Patent Publication Number: US-2006017785-A1

Title: Ink jet head including a filtering member integrally formed with a substrate and method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 2004-57854, filed Jul. 23, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present general inventive concept relates to an ink jet head and a method of fabricating the same and, more particularly, to an ink jet head including a filtering member integrally formed with a substrate and a method of fabricating the same.  
      2. Description of the Related Art  
      An ink jet recording device prints images by ejecting fine droplets of ink to a desired position on a recording medium. Ink jet recording devices have been widely used due to their inexpensive price and their capability of printing numerous colors at a high resolution. The ink jet recording device includes an ink jet head for actually ejecting ink, and an ink container in fluid communication with the ink jet head. The ink jet head can be classified based on a pressure-generating element used for ink ejection as a thermal type that uses an electro-thermal transducer, or a piezo-electric type that uses an electro-mechanical transducer.  
      The ink jet head includes a silicon substrate having a chip shape, and a number of components disposed on a top surface of the silicon substrate. An example of a thermal ink jet head is disclosed in U.S. Pat. No. 4,882,595. The thermal ink jet head has a plurality of heat-generating resistors disposed on the silicon substrate to generate pressure for ink ejection, a chamber layer for defining a sidewall of an flow path including an ink chamber and an ink channel, and a nozzle layer disposed on the chamber layer. The nozzle layer has a plurality of nozzles corresponding to each of the heat-generating resistors. A bottom surface of the silicon substrate is attached to the ink container, and the ink in the ink container is supplied to the ink jet head through an ink-feed passage passing through the silicon substrate. The ink is supplied through the ink-feed passage via the ink channel to the ink chamber, where it is temporarily stored. The ink stored in the ink chamber is instantly heated by the heat-generating resistor and is then ejected by the pressure generated onto the recording medium through the nozzle in a droplet shape. Then, the ink chamber is refilled with ink that flows through the ink channel.  
      Particles may be introduced into the flow path together with the ink. When the particles have a dimension that is larger than that of the flow path, the flow path may be clogged by the particles. This may cause a quality of printing to deteriorate. Further, if a particle clogs one of the nozzles, the ink may not be ejected from the nozzle. To prevent this problem, a mesh filter has been provided between the ink jet head and the ink container to prevent the particles from being introduced into the flow path from the ink container. However, a reduction of the ink droplet size is required for high resolution printing, and thus a dimension of the flow path is reduced. For this reason, use of the mesh filter is limited.  
      As a result, technologies relating to forming a filtering member on the silicon substrate during a process of fabricating the ink jet head have been researched. Ink jet heads provided with the filtering member are disclosed in U.S. Pat. Nos. 5,463,413 and 6,626,522.  
       FIG. 1  is a perspective view of a conventional ink jet head disclosed in U.S. Pat. No. 5,463,413.  
      Referring to  FIG. 1 , heat-generating resistors  3  are disposed on a substrate  1 . A chamber layer  5  defining a flow path including ink chambers and ink channels is disposed on the substrate  1 . A nozzle layer  7 , which is provided with nozzles  7 ′ corresponding to each of the heat-generating resistors  3 , is disposed on the chamber layer  5 . An ink-feed passage  9  is disposed to pass through the substrate  1  at a portion spaced apart from the heat-generating resistors  3 . Pillars  11  are disposed along the ink-feed passage  9  to prevent particles introduced through the ink-feed passage  9  from penetrating into the ink chamber. According to the U.S. Pat. No. 5,463,413, the pillars  11  are formed by the same process and are formed of the same material layer as the chamber layer  5 . For example, the pillars  11  and the chamber layer  5  may be formed by forming a photosensitive resin layer on the substrate  1  and patterning the photosensitive resin layer using a photo process. Generally, the pillars  11  serve as a fluid resistor impeding flow of the ink in the flow path. Therefore, the pillars  11 , which have small dimensions, are intended to prevent the particles from penetrating into the ink chamber. However, since the pillars  11  are formed by patterning the photosensitive resin layer as set forth above, there is a limit to reducing the dimension of the pillars  11 . That is, considering that a thickness of the chamber layer  5  and a height of the ink chamber is greater than about 10 micrometers (μm), it may be difficult for the pillars  11  formed by the photo process to have an aspect ratio greater than about 1. Aspect ratio may be defined as a ratio of a height dimension to a width dimension. In addition, even if the pillars  11  are formed to have an aspect ratio greater than about 1, the pillars may be readily separated from the substrate  1  due to poor adhesive strength between the photosensitive resin layer and the substrate  1 .  
      The conventional ink jet head having the pillars  11 , as set forth above, decreases a speed with which the ink is refilled into the ink chamber after the ink ejection due to the pillars  11  providing fluid resistance. Thus, improvements in an ink ejection frequency may be limited.  
     SUMMARY OF THE INVENTION  
      The present general inventive concept provides an ink jet head having a filtering member capable of preventing particles from penetrating into a flow path with a minimum fluid resistance.  
      The present general inventive concept also provides a method of fabricating an ink jet head having a filtering member.  
      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 head having filtering pillars integrally formed with a substrate. The ink jet head includes a plurality of pressure-generating elements disposed on a substrate to generate pressure to provide ink ejection. An ink-feed passage extending through the substrate is disposed to be spaced apart from the pressure-generating elements. A manifold that is recessed from a top surface of the substrate by a predetermined depth and has a width defined by the ink-feed passage is disposed between the pressure-generating elements and the ink-feed passage. A plurality of filtering pillars is disposed on a bottom surface of the manifold to provide filter openings therebetween. The filtering pillars are integrally formed with the substrate. A flow path structure defining a flow path is disposed on the top surface of the substrate, wherein the flow path may include ink chambers that contain the pressure-generating elements therein, ink channels that open the ink chambers toward a direction of the manifold, and nozzles that are in fluid communication with the ink chambers.  
      The foregoing and/or other aspects and advantages of the present general inventive concept may also be achieved by providing a method of fabricating an ink jet head having a filtering member integrally formed with a substrate. The method includes forming a plurality of pressure-generating elements to generate pressure to provide ink ejection on a substrate. The substrate is patterned to form a trench spaced apart from the pressure-generating elements and defining a plurality of filtering pillars, the filtering pillars being spaced apart from sidewalls of the trench and being formed to provide filter openings therebetween. A flow path structure defining a flow path is formed on the substrate having the filtering pillars, wherein the flow path may include ink chambers that contain the pressure-generating elements therein, ink channels that open the ink chambers toward a direction of the trench, and nozzles that are in fluid communication with the ink chambers. The substrate may be etched to form an ink-feed passage extending through the bottom of the trench and to define a manifold including the filtering pillars. 
    
    
     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 perspective view of a conventional ink jet head;  
       FIG. 2  is a perspective view of an ink jet head in accordance with an embodiment of the present general inventive concept;  
       FIG. 3  is a plan view of the ink jet head illustrated in  FIG. 2 ;  
      FIGS.  4  to  9  are cross-sectional views, taken along the line I-I′ of  FIG. 3 , illustrating a method of fabricating an ink jet head in accordance with an embodiment of the present general inventive concept;  
       FIGS. 10 and 11  are cross-sectional views illustrating a method of fabricating an ink jet head in accordance with another embodiment of the present general inventive concept;  
       FIG. 12  is a plan view illustrating a relationship of a diameter of filtering pillars and filter openings;  
       FIGS. 13A and 13B  are SEM images depicting filtering pillars in accordance with the present general inventive concept; and  
       FIGS. 14A and 14B  are views representing computer simulation results that estimate ink ejection properties of an ink jet head depending upon a dimension of filtering pillars. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures.  
       FIG. 2  is a perspective view of an ink jet head in accordance with an embodiment of the present general inventive concept, and  FIG. 3  is a plan view of the ink jet head shown in  FIG. 2 . In addition, FIGS.  4  to  9  are cross-sectional views, taken along the line I-I′ of  FIG. 3 , illustrating a method of fabricating an ink jet head in accordance with an embodiment of the present general inventive concept.  
      First, an ink jet head in accordance with an embodiment of the present general inventive concept will be described with reference to  FIGS. 2, 3 , and  9 .  
      Referring to  FIGS. 2, 3 , and  9 , pressure-generating elements are disposed on a top surface  10   a  of a substrate  10 . The substrate  10  may be a silicon substrate used in a semiconductor manufacturing process having a thickness of about 500 μm. The pressure-generating elements generate pressure to provide ink ejection. In accordance with embodiments of the present general inventive concept, the pressure-generating elements may be heat-generating resistors  12  provided as an electro-thermal transducer. The heat-generating resistors  12  may be made of a high resistance metal such as tantalum or tungsten, an alloy such as tantalum aluminum including the high resistance metal, or poly-silicon having impurity ions doped therein. In addition, while not shown in the drawings, other elements may also be disposed on the top surface  10   a  of the substrate  10  including, among the other elements, wiring to supply electric signals to the heat-generating resistors  12 , conductive pads to electrically connect the heat-generating resistors  12  with an external circuit, a silicon oxide heat barrier formed at a lowermost layer on the substrate  10 , and a passivation layer formed to protect structures disposed on the substrate  10 .  
      An ink feed passage  26  extends through the substrate  10 . The ink-feed passage  26  may be spaced apart from the heat-generating resistors  12  to extend through a middle portion of the substrate  10 . In addition, the ink-feed passage  26  may have a slot shape, when viewed from a plan view. The heat-generating resistors  12  may be arranged in two rows on both sides of the ink-feed passage  26  along a longitudinal direction of the ink-feed passage  26 . A manifold  14 ′, which is recessed from the top surface  10   a  by a predetermined depth and has a width defined by the ink-feed passage  26 , is disposed between the ink-feed passage  26  and the heat-generating resistors  12 . As mentioned above, when the ink-feed passage  26  has a slot shape, the manifold  14 ′ may be disposed along the longitudinal direction of the ink-feed passage  26 . A plurality of filtering pillars  16  is disposed on a bottom surface of the manifold  14 ′. The filtering pillars  16  are integrally formed with the substrate  10 . The filtering pillars  16  may be formed by etching the substrate  10 . In this case, an etched portion of the substrate  10  is formed into the manifold  14 ′. Therefore, the filtering pillars  16  have a height substantially equal to a depth of the manifold  14 ′ from the top surface  10   a  of the substrate  10 . The filtering pillars  16  may be disposed on the manifold  14 ′ and spaced apart at the same interval, thereby providing filter openings O having the same dimension therebetween.  
      A flow path structure defining a flow path is disposed on the top surface  10   a  of the substrate  10 . The flow path includes ink chambers  28  that contain the heat-generating resistors  12  therein, ink channels  30  that open the ink chambers  28  toward a direction of the manifold  14 ′, and nozzles  24 ′ that are in fluid communication with the ink chambers  28 . The flow path structure may include a chamber layer  20   a , a cover layer  20   b  and a nozzle layer  24 . The chamber layer  20   a  is disposed on the top surface  10   a  of the substrate  10  to define sidewalls of both the ink chambers  28  and the ink channels  30 . A cover layer  20   b  may be disposed at the same level as the chamber layer  20   a  to be in contact with the top surface of the filtering pillars  16  and to cover the ink-feed passage  26 . In addition, the cover layer  20   b  is sufficiently spaced apart from edges E of the manifold  14 ′, located at both sides of the ink channel  30 , so that the ink supplied from an ink container (not shown) flows smoothly into the flow path through the ink-feed passage  26 . The chamber layer  20   a  and the cover layer  20   b  may be formed by the same process and of the same material layer. For example, the chamber layer  20   a  and the cover layer  20   b  may be a photosensitive resin layer. The nozzle layer  24  is disposed on the chamber layer  20   a  and the cover layer  20   b , and nozzles  24 ′ extend through the nozzle layer  24  to correspond to the heat-generating resistors  12 , respectively.  
      The ink supplied from the ink container sequentially passes through the ink-feed passage  26 , the filter openings O provided by the filtering pillars  16 , and the ink channel  30  to be temporarily stored in the ink chambers  28 . In this process, in order for the filtering pillars  16  to filter particles in the ink, the filter openings O can have a dimension that is smaller than a minimum dimension of the flow path including the ink channel  30 , the ink chamber  28 , and the nozzles  24 ′. The dimension of the filter openings O may be defined as a width of the filter openings O, i.e., a gap between the filtering pillars  16 . Therefore, the width of the filter openings O has a dimension smaller than the minimum dimension of the flow path. This allows any particles large enough to clog a part of the flow path having the minimum dimension to be filtered by the filtering pillars  16 . Typically, the minimum dimension of the flow path may be a diameter of the nozzles  24 ′. In addition, the height of the filtering pillars  16  may be substantially equal to a thickness of the chamber layer  20   a , i.e., a height of the ink chambers  28 .  
      The filtering pillars  16  may act as a fluid resistor impeding flow of the ink. The dimension of the filtering pillars  16  may be reduced in order to minimize a fluid resistance created by the filtering pillars  16 . The filtering pillars  16  may each have the same diameter D and may have the same height extending along an axis perpendicular to a moving direction of the ink. If the widths of the filter openings O, i.e., the gap between the filtering pillars  16 , are maintained while increasing the aspect ratio of the filtering pillars  16  by reducing their diameter D, a sum of the widths of all the filter openings O may be increased to minimize the fluid resistance created by the filtering pillars  16 .  
       FIG. 12  is a plan view illustrating a relationship of a diameter of filtering pillars and filter openings.  
      Referring to  FIG. 12 , when filtering pillars  16   a  having a first diameter D 1  and filtering pillars  16   b  having a second diameter D 2  that is smaller than the first diameter D 1  are disposed to provide the filter openings O having the same width, the sum of the widths of all the filter openings O provided by the filtering pillars  16   b  having the second diameter D 2  is increased. For example, when the filtering pillars having a diameter of 10 micrometers (μm) are disposed to provide filter openings having a width of 10 μm on a manifold having a length of 300 μm, the sum of the widths of all the filter openings becomes 150 μm. On the other hand, when the filtering pillars have a diameter of 5 μm, the sum of the widths of all the filter openings becomes 200 μm.  
      Still referring to  FIGS. 2, 3 , and  9 , since the filtering pillars  16  in accordance with the present general inventive concept are integrally formed with the substrate  10 , problems associated with adhesion of the filtering pillars  16  to the top surface  10   a  of the substrate  10  may be alleviated. In addition, although forming the filtering pillars  16  by etching the substrate results in an aspect ratio greater than 1, the filtering pillars  16  may be reliably formed. Therefore, it becomes possible to minimize the fluid resistance created by the filtering pillars  16  since the filter openings O can be made wider on the manifold  14 ′. In addition, as the fluid resistance approaches a minimum, a speed of the ink refilled into the ink chambers  28  after the ink ejection is increased, and an ink ejection frequency is improved.  
      Hereinafter, a method of fabricating an ink jet head in accordance with an embodiment of the present general inventive concept will be described.  
      Referring to  FIGS. 3 and 4 , a substrate  10  is prepared. A plurality of pressure-generating elements to generate pressure to provide ink ejection is formed on a top surface  10   a  of the substrate  10 . The pressure-generating elements may be heat-generating resistors  12  made of a high resistance metal such as tantalum or tungsten, an alloy such as tantalum aluminum including the high resistance metal, or poly-silicon having impurity ions doped therein. Other elements may also be formed on the top surface  10   a  of the substrate including, among other elements, wiring to supply electric signals to the heat-generating resistors  12 , conductive pads to electrically connect the heat-generating resistors  12  with an external circuit, a silicon oxide heat barrier formed at the lowermost layer on the substrate  10 , and a passivation layer formed to protect structures disposed on the substrate  10 .  
      Referring to  FIGS. 3 and 5 , the substrate  10  is patterned to form a trench  14  at a middle portion of the substrate  10  spaced apart from the heat-generating resistors  12 . More specifically, a mask pattern (not shown) is formed on the substrate  10 , and the substrate  10  is etched by a predetermined depth using the mask pattern as an etch mask. As a result, the trench  14  is formed to define the plurality of filtering pillars  16  at the middle portion of the substrate  10 . The filtering pillars  16  are portions masked by the mask pattern. The depth of the trench  14 , i.e., the height of the filtering pillars  16 , is substantially equal to the thickness of a chamber layer, which is to be formed by the following process. In addition, the filtering pillars  16  are formed to be spaced apart from a sidewall of the trench  14  and to be spaced apart from each other at the same interval along the sidewall of the trench  14 , thereby providing the filter openings O having the same width between the filtering pillars  16 . The filtering pillars  16  are formed to have an aspect ratio greater than about 1, and the aspect ratio of the filtering pillars  16  has a proportional relationship with the sum of the widths of all the filter openings O. Conversely, the diameter D of the filtering pillars  16  has a relationship that is inversely proportional to the sum of the widths of all the filter openings O.  
      In accordance with various embodiments of the present general inventive concept, the substrate  10  may be etched by a reactive ion etching (RIE) process or a deep reactive ion etching (DRIE) process. The DRIE process is also known as an inductive coupled plasma (ICP) process. In particular, the DRIE process may form the filtering pillars  16  having a high aspect ratio by using a high-density plasma source and alternately performing the etching and the passivation layer deposition. In this case, SF 6  gas may be used as an etching plasma source, and C 4 F 8  gas may be used as a passivating plasma source.  
      Referring to  FIGS. 3 and 6 , after removing the mask pattern, a lower sacrificial layer  18  is formed to fill the trench  14 . The lower sacrificial layer  18  may be formed of a polyimid-based or polyamide-based positive photosensitive resin layer or a thermoplastic resin layer formed by a spin coating method. A chamber layer  20   a  and a cover layer  20   b  are formed on the substrate  10  having the lower sacrificial layer  18 . The cover layer  20   b  is formed to cover the filtering pillars  16  and is spaced apart from the sidewalls of the trench  14 . The chamber layer  20   a  and the cover layer  20   b  may be formed by forming a photosensitive resin layer on the top surface  10   a  of the substrate  10  and then exposing and developing the photosensitive resin layer. The photosensitive resin layer may be formed by the spin coating method using a liquid photosensitive resin, or by hot-pressing a photosensitive dry film layer by a lamination method. When using the dry film layer, the process of forming the lower sacrificial layer  18  may be omitted.  
      Referring to  FIGS. 3 and 7 , an upper sacrificial layer  22  is formed to fill a space between the chamber layer  20   a  and the cover layer  20   b . The upper sacrificial layer  22  may be formed of a polyimid-based or polyamide-based positive photosensitive resin layer or a thermoplastic resin layer similar to the lower sacrificial layer  18 . Alternatively, the process of forming the chamber layer  20   a  and the cover layer  20   b  described in  FIG. 6  may be performed after the process of forming the upper sacrificial layer  22  described in  FIG. 7 . That is, after forming the lower sacrificial layer  18 , the upper sacrificial layer  22  may be formed on the substrate  10  to cover a region at which a flow path is to be formed. The chamber layer  20   a  and the cover layer  20   b  may then be formed.  
      Referring to  FIGS. 3 and 8 , a nozzle layer  24  having nozzles  24 ′ corresponding to each of the heat-generating resistors  12  is formed on the chamber layer  20   a , the cover layer  20   b , and the upper sacrificial layer  22 . The nozzle layer  24  may be formed by forming a photosensitive resin layer on the chamber layer  20   a , the cover layer  20   b , and the upper sacrificial layer  22 , and then exposing and developing the photosensitive resin layer. The photosensitive resin layer may be formed by a spin coating method using a liquid photosensitive resin, or by hot-pressing a photosensitive dry film layer by a lamination method. When using the dry film layer, the process of forming the upper sacrificial layer  22  may be omitted.  
      Referring to  FIGS. 3 and 9 , after forming the nozzle layer  24 , the substrate  10  at a bottom portion of the trench  14  is etched to form an ink-feed passage  26 . The ink-feed passage  26  may be formed by a dry etching method such as an RIE process or a sandblasting process, or a wet etching method using a strong alkaline solution such as tetramethyl ammonium hydroxide (TMAH) as an etchant. The manifolds  14 ′ including the filtering pillars  16  are defined at side portions of the trench  14  by forming the ink-feed passage  26 . That is, the manifolds  14 ′ have a width defined by the ink-feed passage  26 . Once the ink feed passage  26  is formed, the lower and upper sacrificial layers  18  and  22  are removed by an appropriate solvent, for example, glycol ether, methyl lactate, or ethyl lactate. As a result, the ink chambers  28  and the ink channels  30  are formed at a region from which the upper sacrificial layer  22  is removed. In accordance with an embodiment of the present general inventive concept, the chamber layer  20   a , the cover layer  20   b , and the nozzle layer  24  configure a flow path structure to define the ink chambers  28 , the ink channels  30 , and the nozzles  24 ′.  
       FIGS. 10 and 11  are cross-sectional views illustrating a method of fabricating an ink jet head in accordance with another embodiment of the present general inventive concept.  
      Referring to  FIG. 10 , after forming a trench  14  to define the filtering pillars  16  by performing the processes described in  FIGS. 4 and 5 , a lower sacrificial layer  18  is formed to fill the trench  14 . Then, an upper sacrificial layer  22  is formed on the substrate  10  to cover a region at which a flow path is to be formed.  
      Referring to  FIG. 11 , a flow path material layer (not shown) is formed on the substrate  10  to cover the upper sacrificial layer  22 , the substrate  10 , and the lower sacrificial layer  18 . The flow path material layer is formed to fill a space between parts of the upper sacrificial layer  22 , and to have a predetermined thickness from a top surface of the upper sacrificial layer  22 . The flow path material layer may be formed of a photosensitive resin layer. The flow path material layer is then patterned to form a flow path structure having nozzles  34 ′ corresponding to each of the heat-generating resistors  12 . Thus, in accordance with the present embodiment, a flow path structure including a chamber layer  30   a , a cover layer  30   b  and a nozzle layer  34  may be integrally formed by the same process. After forming the flow path structure, the process as described in  FIG. 9  is performed to form an ink-feed passage.  
     EXAMPLES  
       FIGS. 13A and 13B  are SEM images depicting filtering pillars P in accordance with embodiments of the present general inventive concept. The filtering pillars are formed by forming a photo-resist pattern to cover a region, at which the filtering pillars are to be formed, on a silicon substrate, and then etching the silicon substrate using the photo-resist pattern as an etch mask. The silicon substrate is then dry etched using a DRIE process. The filtering pillars P are formed to have a width X of about 5 micrometers (μm), and a height Y of about 20 μm, thereby having an aspect ratio of about 4. In addition, the filtering pillars P are formed to have a gap (i.e., filter opening) of about 10 μm.  
      Referring to  FIGS. 13A and 13B , and in accordance with embodiments of the present general inventive concept, when the silicon substrate is dry etched to form the filtering pillars P, the filtering pillars P are formed to have a high aspect ratio. Even though the filtering pillars P have a high aspect ratio, the filtering pillars P are capable of embodying a firm and reliable particle filtering system since the filtering pillars P are formed integrally with the substrate and thereafter will not be separated therefrom.  
       FIGS. 14A and 14B  are views representing computer simulation results to estimate ink ejection properties of an ink jet head depending upon a dimension of filtering pillars. In  FIGS. 14A and 14B , ink chambers C are designed to have a three-sided barrier structure. In addition, the filtering pillars are designed to have a diameter of about 10 μm and 5 μm, respectively, and a gap between the pillars, i.e., a width of filter openings of about 10 μm.  FIGS. 14A and 14B  are views that represent results seven seconds after the ink ejection.  
      Referring to  FIGS. 14A and 14B , when the filtering pillars have a diameter of about 5 μm, it appears that the ink is introduced into the ink chambers C after the ink ejection more rapidly than when the filtering pillars have a diameter of about 10 μm. In addition, an ink ejection frequency is calculated to have values of about 72 KHz and 59 KHz when the filtering pillars have diameters of about 5 μm and 10 μm, respectively. The reason for these results is that the sum of the widths of all the filter openings is increased by providing more filter openings, when the filtering pillars have a diameter of about 5 μm.  
      The filtering pillars in accordance with embodiments of the present general inventive concept are integrally formed with the substrate by etching the substrate. Therefore, although the filtering pillars have a high aspect ratio, the filtering pillars can be reliably formed to provide many filter openings in the flow path having a restricted dimension. As a result, deterioration of ink ejection properties can be minimized by not only minimizing the fluid resistance, but also by preventing particles from clogging the flow path.  
      As can be seen from the foregoing, the substrate is etched to form the filtering pillars integrally formed with the substrate. Although the filtering pillars have a high aspect ratio, the filtering pillars are strongly and reliably formed on the substrate. As a result, the present general inventive concept is capable of improving properties of an ink jet head by not only minimizing a fluid resistance but also by preventing foreign materials from penetrating into the flow path.  
      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.