Abstract:
An apparatus for jetting a fluid to an exterior through a nozzle by exerting a driving force to the fluid held within a jetting fluid chamber and method of manufacturing the same. The apparatus employs an electrostatic force as the driving force for a driving part which is to be exerted to the fluid. The driving part for exerting the driving force to the fluid has upper and lower electrodes which are oppositely spaced apart from each other at a predetermined distance. The upper electrode is disposed within the interior of a membrane. Here, the membrane forms the lower surface of the jetting fluid chamber. Accordingly, the membrane is driven by the upper electrode which is displaced upward and downward due to the electrostatic force generated between the upper and lower electrodes, so that the driving force is exerted to the fluid within the jetting fluid chamber, and the fluid is jetted to the exterior through the nozzle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 98-49073, filed Nov. 16, 1998, in the Korean Patent Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for jetting fluid, and method of manufacturing the same, and more particularly to a fluid jetting apparatus of a print head employed in output apparatuses such as an ink jet printer, a facsimile machine, etc., to jet fluid through a nozzle. 
     2. Description of the Related Art 
     A print head is a part or a set of parts which are capable of converting output data into a visible form on a predetermined medium using a type of printer. Generally, such a print head for an ink jet printer and the like, uses a fluid jetting apparatus which is capable of jetting a predetermined amount of fluid through a nozzle to an exterior of the ink jet printer or related device by applying a physical force to a fluid chamber holding the fluid. 
     According to a method for applying a physical force to the fluid within the fluid chamber, a fluid jetting apparatus is roughly grouped into a piezoelectric system and a thermal system. The piezoelectric system pushes the fluid within a fluid chamber through the nozzle by an operation of a piezoelectric element which is mechanically expanded in accordance with a driving signal. The thermal system pushes the fluid through the nozzle by bubbles which are produced in the fluid within a fluid chamber due to heat generated by an exothermic body. Recently, also, a thermal compression system has been developed, which is an improved form of the thermal system. The thermal compression system jets the fluid by driving a membrane by instantly heating a vaporizing fluid which acts as a working fluid. 
     FIG. 1 is a vertical sectional view of a fluid jetting apparatus according to a conventional thermal compression system. A fluid jetting apparatus of the thermal compression system includes a heat driving part  10 , a membrane  20 , and a nozzle part  30 . Referring to the heat driving part  10 , a reference numeral  11  is a silicon substrate,  12  is a nonconductive layer,  13  is an exothermic body, and  14  is an electrode. The reference numeral  15  is a barrier layer for a working fluid,  16  and  17  are working fluid chambers, and  18  is a passage for introduction of the working fluid. 
     Referring to the membrane  20 , a reference numeral  21  is a polyimide coated layer, and  22  is a polyimide adhered layer. 
     Referring to the nozzle part  30 , a reference numeral  34  is a nozzle plate,  35  is a nozzle,  36  is a barrier layer of jetting fluid. Reference numerals  37  and  38  are jetting fluid chambers, and  39  is a passage for introduction of the jetting fluid. 
     The substrate  11  of the heat driving part  10  supports the heat driving part  10  and the whole, complete, structure that will be constructed later. The electrode  14  is a conductive material for supplying an electric power for the heat driving part  10 . The exothermic body  13  is a resistive material having a predetermined resistance for expanding a working fluid by converting electrical energy into thermal energy. The working fluid chambers  16  and  17  contain the working fluid, to maintain the pressure of the working fluid which is expanded by the heat. 
     Further, the membrane  20  is a thin layer which is adhered to an upper portion of the working fluid chambers  16  and  17 , and is moved upward and downward by the pressure of the expanded working fluid. The membrane  20  includes a polyimide coated layer  21  and a polyimide adhered layer  22 . 
     The jetting fluid chambers  37  and  38  are formed in a jetting fluid barrier layer  3   b  to contain the jetting fluid, and designed to jet the fluid only through a nozzle  35  when the pressure transmitted through the membrane  20  is applied to the jetting fluid. Here, the jetting fluid is the fluid which is pushed out of the jetting fluid chambers  37  (through the nozzle  35 ) and  38  (via the jetting passage  39 ) in response to the driving of the membrane  20 , and finally jetted to the exterior. The nozzle  35  is an orifice through which the jetting fluid held within the jetting fluid chambers  37  and  38  is emitted to the exterior. A substrate (not shown) of the nozzle part  30  is temporarily employed for constructing the nozzle part  30 , and the substrate of the nozzle part  30  should be separated before the nozzle part  30  is assembled. 
     A process of manufacturing the fluid jetting apparatus according to the conventional thermal compression system will be described below. 
     FIGS. 2A to  2 C are views for showing a process of manufacturing the heat driving part  10  and the membrane  20  of the fluid jetting apparatus of the prior art. FIGS. 3A to  3 C are views for showing a process for manufacturing the nozzle part  30 . 
     In order to manufacture the conventional fluid jetting apparatus, the heat driving part  10  and the nozzle part  30  should be separately manufactured. Here, the heat driving part  10  is completed and the separately-made membrane  20  is adhered to the substrate  11  of the heat driving part  10 . After that, by reversing and adhering the separately-made nozzle part  30 , the fluid jetting apparatus is completed. 
     FIG. 2A shows a sequential process of diffusing the insulated (non-conductive) layer  12  on the substrate  11  of the heat driving part  10 , for forming the exothermic body  13  and the electrode  14  thereon. FIG. 2B shows a process of performing an etching process through a predetermined mask patterning to make the working fluid chambers  16  and  17  and the passage  18  for introduction of the working fluid. More specifically, the heat driving part  10  is formed as the insulated layer  12 , the exothermic body  13 , the electrode  14 , and the barrier layer  15  for the working fluid are sequentially laminated on the upper portion of the silicon substrate  11 . In such a situation, the working fluid chambers  16  and  17 , formed on the etched portion of the working fluid barrier layer  15 , are filled with the working fluid to be expanded by heat. The working fluid is introduced through the passage  18  for introduction of the working fluid. 
     FIG. 2C shows a process of adhering the separately-made membrane  20  to the upper portion of the completed heat driving part  10 . The membrane  20  is a thin diaphragm, which is to be driven toward a direction of the jetting fluid chamber  37  by the working fluid which is heated by the exothermic body  13 . 
     FIG. 3A shows a process of forming an insulated layer  32  and the nozzle plate  34  on the upper portion of the substrate  31  of the nozzle part  30 , and then forming the nozzle  35  by a laser processing equipment (not shown). FIG. 3B shows a sequential process of forming the jetting fluid barrier layer  36  on the upper portion of the construction shown in FIG. 3A, of forming the jetting fluid chambers  37  and  38  and the fluid introducing passage  39  by an etching process through a predetermined mask patterning. FIG. 3C shows a process of exclusively separating the nozzle part  10  from the substrate  31  of the nozzle part  30 . The nozzle part  30  includes the jetting fluid barrier layer  36  and the nozzle plate  34 . On the etched portion of the jetting fluid barrier layer  36 , the jetting fluid chambers  37  and  38  to be filled with the jetting fluid, are formed. The jetting fluid such as ink and the like is introduced through the jetting fluid introducing passage  39 . The nozzle  35  is formed on the nozzle plate  34  to be interconnected with the jetting fluid chamber  37 , so that the jetting fluid is jetted through the nozzle  35 . 
     The operation of the fluid jetting apparatus according to the thermal compressions system will be described with reference to the above-mentioned FIG.  1 . 
     First, an electric power is supplied through the electrode  14 , and electric current flows through the exothermic body  13  which is connected to the electrode  14 . In such a situation, the exothermic body  13  generates heat due to its resistance. The working fluid within the working fluid chamber  16  is subjected to a resistance heating, so that the working fluid starts to vaporize when the temperature thereof exceeds a predetermined degree. As the amount of the working fluid vaporized by the heat increases, the vapor pressure increases. As a result, the membrane  20  is driven upward. More specifically, as the working fluid undergoes the thermal expansion, the membrane  20  is pushed upward in a direction indicated by the arrow in FIG.  1 . As the membrane  20  is pushed upward, the jetting fluid within the jetting fluid chamber  37  is jetted to the exterior through the nozzle  35 . 
     Then, when the supply of the electric power is stopped, the resistance heating is no longer generated out of the exothermic body  13 . Accordingly, the working fluid within the working fluid chamber  16  is cooled to a liquid state, so that the volume thereof decreases and the membrane  20  recovers its original shape. 
     Meanwhile, a conventional material used for the nozzle plate  34  is mainly nickel, but the trend in using a material of a polyimide synthetic resin has increased recently. When the nozzle plate  34  is made of the polyimide synthetic resin, it is fed by a reel type. The fluid jetting apparatus is completed by the way a chip laminated from the silicon substrate  11  to the jetting fluid barrier layer  36  is bonded on the nozzle plate  34  in the reel type. 
     The conventional fluid jetting apparatuses, however, have the following drawbacks. 
     First, since a piezoelectric element is expensive, the fluid jetting apparatus becomes expensive if the same employs the piezoelectric element. Second, if the fluid jetting apparatus employs a thermal system, or a thermal compression system, then the responsive quality thereof can not be guaranteed due to its mechanism in which the working fluid is heated, vaporized, and then thermally expanded, to generate a pressure for exerting the physical force to the fluid. More specifically, since the working fluid should be heated and then vaporized to generate the pressure for driving the membrane, the responsive quality of the fluid jetting apparatus deteriorates. 
     Third, if the fluid jetting apparatus employs the thermal compression system, a precision process of forming the working fluid introducing passage, and also, the process of introducing the working fluid into the working fluid chamber, are required. This causes productivity to be decreased. Finally, due to the high vapor pressure which is produced while heating the working fluid, leakage may occur between the working fluid chamber and the membrane, or between the working fluid chamber and the substrate, so that the reliability of the fuel jetting apparatus deteriorates. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to overcome the above-described problems of the related art, and accordingly it is a first object of the present invention to provide an apparatus for jetting fluid which employs an electrostatic force and has a greater responsiveness than a fluid jetting apparatus according to a thermal system or a thermal compression system. 
     A second object of the present invention is to provide an apparatus for jetting fluid which employs an electrostatic force for jetting fluid regardless of the property of the fluid by driving an organic membrane with an electrostatic attraction. 
     In order to accomplish the first object, the present invention provides an apparatus for jetting fluid comprising a lower electrode, a membrane, a jetting fluid chamber which contains the fluid, a nozzle, and means including the membrane and the lower electrode, for exerting a driving force to the fluid within the jetting fluid chamber by generating an electrostatic force between the membrane and the lower electrode so as to jet a predetermined amount of the fluid outside of the nozzle. 
     Here, the exerting means further includes an upper electrode so that the upper electrode and the lower electrode are oppositely spaced apart from each other by a predetermined distance. It is preferable that the exerting means exerts the driving force to the fluid within the jetting fluid chamber by the displacement of the upper electrode upward and downward due to the electrostatic force generated between the upper and lower electrodes. 
     It is preferable that the upper electrode is disposed in an interior of the membrane to exert the driving force to the fluid within the jetting fluid chamber by driving the membrane. 
     The membrane has a lower membrane and an electrically conducting metallic layer is formed on the upper surface of the lower membrane. Further, it is preferable that the electrically conductive metallic layer is inserted into the membrane, while being disposed between the lower membrane and an upper membrane, to maintain a secure bond of the metallic layer with the upper and lower membranes which are organic layers. 
     Also, the metallic layer comprises an upper electrode in the form of a plate, and at least two springs. 
     It is still preferable that the upper electrode is supported by the membrane and is applied with the electric power through the at least two springs which are shaped to have less stiffness than if the springs are totally straight. 
     Here, the exerting means further includes a space layer for maintaining a gap defined between the upper and lower electrodes. 
     In order to accomplish the second object, a fluid jetting apparatus for employing an electrostatic force according to the present invention includes a jetting fluid chamber with a nozzle and a lower surface comprising a membrane, and in which the fluid is accommodated; a lower electrode disposed at a lower side of the membrane; a space layer to maintain a gap between the membrane and the lower electrode; and an upper electrode disposed within the membrane, to drive the membrane by the electrostatic force generated between the lower electrode and the upper electrode in response to the electric power being applied thereto so as to jet the fluid through the nozzle. 
     The apparatus for jetting fluid by the electrostatic force according to the present invention, employs the electrostatic force as a driving force exerted to the fluid. The driving force is exerted to the fluid by the upper and lower electrodes which are oppositely spaced apart from each other by a predetermined distance. The upper electrode is disposed within the membrane which forms the lower surface of the jetting fluid chamber. Accordingly, the membrane is driven by the upper electrode which is displaced upward and downward due to the electrostatic force generated between the upper and lower electrodes, so that the driving force is exerted on the fluid within the jetting fluid chamber and the fluid is jetted out through the nozzle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages will be more apparent by describing the preferred embodiment in greater detail with reference to the accompanied drawings, in which; 
     FIG. 1 is a vertical sectional view showing a construction of an apparatus for jetting fluid according to a conventional thermal compression system; 
     FIGS. 2A to  2 B are views showing a manufacturing process of a heat driving part and FIG. 2C is a view showing a manufacturing process of adhering a membrane to the heat driving part of the conventional fluid jetting apparatus shown in FIG. 1; 
     FIGS. 3A to  3 C are views showing a manufacturing process of a nozzle part of the conventional fluid jetting apparatus shown in FIG. 1; 
     FIG. 4 is a vertical sectional view of an apparatus for jetting fluid employing an electrostatic force according to an embodiment of the present invention; 
     FIGS. 5A to  5 C are views showing a manufacturing process of a heat driving part and a membrane of a fluid jetting apparatus employing the electrostatic force according to the embodiment of the present invention; 
     FIG. 6 is a plan view of an upper electrode shown in FIG. 5 according to a first aspect of the present invention; 
     FIG. 7 is a plan view of the upper electrode shown in FIG. 5 according to a second aspect of the present invention; 
     FIG. 8 is circuit diagram for explaining how the fluid jetting apparatus is operated by the electrostatic force according to the embodiment of the present invention; 
     FIG. 9 is a view showing the simplified structure of the fluid jetting apparatus employing the electrostatic force according to the embodiment of the present invention; and 
     FIGS. 10A and 10B are sectional views showing the respective states that an electric power is turned on/off between the upper and lower electrodes of the fluid jetting apparatus employing the electrostatic force according to the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the present preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiment is described below in order to explain the present invention by referring to the figures. 
     FIG. 4 is a vertical sectional view of the apparatus employing an electrostatic force according to the embodiment of the present invention. 
     A reference numeral  112  is a silicon substrate,  114  is an insulating layer, and  122  is a lower electrode. The reference numeral  124  is a space barrier layer,  126  is a space layer, and  132  is a jetting fluid barrier layer. The reference numeral  134  is a nozzle plate,  136  is a jetting fluid chamber, and  138  is a nozzle. The reference numeral  140  is a membrane,  142  is an upper membrane member,  144  is a lower membrane member,  146  is an upper electrode, and  148  represents springs. 
     As shown in FIG. 4, the fluid jetting apparatus according to the embodiment of the present invention has a structure in which the insulating layer  114 , the lower electrode  122 , the space barrier layer  124 , the membrane  140 , the jetting fluid barrier layer  132 , and the nozzle plate  134  are sequentially laminated on the silicon substrate  112 . 
     A heat driving part is formed with the lower electrode  122  and the membrane  140  is formed on the space barrier layer  124 . The jetting fluid chamber  136  is formed between the nozzle plate  134 , the jetting fluid barrier layer  132 , and the membrane  140 . Fluid is held within the jetting fluid chamber  136 . The nozzle  138  is formed in the nozzle plate  134 , so that the fluid within the jetting fluid chamber  136  is jetted there through. 
     FIGS. 5A to  5 C are views showing a manufacturing process of the heat driving part and the membrane of a fluid jetting apparatus employing the electrostatic force according to the present invention. 
     Referring to FIG. 5A, the insulating layer  114  is formed on the upper portion of the substrate  112  of the heat driving part, and then the lower electrode  122  is formed on the upper portion of the insulating layer  114 . To form the lower electrode  122 , an electrically conductive metal is vapor-deposited on the substrate  112  to which the insulating layer  114  is vapor-deposited, and the lower electrode  122  is made through the photo-etching process. Unlike the conventional thermal compression system, no exothermic body is required. Now, referring to FIG. 5B, in the state as shown in FIG. 5A, the space barrier layer  124  is formed on the uppermost portion of the insulating layer  114 , and the space layer  126  is formed by the etching process through the mask patterning. That is, the space barrier layer  124  is formed by a photo-etching process wherein a polyimide, which is an organic film, is applied on the insulating layer  114  which is applied to the substrate  112  formed with the lower electrode  122 . At this time, a working fluid chamber and an introducing passage of the working fluid are not formed as they are in the conventional system shown in FIGS. 1 and 2B, and which are shown as the space layer  126 . FIG. 5C shows the state in which the membrane  140  is bonded to the space barrier layer  124 . The membrane  140  has a structure in which the upper electrode  146  is disposed between the upper membrane member  142  and the lower membrane member  144 . 
     The upper electrode  146  and the springs  148  are made through a photo-etching process, by vapor-depositing electrically conductive metallic layer on the upper portion of the lower membrane member  144 . Then, the upper membrane member  142  is formed by applying an organic film on the metallic layer comprising the upper electrode  146  and the springs  148  for better adhesive strength. Here, the upper membrane  142  may be omitted, so that the upper electrode  146  and the springs  148  only may be made on the lower membrane  144 . 
     The upper and lower membrane members  142  and  144  are formed of an organic material such as a polyimide. The upper and lower membrane members  142  and  144  function to prevent direct contact of the fluid within the jetting fluid chamber  136  with the upper electrode  146 , and are easily adhered to the jetting fluid barrier layer  132  and the space barrier layer  124 . 
     FIG. 6 is a plan view of the upper electrode  146  shown in FIG. 5 according to a first aspect of the present invention, and FIG. 7 is a plan view of the upper electrode  146  shown in FIG. 5 according to a second aspect of the present invention. 
     The upper electrode  146  is a thin elastically conductive metallic layer which has a predetermined elasticity. As shown in FIG. 6, the size of the upper electrode  146  is slightly less than that of the lower membrane member  144  (in FIG. 6, the upper membrane member  142  is not shown). Further, at least two springs  148  are electrically connected to the upper electrode  146 . Through the springs  148 , electric power is applied. Additionally, as shown in FIG. 7, it is preferable that the springs  148  have geometrical shapes to have less stiffness, such as being redirected into a plurality of bent portions. In such a situation, since the stiffness of the springs  148  is decreased, the membrane  140  is enabled to be driven more easily. The space barrier layer  124  is for maintaining a gap defined between the upper and lower electrodes  146  and  122 . 
     The operation of the fluid jetting apparatus constructed as above according to the embodiment of the present invention will be described below. Here, since the construction and operation of the nozzle part are the same as described above, with regard to the conventional thermal compression system any further description thereof will be omitted. 
     FIG. 8 is a circuit diagram for explaining how the fluid jetting apparatus according to the embodiment of the present invention is operated by electrostatic force. 
     As electric power is applied to the upper and lower electrodes  146  and  122 , a potential difference is generated therebetween, so that an electrostatic force is produced. The electrostatic force is given by: 
     
       
           F=εA V   2 /2 D   2   
       
     
     Here, V is the potential difference between the upper and lower electrodes  146  and  122 , D is the distance between the upper and lower electrodes  146  and  122 , and A is the area of the upper electrode  146 . ε is the permittivity between the upper and lower electrodes  146  and  122 , and F is the electrostatic attractive force between the upper and lower electrodes  146  and  122 . The maximum electrostatic force between the lower and upper electrodes  122  and  146  can be expressed by Fmax=2 kd, where k is the elastic modulus of the spring  148 , and d is the maximum displacement of the membrane  140 . In this situation, the distance between the lower and upper electrodes  122  and  146  is the same as the distance that the maximum displacement of the membrane  140  is subtracted from the distance between the lower and upper electrodes  122  and  146  when the electric power is not applied thereto. 
     In such a situation, as the electrostatic attractive force acts with respect to the whole area of the upper electrode  146 , the force is transmitted toward the lower membrane member  144  and the springs  148 . The force transmitted to the lower membrane member  144 , then drives the membrane  140  in the direction of the force. As the membrane  140  is moved  10  downward, the ink is injected into the jetting fluid chamber  136  by the amount which is corresponding to the extended volume. Then when the electric power is turned off, the membrane  140  recovers its original shape, so that the injected ink is jetted out. In order to make the deformation of the membrane  140  much greater, the force itself has to be increased, and at the same time, most of the force should be used to drive the membrane  140 . 
     In order to increase the force, A, V and ε should be increased while D should be decreased based on the above-described formula, and these factors, in practice, are not freely varied due to the limit in design. Since the factor D can be adjusted by freely adjusting the speed of applying the organic layer, the adjustment of the force is rather easier. In this instance, the faster the application speed of the organic layer (i.e., the space layer  124 ) gets for a predetermined period, the thinner the thickness of the space barrier layer  124 , so that the distance D between the lower and upper electrodes  122  and  145  is narrowed. To the contrary, the slower the application speed of the organic layer gets, the thicket the thickness of the space layer  124  ism so that the distance D is widened. Further, in order to use most of the force to drive the membrane  140 , the stiffness of the springs  148  should be decreased. That is, the springs  148  may well only serve as electric wires that the electric current flows through, rather than having the ordinary function of the spring. Accordingly, the stiffness of the springs  148  should be decreased to the extent as possible, by varying the geometrical structure and thickness thereof. 
     FIG. 9 shows a simplified structure of the fluid jetting apparatus employing the electrostatic force according to the embodiment of the present invention. According to FIG. 9, a predetermined voltage is applied between the upper and lower electrodes  146  and  122 , the upper electrode  146  is supported and displaced by the springs  148  at both sides thereof, the electrostatic attractive force F is applied, so that the upper electrode  146  is moved within the limit of the maximum displacement d. At this time, ink enters the jetting fluid chamber  136 . Then, when the electric power is turned off, the upper electrode  146  is moved upward, and the upper electrode  146  pushes the ink within the jetting fluid chamber  136  through the nozzle  138 . 
     FIGS. 10A and 10B are sectional views of the respective states that the electric power is turned on/off between the upper and lower electrodes  146  and  122  of the fluid jetting apparatus employing the electrostatic force according to the embodiment of the present invention. 
     According to FIG. 10A, the electrostatic force is applied to the whole area of the upper electrode  146 , and the membrane  140  is deformed downward. As the membrane  140  is deformed, the volume of the jetting fluid chamber  136  is increased, and the jetting fluid is introduced into the jetting fluid chamber  136  through a jetting fluid introducing passage (not shown) by the amount which corresponds to the increased volume. 
     In such a situation, as the electric power is turned off, the electrostatic force is dissipated. Accordingly, as shown in FIG. 10B, the membrane  140 , inclusive of the upper electrode  146 , recovers its original shape by its elasticity. As the membrane  140  recovers its original shape, the introduced ink is ejected to the exterior through the nozzle  138 . 
     As a result, the apparatus for jetting fluid according to the present invention jets the fluid out of the nozzle  138  by driving the membrane  140  with the electrostatic force which is generated when electric power is applied between the two electrodes  146  and  122 . Accordingly, the fluid jetting apparatus according to the present invention can be manufactured with less manufacturing costs in comparison with the fluid jetting apparatuses according to the conventional piezoelectric system, because the expensive piezoelectric elements are not used. Also, the responsiveness of the fluid jetting apparatus according to the present invention is better than the thermal system, or the thermal compression system. Finally, unlike the thermal compression system, a working fluid chamber is not required according to the present invention, so that the working fluid may not be leaked and reliability is enhanced. 
     Having illustrated and described the principles of the invention, it should be apparent to those persons skilled in the art that the illustrated embodiment and the various aspects thereof may be modified without departing from such principles. We claim as our invention all such embodiments that may come within the scope and spirit of the following claims and equivalents thereto.