Patent Publication Number: US-6702428-B2

Title: Ink-jet printhead

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 2001-62947, filed Oct. 12, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a bubble-jet type ink-jet printhead, and more particularly, to a bubble-jet type ink-jet printhead having a recess formed on a substrate on which a bottom surface of an ink chamber is disposed. 
     2. Description of the Related Art 
     In general, ink-jet printheads are devices printing in a predetermined color image by ejecting a small volume of a droplet of printing ink at a desired position on a recording sheet. Ink ejection mechanisms of an ink-jet printer are largely categorized into two different types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form a bubble in ink to cause the ink to be ejected, and an electro-mechanical transducer type in which ink is ejected by a change in ink volume due to deformation of a piezoelectric element. 
     In the above-mentioned ink-jet printheads, ink is supplied to an ink chamber from an ink reservoir through an ink passage. Ink filled in the ink chamber is heated by a heating element in the ink chamber and is ejected in a droplet shape through a nozzle by a pressure of the bubble generated by the heating element. 
     FIG. 1 is a schematic perspective view illustrating a structure of a conventional bubble-jet type ink-jet printhead, and FIG. 2 is a cross-sectional view illustrating the conventional bubble-jet type ink-jet printhead shown in FIG.  1 . 
     Referring to FIG. 1, the conventional bubble-jet type ink-jet printhead includes a base plate  10  formed of several different material layers stacked on a substrate  11  of FIG. 2, a barrier wall  20  which is stacked on the base plate  10  and defines an ink chamber  22  and an ink passage  26 , and a nozzle plate  30  stacked on the barrier wall  20 . The ink chamber  22  is filled with ink, and a heater ( 13  of FIG. 2) which generates the bubble in the ink by heating the ink, is provided under a bottom surface  24  of the ink chamber  22 . The ink passage  26  is a path for supplying ink to the ink chamber  22  and is connected to an ink reservoir (not shown). A plurality of nozzles  32  through which ink is ejected, is formed at a location corresponding to a center of the ink chamber  22  on the nozzle plate  30 . 
     Referring to FIG. 2, the conventional bubble-jet type ink-jet printhead having the above structure of FIG. 1 includes an adiabatic layer  12  which prevents a thermal energy generated by a heater  13  from being discharged toward the substrate  11 , is formed on the substrate  11  formed of silicon. The adiabatic layer  12  is generally formed of a silicon oxide layer deposited on the substrate  11 . The heater  13  which generates the bubble in the ink by heating the ink in the ink chamber  22 , is formed on the adiabatic layer  12 . The heater  13  is deposited by sputtering a tantalum-aluminum alloy in a thin film shape, for example. A conductor  14  transmitting a current to the heater  13  is formed on the heater  13 . The conductor  14  is formed of an aluminum-copper alloy, for example. 
     Passivation layers  15   a  and  15   b  for passivating the heater  13  and the conductor  14  are formed on the heater thin film  13  and the conductor  14 . The passivation layers  15   a  and  15   b  prevent the heater  13  and the conductor  14  from oxidizing or directly contacting ink and are formed of two layers, such as a first passivation layer  15   a  formed of a silicon nitride layer and a second passivation layer  15   b  formed of a silicon carbide layer. An anticavitation layer  16  is formed on the second passivation layer  15   b  where the ink chamber  22  is formed. The anticavitation layer  16  prevents the heater  13  from being damaged by a high atmospheric pressure generated when the bubble in the ink chamber  22  is removed, by forming the bottom surface  24  of the ink chamber  22  on an upper side of the anticavitation layer  16 , and a tantalum thin film is generally used for the anticavitation layer  16 . 
     The barrier wall  20  defines the ink chamber  22  and the ink passage  26  and is stacked on the base plate  10  that is formed of several different layers stacked on the substrate  11 . The barrier wall  20  is coated through lamination for heating, pressurizing, and compressing a photosensitive polymer on the base plate  10 , followed by patterning. In this case, a coating thickness of the photosensitive polymer is about between 25 μm and 35 μm and is determined by a height of the ink chamber  22  required by a volume of the ink droplet ejected. 
     The nozzle plate  30  on which the plurality of nozzles  32  are formed, is stacked on the barrier wall  20 . The nozzle plate  30  is formed of polyimide or nickel and is heated and pressurized on the barrier wall  20  and attached to the barrier wall  20  using adhesion of the photosensitive polymer forming the barrier wall  20 . 
     In the above structure of the conventional bubble-jet type ink-jet printhead, the photosensitive polymer forming the barrier wall  20  is used to attach the base plate  10  to the nozzle plate  30  and surrounds the ink chamber  22 . Ink filled in the ink chamber  22  contains water of about between 60% and 70%, and water soaks not only into an adhesion interface among the base plate  10 , the barrier wall  20 , and the nozzle plate  30  but also into the photosensitive polymer forming the barrier wall  20 . This phenomenon causes the delamination between elements of the ink-jet printhead and thus is a main factor in causing a defect of the ink-jet printhead. 
     Also, a crosstalk that affects the formation of bubbles and ejection characteristics of ink due to an atmospheric pressure applied to the adjacent ink chamber  22  through the ink passage  26  during ink ejection, may occur easily. 
     Also, the nozzle plate  30  adheres to the barrier wall  20  after the barrier wall  20  is formed on the base plate  10 . Hence, if the height of the barrier wall  20  is large, the barrier wall  20  may be easily deformed when the nozzle plate  30  is heated and pressurized on the barrier wall  20  to be attached to the barrier wall  20 . As a result, a misalignment among the nozzle  32 , the ink chamber  22 , and the heater  13  occurs, and thus results in poor performances of the ink-jet printhead. 
     SUMMARY OF THE INVENTION 
     To solve the above and other problems, it is an object of the present invention to provide a bubble-jet type ink-jet printhead which prevents delamination and improves ejection characteristics of ink droplets by reducing a height of a barrier wall of an ink chamber by forming a recess on a substrate on which a bottom surface of an ink chamber is disposed. 
     Additional objects and advantageous of the invention 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 invention. 
     Accordingly, to achieve the above and other objects, there is provided an ink-jet printhead. The ink-jet printhead includes a base plate including a substrate on which a recess is formed to a predetermined depth, an adiabatic layer formed on the substrate, a heater which is formed on the adiabatic layer and generates a thermal energy, and a passivation layer which is formed on the heater and passivates the heater, a barrier wall which is stacked on the base plate and defines an ink chamber disposed on the recess and having a recessed bottom surface and an ink passage which communicates with the ink chamber, and a nozzle plate stacked on the barrier wall and having nozzles through which ink is ejected, formed at a location corresponding to a center of the ink chamber. 
     Here, the recess is formed by wet or dry etching a predetermined surface of the substrate on which the ink chamber is to be formed, and a depth of the recess is between 1 μm and 20 μm, preferably, between 5 μm and 15 μm. 
     It is possible that the adiabatic layer is formed of a silicon oxide layer formed by oxidizing the surface of the substrate, and a thickness of the silicon oxide layer is between 1 μm and 5 μm. 
     It is also possible that the heater is formed of a tantalum-aluminum alloy or polysilicon, and a thickness of the heater is between 500 Å and 5,000 Å. 
     It is also possible that the passivation layer is formed of a silicon nitride layer deposited on the heater or two layers of a silicon nitride layer and a silicon carbide layer, which are sequentially deposited on the heater. 
     It is also possible that an anticavitation layer which prevents damage of the heater, is formed on the passivation layer, and that the anticavitation layer is formed of a tantalum layer. 
     Here, it is possible that a thickness of each of the silicon nitride layer, the silicon carbide layer, and the tantalum layer is between 0.1 μm and 1.0 μm inclusive. 
     Meanwhile, the barrier wall is formed of photosensitive polymer by a photolithography process. The photosensitive polymer is formed in a dry film shape and is coated on the base plate through lamination. The photosensitive polymer is coated to a thickness of between 5 μm and 24 μm on the base plate. 
     In addition, the nozzle plate is formed of polyimide or nickel. 
     According to the embodiment of the present invention, the height of the barrier wall surrounding the ink chamber is reduced more by forming the recess formed on the substrate, and thus delamination that occurs by ink soaked into the barrier wall, is prevented, and print performances, such as a traveling property in a straight direction of ink droplets and ejection velocity of ink droplets, are improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantageous of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a schematic perspective view illustrating a structure of a conventional bubble-jet type ink-jet printhead; 
     FIG. 2 is a cross-sectional view illustrating the conventional bubble-jet type ink-jet printhead shown in FIG. 1; 
     FIG. 3 is a schematic perspective view illustrating a structure of a bubble-jet type ink-jet printhead according to an embodiment of the present invention; 
     FIG. 4 is a cross-sectional view of the bubble-jet ink-jet printhead shown in FIG. 3; 
     FIG. 5 is a graph illustrating variations in volume and ejection velocity of ink droplets depending on a thickness of a barrier wall surrounding an ink chamber in the bubble-jet ink-jet printhead shown in FIGS. 3 and 4; 
     FIG. 6 is an enlarged cross-sectional photo illustrating a recess formed on a substrate of the bubble-jet type ink-jet printhead shown in FIGS. 3 and 4; and 
     FIG. 7 is an enlarged plan photo illustrating the recess formed on the substrate of the bubble-jet type ink-jet printhead shown in FIGS.  3  and  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiment is described in order to explain the present invention by referring to the figures. 
     Hereinafter, the present invention will be described in detail by describing an embodiment of the invention with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. It will be understood that when a layer is referred to as being on another layer or on a substrate, it can be directly on the other layer or on the substrate, or intervening layers may also be present. 
     FIG. 3 is a schematic perspective view illustrating a bubble-jet type ink-jet printhead according to an embodiment of the present invention. Referring to FIG. 3, the bubble-jet type ink-jet printhead has a structure in which a base plate  110 , a barrier wall  120 , and a nozzle plate  130  are sequentially stacked. The barrier wall  120  defines an ink chamber  122  filled with ink, and an ink passage  126  which supplies ink to the ink chamber  122  from an ink reservoir (not shown). That is, the barrier wall  120  forms a sidewall surrounding the ink chamber  122  and the ink passage  126 . The base plate  110  is formed of several different material layers stacked on a substrate ( 111  of FIG.  4 ), and a recessed portion defining a bottom surface  124  of the ink chamber  122  is formed on an upper side of the base plate  110  to be recessed. Consequently, a height of the barrier wall  120  surrounding (defining) the ink chamber  122  is lowered in accordance with the recessed portion, and this will be later described in detail. A plurality of nozzles  132  through which ink is ejected, are formed at a location corresponding to the ink chamber  122  on the nozzle plate  130 . 
     A cross-sectional view of the bubble-jet type ink-jet printhead having the above structure is shown in FIG.  4 . 
     Referring to FIG. 4, the base plate  110  is formed of several different material layers stacked on the substrate  111 . Here, a silicon substrate is used for the substrate  111 . This is because a silicon wafer that is widely used to manufacture semiconductor devices can be used for manufacturing the substrate  11  of the base plate  110  and thus is effective in mass production of the bubble-jet type ink-jet printhead. 
     A recess  119  is formed on a predetermined surface of the substrate  111 , i.e., a portion where the ink chamber  122  is to be formed. An etching mask defining a region to be etched is formed on the surface of the substrate  111  in a shape corresponding to the ink chamber  122 , and the region is wet etched using an etchant or dry etched using a reactive gas and plasma, thereby forming the recess  119 . The recess  119  is formed to a depth of about between 1 μm and 20 μm. When the depth of the recess  119  is larger than 20 μm, it is difficult to deposit an adiabatic layer  112 , a heater  113 , and a passivation layer  115  on the recess  119 . When the depth of the recess  119  is smaller than 1 μm, the effect of the recess  119  is not large. Thus, the recess  119  is formed to have the proper depth in the above-mentioned range according to a height of the ink chamber  122  and a thickness (height) of the barrier wall  120  that are determined in response to a volume and an ejection velocity of ink droplets ejected. It is possible that the recess  119  is formed to the depth between 5 μm and 15 μm. 
     Referring to FIG. 6, the depth of the recess  119  formed on the surface of the substrate  111  is about 14 μm, and the recess  119  includes inclined sides formed between a major surface of the substrate  111  and a recessed surface recessed from the major surface of the substrate  111  by the depth. This is because different material layers can be stacked more easily on the recess  119 . A plan of the recess  119  may be circular or polygonal according to a shape of a plan of the ink chamber  122 . The recess  119  that is formed in a rectangular shape having each side of the length of about 130 μm, is shown in FIG.  7 . 
     As described above, the adiabatic layer  112  which prevents a thermal energy generated by the heater  113  from being exhausted (discharged) toward the substrate  111 , is formed on the major surface of the substrate  111  and the inclined sides and the recessed surface of the recess  119  of the substrate  111 . It is possible that the adiabatic layer  112  is formed of a silicon oxide layer formed by oxidizing the major surface, the inclined sides, and the recessed surface of the substrate  111 , and a thickness of the adiabatic layer  112  is about between 1 μm and 5 μm. 
     The heater  113  which generates a bubble in ink by heating ink in the ink chamber  122 , is formed on the adiabatic layer  112 . The heater  113 , which is a resistance heating body, may be deposited by sputtering a tantalum-aluminum alloy in a thin film shape having the thickness of between 500 Å and 5,000 Å, preferably, between 500 Å and 2,000 Å, on the substrate  111 . Also, the heater  113  may be formed by depositing an impurity-doped polysilicon layer on the substrate  111 , followed by patterning the impurity-doped polysilicon layer. When the heater  113  is formed of polysilicon, polysilicon is deposited on the entire surface of the substrate  111  with impurities, i.e., a source gas of phosphorus (P), through low pressure chemical vapor deposition (LP CVD), and then, a deposited polysilicon layer is patterned by a photolithography process using a photomask and photoresist and by an etch process using a photoresist pattern as an etch mask. 
     A conductor  114  transmitting a current to the heater  113  is formed on the heater  113 . The conductor  114  is formed of aluminum-copper alloy, for example. 
     A passivation layer  115  passivating the heater thin film  113  and the conductor  114  is formed on the heater thin film  113  and the conductor  114 . The passivation layer  115  prevents the heater  113  and the conductor  114  from oxidizing or directly contacting ink and is preferably formed of a silicon nitride layer (SiN:H). The silicon nitride layer (SiN:H) is deposited to a thickness of about between 0.1 μm and 1.0 μm, preferably, between 0.3 μm and 0.7 μm, through LP CVD. 
     Meanwhile, the passivation layer  115  may be formed of two layers. In this case, a silicon carbide layer (SiC:H) improving a chemical resistant property is deposited to a thickness of about between 0.1 μm and 1.0 μm, preferably, between 0.3 μm and 0.7 μm, on the silicon nitride layer (SiN:H). 
     An anticavitation layer  116  is formed on the passivation layer  115  where the ink chamber  122  is formed. The anticavitation layer  116  prevents the heater  113  from being damaged by a high atmospheric pressure generated when the bubble in the ink chamber  122  is removed, by forming the bottom side  124  of the ink chamber  122  on the upper side of the anticavitation layer  116 . It is possible that the anticavitation layer  116  is formed of a tantalum thin film having a thickness of about between 0.1 μm and 1.0 μm, preferably, between 0.3 μm and 0.7 μm. 
     As described above, the base plate  110  is formed of several different layers stacked on the substrate  111 , and the upper side of the anticavitation layer  116  is recessed in accordance with the recess  119  formed on the substrate  111 . Consequently, the bottom surface  124  of the ink chamber  122  is recessed to the depth of the recess  119 . Thus, the height of the barrier wall  120  which is stacked on the base plate  110  and forms the ink chamber  122  and an ink passage ( 126  of FIG.  3 ), can be reduced by the depth of the recess  119 . Since the bottom surface  124  of the ink chamber  122  is recessed to a predetermined depth, the same height of the ink chamber  122  as a conventional ink chamber shown in FIG. 2 can be obtained even when the height of the barrier wall  120  is lower than a conventional barrier wall shown in FIG.  2 . 
     The barrier wall  120  is formed by a photolithography process after photosensitive polymer is coated to a predetermined thickness on the base plate  110 . According to the present invention, the thickness of the barrier wall  120  is about between 5 μm and 24 μm, preferably, between 5 μm and 20 μm. The thickness (height) of the barrier wall  120  decreases by the depth of the recess  119 , i.e., by a thickness of between 1 μm and 20 μm, compared with the thickness of between 25 μm and 35 μm in the conventional barrier wall of the prior art. If the height of the barrier wall  120  is smaller than the conventional barrier wall of the prior art, an amount of ink soaked into the photosensitive polymer forming the barrier wall  120  is reduced, and thus the delamination between elements of the ink-jet printhead can be prevented. In addition, if the photosensitive polymer forming the barrier wall  120  is thinner than the conventional barrier wall in the prior art, a critical dimension (CD) patterned by exposure becomes small, and thus it becomes easy to manufacture the ink-jet printhead with high resolution having a higher density. 
     If the photosensitive polymer forming the barrier wall  120  is exposed to light, the photosensitive polymer has a property in which a low molecular weight is changed to a high molecular weight and the photosensitive polymer is cured by a network structure formed by a high molecular chain. The uncured portion of the photosensitive polymer exists in a low molecular weight, i.e., in a monomer or oligomer state, and is easily dissolved by solvent. 
     The photosensitive polymer having the above property may be dry film or liquid. If the photosensitive polymer is dry film, the photosensitive polymer is coated on the base plate  110  through lamination for heating, pressurizing, and compressing the dry film. If the photosensitive polymer is liquid, the photosensitive polymer is coated on the base plate  110  through spin coating. It is possible that the photosensitive polymer formed in a dry film shape is coated through lamination. This method has an advantage that the photosensitive polymer formed in the dry film shape does not contact the bottom surface  124  of the ink chamber  122  and thus polymer or the residual of solvent does not remain in the bottom surface  124  after patterning because the bottom surface  124  of the ink chamber  122  is recessed. 
     If the photosensitive polymer coated on the base plate  110  is selectively exposed to the light using a photomask protecting a portion where the ink chamber  122  and the ink passage  126  are to be formed, the exposed portion is cured, and thus has a chemical resistant property and a high mechanical strength. Subsequently, the uncured portion of the photosensitive polymer is dissolved and removed using solvent, the ink chamber  122  and the ink passage  126  are formed, and simultaneously the barrier wall  120  surrounding the ink chamber  122  and the ink passage  126  are formed by the portion cured by exposure. In this case, an internal side of the barrier wall  120  is patterned to be spaced-apart from edges of the recessed portion of the bottom surface  124  of the ink chamber  122 , about between 1 μm and 5 μm. 
     The nozzle plate  130  on which the plurality of nozzles  132  are formed, is stacked on the barrier wall  120 . The nozzle plate  130  is formed of polyimide or nickel and is heated and pressurized on the barrier wall  120  to be attached to the barrier wall  120  using adhesion of the photosensitive polymer forming the barrier wall  120 . In this case, since the height of the barrier wall  120  is smaller than the conventional barrier wall in the prior art, the barrier wall  120  is hardly deformed when the nozzle plate  130  is heated and pressurized on the barrier wall  120  and adheres to the barrier wall  120 , and misalignment between elements caused by deformation of the barrier wall  120  can be prevented. 
     FIG. 5 is a graph illustrating variations in volume and ejection velocity of the ink droplets depending on the thickness of the barrier wall  120  surrounding the ink chamber  122 . Referring to FIG. 5, the volume of the ink droplets ejected is increased as the barrier wall  120  becomes thinner, and the ejection velocity of the ink droplets is increased as the barrier wall  120  becomes thinner on conditions that the ink droplets having more than a predetermined volume can be ejected. Since the bottom surface  124  of the ink chamber  120  is recessed, the ink chamber  122  becomes open toward the nozzles disposed on an upper portion of the ink chamber  122 , a growing direction of the bubble is toward the nozzles, and thus a traveling property in a straight direction of ink droplets ejected is improved. Also, a pressure generated by the bubble moves toward the nozzles disposed on the upper portion of the ink chamber  122  according to the shape of the ink chamber  122 , an orientation of the ink toward the ink passage  126  disposed on a side of the ink chamber  122  is reduced, and thus the crosstalk that affects the ink supplied to the adjacent ink chamber  122  though the ink passage  126  during ink ejection can be reduced. In this way, according to the present invention, the ejection performances of the ink droplets are improved. 
     As described above, the bubble-jet type ink-jet printhead according to the present invention has the following advantages. 
     First, the height of the barrier wall surrounding the ink chamber is smaller than the conventional barrier wall of the prior art, the delamination caused by ink soaked into the barrier wall can be reduced and prevented. In addition, the photosensitive polymer forming the barrier wall is thinner than that of the prior art, the critical dimension (CD) patterned by the exposure becomes small, and thus it becomes easy to manufacture an ink-jet printhead with the high resolution having the higher density. 
     Second, since the bottom surface of the ink chamber is recessed, the growing direction of the bubble is toward the nozzles, and thus the traveling property in the straight direction of the ink droplets ejected is improved, and the ejection velocity of ink droplets is improved. In addition, the crosstalk that affects the ink supplied to the adjacent ink chamber through the ink passage during ink ejection, can be reduced, and thus the ejection performances of the ink droplets are improved. 
     Third, since the bottom surface of the ink chamber is recessed, the photosensitive polymer formed in the film shape does not contact the bottom surface, and thus polymer or residual of solvent does not remain in the bottom surface of the ink chamber after patterning. In addition, the height of the barrier wall is smaller than that of the prior art, the deformation of the barrier wall is reduced when the nozzle plate adheres to the barrier wall, and thus the misalignment between elements can be prevented. 
     Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and sprit of the invention, the scope of which is defined in the claims and their equivalents. 
     For example, other materials may be used for materials used in constituting each element of the ink-jet printhead in the present invention. That is, the substrate may be formed of another material having good processability instead of silicon. In addition, the methods of stacking materials and forming elements suggested above are provided only for illustration. Various deposition methods and etching methods may be employed within the scope of the present invention.