FIG. 5C  to a predetermined thickness and then baked. The polyamic acid may be converted to polyimide by imidizing at a temperature of 240° C. to 400° C. The polyamic acid film may be formed to a thickness of about 10 μm to 100 μm.  
      Next, the chamber layer  120  defining the ink chamber  122  can be formed by patterning the polyamic acid film to a predetermined shape. In this case, the polyamic acid film may be patterned by one of two methods. One method includes patterning the polyamic acid including a photosensitive additive by photolithography using a mask. The other method includes patterning the polyamic acid film by dry etching.  
      Referring to  FIG. 5E , the nozzle plate  130 , on which the nozzles  132  can be formed, can be attached to the upper surface of the chamber layer  120 . The nozzle plate  130  can be attached to the upper surface of the chamber layer  120  at the temperature of 240° C. to 400° C. at which the polyacmic acid is imidized. The nozzle plate  130  may be composed of a polyimide film processed by a laser or a nickel Ni plate plated with gold Au. When the nozzle plate  130  is attached to the upper surface of the chamber layer  120 , a part or the entire polyamic acid forming the chamber layer  120  of  FIG. 5D  is imidized and converted into polyimide having a good swelling characteristic against ink.  
      Referring to  FIG. 5F , the ink feedhole  102  to supply the ink to the ink chamber  122  may be formed in the substrate  111 . The ink feedhole  102  may be formed by installing an etching mask (not shown) on a rear portion of the substrate  111  and etching the rear portion of the substrate  111  exposed by the etching mask to perforate the substrate  111 . In this case, the etching of the substrate  111  may be performed by dry etching using plasma or wet etching using an etchant as tetramethyl ammonium hidroxide TMAH or KOH.  
       FIGS. 6A and 6B  are a top view and a side view, respectively, illustrating a sample to test the adhesive strength between the inter-layers. Referring to  FIGS. 6A and 6B , the sample has a single over-lap joint that attaches an upper and lower film  150  and  152  to an intermediate film  154 . In this case, the length and width of the upper and lower films  150  and  152  are respectively 60 mm and 5 mm, and the length and width of the intermediate film  154  are respectively 20 mm and 5 mm. Polyimide films can be used as the upper and lower films  150  and  152 .  
      The sample as described above was manufactured in three types and the adhesive strength of each of the samples was measured. In the first sample, the intermediate film  154  was a polyacrylate film, and was manufactured with an attachment pressure of 15 atm, at an attachment temperature of 220° C., and for an attachment period of 30 minutes. The tensile strength of the first sample was 0.57 MPa. In the second sample, the intermediate film  154  was a polyamic acid film, and was manufactured with an attachment pressure of 15 atm, at an attachment temperature of 220° C., and for an attachment period of 30 minutes. The tensile strength of the second sample was 0.33 MPa. In the third sample, the intermediate film  154  was the polyamic acid film, and was manufactured with an attachment pressure of 15 atm, at an attachment temperature of 250° C., and for an attachment period of 30 minutes. The tensile strength of the third sample was 0.61 MPa.  
      Considering these results, when the intermediate film  154  was a polyacrylate film which was used to form the chamber layer of a conventional ink-jet printhead, the tensile strength of the sample was 0.57 MPa. But if the intermediate film contacts ink at a high temperature, the separation of the inter-layer occurs due to the swelling of the intermediate film  154 . When the intermediate film  154  was a polyamic acid film and an attachment was made under the same conditions, the tensile strength was 0.33 MPa, which is weaker than the first example.  
      However, when the intermediate film  154  is a polyamic acid film and an attachment temperature is 250° C., as in the ink-jet printhead according to an embodiment of the present general inventive concept, the tensile strength is 0.61 MPa. A part or the entire polyamic acid is imidized and converted into polyimide at an attachment temperature of 250° C. Comparing this with conventional polyacrylate, polyamic acid, or polyimide, has a good characteristic against ink.  
      As described above, according to embodiments of the present general inventive concept, the chamber layer  120  defining an ink chamber  122  can be composed of polyimide having a good characteristic against ink. The polyimide is formed by imidization of polyamic acid at a predetermined temperature. Thus the chamber layer  120  does not separate from the substrate  111  or the nozzle plate  130  and an ejecting efficiency of the ink is 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.