Abstract:
A printer head using a radio frequency micro-electromechanical system (RF MEMS) sprayer includes an inner pressure chamber having a liquid inlet and a liquid outlet; a cavity resonator surrounding the inner pressure chamber, wherein the cavity resonator inputs a predetermined cavity resonance frequency signal to increase an inner pressure of the inner pressure chamber; a signal transmitting unit for generating the predetermined cavity resonance frequency signal and for inputting the generated cavity resonance frequency signal into the inner pressure chamber through the cavity resonator in response to an external input control signal; and a liquid chamber for supplying a liquid, wherein the liquid inlet and the liquid outlet each extend through the inner pressure chamber and the cavity resonator so that when an inner pressure of the inner pressure chamber is increased by the cavity resonator, a liquid from within the inner pressure chamber is ejected.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inkjet printer head. More particularly, the present invention relates to a printer head using a radio frequency micro-electromechanical system (RF MEMS) sprayer including an RF cavity resonator. 
     2. Background of the Related Art 
     In general, a spraying device for spraying a droplet of a liquid may be used in an inkjet printer head, a MEMS cooling device, or the like. A driving method for an inkjet printer head may be classified into a mechanical driving method using a piezoelectric element or a thermal driving method. 
       FIG. 1  illustrates a cross-sectional view of a conventional printer head using a piezoelectric element. 
     As shown in  FIG. 1 , a conventional printer head using a piezoelectric element includes a plate-shaped piezoelectric body  7 , a vibrating plate  6  disposed under the piezoelectric body  7  for converting a longitudinally expanding motion of the piezoelectric body  7  into a bending motion, a liquid chamber layer  1  disposed under the vibrating plate  6  and including a liquid chamber  2  for storing ink, and a nozzle plate  5  having a nozzle  5   a  for spraying a droplet of ink and covering the liquid chamber layer  1 . The nozzle plate  5  has may have a plurality of nozzles  5   a  each spaced at a predetermined distance interval. 
     The liquid chamber layer  1  is formed of a plurality of metal layers welded with pressure. The liquid chamber  2  for storing ink and a restrictor  3  for controlling a flow of ink are provided in the liquid chamber layer  1 . The nozzle plate  5  having the plurality of nozzles  5   a  is positioned under the liquid chamber layer  1 . The vibrating plate  6  is provided to cover a pressure chamber  4  above the liquid chamber layer  1 . The restrictor  3  provides flow communication between the liquid chamber  2  and the pressure chamber  4 . The nozzles  5   a  are connected to the pressure chamber  4 . An electrode (not shown) for operating the piezoelectric body  7  is disposed above the vibrating plate  6 . 
     When the piezoelectric body  7  is polled (i.e., generating an orientation in a piezoelectric body by applying an electric field to the piezoelectric body) to expand longitudinally, the vibrating plate  6  is bent and an inner pressure of the pressure chamber  4  increases to spray a droplet of ink outwardly through the nozzles  5   a . While the droplet of ink is sprayed, the restrictor  3  blocks ink remaining in the pressure chamber  4  from flowing back into the liquid chamber  2 . When the shape and position of the vibrating plate  6  are restored, the pressure chamber  4  is replenished with ink from the liquid chamber  2  through the restrictor  3 . 
     To manufacture the vibrating plate  6 , a green sheet is made of ZrO 2 . Then, holes of a predetermined size are bored into predetermined positions of the sheet. Subsequently, the sheet is heated to a high temperature, e.g., at least about 1,000° C. In addition, a lower electrode of an identical size is formed on the thin ZrO 2  plate. 
     To manufacture the piezoelectric body  7 , the ZrO 2  plate with the lower electrode being formed thereon is screen-printed by precisely arraying a piezoelectric body paste. The piezoelectric body paste, having been screen-painted onto the ZrO 2  plate, is then heated at a high temperature to form an upper electrode on the piezoelectric body  7 . 
     A conventional inkjet printer head using the above-described piezoelectric body has a disadvantage of a low printing speed due to an operating speed limit of the piezoelectric body. In addition, such a conventional inkjet printer head has difficulty in controlling an amount of ink discharged. Further, the manufacturing process is complex and the structure is overly complicated thereby rendering high integration difficult. 
     In the alternate driving method of an inkjet printer head, i.e., the thermal driving method, heat is applied to a thin pipe so that an air bubble is generated to increase an inner pressure of the pipe. This increase in inner pressure causes the discharge of a liquid. 
     More specifically, a passage for ink is formed inside a semiconductor and a thermal resistor is disposed around the passage. Then, a current is applied to the resistor to cause the resistor to be heated and to generate an air bubble in the passage. The generated air bubble increases the inner pressure of the pipe thereby discharging ink from the pipe. 
     Output quality of an output device using an inkjet printer head varies severely according to ink quality and an amount of discharged ink. In printing a color image, if an amount of ink discharged is too great, then the printed image becomes dark overall, thereby lowering a resolution of the printed image. 
     Alternately, if an amount of ink discharged is too small, an output image becomes unclear or a quality of the image is degraded since some of the nozzles do not discharge any ink. Thus, a thermal driving inkjet printer head attempts to discharge ink adequately by regulating a voltage applied to the thermal resistor or a time for the heating. 
     The thermal driving inkjet printer head, however, is severely affected by ambient temperature and humidity conditions. Under high temperature and humidity conditions, such a printer head has problems in that an output image is too dark. Under low temperature and humidity conditions, ink is not discharged or an output image becomes unclear. Further, such a printer head has problems in that it is not easy to precisely regulate an amount of ink discharged and a discharging reaction rate of ink is low due to a limited operating reaction rate of the thermal resistor. Moreover, the printer head has additional problems in that the structure thereof is so complicated that it is not easy to highly integrate a plurality of nozzles, thereby further limiting the resolution of an output image. 
     SUMMARY OF THE INVENTION 
     It is a feature of an embodiment of the present invention to attempt to solve at least some of the above problems and/or disadvantages and to provide a printer head using an RF MEMS sprayer that is capable of a fast discharging reaction rate of ink, an easy and precise regulation of discharging ink and a simple structure to permit high integration of nozzles. 
     The foregoing and other features and advantages may be realized by providing a MEMS sprayer including an inner pressure chamber having a liquid inlet and a liquid outlet; a cavity resonator surrounding the inner pressure chamber, wherein the cavity resonator provides a predetermined cavity resonance frequency signal to increase an inner pressure of the inner pressure chamber; a signal transmitting unit for generating the predetermined cavity resonance frequency signal and for inputting the generated cavity resonance frequency signal into the inner pressure chamber through the cavity resonator in response to an external input control signal; and a liquid chamber for supplying a liquid to the inner pressure chamber, the liquid chamber being in flow communication with the inner pressure chamber through the liquid inlet, wherein the liquid inlet and the liquid outlet each extend through the inner pressure chamber and the cavity resonator so that when an inner pressure of the inner pressure chamber is increased by the cavity resonator, a liquid from within the inner pressure chamber is ejected outwardly through the liquid outlet. 
     Preferably, the cavity resonator is formed of a metal having a hermetically sealed structure. 
     Preferably, the RF MEMS sprayer may further include a substrate having a nozzle disposed in a position corresponding to the liquid outlet, the substrate being welded to a lower side of the cavity resonator where the liquid outlets are formed. 
     The cavity resonator may include a coupling slot formed on a lower side of the cavity resonator, which is in contact with the substrate, the coupling slot receiving the cavity resonance frequency signal from the cavity resonator. The signal transmitting unit may be disposed at a position corresponding to the coupling slot with the substrate being disposed therebetween. 
     The signal transmitting unit may include a signal generator for generating the cavity resonance frequency signal; and a signal input terminal disposed at a position corresponding to the coupling slot for inputting the cavity resonance signal to the cavity resonator through the coupling slot. The signal transmitting unit may further include a signal amplifier for amplifying the cavity resonance frequency signal from the signal generator. 
     The signal transmitting unit may be disposed at a position on the substrate corresponding to the liquid outlet, the substrate being disposed therebetween, the signal transmitting unit inputs the cavity resonance signal into the cavity resonator through the liquid outlet, wherein the nozzle extends to a position corresponding to the liquid outlet. 
     In the RF MEMS sprayer, the liquid inlet prevents a liquid inside the inner pressure chamber from flowing back into the liquid chamber when an inner pressure of the inner pressure chamber is increased by the cavity resonator. 
     In an embodiment of the present invention, the substrate may further include a plurality of nozzles, each nozzle corresponding to a position of one of a plurality of liquid outlets. Similarly, the inner pressure chamber surrounded by the cavity resonator may be a plurality of inner pressure chambers, each being surrounded by a respective one of a plurality of cavity resonators, and wherein each of the plurality of inner pressure chambers is disposed at a predetermined distance interval from an adjacent one of the plurality of inner pressure chambers. 
    
    
     
       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 preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a cross-sectional view of a conventional printer head using a piezoelectric element; 
         FIG. 2A  illustrates a cross-sectional view of a printer head using an RF MEMS sprayer in accordance with a first embodiment of the present invention; 
         FIG. 2B  illustrates a bottom view of the printer head in  FIG. 2A ; 
         FIG. 3A  illustrates a cross-sectional view of a printer head using an RF MEMS sprayer in accordance with a second embodiment of the present invention; and 
         FIG. 3B  illustrates a bottom view of the printer head in  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 2002-63573, filed on Oct. 17, 2002, and entitled: “Printer Head Using RF MEMS Sprayer,” 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 preferred 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 drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. 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 numbers refer to like elements throughout. 
       FIG. 2A  illustrates a cross-sectional view of a printer head using an RF MEMS sprayer in accordance with a first embodiment of the present invention.  FIG. 2B  illustrates a bottom view of the printer head in  FIG. 2A . 
     As shown in  FIGS. 2A and 2B , an RF MEMS sprayer includes an inner pressure chamber  27  disposed inside thereof, a liquid inlet  21  disposed at an upper side of the inner pressure chamber  27 , and a cavity resonator  20  having a coupling slot  23  for receiving a cavity resonance frequency signal, and a liquid outlet  30  disposed at a lower side of the inner pressure chamber. 
     The MEMS sprayer  20  further includes a substrate  29  having a nozzle  22  at a position corresponding to the liquid outlet  30 . The substrate  29  is welded to the lower side of the cavity resonator  20  and a signal transmitting unit  31  is welded under the substrate  29 . 
     The signal transmitting unit  31  includes a signal input terminal  24  disposed at a position facing the coupling slot  23  with the substrate  29  positioned therebetween, a signal generator  25  disposed at an opposite end of the signal transmitting unit  31  from the signal input terminal  24  for generating a cavity resonance frequency signal and a signal amplifier  26  for amplifying the generated cavity resonance frequency signal. 
     It is well known that a cavity resonance frequency resonated by the cavity resonator  20  is a function of a cavity volume and thus a detailed description thereof will be omitted. 
     Regarding the process of discharging an inner material, e.g., a liquid, from the inner pressure chamber  27  surrounded by the cavity resonator  20 , the process is as follows. 
     The cavity resonator  20  is made of metal having a hermetically sealed structure, a cavity resonance frequency input thereinto causes the resonator  20  to resonate, which causes the inner material to expand, thereby increasing an inner pressure of the cavity resonator  20  and the inner pressure chamber  27 . As a result, the inner material is sprayed outwardly through a small outlet, e.g., a liquid outlet  30 . 
     When a cavity volume of the resonator  20  is about 2.86×10 −14  mm 3 , and a corresponding cavity resonance frequency signal is input to the cavity resonator  20 , it is preferable to have input energy ranging from about 3.9 to 8.0 μJ. Output energy, which is an energy with which the inner material of the inner pressure chamber  27  and the cavity resonator  20  is outwardly discharged, is about 5×10 −17  J. In  FIGS. 2A ,  2 B,  3 A, and  3 B, the dimensions of the inner pressure cavity chamber  27  are represented by reference characters a and b for width and length, respectively. Reference character h indicates a height of an inner wall of the inner pressure cavity chamber  27 . 
     The cavity resonator  20  and the inner pressure chamber include a liquid inlet  21 , which provides flow communication from a liquid chamber  28  into the cavity resonator  20  and the inner pressure chamber  27 , at an upper side of the cavity resonator  20 . The liquid inlet  21  prevents a liquid remaining in the inner pressure chamber  27  and the cavity resonator  20  from flowing back through the liquid inlet and into the liquid chamber  28  when an inner pressure of the inner pressure chamber  27  is increased. The cavity resonator  20  further includes the liquid outlet  30  at a lower side thereof. 
     When the cavity resonator  20  provides a cavity resonance frequency signal to resonate, the inner pressure of the inner pressure chamber  27  is increased and thus the liquid inside the inner pressure chamber  27  is discharged outwardly through the liquid outlet  30 . The liquid outlet  30  extends through the inner pressure chamber  27 , the cavity resonator  20 , and the substrate  29 , which may be welded to a lower side of the cavity resonator  20 . 
     The substrate  29  includes the nozzle  22  at a position corresponding to the liquid outlet  30 , so that liquid inside the inner pressure chamber  27  is discharged in a droplet outwardly through the nozzle  22 . The substrate  29  is provided below the inner pressure chamber  27 , with the signal generator  25 , signal amplifier  26  and signal transmitting unit  31  having the signal input terminal  24  provided on the substrate  29 . 
     The signal generator  25  generates a cavity resonance frequency signal, for the cavity resonator  20  to resonate, in response to an external input control signal (not shown) and outputs the cavity resonance frequency signal to the signal amplifier  26 . The signal amplifier  26  inputs the cavity resonance frequency signal from the signal generator  25  in response to the external input control signal and amplifies the input signal to transmit the amplified signal to the signal input terminal  24 . The signal input terminal  24  is disposed at a position facing the coupling slot  23  at the lower side of the substrate  29 . 
     In operation, liquid flowed in through the liquid inlet  21  increases the volume to raise an inner pressure of the inner pressure chamber  27  so that the in-flowed liquid is sprayed in drops outwardly through the liquid outlet  30  and the nozzle  22 . 
     When a signal input is stopped to the cavity resonator  20 , a volume of liquid remaining inside the inner pressure chamber  27  decreases, and an inner pressure of the inner pressure chamber  27  is consequently lowered so that liquid flows into the inner pressure chamber  27  from the liquid chamber  28  through the liquid inlet  21 . 
     The printer head using the RF MEMS sprayer according to an embodiment of the present invention may include a plurality of RF MEMS sprayers each having the above-described structure. When a plurality of sprayers are provided, each may be positioned at a predetermined distance interval from an adjacent sprayer. Similarly, a liquid chamber  28 , as illustrated in the attached figures, may be disposed at an upper portion of cavity resonators  20  for providing ink to the inner pressure chamber  27  through liquid inlets  21 . 
     In operation, a signal input unit  31  corresponding to the cavity resonator  20  generates a cavity resonance frequency signal in response to an external input control signal and inputs the generated signal into the cavity resonator  20 , thereby resonating the cavity resonator  20 . As a result of this resonance, the inner pressure of the inner pressure chamber  27  increases and, since liquid inside the inner pressure chamber  27  is not able to flow backward through the liquid inlets  21 , a droplet of liquid from inside the inner pressure chamber  27  is sprayed outwardly through the liquid outlet  30  and the nozzle  22 . 
     Preferably, an amplification factor of the signal amplifier  26  and an input time of a cavity resonance frequency signal to the cavity resonator  20  may be finely adjusted to facilitate control of the inner pressure of the inner pressure chamber  27  and precise regulation of an amount of discharged ink. 
     With reference to  FIGS. 3A and 3B , a printer head using an RF MEMS sprayer in accordance with a second embodiment of the present invention will now be described. 
       FIG. 3A  illustrates a cross-sectional view of the printer head using the RF MEMS sprayer according to a second embodiment of the present invention.  FIG. 3B  illustrates a bottom view of the printer head in  FIG. 3A . 
     As shown, the printer head according to the second embodiment has a similar structure as the printer head according to the first embodiment except that the coupling slot  23  is omitted from the second embodiment and a signal input terminal  24  is extended to a nozzle  22 . 
     In operation, a cavity resonance frequency signal from a signal amplifier  26  is inputted to a cavity resonator  20  through a liquid outlet  30 . In all other respects, the printer head using the RF MEMS sprayer having the structure of the second embodiment operates the same as the printer head according to the first embodiment. 
     More specifically, a cavity resonance frequency signal generated from a signal generator  25  is amplified by the signal amplifier  26  and then inputted to the cavity resonator  20  through the liquid outlet  30  to resonate the cavity resonator  20 . An inner pressure of an inner pressure chamber  27  is then raised and thus a droplet of liquid from inside the inner pressure chamber  27  is sprayed outwardly through a liquid outlet  30  and nozzle  22  since the liquid inside the inner pressure chamber  27  is not able to flow back through the liquid inlet  21 . 
     With the printer head using the RF MEMS sprayer according to an embodiment of the present invention, a discharging reaction rate of ink increases and a precise regulation of the discharge of a liquid, e.g., ink, becomes less complicated so that a printer head having a simple structure that permits a high integration of the nozzles may be provided. 
     Preferred 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.