Patent Publication Number: US-2005128267-A1

Title: Method of manufacturing electronic device, electron source substrate, and image forming apparatus, and apparatus for manufacturing electronic device and electron source substrate

Description:
TECHNICAL FIELD  
      The present invention relates to an electronic device manufacturing method and a manufacturing apparatus therefor and, more particularly, to a manufacturing method for an electronic device by the step of applying, to a substrate, droplets of a liquid containing the formation material of a member which constitutes the electronic device, and a manufacturing apparatus therefor.  
     BACKGROUND ART  
      As a method of easily manufacturing a surface-conduction type electron-emitting element at low cost, there is conventionally proposed a method like the one disclosed in Japanese Laid-Open Patent Application No. 8-171850 in which droplets of a metal-containing solution are discharged onto a substrate using a droplet discharge unit to form element electrodes and a conductive film between them, thereby manufacturing an element, as shown in  FIG. 11 . In  FIG. 11 , reference numeral  1  denotes a substrate;  2  and  3 , element electrodes;  4 , a conductive film; and  5 , an electron-emitting portion.  
      An electron source substrate having electron-emitting elements arrayed in a matrix, and an image forming apparatus are formed on an insulating substrate.  
      As another example of manufacturing an electronic device other than the electron-emitting element and electron source by using an ink-jet method, Japanese Laid-Open Patent Application No. 8-327816 discloses a color filter manufacturing method using the ink-jet method.  
      However, forming the building component of the electronic device using the ink-jet method suffers the following problems. That is, discharge of a solution is inhibited by a gas dissolved in the solution when the solution containing a material for forming the building component of the electronic device contacts air, and by bubbles and the like mixed in injecting the solution into the droplet discharge unit. As a result, the droplet discharge amount may vary. The droplet discharge direction may be influenced by this state, and the landing position when a droplet lands on the insulating substrate may offset from a design value.  
      In addition, the temperature of the solution changes depending on the ambient temperature of the unit to change physical properties such as the viscosity of the solution. The droplet discharge amount may vary. The droplet discharge direction may be influenced by this state, and the landing position when a droplet lands on the insulating substrate may offset from a design value.  
      Hence, the yield in manufacturing an electronic device is difficult to increase, and the production cost increases. In the electron source, the uniformity of the conductive thin film of an electron-emitting element is impaired to decrease the yield of an electron source substrate.  
      It is, therefore, an object of the present invention to provide an electronic device manufacturing method and manufacturing apparatus which can discharge a solution to an accurate position on a substrate, and are excellent in reproducibility of the characteristics of a manufactured electronic device.  
      It is another object of the present invention to provide a manufacturing method and manufacturing apparatus which can discharge a solution to an accurate position on a substrate, for an electron source having a plurality of electron-emitting portions with uniform electron emission characteristics.  
      It is still another object of the present invention to provide a manufacturing method for a high-quality image forming apparatus having uniform emission luminance.  
     DISCLOSURE OF THE INVENTION  
      According to one aspect of the present invention, an electronic device manufacturing apparatus is characterized by comprising gas removal means for removing a gas dissolved in a liquid containing a formation material of a member constituting an electronic device, droplet discharge means for discharging droplets of the liquid, and means for controlling relative positions of the droplet discharge means and a substrate on which the electronic device is formed, wherein the droplets are applied to a predetermined position on the substrate.  
      In this invention, the gas removal means comprises a closed vessel filled with a membrane formed from a semi-transmitting film capable of transmitting a gas, and a vacuum unit for evacuating the closed vessel.  
      In this invention, the gas removal means comprises means for adjusting a flow rate of the liquid in the membrane.  
      In this invention, the gas removal means comprises means for detecting an amount of gas contained in the liquid.  
      In this invention, the gas removal means comprises a vacuum unit, and exposes a solution containing the liquid to vacuum.  
      In this invention, the vacuum unit has a variable exhaust speed.  
      In this invention, the gas removal means comprises means for detecting a vacuum degree of the vacuum unit.  
      In this invention, the droplet discharge means generates a bubble in the liquid using thermal energy, and discharges the liquid on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the liquid using kinematic energy.  
      According to another aspect of the present invention, an electronic device manufacturing apparatus comprises means for adjusting a temperature of a liquid containing a formation material of a member constituting the electronic device, droplet discharge means for discharging droplets of the liquid, and means for controlling relative positions of the droplet discharge means and a substrate on which the electronic device is formed, wherein the droplets are applied to a predetermined position on the substrate.  
      In this invention, the droplet discharge means generates a bubble in the liquid using thermal energy, and discharges the liquid on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the liquid using kinematic energy.  
      In this invention, the electronic device includes an electron source having a plurality of electron-emitting elements.  
      In this invention, each electron-emitting element includes an electron-emitting element having a pair of conductors arranged at a gap.  
      In this invention, the droplet discharge means includes means for discharging droplets of the liquid containing a formation material of the conductors.  
      In this invention, the electron source includes an electron source having a plurality of electron-emitting element arrays each formed by connecting a plurality of electron-emitting elements between a pair of wiring lines.  
      In this invention, the electron source includes an electron source constituted by connecting a plurality of electron-emitting elements in a matrix by a plurality of row-direction wiring lines and a plurality of column-direction wiring lines.  
      According to still another aspect of the present invention, an electron source substrate manufacturing apparatus for manufacturing an electron source substrate having a plurality of pairs of element electrodes formed on a substrate, conductive films each having an electron-emitting portion formed between each pair of element electrodes, and a voltage application terminal to each element electrode, is characterized by comprising gas removal means for removing a gas dissolved in a solution containing a metal element, droplet discharge means for discharging droplets of the solution containing the metal element, and means for controlling relative positions of the droplet discharge means and the substrate, wherein the droplets are applied to a predetermined position on the substrate.  
      In this invention, the gas removal means comprises a closed vessel filled with a membrane formed from a semi-transmitting film capable of transmitting a gas, and a vacuum unit for evacuating the closed vessel.  
      In this invention, the gas removal means comprises means for adjusting a flow rate of a metal solution in the membrane.  
      In this invention, the gas removal means comprises means for detecting an amount of gas contained in the solution.  
      In this invention, the gas removal means comprises a vacuum unit, and exposes a solution containing a metal solution to vacuum.  
      In this invention, the vacuum unit has a variable exhaust speed.  
      In this invention, the gas removal means comprises means for detecting a vacuum degree of the vacuum unit.  
      According to still another aspect of the present invention, an electron source substrate manufacturing apparatus for manufacturing an electron source substrate having a plurality of pairs of element electrodes formed on a substrate, conductive films each having an electron-emitting portion between each pair of element electrodes, and a voltage application terminal to each element electrode, is characterized by comprising means for adjusting a temperature of a solution containing a metal element, droplet discharge means for discharging droplets of the solution containing the metal element, and means for controlling relative positions of the droplet discharge means and the substrate, wherein the droplets are applied to a predetermined position on the substrate.  
      In this invention, the droplet discharge means generates a bubble in the solution using thermal energy, and discharges the solution on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the solution using kinematic energy.  
      In this invention, the solution containing the metal element contains a formation material of the conductive film in which the electron-emitting portion is formed.  
      According to still another aspect of the present invention, an electronic device manufacturing method is characterized by comprising the gas removal step of removing a gas dissolved in a liquid containing a formation material of a member constituting an electronic device, and the droplet discharge step of discharging droplets by droplet discharge means while controlling relative positions of the droplet discharge means for discharging droplets of the liquid and a substrate on which the electronic device is formed, thereby applying the droplets to a predetermined position on the substrate.  
      In this invention, the gas removal step comprises controlling a concentration of the gas dissolved in the liquid so as to be kept at a default value.  
      In this invention, the droplet discharge means generates a bubble in the liquid using thermal energy, and discharges a solution on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the liquid using kinematic energy.  
      According to still another aspect of the present invention, an electronic device manufacturing method is characterized by comprising the temperature adjusting step of adjusting a temperature of a liquid containing a formation material of a member constituting an electronic device, and the droplet discharge step of discharging droplets by droplet discharge means while controlling relative positions of the droplet discharge means for discharging droplets of the liquid and a substrate on which the electronic device is formed, thereby applying the droplets to a predetermined position on the substrate.  
      In this invention, the droplet discharge means generates a bubble in the liquid using thermal energy, and discharges the liquid on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the liquid using kinematic energy.  
      In this invention, the electronic device includes an electron source having a plurality of electron-emitting elements.  
      In this invention, each electron-emitting element includes an electron-emitting element having a pair of conductors arranged at a gap.  
      In this invention, the liquid includes a liquid containing a formation material of the conductors.  
      In this invention, the electron source includes an electron source having a plurality of electron-emitting element arrays each formed by connecting a plurality of electron-emitting elements between a pair of wiring lines.  
      In this invention, the electron source includes an electron source constituted by connecting a plurality of electron-emitting elements in a matrix by a plurality of row-direction wiring lines and a plurality of column-direction wiring lines.  
      According to still another aspect of the present invention, an electron source substrate manufacturing method of manufacturing an electron source substrate having a plurality of pairs of element electrodes formed on a substrate, conductive films each having an electron-emitting portion formed between each pair of element electrodes, and a voltage application terminal to each element electrode, is characterized by comprising the gas removal step of removing a gas dissolved in a solution containing a metal element, and the droplet discharge step of discharging droplets by droplet discharge means while controlling relative positions of the substrate and the droplet discharge means for discharging droplets of the solution, thereby applying the droplets to a predetermined position on the substrate.  
      In this invention, the gas removal step comprises controlling a concentration of the gas dissolved in the solution so as to be kept at a default value.  
      In this invention, the droplet discharge means generates a bubble in the solution using thermal energy, and discharges the solution on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the solution using kinematic energy.  
      According to still another aspect of the present invention, an electron source substrate manufacturing method of manufacturing an electron source substrate having a plurality of pairs of element electrodes formed on a substrate, conductive films each having an electron-emitting portion formed between each pair of element electrodes, and a voltage application terminal to each element electrode, is characterized by comprising the temperature adjusting step of adjusting a temperature of a solution containing a metal element, and the droplet discharge step of discharging droplets by droplet discharge means while controlling relative positions of the substrate and the droplet discharge means for discharging droplets of the solution, thereby applying the droplets to a predetermined position on the substrate.  
      In this invention, the droplet discharge means generates a bubble in the solution using thermal energy, and discharges the solution on the basis of generation of the bubble.  
      In this invention, the droplet discharge means discharges the solution using kinematic energy.  
      In this invention, the solution containing the metal element contains a formation material of the conductive film in which the electron-emitting portion is formed.  
      According to still another aspect of the present invention, an image forming apparatus manufacturing method of manufacturing an image forming apparatus having an electron source substrate and a light-emitting member which emits light upon irradiation of electrons from the electron source substrate, is characterized in that the electron source substrate is manufactured by the electron source substrate manufacturing method described above.  
      In this case, the electronic device in the present invention includes a color filter for a liquid crystal display, a driving circuit for various displays such as a liquid crystal display, plasma display, and electron beam display, and an electron source substrate itself. The building member of the electronic device formed by the manufacturing method and manufacturing apparatus of the present invention includes a filter element particularly in the color filter, a conductor patterned on a circuit board or an insulator for insulating conductors in the driving circuit for various displays, and building members of a plurality of electron-emitting elements or conductors for connecting the electron-emitting elements to driving wiring lines in the electron source substrate.  
      By these apparatus and method, the present invention can discharge a solution to an accurate position on a substrate, and can manufacture an electronic device excellent in reproducibility of characteristics.  
      By these apparatus and method, the present invention can discharge a solution to an accurate position on a substrate, and can manufacture an electron source having a plurality of electron-emitting portions with uniform electron emission characteristics.  
      By these apparatus and method, the present invention can effectively prevent any color misregistration of the filter element in the color filter, and can prevent any unwanted short-circuiting between driving conductors in the driving circuit for various displays.  
      By these apparatus and method, the present invention can also realize a small number of steps, high yield, and low cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view showing the whole arrangement of an electron source substrate manufacturing apparatus according to the present invention;  
       FIG. 2  is an enlarged view showing a system for supplying a metal solution to the droplet applying unit of the electron source substrate manufacturing apparatus according to the present invention;  
       FIG. 3 ( a ) is a view showing in detail a unit for removing a dissolved gas according to the first embodiment of the present invention, and  FIG. 3 ( b ) is a perspective view showing a membrane;  
       FIG. 4  is an enlarged view showing details of a temperature adjusting unit according to the first embodiment of the present invention;  
       FIG. 5  is a view showing in detail a unit for removing a dissolved gas according to the second embodiment of the present invention;  
       FIG. 6  is a view showing in detail a unit for removing a dissolved gas according to the third embodiment of the present invention;  
       FIG. 7  is a plan view showing an electron source substrate manufactured by the manufacturing apparatus according to the present invention;  
       FIG. 8  is a perspective view showing an image forming apparatus manufactured by the manufacturing apparatus according to the present invention;  
      FIGS.  9 ( a ) and  9 ( b ) are a plan view and a sectional view, respectively, for explaining an example of an electron-emitting element according to the present invention;  
      FIGS.  10 ( a ) and  10 ( b ) are a plan view and a sectional view, respectively, for explaining another example of the electron-emitting element according to the present invention; and  
      FIGS.  11 ( a ) and  11 ( b ) are a plan view and a sectional view, respectively, showing a conventional electron-emitting element. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.  
       FIG. 9  shows schematic views of an arrangement of a surface-conduction type electron-emitting element used in the following embodiments, in which  FIG. 9 ( a ) is a plan view, and  FIG. 9 ( b ) is a sectional view. In  FIG. 9 , reference numeral  1  denotes a substrate;  2  and  3 , element electrodes (conductors);  4 , a pair of conductive films (conductors); and  5 , a gap between the pair of conductive films.  
      As another arrangement, as shown in FIGS.  10 ( a ) and  10 ( b ), films  4   a  of carbon or a carbon compound may be formed in the gap  5  and on the conductive films  4 . The films of carbon or a carbon compound form a gap  5   a  narrower than the gap  5  to further increase the service life and electron emission efficiency.  
      This surface-conduction type electron-emitting element emits electrons from the conductive films  4  near the gap  5  or  5   a  by applying a voltage between the element electrodes  2  and  3 .  
      As an embodiment of the present invention, a method of forming the conductive film  4  of the surface-conduction type electron-emitting element will be described.  FIG. 1  is a schematic view showing an electron source substrate manufacturing apparatus using a droplet applying unit of the present invention.  FIG. 2  is an enlarged view showing a system for supplying a metal solution to the droplet applying unit in  FIG. 1 . In  FIG. 1 , reference numeral  8  denotes a droplet discharge unit;  9 , a droplet;  101 , a substrate (to be referred to as an MTX substrate hereinafter) immediately before a conductive thin film is formed;  15 , a stage having X- and Y-direction scanning mechanisms;  16 , a position detecting mechanism; and  19 , a control computer. In  FIG. 2 , reference numeral  102  denotes a temperature adjusting unit;  103 , a unit for removing a dissolved gas;  104 , a unit for measuring the concentration of the dissolved gas;  105 , a chamber;  106 , a vacuum pump;  107 , a solution containing metal elements; and  108 , a tank for this solution.  
      The droplet discharge unit  8  is not limited to a particular unit as far as it can form an arbitrary droplet. The unit  8  can be an ink-jet type unit. The materials of the droplet  9  and solution  107  are not limited to a particular state as far as they can form droplets. The materials can be a solution, organic metal solution, or the like prepared by dispersing/dissolving a metal or the like serving as the component of the conductive thin film in water, a solvent, or the like.  
      This solution  107  is applied as the droplets  9  to desired positions on the element electrodes  2  and  3  by the droplet discharge unit  6 . When the solution  107  contacts outside air, a gas may be dissolved in the solution to increase the dissolved gas amount in the solution  107 , or the gas may form bubbles  109 , as shown in  FIG. 2 . If such a gas is directly discharged by the droplet discharge unit, the dissolved gas abnormally bubbles due to abrupt changes in pressure or temperature in the droplet discharge unit to make the discharge amount or discharge direction of the droplet  9  nonuniform.  
      If the bubbles  109  exist in the solution  107 , the solution may not be sufficiently filled depending on the bubble size, and may be injected into the droplet discharge unit  6 , failing to discharge the droplets  9 . If the temperature of the solution changes depending on the temperature of outside air or the like, the physical properties (concentration, viscosity, and the like) of the solution  107  change to make the discharge amount of the droplet  9  nonuniform.  
      For this reason, droplets cannot be applied to designed positions, and the yield decreases. To prevent this, the present invention adopts the apparatus shown in  FIGS. 1 and 2  to apply droplets to optimal positions for all the elements and increase the yield. The procedures will be described below.  
      The solution  107  containing a gas is introduced into the unit  103  for removing a dissolved gas. The chamber  105  in the unit  103  selectively transmits the gas to the outside in accordance with the molecular size. In this case, the chamber  105  is formed from a semi-transmitting film. The exhaust speed of the vacuum pump  106  can be controlled by an external signal. The dissolved gas analyzer  104  measures the concentration of the gas dissolved in the solution  107  which has passed through the chamber  105 , and can output the concentration.  
      The solution introduced into the unit  103  is supplied to the chamber  105 . The chamber  105  is evacuated by the vacuum pump  106  to selectively exhaust and remove the gas dissolved in the solution  107  through the vacuum pump  106 . The gas-removed solution is introduced into the dissolved gas analyzer  104  where the concentration of the gas in the solution is measured. Based on the measurement value, the exhaust speed of the vacuum pump  106  is adjusted to control the concentration of the gas dissolved in the solution  107  to a sufficiently small value.  
      After these steps, the solution  107  having passed through the dissolved-gas removing unit is controlled to a desired temperature by the temperature adjusting unit  102 . As shown in  FIG. 4 , the temperature adjusting unit  102  is constituted by a circulator  120 , tube  123 , constant-temperature bath  121 , and water thermometer  122 . The circulator  120  is controlled to set the temperature of the metal solution  107  detected by the water thermometer  121  to a default value.  
      After these steps, the metal solution  107  kept at the temperature of the default value is introduced into the droplet discharge unit  8 . The droplet discharge unit  8  discharges the droplets  9  in synchronism with scanning of the stage  15 , and applies them to desired positions on the MTX substrate  101 .  
      Then, the droplet-applied MTX substrate  101  is calcinated at 300° C. to 400° C. to form the conductive films  4 .  
      A step, called the electrification forming step, of applying a voltage between the element electrodes  2  and  3  from a power supply (not shown) is performed to form a fissure (gap  5 ) in part of the conductive films  4 , thereby forming electron-emitting portions in the conductive films  4 . Processing called the activation step is performed for an element having undergone the electrification forming step to deposit the films  4   a  of carbon or a carbon compound on the conductive films (see  FIG. 10 ).  
      A method of manufacturing an image forming apparatus according to the present invention will be described below.  
      An electron source substrate used for the image forming apparatus is formed by arraying a plurality of surface-conduction type electron-emitting elements on a substrate.  
      As shown in  FIG. 7 , the surface-conduction type electron-emitting elements are arrayed in a simple matrix (to be referred to as a matrix layout electron source substrate hereinafter) in which a pair of element electrodes are respectively connected to X- and Y-direction wiring lines. In  FIG. 7 , reference numeral  71  denotes an electron source substrate;  72 , an X-direction wiring line;  73 , a Y-direction wiring line;  74 , a surface-conduction type electron-emitting element; and  75 , a connection line.  
      In  FIG. 7 , a substrate used for the electron source substrate  71  is the above-mentioned glass substrate or the like, and the shape of the substrate is appropriately set in accordance with the intended use. M X-direction wiring lines  72  are lines Dx 1 , Dx 2 , . . . , Dxm, whereas n Y-direction wiring lines  73  are lines Dy 1 , Dy 2 , . . . , Dyn.  
      The wiring line is formed from a conductive metal or the like by vacuum evaporation, printing, sputtering, or the like. The m X-direction wiring lines  72  and n Y-direction wiring lines  73  are electrically isolated by interlevel insulating films (not shown), and constitute matrix wiring (m and n are positive integers). The interlevel insulating film (not shown) is formed from SiO 2  or the like by vacuum evaporation, printing, sputtering, or the like. The X-direction wiring lines  72  and Y-direction wiring lines  73  are extracted as external terminals. The surface-conduction type electron-emitting elements  74  are electrically connected to each other by the m X-direction wiring lines  72 , n Y-direction wiring lines  73 , and connection lines  75 .  
      In this arrangement, individual elements can be selected and independently driven only by simple matrix wiring.  
      The image forming apparatus using the manufactured electron source having the simple matrix layout will be explained with reference to  FIG. 8 .  FIG. 8  is a perspective view showing the display panel of the image forming apparatus. In  FIG. 8 , reference numeral  81  denotes an electron source substrate on which a plurality of surface-conduction type electron-emitting elements are arrayed;  91 , a rear plate to which the electron source substrate  81  is fixed;  96 , a face plate on which a fluorescent film  94 , metal back  95 , and the like are formed on the inner surface of a glass substrate  93 ; and  92 , a support frame. By applying and calcinating frit glass, the rear plate  91 , support frame  92 , and face plate  96  are sealed to constitute an envelope  98 . In  FIG. 8 , reference numerals  82  and  83  denote X- and Y-direction wiring lines respectively connected to a pair of element electrodes of a surface-conduction type electron-emitting element.  
      The glass substrate  93  is comprised of the face plate  96 , support frame  92 , and rear plate  91 , as described above. Further, an atmospheric pressure resistant support member called a spacer is interposed between the face plate  96  and the rear plate  91  to obtain the envelope  98  highly resistant to the atmospheric pressure.  
      The envelope  98  is sealed after being evacuated through an exhaust pipe (not shown). To maintain the vacuum degree after the envelope  98  is sealed, getter processing is done. In the image forming apparatus manufactured in this way, voltages are applied to respective surface-conduction type electron-emitting elements via the external terminals D 0   x   1  to D 0   xm  and D 0   y   1  to D 0   yn  of the vessel to emit electrons. A high voltage is applied to the face plate via a high-voltage terminal Hv to accelerate the electron beam. The electron beam is collided against the fluorescent film  94  to excite the fluorescent film  94 . The fluorescent film  94  emits light to display an image.  
     First Embodiment  
       FIG. 1  is a view best showing the feature of the present invention, and shows an apparatus for forming the conductive film of a surface-conduction type electron-emitting element on an electron source substrate according to the present invention.  FIG. 1  is a schematic view showing an electron source substrate manufacturing apparatus according to the first embodiment of the present invention.  FIG. 2  is an enlarged view showing a system for supplying a metal solution to a droplet applying unit in  FIG. 1 .  FIG. 3  is a view showing in detail a unit for removing a dissolved gas in  FIG. 1 .  
      The arrangement of this apparatus, and an electron source substrate manufacturing method using this apparatus will be explained. In  FIG. 1 , reference numeral  15  denotes a stage to which an MTX substrate  101  is fixed. The stage  15  is coupled to X- and Y-direction scanning mechanisms for moving the stage  15  in the X and Y directions, and can be moved to an arbitrary position in accordance with a signal from a stage scanning controller. The MTX substrate  101  is placed on the stage  15 . A surface-conduction type electron-emitting element to be formed on an electron source substrate has the same structure as that shown in  FIG. 9 , and is made up of a substrate  1 , element electrodes  2  and  3 , and conductive films  4 .  
      A droplet discharge unit  8  for applying droplets is located above the MTX substrate  101 . In the first embodiment, the droplet discharge unit  8  is fixed to the apparatus on the XY plane. The MTX substrate  101  is moved to an arbitrary position by the XY-direction scanning mechanism  15  to realize relative movement of the droplet discharge unit  8  and MTX substrate  101 .  
      The system for supplying a metal solution to the droplet discharge unit will be explained with reference to  FIG. 2 . In  FIG. 2 , a metal solution  107  is temporarily stored in a tank  108 , and introduced into the droplet discharge unit  8  via a temperature adjusting unit  102  and a unit  103  for removing a dissolved gas. The unit  103  is made up of a chamber  105 , a vacuum pump for evacuating the chamber  105 , and a dissolved gas analyzer  104 . The exhaust speed of the pump is changed based on an output from the dissolved gas analyzer to control the internal pressure of the chamber.  
      FIGS.  3 ( a ) and  3 ( b ) show details of the dissolved gas analyzer  104 , and the unit  103  for removing a dissolved gas, and  FIG. 4  shows details of the temperature adjusting unit. The chamber  105  is comprised of a membrane  112  having a semi-transmitting film, and a vessel  111  which encloses the membrane  112 . The vessel  111  is evacuated by a pump  106 . As shown in  FIG. 3 ( b ), the membrane  112  selectively transmits small-size molecules such as a gas via small holes formed in the surface of the membrane. The membrane  112  having this function can be mainly made of poly4-methylpenten. In the first embodiment, the chamber  105  is formed from “SEPAREL” available from Dainippon Ink &amp; Chemicals. The dissolved gas analyzer  104  is formed from a closed vessel  114 , and a DO meter  113  for measuring the concentration of oxygen dissolved in the solution. The dissolved gas analyzer  104  determines the concentration of a gas dissolved in the solution on the basis of oxygen dissolved in the solution  107  in the closed vessel  114 .  
       FIG. 4  shows details of the temperature adjusting unit  102 . The temperature adjusting unit  102  comprises a circulator  120 , tube  123 , constant-temperature bath  121 , and water thermometer  122 . The circulator is used to circulate through the tube  123  a liquid kept at a constant temperature, thereby keeping the temperature of a liquid in the constant-temperature bath  121  constant.  
      Driving of the droplet discharge unit  6  is controlled by an ink-jet head control/driving unit  18  so as to discharge droplets from the droplet discharge unit  6  at an arbitrary timing. The ink-jet head control/driving unit is controlled by a control computer  19 . As the droplet discharge unit  6 , an ink-jet type unit can be adopted. This embodiment adopts a bubble-jet type unit.  
      A method of operating the electron source substrate manufacturing apparatus in the first embodiment will be explained with reference to FIGS.  1  to  3 . As described above, the metal solution  107  is introduced into the droplet discharge unit  6 , and applied as a droplet  9  to a predetermined position on the MTX substrate  101 . The metal solution  107  contains a dissolved gas with an irregular concentration that dissolves from contact air, and bubbles  109  generated by shock or the like. If the metal solution is introduced into the droplet discharge unit  6  in this state, in discharging the droplet  9 , 
          (1) The gas dissolved in the metal solution abnormally bubbles owing to abrupt changes in heat or pressure to nonuniformly change the discharge amount or discharge direction of the droplet  9 .     (2) The droplet discharge unit  6  is not satisfactorily filled with the metal solution  107  due to bubbles in the metal solution  107 , and the droplet  9  greatly decreases in discharge amount or cannot be discharged.        

      At the same time, the discharge direction also changes nonuniformly to impair the uniformity of the manufactured electron source substrate. Furthermore, the temperature of the solution changes depending on the temperature of outside air or the like, and the physical properties (concentration, viscosity, and the like) of the solution  107  change to make the discharge amount of the droplet  9  nonuniform.  
      This phenomenon occurs not only when the droplet discharge unit  6  is a bubble-jet type unit as in the first embodiment, but also when the droplet discharge unit  6  is a piezo-jet type unit. The uniformity of the electron source substrate  71  is difficult to maintain, which decreases the yield.  
      The apparatus of the first embodiment solves this problem by the following procedures, which will be explained with reference to FIGS.  1  to  3 .  
      1. The metal solution  107  is introduced from the solution tank  108  to the chamber  105 . At this time, the metal solution  107  contains a gas and the bubbles  109  at an irregular concentration that are generated when the metal solution  107  contacts outside air or shock is applied to the metal solution  107  in the manufacture or safekeeping.  
      2. The metal solution  107  introduced into the chamber  105  is injected into the membrane  112 . By evacuating the chamber by the vacuum pump  106 , small-size molecules in the gas and bubbles dissolved in the metal solution  107  transmit through the wall surface of the membrane, and are exhausted outside the chamber. Since the gas and bubbles  109  dissolved in the solution are mainly N 2 , O 2 , CO 2 , the gas in the metal solution can be selectively removed by this method.  
      3. The metal solution  107  from which the dissolved gas and bubbles  109  are removed in the chamber  105  in step  2  is introduced into the dissolved gas analyzer  104 . The metal solution  107  is injected into the closed vessel  114 , and the DO meter  113  is inserted into the closed vessel  114  to measure the concentration of the gas dissolved in the metal solution  107 . The first embodiment pays attention to O 2  among the components of the dissolved gas because the amount of O 2  is relatively large and its dissolved amount can be measured at high precision. The dissolved amount of O 2  is measured to determine an expected amount of dissolved gas. During measurement, the metal solution  107  is always stirred using a rotator  115  to increase the measurement precision.  
      4. The exhaust speed of the pump is controlled based on the dissolved O 2  concentration measured in step  3  so as to set the dissolved O 2  concentration to a proper value for the following purposes.  
      (i) The dissolved gas is exhausted to a value at which discharge of droplets from the droplet discharge unit  8  satisfactorily stabilizes.  
      (ii) If the vacuum degree in the chamber  105  excessively decreases, the main component (solvent and the like) of the metal solution  107  is exhausted to change the concentration. To prevent this, the dissolved gas amount must be prevented from excessively decreasing.  
      5. The metal solution  107  after steps  2  to  4  is introduced into the temperature adjusting unit  102 . In the temperature adjusting unit  102 , the circulator  120  circulates through the tube  123  a liquid kept at a temperature of 20° C.±0.2° C. to keep the temperature of the metal solution  107  in the constant-temperature bath  121  constant. The structure of the temperature adjusting unit (the volume of the constant-temperature bath  121 , the shape of the fluid passage of the tube  123 , and the like) is designed to set the temperature of the metal solution  107  in use to 20° C.±0.3° C. The first embodiment assumes application of droplets at a discharge amount of 50 pl per operation and a discharge frequency of 1 kHz. The volume of the constant-temperature bath is designed to 15 ml.  
      After the temperature of the metal solution is controlled to a predetermined value by this method, the metal solution is introduced into the droplet discharge unit  6 .  
      In this manner, the droplets  9  containing a conductive film formation material are applied four times. The resultant substrate is heated at 300° C. for 10 min to form thin films from palladium oxide (PdO) at a film thickness of 100 Å as conductive films. A voltage is applied between the pair of electrodes  2  and  3 , and electrification processing (electrification forming processing) is performed for the conductive films  4  to form a gap  5  between the conductive films  4 .  
      The manufactured electron source substrate is used to constitute an envelope  98  by a face plate  96 , support frame  92 , and rear plate  91 , as shown in  FIG. 8 . The envelope  98  is sealed to manufacture a display panel and an image forming apparatus having a driving circuit for performing television display on the basis of an NTSC television signal.  
      An electron-emitting element manufactured by the manufacturing method of the first embodiment exhibits good characteristics, and the conductive thin film can be uniformly implemented on the substrate with high quality. The present invention can obtain at high yield a high-quality image forming apparatus almost free from variations in element characteristics at the same degree as element characteristics attained by photolithography.  
     Second Embodiment  
      A method of manufacturing an image forming apparatus having a surface-conduction type electron-emitting element according to the second embodiment of the present invention will be described with reference to  FIG. 5 . The second embodiment is the same as the first embodiment except that the concentration of a gas dissolved in a metal solution  107  is controlled by the opening degree of a valve  117 .  
      When the exhaust speed of a vacuum pump  106  is set constant, the concentration of the gas dissolved in the metal solution  107  depends on the stay time in a chamber  105 . In the second embodiment, the three-way valve  117  is interposed between the chamber  105  and a dissolved gas analyzer  104 . The opening degree of the three-way valve  117  is controlled based on a dissolved O 2  concentration detected by a DO meter  113 , and part of the metal solution  107  is exhausted to the outside. This changes the stay time in the chamber  105  so as to keep the concentration of the gas dissolved in the metal solution  117  constant.  
      This method can also control the concentration of the gas dissolved in the metal solution  107  to a predetermined value or less, and can increase the yield of the electron source substrate, similar to the first embodiment. The second embodiment realizes the control method using the opening degree of the valve, and thus can simplify the apparatus.  
     Third Embodiment  
      A method of manufacturing an image forming apparatus having a surface-conduction type electron-emitting element according to the third embodiment of the present invention will be described with reference to  FIG. 6 . The third embodiment is the same as the first embodiment except that the concentration of a gas dissolved in a metal solution  107  is controlled by a pressure value in a chamber  105 .  
      When discharge of droplets  9  from a droplet discharge unit  6  is maintained at a predetermined speed in manufacturing an electron source substrate, the stay time of the metal solution  107  in the chamber  105  is constant. At this time, the concentration of the gas dissolved in the metal solution  107  depends on the vacuum degree in the chamber  105 . From this, as shown in  FIG. 6 , a vacuum gauge  119  is arranged in the chamber  105 . A pump control unit  110  is controlled based on the value of the pressure gauge  119  to keep the vacuum degree in the chamber  105  at a proper value.  
      This method can also control the concentration of the gas dissolved in the metal solution  107  to a predetermined value or less, and can increase the yield of the electron source substrate, similar to the first embodiment. The third embodiment uses the pressure gauge  119  as a method of obtaining the concentration of the dissolved gas, and thus can simplify the apparatus.  
     Industrial Applicability  
      The present invention can provide an electronic device manufacturing method and manufacturing apparatus which can discharge a solution to an accurate position on a substrate, and are excellent in reproducibility of the characteristics of a manufactured electronic device.  
      The present invention can provide a manufacturing method and manufacturing apparatus which can discharge a solution to an accurate position on a substrate, for an electron source having a plurality of electron-emitting portions with uniform electron emission characteristics.  
      The present invention can provide a manufacturing method for a high-quality image forming apparatus having uniform emission luminance.  
      An electron source substrate manufactured by these apparatus and method can realize a smaller number of steps, higher yield, and lower cost, compared to the conventional manufacturing method.