Patent Publication Number: US-7722160-B2

Title: Nozzle plate, printhead having the same and methods of operating and manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printhead. More particularly, the present invention relates to a nozzle plate and printhead that provide for control of a deflection direction of fluid ejected through a nozzle to improve a resolution of a printed image, and a method of manufacturing the same. 
     2. Description of the Related Art 
     Generally, a printhead is a device for printing an image on a surface of an object by ejecting droplets of fluid on a desired location of the object. A common printhead is an inkjet printhead that may print using a plurality of colors. Such an inkjet printhead may be classified, according to the method of ink ejection, into a thermal inkjet printhead and a piezoelectric inkjet printhead. 
     In the thermal inkjet printhead, ink is quickly heated by a heater, formed of a heating element, when a pulsed current is applied to the heater. The ink is heated until it boils and generates bubbles. The bubbles expand and apply pressure to ink filled in an ink chamber, thereby ejecting the ink out of the ink chamber through a nozzle in the form of droplets. Thus, in the thermal inkjet printhead, the heater functions as an actuator that generates the ejecting force for the ink. 
     In the piezoelectric inkjet printhead, a piezoelectric material is used as an actuator. A shape transformation of the piezoelectric material generates pressure, thereby ejecting the ink out of an ink chamber. 
       FIG. 1  illustrates a typical piezoelectric inkjet printhead. Referring to  FIG. 1 , a channel plate  10  is provided with an ink channel including a manifold  13 , a plurality of restrictors  12  and a plurality of ink chambers  11 . A nozzle plate  20  is provided having a plurality of nozzles  22  that corresponds to the plurality of ink chambers  11 . A plurality of piezoelectric actuators  40  is disposed on the channel plate  10 . The manifold  13  functions to supply ink from an ink storage region (not shown) to the plurality of ink chambers  11 . The restrictor  12  functions as a channel through which ink is introduced from the manifold  13  to the corresponding ink chamber  11 . The ink chamber  11  stores ink that is to be ejected. Ink chambers  11  may be arranged on one or both sides of the manifold  13 . The volume of the ink chamber  11  varies as the corresponding piezoelectric actuator  40  is driven, thereby generating pressure variations to eject ink through the nozzle  22  and draw ink through the restrictor  12 . In detail, a top wall (i.e., ceiling) portion of each ink chamber  11  on the channel plate  10  is designed to function as a vibration plate  14  that is deformed by the piezoelectric actuator  40 . 
     The piezoelectric actuator  40  includes a lower electrode  41  disposed on the channel plate  10 , a piezoelectric layer  42  disposed on the lower electrode  41  and an upper electrode  43  disposed on the piezoelectric layer  42 . Disposed between the lower electrode  41  and the channel plate  10  is an insulating layer  31  such as a silicon oxide layer. The lower electrode  41  is formed on an overall top surface of the insulating layer  31  to function as a common electrode. The piezoelectric layer  42  is formed on the lower electrode  41  and is located above the corresponding ink chamber  11 . The upper electrode  43  is formed on the piezoelectric layer  42  and functions as a driving electrode, applying voltage to the piezoelectric layer  42 . 
     When an image is printed using the above-described typical inkjet printhead, the resolution of the image is significantly affected by the number of nozzles per inch. The number of nozzles per inch is represented by “Channels per Inch (CPI)” and the image resolution is represented by “Dots per Inch (DPI).” In the typical inkjet printhead, the improvement of the CIP depends on continuing improvements in processing technology. However, current trends in processing technology may not keep pace with demands for increasingly higher resolution images. Therefore, a variety of technologies for printing a higher DPI image using a low CPI printhead have been developed. 
       FIGS. 2 and 3  illustrate examples of technologies for printing a higher DPI image using a low CPI printhead. Referring to  FIG. 2 , a plurality of nozzles  51  and  52  are arranged along two or more rows and may be staggered. The array of the nozzles  51  and  52  may be used to print an image forming a single line. That is, dots  61 , formed by the nozzles  51  arranged along the first row, and dots  62 , formed by the nozzles  52  arranged along the second row, alternate on a print medium  60 , e.g., a sheet of paper. In the illustrated example, the image DPI formed on the paper  60  is two times the CPI of the printhead  50 . 
     However, in order to precisely print the image, the nozzles  51  and  52  must be arranged accurately along the respective rows. Therefore, this requires an alignment system that can precisely arrange the nozzles  51  and  52 , which may increase the printhead size and cost. 
     In the example depicted in  FIG. 3 , printing utilizes a printhead  70 , having a relatively low CPI, which is inclined at a predetermined angle Θ with respect to a print medium  80 , e.g., a flexible substrate or a sheet of paper. The inclination of the printhead  70  results in the intervals between dots  81  formed on the paper  80  becoming less than the intervals between the nozzles  71  of the printhead  70 . Thus, the DPI of the image printed on the paper  80  is higher than the CPI of the printhead  70 . In this example, the greater the inclined angle Θ, the higher the DPI. However, the inclination of the printhead causes the printing area to be reduced so that the length of the printhead  70  must be increased in order to maintain coverage of the paper  80 . 
     SUMMARY OF THE INVENTION 
     The present invention is therefore directed to a nozzle plate and printhead that provide for control of a deflection direction of fluid ejected through a nozzle to improve a resolution of a printed image, and to methods of operating and manufacturing the same, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art. 
     It is a feature of an embodiment of the present invention to provide a nozzle plate and printhead that enable printing of images at a DPI higher than a CPI of the nozzle plate. 
     It is another feature of an embodiment of the present invention to provide a nozzle plate and printhead that can control a deflection direction of fluid ejected through a nozzle using electro-wetting. 
     It is a further feature of an embodiment of the present invention to provide a nozzle plate and printhead including electrode segments to control a contact angle of a fluid to be ejected using electro-wetting. 
     It is yet another feature of an embodiment of the present invention to provide methods of operating a printhead and forming an electro-wetting nozzle plate. 
     At least one of the above and other features and advantages of the present invention may be realized by providing a nozzle plate having at least one nozzle for ejecting fluid, the nozzle plate including at least one electrode segment disposed along a circumference of the nozzle, an insulating layer disposed on a surface of the electrode segment so as to contact fluid in the nozzle, and a wire pattern electrically coupled to the electrode segment. 
     The electrode segment may extend along less than about half of the circumference of the nozzle. There may be at least two electrode segments disposed along the circumference of the nozzle, the insulating layer may be divided into at least two insulating layer segments corresponding to the electrode segments, and the wire pattern may be electrically coupled to the electrode segments. The wire pattern may be individually coupled to each electrode segment, such that each electrode segment can be alternately energized. The insulating layer segments may form a portion of an inner surface of the nozzle, such that the inner surface of the nozzle includes at least two separate sections defined by the insulating layer segments. The nozzle may have four insulating layer segments and four corresponding electrode segments arranged at equal intervals along the circumference of the nozzle. The nozzle plate may further include a substrate through which the nozzle penetrates and on which the electrode segments and the wire pattern are disposed. The substrate may be a base substrate for a printed circuit board. The nozzle plate may further include a protective layer disposed on the substrate so as to cover the electrode segments and the wire pattern. The protective layer may be a hydrophobic insulating material. The protective layer may be a photo solder resist. The electrode segment may be a low resistance material. The electrode segment and the wire pattern may be copper. The insulating layer may be a hydrophobic layer. The insulating layer may include at least one of SiO 2 , SiN, and Ta 2 O 5 . The insulating layer may be a hydrophilic layer. 
     At least one of the above and other features and advantages of the present invention may also be realized by providing a printhead including a channel region including a plurality of fluid chambers, an actuator, and a nozzle region including a plurality of nozzles, each nozzle coupled to a corresponding fluid chamber, wherein each nozzle may include at least one electrode segment disposed along a circumference of the nozzle, an insulating layer disposed on a surface of the electrode segment so as to contact fluid in the nozzle, and a wire pattern electrically coupled to the electrode segment. 
     The printhead may further include an electric circuit, the electric circuit coupled to the wire pattern and configured to supply a voltage having a first polarity to the fluid and to supply a voltage having a second polarity opposite the first polarity to the wire pattern. There may be at least two electrode segments disposed along the circumference of the nozzle, the insulating layer may be divided into at least two segments corresponding to the electrode segments, and the wire pattern may be electrically coupled to the electrode segments. The at least two electrode segments may include a first electrode segment and a second electrode segment, such that the nozzle plate includes a plurality of first electrode segments and a plurality of second electrode segments, the printhead further including an electric circuit coupled to the wire pattern and configured to supply a voltage having a first polarity to the fluid and to alternately supply a voltage having a second polarity to the first and second electrode segments. The electric circuit may be configured to supply the voltage having the second polarity to the plurality of first electrode segments simultaneously. The nozzle may include four insulating layer segments and four corresponding electrode segments arranged at equal intervals along the circumference of the nozzle. The printhead may further include a substrate on which the electrode segment and the wire pattern are disposed, and a protective layer disposed on the substrate so as to cover the electrode segment and the wire pattern. 
     At least one of the above and other features and advantages of the present invention may further be realized by providing a method of manufacturing a nozzle plate having at least one nozzle for ejecting fluid, including forming an electrode having at least one segment and a wire pattern connected to the segment of the electrode on a substrate, forming a protective layer on the substrate, forming the nozzle, and forming an insulating layer only on the segment of the electrode. 
     Forming the electrode and the wire pattern may include depositing a metal layer on the substrate and patterning the metal layer to form both the electrode and the wire pattern. Forming the protective layer may include depositing a hydrophobic insulating material. Forming the nozzle may include forming a first portion of the nozzle by forming a tapered void in the substrate using a laser, and forming a second portion of the nozzle by forming a cylindrical void in the electrode and the protective layer using drilling or etching. Forming the second portion of the nozzle may expose the segment of electrode along a circumference of the cylindrical void. The electrode may have at least two segments, the insulating layer may be formed only on each of the segments of the electrode, and forming the insulating layer only on each of the segments of the electrode may include forming a number of hydrophobic insulating layer segments on the segments of the electrode, the number of hydrophobic insulating layer segments equal to the number of segments of the electrode. Forming the insulating layer only on each of the segments of the electrode may include using plasma enhanced chemical vapor deposition to selectively deposit SiO 2  or SiN directly on an exposed surface of each segment of the electrode and not on any adjacent regions of the nozzle plate. Forming the insulating layer only on each of the segments of the electrode may include using atomic layer deposition to selectively deposit Ta 2 O 5  directly on an exposed surface of each segment of the electrode and not on any adjacent regions of the nozzle plate. 
     At least one of the above and other features and advantages of the present invention may also be realized by providing a method of operating a printhead including a nozzle having at least one electrode segment disposed adjacent thereto, the method including applying pressure to a fluid contained in the printhead in order to eject a first droplet of the fluid from the nozzle, applying a voltage having a first polarity to the fluid contained in the printhead, and applying a voltage having a second polarity opposite the first polarity to the electrode segment in order to eject the first droplet in a first direction. 
     The electrode segment may be electrically insulated from the fluid by an insulating layer and applying the voltages having the first and second polarities may create an electric potential across the insulating layer to change a contact angle of the fluid with respect to the nozzle. The method may further include applying pressure to the fluid contained in the printhead in order to eject a second droplet of the fluid from the nozzle, and removing the voltage having the second polarity in order to eject the second droplet in a second direction, wherein the first direction is not coaxial with the nozzle and the second direction is coaxial with the nozzle. The nozzle may have two electrode segments disposed adjacent thereto, the electrode segments formed on opposite sides of the nozzle, the method further including alternately applying the voltage having the second polarity to each of the two electrode segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a schematic sectional view of a conventional inkjet printhead; 
         FIGS. 2 and 3  illustrate schematic views of technologies for printing a high DPI image using a low CPI printhead; 
         FIGS. 4A and 4B  illustrate schematic views explaining electro-wetting according to the present invention; 
         FIGS. 5A-5D  illustrate sectional views of a printhead explaining droplet deflection according to the present invention; 
         FIG. 6  illustrates a schematic sectional view of a printhead according to an embodiment of the present invention; 
         FIG. 7  illustrates a partial plan view of a printhead according to an embodiment of the present invention; 
         FIG. 8  illustrates a partial plan view of a printhead according to another embodiment of the present invention; and 
         FIGS. 9A-9E  illustrate sectional views of stages in a method of manufacturing a nozzle plate according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 10-2004-0087039, filed on Oct. 29, 2004, in the Korean Intellectual Property Office, and entitled: “Nozzle Plate Unit, Inkjet Print Head with the Same and Method of Manufacturing the Same,” is incorporated by reference herein in its entirety. 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. 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. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
     A printhead according to the present invention may be used to eject fluid droplets through a nozzle and control the deflection of the droplets in a variety of directions using electro-wetting. A printhead according to the present invention may be used to print a high resolution image using a printhead having a relatively low CPI. 
       FIGS. 4A and 4B  illustrate schematic views explaining electro-wetting according to the present invention. In these views, a spherical droplet (or hemispherical droplet in  FIG. 4B ) is shown positioned in contact with an electrically insulating layer, the insulating layer adjacent to an electro-wetting electrode. An external circuit having an energy source E is electrically coupled to the droplet and the electrode and is configured to supply a voltage thereto upon closing a switch. It will be appreciated that these illustrations are simplified so as not to obscure an understanding of the operation of the nozzle plate and printhead according to the present invention. Thus, the present invention is not limited to the illustrated configurations. 
       FIG. 4A  illustrates an unenergized state, wherein no voltage is applied to the electro-wetting electrode. Where the fluid is, e.g., a hydrophilic ink, and the insulating layer is, e.g., hydrophobic, ink contacts the surface of the insulating layer at a first contact angle Θ 1 , which may be relatively large, due to a first surface tension of the fluid.  FIG. 4B  illustrates an energized state, wherein a voltage is applied to the ink, across the insulating layer. That is, a first polarity of the voltage is applied to the ink and a second polarity of the voltage, opposite the first polarity, is applied to the electrode. When the voltage is applied to the ink and the electrode, forming an electric field across the insulator, i.e., between the ink and the electrode, the ink contacts the surface of the hydrophobic insulating layer at a second contact angle Θ 2 , which may be relatively small, due to electro-wetting. Thus, the contact area between the ink and the insulating layer may be increased. It will be appreciated that the fluid to be ejected may be hydrophobic and the insulating layer may be hydrophilic while maintaining the described electro-wetting operation. 
     A more detailed explanation will now be provided, although the present invention is not bound by any particular theory. In detail, when the voltage is applied, an electric field is formed between the electrode and the ink, and negative electric charges accumulate on the electrode while positive electric charges accumulate on a surface of the ink opposite the electrode. Of course, where the polarity of the applied voltage is reversed, the accumulated charges will also be reversed. A repulsive force between the positive electric charges accumulated on the surface of the ink may result in the surface tension of the ink being reduced. Further, there is an attractive force between the negative electric charges accumulated on the electrode and the positive electric charges accumulated on the surface of the ink. Thus, where the fluid is a hydrophilic ink and the insulating layer interposed between the electrode and the ink is hydrophobic, the contact angle Θ 2  of the ink with the hydrophobic insulating layer is reduced as a result of the voltage applied to the ink and the resulting reduction of the surface tension of the ink. 
       FIGS. 5A-5D  illustrate sectional views of a printhead explaining droplet deflection according to the present invention. Referring to  FIG. 5A , a printhead  100  may include a substrate  110 , a wire pattern  122  and a protective layer  130 . The printhead  100  may further include first and second electrode segments  120   a  and  120   b , covered by respective insulating layer segments  140   a  and  140   b  and disposed along a circumference of a nozzle  150 . A pressure applied to a fluid may cause the fluid to be ejected through the nozzle  150  in the form of a droplet D. In the illustrations, the fluid is ejected in a downward direction. 
     In operation, when no voltage is applied to either of the first and second electrode segments  120   a ,  120   b , the contact angles of the fluid, e.g., ink, with the first and second insulating segments  140   a ,  140   b , e.g., hydrophobic insulating segments, may be essentially identical. In this case, as shown in  FIG. 5A , a convex meniscus M is formed. The meniscus M is symmetric with respect to the first and second electrode segments  120   a ,  120   b . When pressure is applied to fluid in the nozzle  150  by, e.g., a piezoelectric actuator, thermal energy, etc., the fluid is ejected from the nozzle  150  in the form of droplets. In particular, the fluid droplets D are ejected straight from the nozzle  150 , i.e., in a direction coaxial with the nozzle  150  and perpendicular to the substrate  110 . 
     Referring to  FIG. 5B , when a voltage is applied to the fluid and only the first electrode segment  120   a , i.e., applied across the fluid and the first electrode segment  120   a , the contact angle of the ink with the surface of the first hydrophobic insulating segment  140   a  is reduced. As a result, a meniscus M′ is formed that is asymmetric with respect to the first and second electrode segments  120   a ,  120   b , as illustrated in  FIG. 5B . When pressure is applied to the fluid in the nozzle  150 , the fluid droplet D′ is ejected from the nozzle  150  at an angle, e.g., deflected to the right. 
     Referring to  FIG. 5C , when a voltage is applied to only the second electrode segment  120   b , the contact angle of the ink with the surface of the second hydrophobic insulating segment  140   b  is reduced. As a result, a meniscus M″ is formed that is asymmetric with respect to the first and second electrode segments  120   a ,  120   b . In particular, in this instance the meniscus M″ is essentially the mirror image of the meniscus M′ illustrated in  FIG. 5B . Accordingly, when pressure is applied to the fluid in the nozzle  150 , the ejected droplet D″ exits the nozzle  150  with the opposite deflection, e.g., deflected to the left. 
     As described above, when a voltage is selectively applied to one or the other of the electrode segments  120   a ,  120   b , the direction of ejected fluid droplets may be changed, e.g., to deflect the fluid to the right or left. In operation, the printhead may eject fluid to the left and the right alternately by alternately applying voltage to the first and second electrode segments  120   a ,  120   b , i.e., by applying voltage only to the fluid and the electrode segment  120   a , then applying voltage only to the fluid and the electrode segment  120   b , in alternating cycles. Of course, simpler or more complex arrangements may also be provided. For example, a single electrode segment may be provided along one side of the nozzle, without a complementary electrode segment on the opposing side of the nozzle  150 . That is, e.g., the electrode segment  120   a  may be provided while the electrode segment  120   b  is omitted. In that case, a fluid droplet D may be ejected straight from the nozzle  150  when no voltage is applied to the electrode segment  120   a , and a fluid droplet D′ may be ejected at an angle, without provisions for ejecting droplets with an opposite deflection. Thus, the DPI of a printed image may be twice the CPI of the printhead nozzles. 
     Referring to  FIG. 5D , a plurality of nozzles  150  may be arranged on the printhead  100 . Thus, the printhead has a predetermined CPI. When voltage is selectively applied to the electrode segments  120   a  and  120   b  of the electrode  120  formed on the nozzle  150 , the contact angles of the ink with the hydrophobic insulating segments  140   a  and  140   b  of the insulating layer  140  vary due to electro-wetting, thereby varying the direction of ejected fluid droplets. Thus, dots  401 , formed by droplets that are ejected straight from the nozzle  150 , and deflected dots  402  and  403 , formed by deflected droplets, are formed in a single line on the print medium  400 , e.g., a sheet of paper, and spaced apart by a predetermined interval. As a result, the DPI of an image formed on the print medium, e.g., the paper  400 , may be three times the CPI of the printhead  100 . 
       FIG. 6  illustrates a schematic sectional view of a printhead according to an embodiment of the present invention,  FIG. 7  illustrates a partial plan view of a printhead according to an embodiment of the present invention and  FIG. 8  illustrates a partial plan view of a printhead according to another embodiment of the present invention. In particular,  FIG. 6  illustrates a piezoelectric inkjet printhead, the printhead illustrated in  FIG. 7  includes a pair of independently operable electrodes and the printhead illustrated in  FIG. 8  includes four independently operable electrodes. 
     Referring to  FIG. 6 , the exemplary inkjet printhead may include a channel plate  200  having an ink channel including an ink chamber  204 , and a piezoelectric actuator  300  disposed on a top surface of the channel plate  200  to generate a driving force for ejecting ink from the ink chambers  204 . A nozzle plate  100  may be attached to a bottom surface of the channel plate unit  200  and may be provided with a plurality of nozzles  150  penetrating therethrough to eject ink out of the ink chambers  204 . 
     The ink channel may include, in addition to the ink chamber  204 , a manifold  202 , functioning as a common channel supplying ink introduced from an ink inlet (not shown) to multiple ink chambers  204 , and a restrictor  203  corresponding to the ink chamber  204 , functioning as an individual channel supplying ink from the manifold  202  to the ink chamber  204 . A damper  205  may be disposed between the ink chamber  204  and the nozzle  150  to concentrate energy, which is generated in the ink chamber by the piezoelectric actuator  300 , on the nozzle  150  and to buffer or dampen sudden pressure variations. 
     A portion of the channel plate  200  may define a top wall, i.e., ceiling, of the pressure chamber  204  and function as a vibration plate upon which the piezoelectric actuator  300  operates. The channel plate  200  may be a unit assembled from first and second channel plates  210  and  220 . In this case, the ink chambers  204  may be formed on a bottom surface of the first channel plate  210  to a predetermined depth. The ink chamber  204  may be formed in a rectangular shape having a longitudinal direction corresponding to a direction of ink flow from the manifold  202  to the nozzle  150 . 
     The manifold  202  may be formed on the second channel plate  220  and may be formed on a top surface of the second channel plate  220  to a predetermined depth. Alternatively, the manifold  202  may be formed completely penetrating the second channel plate  220  in a vertical direction. The restrictor  203  may be formed in the top surface of the second channel plate  220  to a predetermined depth and connect the manifold  202  to a first end of the ink chamber  204 . The restrictor  203  may be also formed penetrating the second channel plate  220  in a vertical direction. The damper  205  may be formed penetrating a portion of the second channel plate  220  in a vertical direction and corresponding to a second end of the ink chamber  204 . The damper  205  may connect the ink chamber  204  to the nozzle  150 . 
     Although the elements constituting the ink channel are separately arranged on the two channel plates  210  and  220  in the above description, this is only an exemplary embodiment. That is, a variety of ink channels may be provided on the inkjet printhead. In addition, the channel plate  200  may be formed of a single plate, two or more plates, etc. 
     The piezoelectric actuator  300  is provided on a top surface of the first channel plate  210  to provide the driving force for ejecting ink out of the ink chambers  204 . The piezoelectric actuator  300  may include a lower electrode  310  disposed on the top surface of the first channel plate  210 , to function as a common electrode, a piezoelectric layer  320  disposed on the lower electrode  310 , to be transformed by a voltage applied thereto, and an upper electrode  330  disposed on the piezoelectric layer  320 , to function as a driving electrode. In detail, an insulating layer  212  may be formed between the lower electrode  310  and the first channel plate  210 . The lower electrode  310  may be formed of a single conductive material layer applied on an overall top surface of the insulating layer  212 , or may be formed of stacked Ti and Pt layers. The lower electrode  310  may function as a diffusion barrier layer, which prevents inter-diffusion between the first channel plate  210  and the piezoelectric layer  320  formed thereon, as well as functioning as a common electrode. The piezoelectric layer  320  corresponds to the ink chamber  204  and is transformed by a voltage applied thereto, such that a vibration plate defined by the top of the ink chamber  204  is reversibly deformed. The piezoelectric layer  320  may be formed of a piezoelectric material, e.g., a lead zirconate titanate (PZT) ceramic material. The upper electrode  330  functions to apply a driving voltage to the piezoelectric layer  320  and is disposed on the piezoelectric layer  320 . 
     The printhead may also include a nozzle plate  100 . As illustrated, the nozzle plate may be attached or formed on the bottom of the second channel plate  220  and have a nozzle  150  defined therein so as to communicate with the damper  205 . The nozzle plate  100  may include an electrode  120  disposed around an inner circumference of the nozzle  150 , a hydrophobic insulating layer  140  formed on a surface of the electrode  120  so as to contact the ink, and a wire pattern  122  connected to the electrode  120 . The nozzle plate  100  may include a substrate  110  in which part of the nozzle  150  is defined. The part of the nozzle  150  defined in the substrate  110  may have a tapered cylindrical shape, i.e., a conical shape. The electrode  120  and the wire pattern  122  may be formed on the substrate  110  and be covered with a protective layer  130 . The substrate  110  may be formed of a silicon wafer or an inexpensive base substrate for a printed circuit board (PCB). 
     Where multiple nozzles  150  are included on the printhead, a corresponding electrode  120  may be formed along the inner circumference of each nozzle  150 . The electrode  120  may be formed of highly conductive material, e.g., a metal such as copper (Cu), and may be formed of a material, e.g., Cu again, that is commonly used in manufacturing PCBs. 
     Referring to  FIG. 7 , the electrode  120  may include one or more electrode segments. As illustrated, electrode  120  includes two arc-shaped electrode segments  120   a  and  120   b  arranged along the inner circumference of the nozzle  150 . Of course, the present invention is not limited to one or two electrode segments, and 3, 4, etc. electrode segments may be provided as necessary. The insulating layer  140  may be formed of a hydrophobic material as two arc-shaped insulating segments  140   a  and  140   b  formed on the electrode segments  120   a  and  120   b , respectively. The two arc-shaped segments  140   a  and  140   b  are disposed so as to contact the fluid, e.g., ink in the nozzle  150 . As described above, when a voltage is applied between the ink in the nozzle  150  and the respective electrode segments  120   a  and  120   b , the contact angle of the ink with the respective insulating segments  140   a  and  140   b  varies due to electro-wetting, thereby enabling deflection of the ink droplets ejected through the nozzle  150 . 
     A variety of wire patterns  122  may be formed. The wire pattern  122  may be formed such that it can be connected to the respective electrode segments  120   a  and  120   b  to independently apply a voltage to the respective electrode segments  120   a  and  120   b , i.e., configured to apply the voltage between ink in the nozzle  150  and the respective segments  120   a  and  120   b , such that the electrode segments  120   a  and  120   b  may be independently and alternately energized. That is, the wire pattern  122  is patterned so as to enable individual control of the electrode segments  120   a  and  120   b , wherein the contact angle can be varied in two directions. The wire pattern  122  may be formed of, e.g., Cu, and may be formed of the same material used for the electrode  120 . That is, both may be formed of, e.g., Cu. 
     The protective layer  130  may be disposed to cover the electrode  120  and the wire pattern  122  that are formed on the substrate  110 , thereby protecting and insulating them. Since the protective layer  130  may define an outer surface of the nozzle plate  100 , it may be formed of a hydrophobic material, e.g., a photo solder resist (PSR) material. 
     In another embodiment, illustrated in  FIG. 8 , a nozzle plate  800  may include an insulating layer  240  having four insulating segments  240   a ,  240   b ,  240   c  and  240   d , which are evenly arranged along the inner circumference of the nozzle  150 , e.g., at 90° intervals, i.e., 90° on center. An electrode  220  may include four electrode segments  220   a ,  220   b ,  220   c  and  220   d , which may be formed along the inner circumference of the nozzle  150  at, e.g., 90° intervals, and correspond to the insulating segments  240   a ,  240   b ,  240   c  and  240   d . It will be appreciated that, when each of the electrode  220  and the hydrophobic insulating layer  240  is divided into four segments, the deflection of ejected ink droplets may be varied in greater variety of directions than when they are divided into a lesser number of segments. 
     The insulating and electrode segments may all be formed in an arc shape. The wire pattern  222  may be formed such that it can be connected to the respective electrode segments  220   a ,  220   b ,  220   c  and  220   d  to independently apply a voltage to the respective electrode segments  220   a ,  220   b ,  220   c  and  220   d , although the wire pattern  222  is not limited to this configuration and a variety of wire patterns may be formed. 
     In the examples described in detail above, the insulating layers and the electrodes are divided into two or four segments. However, the present invention is not limited to the illustrated examples, and printheads according to the present invention may include one, three, five, six, etc. segments, as required by the particular application. 
     Further, although described above in the context of a piezoelectric inkjet printhead, the present invention is not limited to such printheads and may be applied to a thermal inkjet printhead and a variety of other fluid ejecting systems besides inkjet printheads. 
     A method of manufacturing the nozzle plate will be described with reference to  FIGS. 9A-9E , which illustrate sectional views of stages in a method of manufacturing a nozzle plate according to the present invention. Referring to  FIG. 9A , a starting substrate  101  may be provided and a conductive layer  102  may be formed thereon, to be patterned to form the electrode  120  and the wire pattern  122 . In detail, the starting substrate  101  may be formed of a base substrate for a PCB, e.g., a polyamide base substrate. In order to form the electrode  120  and the wire pattern  122 , a conductive material, e.g., a metal such as Cu, is deposited to form conductive layer  102  and patterned to form an electrode  120  having a shape such as that shown in  FIGS. 7 and 8 . The electrode  120  may be divided into two, four, etc., segments and the wire pattern  122  may be connected thereto and configured so as to allow independent control of each electrode segment. 
     Referring to  FIG. 9B , the starting substrate  101  may be processed to yield the substrate  110  including a partially formed nozzle  150   a . Partially forming the nozzle  150   a  may include processing the starting substrate  101  to form a void therein using, e.g., a laser. The void may have a tapered cylindrical shape, i.e., a conical or truncated conical shape. 
     Referring to  FIG. 9C , a layer  103  may be formed on the substrate  110 , the electrode  120  and the wire pattern  122  (layer  103  will be referred to as protective layer  130  after it is patterned). The layer  103  may be formed of, e.g., a hydrophobic insulating material such as PSR, which is widely used in PCB manufacturing. The layer  103  may be formed before or after formation of the nozzle  150 , including prior to the partial formation of the nozzle  150   a  described above. 
     Referring to  FIG. 9D , a second portion of the nozzle  150 , e.g., the remaining portion, may be formed by processing the electrode  120  and the layer  103 . The perforation of the nozzle  150  through the layer  103  yields the protective layer  130 . The formation of this second portion of the nozzle  150  may be performed by, e.g., drilling or etching the electrode  120  and the layer  103 . Note that initial patterning of the electrode  120  may leave the electrode segments conjoined by a central region (not shown), in which case the formation of the second portion of the nozzle may include removing the central region of the electrode, so as to completely separate the electrode segments from each other. Thus, the electrode segments may be self-aligned, i.e., precisely formed on the inner circumference of the nozzle  150 , and exposed only at the inner circumference of the nozzle  150 . 
     Referring to  FIG. 9E , a hydrophobic insulating layer  140  may be formed on the exposed surfaces of the electrode  120 , i.e., on the individual electrode segments. In detail, the insulating layer  140 , e.g., a hydrophobic layer, may be formed by depositing, e.g., SiO 2  or SiN through a plasma enhanced chemical vapor deposition (PECVD) method, or by depositing, e.g., Ta 2 O 5 through an atomic layer deposition (ALD) method. The insulating layer  140  is deposited only on the exposed surfaces of the segments of the electrode  120  using the described deposition methods. As a result, the insulating layer  140  formed thereby is also divided into segments, the number of which corresponds to the number of electrode segments. That is, the deposition of the insulating layer  140  may directly form the insulating layer segments, with no need for a separate patterning step. 
     As described above, since the nozzle plate  100  may use a base substrate  110  for the PCB, it may be manufactured using PCB manufacturing processes that are simple and well developed, thereby reducing manufacturing costs. 
     Exemplary embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims. For example, the nozzle plate according to the present invention may be applied to a thermal inkjet printhead as well as the illustrated piezoelectric inkjet printhead, or to a variety of other fluid ejecting systems.