Patent Publication Number: US-2011074744-A1

Title: Electron-emitting device, display panel, and image display apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electron-emitting device for use in a display or the like. 
     2. Description of the Related Art 
     A field emission type electron-emitting device is known in which a majority of electrons field-emitted from one of a pair of opposing conductive films collides with the other conductive film, are scattered, and thereafter reaches an anode. Japanese Patent Laid-Open No. 2001-167693 discloses an electron-emitting device in which an insulating layer is disposed between a pair of conductive films, and depressions are provided on the surface of the insulating layer. Japanese Patent Laid-Open No. 2006-185820 discloses an electron-emitting device in which depressions and protrusions are provided on the surface of the conductive film. 
     SUMMARY OF THE INVENTION 
     An electron-emitting device according to an aspect of the present invention includes an insulating member including an upper surface and a side surface connected to the upper surface; a cathode extending from a first part of the upper surface to the side surface and including a first plurality of protrusions disposed along a boundary between the upper surface and the side surface; and a gate including a base connected to a second part of the insulating member and a second plurality of protrusions each protruding from the base toward the cathode and forming a gap between the second plurality of protrusions and the first plurality of protrusions. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic plan view of an electron-emitting device according to an embodiment of the present invention. 
         FIG. 1B  is a cross-sectional view taken on line IB-IB in  FIG. 1A  and  FIG. 1D . 
         FIG. 1C  is a cross-sectional view taken on line IC-IC in  FIG. 1A  and  FIG. 1D . 
         FIG. 1D  is a side view of the electron-emitting device of this embodiment as viewed from the right in  FIG. 1A . 
         FIG. 2  is a schematic perspective view of an electron-emitting device according to an embodiment of the present invention. 
         FIG. 3A  is a schematic diagram of a system that measures the electron emission characteristics. 
         FIG. 3B  is a partial enlarged schematic diagram of  FIG. 2B . 
         FIG. 4A  is a schematic diagram illustrating the locus of an emitted electron. 
         FIG. 4B  is a schematic diagram illustrating the locus of an emitted electron. 
         FIG. 5A  is a graph showing the relationship between the protrusions of a gate and the electron emission efficiency. 
         FIG. 5B  is a graph showing the relationship between the protrusions of a gate and the electron emission efficiency. 
         FIG. 6A  is a schematic diagram illustrating an example of a method for manufacturing the electron-emitting device. 
         FIG. 6B  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6C  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6D  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6E  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6F  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6G  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 6H  is a schematic diagram illustrating the method for manufacturing the electron-emitting device. 
         FIG. 7A  is a schematic diagram illustrating the process of forming a cathode and an example of the configuration of the cathode. 
         FIG. 7B  is a schematic diagram illustrating the process of forming the cathode and an example of the configuration of the cathode. 
         FIG. 8  is a schematic diagram of a modification of the electron-emitting device. 
         FIG. 9  is a schematic cross-sectional view illustrating the process of manufacturing the modification of the electron-emitting device. 
         FIG. 10A  is a graph showing the relationship between the protrusions of the gate of the modification and the efficiency. 
         FIG. 10B  is a graph showing the relationship between the protrusions of the gate of the modification and the efficiency. 
         FIG. 11A  is a schematic diagram illustrating the configuration of a display panel and a television set. 
         FIG. 11B  is a block diagram of the television set. 
         FIG. 12A  is a diagram showing emission current plotted against temporal changes thereof. 
         FIG. 12B  is a diagram showing emission current plotted against temporal changes thereof. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     A field emission type electron-emitting device according to an embodiment will be illustrated in detail with reference to the drawings. However, it is to be understood that the sizes, materials, shapes, and the relative configurations described hereinbelow do not limit the scope of the present invention unless otherwise specified. 
     An example of the electron-emitting device of this embodiment will be described with reference to  FIGS. 1A to 1D ,  FIG. 2 , and  FIG. 3B . A modification of the electron-emitting device of this embodiment will be described with reference to  FIG. 8 . 
       FIG. 1A  is a schematic plan view of the electron-emitting device;  FIG. 1B  is a cross-sectional view taken on line IB-IB in  FIG. 1A  and  FIG. 1D ;  FIG. 1C  is a cross-sectional view taken on line IC-IC in  FIG. 1A  and  FIG. 1D ; and  FIG. 1D  is a side view of the electron-emitting device of this embodiment as viewed from the right in the drawing.  FIG. 2  is a partially enlarged schematic perspective view of the electron-emitting device shown in  FIGS. 1A to 1D . In  FIG. 2 , the number of protrusions  15  of a gate  5  and the number of protrusions  16  of a cathode, described below in more detail, are set at two for ease of explanation.  FIG. 3B  is a partial enlarged schematic diagram of  FIG. 2B . 
     First, the overall configuration of the electron-emitting device of this embodiment will be described. 
     The electron-emitting device includes an insulating member  3  stacked on the surface of a substrate  1  and a gate  5  provided on the upper surface of the insulating member  3  such that the insulating member  3  is sandwiched between the gate  5  and the substrate  1 . The electron-emitting device further includes a cathode  6  on a side surface of the insulating member  3 . Part of the cathode  6  extends to part of the upper surface of the insulating member  3  and has a plurality of protrusions  16 . The plurality of protrusions  16  are provided along a corner  32  at which the side surface and the upper surface of the insulating member  3  connect to each other. Each of the plurality of protrusions  16  corresponds to an electron-emitting portion. The gate  5  also has a plurality of protrusions  15 . A gap  8  is formed between the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6 . By applying voltage between the cathode  6  and the gate  5  so that the potential of the gate  5  becomes higher than the potential of the cathode  6 , electrons are field emitted from the each of the plurality of protrusions  16  of the cathode  6 . 
     The provision of the plurality of protrusions  16  on the cathode  6  allows the positions of electron emitting portions to be specified and electrons to be emitted at a lower voltage than a configuration without the protrusions  16 . Furthermore, the provision of the protrusions  15  on the gate  5  can increase the rate of arrival of electrons emitted from the protrusions  16  at an anode  11 , to be described below, (electron emission efficiency η) as compared with a configuration in which the protrusions  15  are not provided on the gate  5 . Furthermore, the provision of the protrusions  15  on the gate  5 , in addition to the provision of the protrusions  16  on the cathode  6 , further ensures positioning of the electron emitting portions and increases controllability on the loci of emitted electrons as compared with a configuration in which the protrusions are provided only on the cathode  6 . Thus, the range of electrons emitted to the anode  11  (electron-beam spot diameter) can be controlled. 
       FIGS. 1A to 1D  and  FIG. 2  illustrate an example in which the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  are located on the same straight line parallel to the Z-direction (located on a line perpendicular to the surface of the substrate  1 ), as shown in  FIGS. 1B and 1D . In other words, the protrusions  15  of the gate  5  are provided directly above the protrusions  16  of the cathode  6 . However, in the present invention, the relative positional relationship between the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  is not particularly limited. It is also possible that although the protrusions  15  of the gate  5  are located directly above the protrusions  16  of the cathode  6 , as viewed from the Z-Y plane (at the angle in  FIG. 1D ), the protrusions  15  of the gate  5  are not be located directly above the protrusions  16  of the cathode  6 , as viewed from the Z-X plane (the cross section in  FIG. 1B ). In other words, as in  FIG. 3B , a side surface  5   a  or an end of the gate  5  may be located closer than the protrusions  16  of the cathode  6  (particularly, its ends) to a second insulating layer  3   b.  This can enhance the electron emission efficiency η as compared with a configuration in which the protrusions  15  of the gate  5  overhang directly over the protrusions  16  of the cathode  6 , like eaves. 
     Furthermore, as in a modification of the electron-emitting device of this embodiment, shown later in detail in  FIG. 8 , the protrusions  16  of the cathode  6  may be disposed between two adjacent protrusions of the plurality of protrusions  15  of the gate  5 . That is, the protrusions  15  of the gate  5  may be provided not directly above the protrusions  16  of the cathode  6  but diagonally above the protrusions  16  of the cathode  6 . In other words, the gate  5  are not present directly above the protrusions  16  of the cathode  6  in any of cross sections perpendicular to the surface of the substrate  1  and passing the ends of the protrusions  16 . With this configuration, the protrusions  16  of the cathode  6  are exposed between the two adjacent protrusions  15  of the gate  5 , in plan view as in  FIG. 1A . As a result, in the electron-emitting device with this configuration, the protrusions  16  are exposed to the anode  11 , described below. This allows the electron-emitting device with this configuration to have higher electron emission efficiency r than the electron-emitting devices with the configuration, as shown in  FIGS. 1A to 1D  and  FIG. 2 . 
     Next, the insulating member  3  that constitutes the electron-emitting device will be described. 
     The insulating member  3  of this embodiment has a layered structure having a first insulating layer  3   a  and a second insulating layer  3   b.  However, the insulating member  3  may be formed of one insulating layer, or alternatively, may be formed of a plurality of insulating layers. With the configuration shown in  FIGS. 1A to 1D , the second insulating layer  3   b  is stacked on part of the upper surface  3   e  of the first insulating layer  3   a.  In other words, a side surface  3   d  of the second insulating layer  3   b  is more away from the cathode  6  than a side surface  3   f  of the first insulating layer  3   a.  This allows the upper surface of the insulating member  3  to have depressions  7 . Thus, the upper surface of the insulating member  3  is provided with a level difference. 
     The upper surface of the insulating member  3  is a surface opposing the gate  5 . With the configuration shown in  FIG. 1B , the upper surface of the insulating member  3  is constituted of a portion that is part of the upper surface  3   e  of the first insulating layer  3   a  and is not covered with the second insulating layer  3   b,  the upper surface (a surface opposing the gate  5 )  3   c  of the second insulating layer  3   b,  and the side surface  3   d  of the second insulating layer  3   b  adjacent to the cathode  6 . The upper surface  3   e  of the first insulating layer  3   a  and the upper surface  3   c  of the second insulating layer  3   b  are parallel to the surface of the substrate  1  if the surface of the substrate  1  is flat. Thus, the upper surface of the insulating member  3  generally includes a first surface (the upper surface of the second insulating layer  3   b ) and a second surface (part of the upper surface  3   e  of the first insulating layer  3   a,  not covered with the second insulating layer  3   b ), which are different in distance from the surface of the substrate  1 . In other words, the first surface and the second surface are different in distance from the back surface  5   b  of the gate  5 . 
     The insulating member  3  has a side surface  3   f  connecting to the upper surface of the insulating member  3 . The upper surface and the side surface of the insulating member  3  do not necessarily connect to each other at right angles but may connect at an obtuse angle. Furthermore, as shown in  FIG. 3B , a corner  32  at which the upper surface and the side surface of the insulating member  3  connect to each other may have a predetermined curvature. In the case where the insulating member  3  is constituted of the first insulating layer  3   a  and the second insulating layer  3   b,  the side surface of the first insulating layer  3   a  corresponds to the side surface of the insulating member  3 . 
     The side surface of the insulating member  3  (the side surface  3   f  of the first insulating layer  3   a ) may have a shape similar to the side surface  5   a  of the gate  5 , to be described below (see  FIGS. 1A and 2 ). In other words, the side surface of the insulating member  3  may have a plurality of protrusions. Since the side surface has the plurality of protrusions, the creepage distance between the plurality of protrusions  16 , serving as electron emitting portions, to be described below, can be increased. This can reduce the mutual influence between adjacent electron emitting portions. Furthermore, as will be described below, with the side surface having the plurality of protrusions provided on the insulating member  3 , the material of the cathode  6  is deposited on the side surface of the insulating member  3  by directional sputtering or the like, so that much more material can be deposited on the protrusions of the side surface of the insulating member  3 . As a result, a controlled film-thickness distribution can be achieved on the cathode  6  on the side surface of the insulating member  3 , and as shown in  FIG. 7B , high-resistance portions  6   b  and low-resistance portions  6   a  can be alternately formed in the cathode  6  on the side surface of the insulating member  3 . Thus, resistors (high-resistance portions  6   b ) can be provided between two adjacent protrusions  16  of the cathode  6 , which can reduce the mutual influence between the protrusions  16  serving as electron emitting portions, thereby maintaining stable electron emission characteristics. 
     In  FIGS. 1B and 1C , the side surface of the insulating member  3  (the side surface  3   f  of the first insulating layer  3   a ) is substantially perpendicular to the surface of the substrate  1 . However, the side surface of the insulating member  3  can be a slope having an inclination smaller than 90° (for example, between 45° and 80°) to the surface of the substrate  1 . 
     Next, the cathode  6  will be described. 
     The side surface  3   f  of the insulating member  3  has the cathode  6 . In this example, the end of the cathode  6  opposite to the end adjacent to the gate  5  is electrically connected to a cathode electrode  2 . However, if the cathode  6  has sufficiently low resistance, the cathode electrode  2  may be omitted. At least part of the cathode  6 , located on the side surface  3   f  of the insulating member  3 , may have resistors having a predetermined resistance for limiting current. In this case, the resistors are provided between the cathode electrode  2  and the individual protrusions  16 . 
     The cathode  6  extends from part of the upper surface of the insulating member  3  to the side surface  3   f  of the insulating member  3 . In the configuration shown in  FIG. 1B , the cathode  6  further extends to the surface of the substrate  1 . 
     The cathode  6  includes the plurality of protrusions  16  provided along the corner  32  (see  FIGS. 2 and 3B ), which is the boundary between the upper surface of the insulating member  3  and the side surface  3   f  of the insulating member  3 . The protrusions  16  have the shape of protrusion in the Z-X plane, as in  FIG. 1B , and also have the shape of protrusion in the Z-Y plane, as shown in  FIG. 1D . The individual plurality of protrusions  16  protrude from the corner  32  of the insulating member  3  so as to be away from the upper surface of the insulating member  3 . In an electron-beam emitting unit, described below with reference to  FIG. 3A , the individual plurality of protrusions  16  protrude from the corner  32  of the insulating member  3  toward the anode  11 , described below. In other words, the individual protrusions  16  protrude in the direction in which the insulating member  3  is stacked on the substrate  1 , or in the direction perpendicular to the surface of the substrate  1 . 
     In the case where the cathode  6  has the protrusions  16 , the distance between the peripheral portions of the protrusions  16  and the gate  5  is wider than the distance between the protrusions  16  and the gate  5 . As a result, although electrons emitted from the protrusions  16  are isotropically scattered at the gate  5 , as will be described below, among the scattered electrons, electrons scattered to both side of the protrusions  16  can arrive at the anode  11  through the wide interval between the protrusions  16  and the gate  5 . This can therefore enhance the electron emission efficiency η as compared with a case in which the cathode  6  is flat along the corner  32 , that is, the interval between the gate and the cathode along the corner  32  is constant. 
     As shown in  FIGS. 1B and 3B , the end of the cathode  6  adjacent to the gate  5  covers at least part of the upper surface  3   e  of the insulating member  3  adjacent to the side surface  3   f.  The plurality of protrusions  16  that constitute the end of the cathode  6  are arranged along the corner  32  (see  FIGS. 2 and 3B ) that is the boundary between the upper surface of the insulating member  3  ( 3   e ) and the side surface  3   f  of the insulating member  3 . In other words, the individual protrusions  16  of the cathode  6  covers part of the upper surface  3   e  of the insulating member  3  adjacent to the side surface  3   f.  In other words, part of the protrusions  16  of the cathode  6  is fitted in the depressions  7  of the insulating member  3 , and part of the protrusions  16  connects to the upper surface of the insulating member  3 . 
     An enlarged view of the end of each protrusion  16  is shown in  FIG. 3B . The end has a shape represented by a radius of curvature r. The field intensity at the end varies depending on the radius of curvature r. The smaller the radius of curvature r, the more electric flux lines concentrate, which allows high electric fields to be formed at the ends of the protrusions  16 . Since the shortest distance d 1  between the gate  5  and the cathode  6  influences differences in the number of times of scattering, to be described below, the smaller the radius of curvature r is and the larger the distance d 1  is, the higher the electron emission efficiency η becomes. If the distance d 1  is larger than 10 nm, the driving voltage is increased. However, the distance d 1  is preferably 10 nm or less from the viewpoint of reducing driving voltage necessary for emitting electrons. Furthermore, d 1  is preferably 1 nm or more from the viewpoint of stability of driving. This is because if d 1  is smaller than 1 nm, the protrusions  16  of the cathode  6  may be broken during driving due to field evaporation, discharge, or short-circuit. Therefore, preferably, the distance d 1  is practically 1 nm or more but not more than 10 nm. 
     The protrusions  16  cover part of the upper surface  3   e  of the insulating member  3 , as described above. In other words, the cathode  6  is provided from the side surface  3   f  of the insulating member  3  to part of the upper surface  3   e  of the insulating member  3 . Such a configuration depends on the method for forming the cathode  6 , in which for EB evaporation or the like, not only the angle and time of evaporation but also the thicknesses of the gate  5  and a portion corresponding to the second insulating layer  3   b  serve as parameters. Furthermore, it is difficult for general sputtering to control the shape because of much wraparound. Therefore, it is necessary to employ a special method, such as directional sputtering. 
     The covering of part of the upper surface of the insulating member  3  with the protrusions  16  may offer the following four merits: a first merit is that mechanical adhesion is increased (adhesion strength is increased) because the protrusions  16  serving as electron emitting portions are in contact with the wide area of the insulating member  3 ; a second merit is that the area of thermal contact between the protrusions  16  serving as electron emitting portions and the insulating member  3  is increased to allow heat generated at the electron emitting portions to be efficiently released to the insulating layer  3  (to reduce heat resistance); a third merit is that the field strength at the triple junction at the boundary of the insulating member, vacuum, and metal can be decreased, thereby reducing the possibility of generating an abnormal electric field due to a discharge phenomenon because the protrusions  16  are in contact, with a gentle slope, with the upper surface of the insulating member  3 ; and a fourth merit is that the electron emission efficiency η is increased because the surface of the protrusions  16  adjacent to the second insulating layer  3   b  is inclined relative to the normal of the back surface  5   d  of the gate  5 . 
     Here, the merit of the protrusions  16  covering not only the side surface  3   f  of the insulating member  3  but also part of the upper surface of the insulating member  3  will be described in more detail. 
       FIG. 12A  shows initial Ie and its variations with time when the length x of the end (protrusion  16 ) of the cathode  6  adjacent to the gate  5  entering from the side surface  3   f  of the insulating member  3  into the depression  7  of the insulating member  3  is varied. The length x corresponds to x in  FIG. 3B , which can be regarded as the length of the protrusion  16  connecting to the upper surface of the insulating member  3 . Reference sign Ie denotes the amount of electrons emitted, which corresponds to the amount of electrons that reaches the anode  11  in  FIG. 3A , to be described below. The average amount Ie of emitted electrons detected during the first ten seconds after the driving of the electron-emitting device is started is standardized as the initial value, and changes in the amount of electrons emitted are plotted as common logarithms versus time. 
     There is an apparent tendency to increase in the initial decrease in the amount of emitted electrons as the value x decreases. 
       FIG. 12B  is a plot of the amount of emitted electrons after a lapse of one hour from the same measurement as in  FIG. 12A  performed on several electron-emitting devices, in which the value x is standardized with the initial amount of emitted electrons as 100. As evident from this graph, the smaller the value x, the larger the initial decrease in amount. However, when the value x exceeds 20 nm, there is a tendency to decrease the dependency on the value x. 
     Those results shows that the heat resistance is probably decreased since the protrusions  16  are in contact with the large area of insulating member  3  due to an increase in the value x. Furthermore, initial changes are probably decreased due to a decrease in temperature at the ends of the protrusions  16  because of an increase in heat capacity due to an increase in the volume of the protrusions  16 . 
     A larger value x is not necessarily be desirable. The value x is practically set more than or equal to 10 nm but not more than 30 nm. The value x can be controlled by controlling the angle of evaporation of the material of the cathode  6 , the thickness of the second insulating layer  3   b,  and the thickness of the gate  5 . Setting the value x larger than 30 nm causes leakage between the cathode  6  and the gate  5  via the upper surface of the insulating member  3 , thus increasing leakage-current. 
     Preferably, the ends of the protrusions  16  of the cathode  6  are separated from the gate  5  (the distance d 1  is increased) as much as possible. This can reduce the scattering of electrons at the gate  5 , thereby enhancing the electron emission efficiency η. 
     As shown in  FIG. 3B , it is preferable to have a shift Dx between the ends of the protrusions  16  of the cathode  6  and the side surface  5   a  of the gate  5 . In other words, it is preferable to dispose the gate  5  so that the side surface  5   a  of the gate  5  is located closer to the second insulating layer  3   b  than the protrusions (particularly, the ends) of the cathode  6 . This is for enhancing the electron emission efficiency η and stabilizing emission of electrons. Since the gate  5  is not present directly above the ends of the protrusions  16 , the possibility that electrons that are field-emitted from the ends of the protrusions  16  collide with the back surface  5   b  of the gate  5  can be reduced. This can enhance the electron emission efficiency η and also reduce ineffective current flowing to the gate  5  to prevent the thermal deformation of the gate  5 , thus allowing stable electron emission to be achieved. 
     Next, the triple junction will be described. In general, a portion at which three kinds of material, such as vacuum, insulator, and metal, are in contact is called a triple junction, at which field strength is extremely higher than the surroundings to sometimes cause discharge or the like. Therefore, if an angle θ at which the protrusions  16  and the upper surface of the insulating member  3  are in contact is larger than 90°, its electric field does not significantly differ from a surrounding electric field. However, for example, if the cathode  6  comes off the upper surface of the insulating member  3  due to insufficient mechanical strength to form a gap between the upper surface of the insulating member  3  and the cathode  6 , the angle θ becomes 90° or less. As a result, a strong electric field is formed at the portion where the cathode  6  comes off, from which electrons may be sometimes omitted, or the electron-emitting device may be sometimes broken due to creeping discharge triggered by this electron emission. Accordingly, a desire angle θ at which the protrusions  16  of the cathode  6  and the upper surface of the insulating member  3  are in contact is larger than 90°. 
     To stabilize electron emission characteristics, particularly, to stabilize an emission current, it is preferable to reduce the mutual influence of the plurality of protrusions  16  of the cathode  6 . Thus, it is preferable that the portions  6   b  of the cathode  6 , located between the plurality of protrusions  16 , have higher resistance along the flow of electrons from the cathode electrode  2  to the protrusions  16  than the other portions  6   a,  as shown in  FIG. 7B . More specifically, it is preferable that the resistance between two adjacent protrusions  16  of the plurality of protrusions  16  be higher than the resistance between the individual protrusions  16  and the cathode electrode  2 . This can reduce the mutual influence of the plurality of protrusions  16  of the cathode  6 . 
     In addition to the above configuration, it is more preferable to have resistors at all or part of the portions  6   a  in  FIG. 7B . This allows the individual electron emitting portions (protrusions  16 ) to have resistors, so that temporal changes in emission current from the individual electron emitting portions can be advantageously reduced. Also in this configuration, the resistance between two adjacent protrusions of the plurality of protrusions  16  is set higher than the resistance between the individual protrusions  16  and the cathode electrode  2 . 
     If the side surface of the insulating layer  3  is flat, the portions  6   a  in  FIG. 7B  are preferably thicker than the portions  6   b.  This can increase the creepage distance between the plurality of protrusions  16  serving as electron emitting portions as compared with a case in which the thickness of the portions  6   a  and the thickness of the portions  6   b  are equal. Furthermore, since the portions  6   a  can be higher in resistance than the portions  6   a,  the mutual influence of the protrusions  16  can be reduced, as described above. 
     In the electron-emitting device of this embodiment, the cathode  6  has the portions  6   b  in addition to the absolutely necessary portions  6   a,  shown in  FIG. 7B , for connecting the individual plurality of protrusions  16  and the cathode electrode  2  together. The portions  6   b  serve to prevent part of the side surface  3   f  of the insulating member  3 , located between the plurality of protrusions  16 , from being exposed to vacuum and being charged. If the cathode  6  has not the portions  6   b,  part of electrons emitted from the protrusions  16  and is isotropically scattered at the gate  5  charges part of the side surface  3   f  of the insulating member  3 , located between the protrusions  16 . As a result, emission of electrons becomes unstable or the loci of emitted electrons change with time. Therefore, the cathode  6  has portions  6   b  located on the surface of the insulating member  3   b  located between the plurality of protrusions  16  in addition to the absolutely necessary portions  6   a,  shown in  FIG. 7B , for connecting the individual plurality of protrusions  16  to the cathode electrode  2 . As shown in  FIGS. 1C and 2 , the electron-emitting device of this embodiment is configured such that part of the cathode  6  covers not only the side surface  3   f  of the insulating member  3   b  but also part of the corner  32  of the insulating member  3 , located between two adjacent protrusions  16 . By disposing part of the cathode  6  between the plurality of protrusions  16  in such a manner, the surface of the insulating member  3  between the plurality of protrusions  16  is prevented from being charged, thus stabilizing emission of electrons. 
     Merely providing high resistance not only to the portions  6   b  in  FIG. 7B  but also to the cathode  6  including the protrusions  16  in  FIG. 7A  contributes to stabilization of emission current. For that purpose, the process of providing high resistance to the cathode  6  (for example, the process of oxidizing the cathode  6 ) should be performed. 
     Next, the gate  5  will be described. 
     The gate  5  connects to a portion, not covered with the cathode  6 , of the upper surface of the insulating member  3  and is supported by the insulating member  3 . The gate  5  includes a base  50  and the plurality of protrusions  15  protruding from the base  50  so as to come close to the cathode  6  (particularly, to the protrusions  16  of the cathode  6 ). Preferably, one protrusion  16  of the cathode  6  is provided to one protrusion  15  of the gate  5  (the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  are provided in one-to-one correspondence. In that case, if the number of the protrusions  15  of the gate  5  is n, the number of the protrusions  16  of the cathode  6  is n. 
     The individual protrusions  15  protrude substantially in the same direction from the base  50 . If the surface of the substrate  1  is flat, the protrusions  15  of the gate  5  generally protrude (substantially) parallel to the surface of the substrate  1 . The protruding direction of the protrusions  15  of the gate  5  and the protruding direction of the protrusions  16  of the cathode  6  cross each other. In other words, in  FIG. 1B , the protruding direction of the protrusions  15  of the gate  5  and the protruding direction of the protrusions  16  of the cathode  6  intersect at right angles (intersect at 90°). Preferably, the protruding direction of the protrusions  15  of the gate  5  and the protruding direction of the protrusions  16  of the cathode  6  intersect at 90° or less). 
     The base  50  and the protrusions  15  are employed for ease of understanding; the present invention may employ a configuration in which the base  50  and the protrusions  15  are formed of one member, that is, there is no distinct boundary between the base  50  and the protrusions  15 . 
     The base  50  connects to part of the upper surface of the insulating member  3  (is placed on the upper surface of the insulating member  3 ). In the case where the insulating member  3  is constituted of the first insulating layer  3   a  and the second insulating layer  3   b,  as shown in  FIG. 1 , the base  50  connects to the upper surface  3   c  of the second insulating layer  3   b.  As a result, the gate  5  is supported by the second insulating layer  3   b.  As shown in  FIGS. 1B and 1C , the base  50  may be configured such that part of the bottom does not connect to the upper surface of the insulating member  3 . In other words, there may be a gap between part of the base  50  (the end adjacent to the cathode  6 ) and the upper surface of the insulating member  3 . In contrast, the entire bottom of the base  50  may connect to part of the upper surface of the insulating member  3 . 
     The individual protrusions  15  of the gate  5  protrude from the base  50  so that at least the ends thereof and the cathode  6  form the gap  8  therebetween. Accordingly, the gate  5  is shaped like comb teeth in plan view (in a plane parallel to the surface of the substrate  1 ), as shown in  FIG. 1A . Although  FIG. 3B  shows an example in which the angle of the side surface  5   a  of the gate  5  with respect to the bottom surface  5   b  of the gate  5  is 90°, it is preferable that angle be set at less than 90° to enhance the electron emission efficiency η. The shortest distance of the gap  8  corresponds to the shortest distance d 1 , described above. Here, the outer periphery (side surface  5   a ) of the protrusions  15  of the gate  5  is like a rectangular wave in which straight lines connect to each other at right angles when the electron-emitting device is viewed from the top (viewed from the direction of  FIG. 1A ). However, the configuration of the electron-emitting device of this embodiment is not limited thereto. For example, it is possible to have either an outer periphery (side surface  5   a ) in which arcs continue like a sine wave or an outer periphery (side surface  5   a ) in which straight lines are connected together at an acute angle like a triangle wave. It is also possible that the side surface  5   a  of the protrusions  15  has an arc shape (having a curvature), and portions between the protrusions  15  have a linear shape. In view of registration with the protrusions  16  of the cathode  6 , it is preferable that at least the side surface  5   a  of the protrusions  15  of the gate  5  (particularly, the side surface  5   a  at the ends of the protrusions  15  farthest from the base  50 ) have an arc shape (having a curvature). 
     Next, the operation of the protrusions  15  of the gate  5  will be described. 
       FIG. 4A  shows a configuration in which the gate  5  has not the protrusions  15  (the side surface  5   a  of the gate  5  is flat); and  FIG. 4B  shows a configuration in which the gate  5  has the protrusions  15  (the side surface  5   a  of the gate  5  has depressions and protrusions). The drawings schematically show only part of the electron-emitting device for ease of explanation. 
     As shown in  FIG. 4A , in the case where the gate  5  has not the protrusions  15  and the gate  5  is wider than the cathode  6  in the area where the gate  5  and the cathode  6  oppose, electrons emitted from the protrusions  16  of the cathode  6  are scattered. Specifically, as indicated by the broken lines in the drawings, electrons emitted from the protrusions  16  of the cathode  6  are isotropically scattered on the bottom surface  5   b  or the side surface  5   a  of the gate  5 . Part of the scattered electrons collides with the gate  5  again to repeat scattering. 
     On the other hand, as shown in  FIG. 4B , by providing the protrusions  15  at the area of the gate  5  opposing the protrusions  16  of the cathode  6  (by backspacing both sides of the area of the gate  5  opposing the protrusions  16  of the cathode  6 ), collision of electrons against the gate  5  can be reduced as compared with the configuration of  FIG. 4A . This can reduce scattering of electrons on the gate  5 . The configuration of  FIG. 4B  can therefore increase electrons that reach the anode  11 , thus enhancing the efficiency η. 
     Next, a method for evaluating the electron emission characteristics of the electron-emitting device and the efficiency of arrival of electrons emitted from the cathode  6  to the anode  11 , that is, the electron emission efficiency η), will be described. The electron emission efficiency η is given by η=Ie/(If+Ie) where If is a current detected when voltage is applied to the electron-emitting device and Ie is a current taken in vacuum (a current that reaches the anode  11 ). 
     The electron emission characteristics of the electron-emitting device can be measured using the configuration shown in  FIG. 3A . In  FIG. 3A , Vf is a voltage applied between the gate  5  and the cathode  6 ; If is a device current flowing between the gate  5  and the cathode  6  when the voltage Vf is applied between the gate  5  and the cathode  6 ; Va is a voltage applied between the cathode  6  and the anode  11 ; and Ie is an electron emission current. Although  FIG. 3A  shows an example in which the voltage Va is applied between the cathode  6  and the anode  11 , a power source that applies potential to the anode  11  and a power source that applies potential to the cathode  6  may be separately provided. As shown in  FIG. 3A , the anode  11  that is set at higher potential than the gate  5  and cathode  6  is provided above the substrate  1  having the electron-emitting device to thereby configure an electron-beam emitting unit in which electrons emitted from the plurality of protrusions  16  brought to the anode  11 . 
     Next, the relationship between the electron emission efficiency η and the sizes of the components of the electron-emitting device will be described using simulated calculations. As shown in  FIG. 2 , the amplitude of the protrusions  15  of the gate  5  (the distance from the base  50  to the ends of the protrusions  15  (the length in the X-direction)) is defined as A 1 , the period of the protrusions  15  of the gate  5  (the length in the Y-direction) is defined as T 1 , the interval between the protrusions  15  of the gate  5  is defined as W 2 , and the width of the protrusions  15  of the gate  5  is defined as W 1 . 
     Typical examples of the values in calculations below are as follows: the thickness of the insulating layer  3   a  is 10 nm; the thickness of the insulating layer  3   b  is 200 nm; the thickness of the gate  5  is 5 nm; the distance d 1  between the gate  5  and the cathode  6  is 5 nm; the amplitude A 1  of the gate  5  is 6 nm; the period T 1  is 12 nm; the driving voltage Vf is 21 V; the anode applied voltage Va is 11.8 kV; and the work function Wf of the cathode  6  is 4.6 eV. 
     First, the relationship between the amplitude A 1  of the protrusions  15  of the gate  5  and the efficiency η will be described using  FIG. 5A . The horizontal axis in  FIG. 5A  shows values of the amplitude A 1  of the protrusions  15  of the gate  5  standardized by the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5 , and the vertical axis shows the electron emission efficiency η.  FIG. 5A  shows that when the amplitude A 1  of the protrusions  15  of the gate  5  is increased, the electron emission efficiency η increases significantly at a certain amplitude or more and is thereafter held substantially constant. Letting Alsta be an amplitude at which the electron emission efficiency η begins to increase, Alsta is read to be 0.5×d 1 . The tendency shown in  FIG. 5A  does not significantly change depending on the thicknesses, widths, depths, and materials of the components of the electron-emitting device. Accordingly, it is preferable that the amplitude A 1  of the protrusions  15  of the gate  5  be set at 0.5×d 1  or more in consideration of the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5 . The calculation is made, with the centers of the protrusions  16  of the cathode  6  and the centers of the protrusions  15  of the gate  5  agreed with each other in the vertical direction. 
     The reason that the electron emission efficiency η is significantly increased when the amplitude A 1  exceeds Alsta seems to be because electrons emitted from the electron emitting portions (more specifically, electrons scattered at the gate  5 ) pass between two adjacent protrusions  15  of the gate  5  to easily reach the anode  11 . In contrast, the reason that the electron emission efficiency η is substantially constant when the amplitude A 1  is smaller than A 1 sta seems to be because there is little difference from the case in which the gate  5  has not the protrusions  15 . The reason that the electron emission efficiency η is saturated is because the amplitude A 1  of the protrusions  15  of the gate  5  becomes sufficiently large, so that there is no difference in the amount of emitted electrons passing between two adjacent protrusions  15  of the gate  5 . 
     Next, the relationship between the period T 1  of the protrusions  15  of the gate  5  and the electron emission efficiency η will be described using  FIG. 5B . The horizontal axis in  FIG. 5B  shows values of the period T 1  of the protrusions  15  of the gate  5  standardized by the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5 , and the vertical axis shows the electron emission efficiency η.  FIG. 5B  shows that when the period T 1  of the protrusions  15  of the gate  5  is increased, the electron emission efficiency η decreases significantly and is held substantially constant at a certain period or more. Letting T 1 sat be a period at which the electron emission efficiency η becomes substantially constant, T 1 sat is read to be 10×d 1 . The tendency shown in  FIG. 5B  does not significantly change depending on the thicknesses, widths, depths, and materials of the components of the electron-emitting device. Accordingly, it is preferable that the period T 1  of the gate  5  be set at 10×d 1  or less. 
     T 1  is the sum of W 1  and W 2  in  FIG. 2 . In the calculation in  FIG. 5B , W 1 =W 2  is assumed, and the centers of the protrusions  16  of the cathode  6  and the centers of the protrusions  15  of the gate  5  agree with each other in the vertical direction. Accordingly, an increase in the period T 1  of the protrusions  15  of the gate  5  means that W 1  and W 2  increase. Therefore, the reason that the electron emission efficiency η is decreased when the period T 1  of the protrusions  15  of the gate  5  increases seems to be because the width W 1  of the protrusions  15  of the gate  5  that overhang the protrusions  16  of the cathode  6  increases. In other words, it seems to be because the width W 1  of the protrusions  15  of the gate  5  located directly above the protrusions  16  increases. The reason that the electron emission efficiency η becomes substantially constant when the T 1  exceeds T 1 sat seems to be because there is little difference from the case in which the gate  5  does not have the protrusions  15 . 
     Next, a modification of the electron-emitting device, in which the relative positional relationship between the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  is different from the electron-emitting device, as shown in  FIG. 2 , will be described using  FIG. 8 . 
     The electron-emitting device of the modification is configured such that each of the protrusions  16  of the cathode  6  faces a portion between two adjacent protrusions  15  of the gate  5 . Typically, the phases of the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  are shifted by half period from the configuration described in  FIG. 2  etc. Although  FIG. 8  shows only one of the protrusions  16  of the cathode  6  for ease of explanation, a plurality of protrusions  16  is actually provided along the corner  32 . Likewise, only two of the protrusions  15  of the gate  5  are shown, a plurality of (≧2) protrusions  15  of the gate  5  are actually provided. That is, one protrusion  16  of the cathode  6  is provided for two protrusions  15  of the gate  5 . Therefore, the number of the protrusions  16  of the cathode  6  is n-1 at the minimum, where n is the number of the protrusions  15  of the gate  5 . 
     In the electron-emitting device of the modification, each protrusion  16  of the cathode  6  is opposed to a portion between two adjacent protrusions  15  of the gate  5 . Therefore, electric flux lines immediately above the protrusions  16  do not directly proceed to the gate  5 , and a direction in which electrons are emitted from the protrusions  16  are nearly vertical to the surface of the substrate  1 . Accordingly, as shown in  FIG. 8 , the amount of electrons emitted toward an anode (not shown) without colliding with the gate  5  are larger than that of the electron-emitting device of the embodiment, shown in  FIG. 2  etc. The electron emission efficiency η is therefore enhanced as compared with the electron-emitting device of the embodiment, shown in  FIG. 2  etc. Since the amount of electrons scattered at the gate  5  is smaller than the electron-emitting device of the embodiment, shown in  FIG. 2  etc., the area (spot diameter) of the anode irradiated with electrons emitted from the electron-emitting device can be decreased. 
     Next, the electron emission efficiency η of this modification will be described. 
     First, the relationship between the amplitude A 1  of the protrusions  15  of the gate  5  and the electron emission efficiency η will be described. 
       FIG. 10A  shows the relationship between the amplitude A 1  of the protrusions  15  of the gate  5  and the efficiency η. The horizontal axis in  FIG. 10A  shows values of the amplitude A 1  standardized by the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5 , and the vertical axis shows the efficiency η. 
       FIG. 10A  shows that when the amplitude A 1  is increased, the efficiency η also increases, and the increase in the efficiency η slows at a certain value or more to be substantially saturated. Letting A 1 sat be an amplitude at which the increase in efficiency η begins to slow, A 1 sat is read to be about 1×d 1 . The tendency shown in  FIG. 10A  does not significantly change depending on the thicknesses, widths, depths, and materials of the components of the electron-emitting device. The reason that the efficiency η increases as the amplitude A 1  is increased seems to be because the area of the gate  5  that overhangs the protrusions  16  of the cathode  6  decreases (the gate  5  is separated from directly above the protrusions  16 ). This may make it easy for electrons emitted from the protrusions  16  to pass between two adjacent protrusions  15  of the gate  5 , thus enhancing the efficiency η. The reason when the increase in efficiency η slows at A 1 sat or more may be that the amplitude A 1  is large enough, so that the number of electrons that do not strike the gate  5  becomes substantially constant. 
     Therefore, it is preferable for the electron-emitting device of the modification that the amplitude A 1  of the protrusions  15  of the gate  5  and the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  satisfies the relationship A 1 ≧d 1 . This can reduce the collision of electrons emitted from the protrusions  16  of the cathode  6  against the gate  5 , thus enhancing the efficiency η. 
     Next, the relationship between the interval W 2  between two adjacent protrusions  15  of the gate  5  and the efficiency η will be described. 
       FIG. 10B  shows the relationship between the interval W 2  between two adjacent protrusions  15  of the gate  5  and the efficiency η. The horizontal axis in  FIG. 10B  shows values of the interval W 2  standardized by the shortest distance d 1  between the cathode  6  and the gate  5 , and the vertical axis shows the electron emission efficiency η.  FIG. 10B  shows that when the interval W 2  is increased, the efficiency η increases, and the efficiency η becomes substantially constant at a certain value or more, and when the interval W 2  is further increased, the efficiency η begins to decrease. Letting W 2 sat be a value at which the efficiency η begins to be saturated, W 2 sat is read to be about 1×d 1 . Letting W 2 dec be a value at which the efficiency η begins to decrease, W 2 dec is read to be 3×d 1 . The tendency shown in  FIG. 5A  does not significantly change depending on the thicknesses, widths, depths, and materials of the components of the electron-emitting device. The reason that the efficiency η increases as the interval W 2  is increased to W 2 sat seems to be because the width of the gate  5  that overhangs the protrusions  16  of the cathode  6  decreases. The reason that the efficiency η is substantially constant from the interval W 2 =W 2 sat to W 2 dec seems to be because the number of electrons that do not collide with the gate  5  is substantially constant. The reason that the efficiency η is decreased when the interval W 2  becomes larger than W 2 dec may be because this configuration does not differ from a configuration in which the gate  5  has not the protrusions  15 . 
     Therefore, it is preferable for the electron-emitting device of the modification that the interval W 2  between two adjacent protrusions  15  of the gate  5  and the shortest distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  satisfy the relationship, d 1 ≦W 2 ≦3×d 1 . 
     In the electron-emitting device of the modification, collision of electrons emitted from the protrusions  16  of the cathode  6  against the gate  5  can be reduced, thus enhancing the efficiency η. 
     The electron-emitting device of the present invention may have the relative positional relationship between the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6 , shown in  FIG. 8 , in addition to the relative positional relationship between the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6 , shown in  FIG. 2  etc. 
     An example of the method for manufacturing the electron-emitting device of this embodiment, described above, will be described with reference to  FIGS. 6A to 6H . A method for manufacturing the electron-emitting device of the modification, described using  FIG. 8 , will be described later. 
       FIGS. 6A to 6H  are schematic diagrams illustrating an example of the process of manufacturing the electron-emitting device shown in  FIG. 1A to 1D  in sequence. 
     First, an insulating layer  23  serving as the first insulating layer  3   a,  an insulating layer  24  serving as the second insulating layer  3   b,  and a conductive layer  25  serving as the gate  5  are stacked on the surface of the substrate  1  ( FIG. 6A ). 
     The substrate  1  is an insulative substrate made of, for example, quartz glass, glass in which impurities, such as sodium, are reduced, soda-lime glass, and silicon. The insulating layers  23  and  24  are insulative films made of a material with high processability, such as, SiN(Si x N y ) and SiO 2 . The insulating layers  23  and  24  are manufactured by a general vacuum film forming method, such as a sputtering method, a CDV method, or a vapor deposition method. The thicknesses of the insulating layers  23  and  24  are set in the range between 5 nm and 50 μm, preferably, between 50 nm and 500 nm. Since the depressions  7  need to be formed after the insulating layers  23  and  24  are stacked on the substrate  1 , the insulating layer  23  and the insulating layer  24  need to have different etching rate from each other. Preferably, a selection ratio of the insulating layer  23  to the insulating layer  24  is 10 or more, and 50 or more if possible. Specifically, for example, the insulating layer  23  can employ an insulating material, such as Si x N y , and the insulating layer  24  can employ an insulating material, such as SiO 2 , a PSG film having a high phosphorous concentration, or a BSG film having a high boron concentration. 
     The conductive layer  25  is formed by a general vacuum film forming technology, such as a vapor deposition method and a sputtering method. A material for the conductive layer  25  is preferably a material having high conductivity, high thermal conductivity, and high melting point, for example, metals, such as Be, Mg, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Al, Cu, Ni, Cr, Au, Pt, and Pd, alloys thereof, and carbides, such as TiC, ZrC, HfC, TaC, SiC, and WC. Examples of the material also include borides, such as HfB 2 , ZrB 2 , CeB 6 , YB 4 , and GdB 4 , and nitrides, such as TiN, ZrN, HfN, and TaN. The thickness of the conductive layer  25  is set in the range between 5 nm and 500 nm. 
     Next, after a resist pattern is formed on the conductive layer  25  by a photolithography technology, the conductive layer  25 , the insulating layer  24 , and the insulating layer  23  are processed in sequence with an etching technique. Thus, the gate  5  and the insulating member  3  formed of the insulating layer  3   b  and the insulating layer  3   a  can be obtained ( FIG. 6B ). 
     For such an etching process, reactive ion etching (RIE) is generally used which can precisely etch the materials by irradiating the materials with a plasma of etching gas. Examples of the processing gas to be used at this time include fluorine-based gases, such as CF 4 , CHF 3 , and SF 6 , when the target member forms fluoride. When the target member forms chloride, such as Si and Al, chloride-based gases, such as Cl 2  and BCl 3 , are selected. To obtain the selection ratio to the resist, to ensure the smoothness of the etched surface, or to increase the etching speed, hydrogen, oxygen, argon gas, or the like is added when necessary. 
     Next, protrusions are formed on the side surface of the gate  5  and the side surface of the insulating member  3  formed of the insulating layers  3   a  and  3   b  using focused ion beams (FIB) ( FIG. 6C ). 
     In the FIB processing, the side surface of the gate  5  is cut off so that the amplitude A 1  and the period T 1  of the protrusions  15  of the gate  5  reach desired values. The following description is made with reference to the drawings as viewed along the cross section VI-VI in  FIG. 6C . 
     Subsequently, only the side surface of the insulating layer  3   b  is partly removed by etching to form the depressions  7  ( FIG. 6D ). 
     For the etching technique, for example, a mixture solution of ammonium fluoride and hydrofluoric acid, which is referred to as a buffer hydrofluoric acid (BHF), can be used if the insulating layer  3   b  is formed of a material made from SiO 2 . If the insulating layer  3   b  is formed of a material made from Si x N y , the insulating layer  3   b  can be etched using a phosphoric-acid-based hot etching solution. 
     The depth of the depressions  7 , that is, the distance, of the depressions  7 , between the side surface of the insulating layer  3   b  and the side surfaces of the insulating layer  3   a  and the gate  5  have close connection with leakage-current after the electron-emitting device is formed. The deeper the depressions  7 , the smaller the leakage-current. However, since excessively deep depressions  7  will cause problems, such as deformation of the gate  5 , the depth of the depressions  7  is practically set at 30 nm or more but not more than 200 nm. 
     Next, a release layer  20  is formed on the surface of the gate  5  ( FIG. 6E ). 
     The release layer  20  is formed for the purpose of releasing the material of the cathode  6 , which is deposited in the next process, from the gate  5 . For this purpose, the release layer  20  is formed, for example, by forming an oxide film on the gate  5  through oxidation or by depositing release metal by electrolytic plating. 
     Next, the material of the cathode  6  is deposited on the substrate  1 , the side surface of the insulating member  3 , and the gate  5  ( FIG. 6F ). 
     The material of the cathode  6  should be a conductive material capable of field emission, generally having a high melting point of 2,000° C. or higher and a work function of 5 eV or less, and preferably, a material that hardly forms a chemical reaction layer, such as oxide, or from which the reaction layer can easily removed. Examples of the material include metals, such as Hf, V, Nb, Ta, Mo, W, Au, Pt, and Pd, alloys thereof, carbides, such as TiC, ZrC, HfC, TaC, SiC, and WC, and borides, such as HfB 2 , ZrB 2 , CeB 6 , YB 4 , and GdB 4 . 
     A method for depositing the material of the cathode  6  (cathode material) is preferably a directional sputtering method. The reason why the directional sputtering method is preferable is that the plurality of protrusions  16  are formed along the corner  32  so as to cover part of the interior of the depressions  7  (part of the upper surface of the insulating member  3 ). With the sputtering method, the energy of the sputtered particles of the cathode material is small. Therefore, the plurality of protrusions  16  seems to be easily formed along the corner  32  of the insulating member  3  since the sputtered particles come flying to the corner  32  of the insulating member  3  through the space between two adjacent protrusions  15  of the gate  5  (space  15   b  in  FIG. 7A ), in other words, because the cathode material can easily be deposited directly below the protrusions  15  of the gate  5 . 
       FIG. 7A  is a schematic diagram illustrating a state in which the material of the cathode  6  is deposited on the side surface of the insulating member  3  from the same direction as in  FIG. 1D , in which typical flying loci of the cathode material are indicated by broken lines  26   a  to  26   d.  As shown in  FIG. 7A , if protrusions are formed on the side surface of the insulating layer  3   a,  the sputtering method affixes much more cathode material to the protrusion of the side surface of the insulating layer  3   a  than to the other portion of the side surface of the insulating layer  3   a  due to projection effect. Furthermore, as indicated by the broken lines  26   a  to  26   c,  sputtered particles (cathode material) pass through the space ( 15   b ) between two adjacent protrusions  15  of the gate  5 . Therefore, the much more cathode material is deposited on the corner  32  of the insulating layer  3   a  in the vicinity of the joint between the upper surface of the insulating layer  3   a  and the protrusions on the side surface of the insulating layer  3   a.  As a result, the plurality of protrusions  16  are formed along the corner  32  in correspondence with the period of the protrusions  15  of the gate  5 . Thus, the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  can be provided in one-to-one correspondence. Meanwhile, the flying loci of the cathode material include a flying locus perpendicular to the surface of the substrate  1  through the space ( 15   b ) between two adjacent protrusions  15  of the gate  5 , as indicated by the broken line  26   d.  Most of the cathode material flying along such a locus is not affixed to the surface (side surface) of the insulating member  3 , depending on the degree of inclination of the side surface of the insulating member  3 , but is affixed to the substrate  1 . In view of such a phenomenon, by controlling the angle of sputtering, the time, temperature, and the degree of vacuum for deposition, protrusions  16  with a desired shape can be provided. 
     As shown in  FIG. 2 , the electron-emitting device is configured such that the cathode  6  covers the portion from the side surface  3   f  of the insulating layer  3   a  through the corner  32  of the insulating layer  3   a  to the corner- 32 -side upper surface  3   e  of the insulating layer  3   a  between the plurality of protrusions  16 . This configuration can be achieved, for example, by providing (setting back) the side surface  5   a  of the gate  5  in the -X direction relative to the side surface  3   f  of the insulating layer  3   a  or by sputtering the material of the cathode  6  from diagonally above to the side surface  5   a  of the gate  5  and the side surface  3   f  of the insulating member  3 . Alternatively, this configuration can also be achieved by inclining both the side surface  5   a  of the gate  5  and the side surface  3   f  of the insulating member  3  at a predetermined angle (&lt;90°) with respect to the surface of the substrate  1 . 
     Next, the cathode material  6 C on the gate  5  is removed by removing the release layer  20  by etching ( FIG. 6G ). Although the cathode material  6 C on the gate  5  is removed here, the cathode material  6 C may be left on the gate  5 . 
     Next, the cathode electrode  2  is formed for electrical conduction with the cathode  6  ( FIG. 6H ). 
     The cathode electrode  2  has conductivity like the cathode  6  and is formed by a general vacuum film-forming technology, such as a vapor deposition method and a sputtering method, or a photolithographic technology. Examples of the material of the electrode  2  include metals, such as Be, Mg, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Al, Cu, Ni, Cr, Au, Pt, and Pd, alloys thereof, carbides, such as TiC, ZrC, HfC, TaC, SiC, and WC, borides, such as HfB 2 , ZrB 2 , CeB 6 , YB 4 , and GdB 4 , and nitrides, such as TiN, ZrN, HfN. The thickness of the cathode electrode  2  is set in the range between 5 nm and 50 μm. The cathode electrode  2  and the gate  5  may be made of either the same material or different materials and may be made either by the same forming method or by different methods. The gate  5  is sometimes set thinner than the gate  5  in thickness and is preferably made of a low-resistance material. 
     The electron-emitting device with the configuration shown in  FIGS. 1A to 1D  can be formed by the process described above. 
     Next, a method for manufacturing the electron-emitting device of the modification described using  FIG. 8  will be described. Since the basic manufacturing method is the same as that described using  FIG. 6 , only differences from the above description will be described here. 
     In the case of the electron-emitting device of the modification, protrusions are formed only on the gate  5  and the insulating layer  3   b  using FIB in the process of  FIG. 6C , and are not formed on the insulating layer  3   a  ( FIG. 9 ). The FIB process should be performed so that the amplitude A 1  of the gate  5  and the interval W 2  between the protrusions  15  of the gate  5  reach desired values. The subsequent process for manufacturing the electron-emitting device is the same as in the first embodiment. Since the side surface  3   f  of the insulating layer  3   a  is not provided with protrusions, the upper surface of the insulating layer  3   a  is exposed between two adjacent protrusions  15  of the gate  5  in plan view. This allows a large amount of cathode material to be locally affixed to the corner  32  of the insulating layer  3   a  corresponding to the portion between two adjacent protrusions  15  of the gate  5 . As a result, the protrusions  16  can be formed on the corner  32  of the insulating layer  3   a  corresponding to the two adjacent protrusions  15  of the gate  5 . 
     An electron source in which the plurality of electron-emitting devices described above are provided on a substrate and a display panel including the electron source will be described hereinbelow using  FIGS. 11A and 11B . 
       FIG. 11A  is a schematic diagram illustrating an example of a display panel  47  including an electron source in which the electron-emitting devices are disposed in matrix form, part of which is cut away to show the interior. In  FIG. 11A , reference numeral  31  denotes an electron source substrate, numeral  32  denotes an X-direction wire, numeral  33  denotes a Y-direction wire, and the electron source substrate  31  corresponds to the substrate  1  of the electron-emitting device described above. Numeral  34  denotes the electron-emitting device described above. The X-direction wires  32  connect the electrodes  2  in common, and the Y-direction wires  33  connect the gates  5  in common. Here, an example in which the electron-emitting devices are provided at the intersections of the X-direction wires  32  and the Y-direction wires  33  is schematically shown. Alternatively, the electron-emitting devices may be provided by the side of the intersections of the X-direction wires  32  and the Y-direction wires  33  on the electron source substrate  31 . 
     The X-direction wires  32  are connected to a scanning-signal apply unit (not shown) that applies a scanning signal for selecting a row of the electron-emitting devices  34  arrayed in the X-direction. The Y-direction wire  33  is connected to a modulation-signal generation unit (not shown) for modulating the individual columns of the electron-emitting devices  34  in response to input signals. Driving voltages applied to the individual electron-emitting devices are supplied as difference voltages between the scanning signals applied to the devices and the modulation signals. 
     The above configuration allows individual devices to be selected and driven independently using simple matrix wiring. 
     In  FIG. 11A , the electron source substrate  31  is fixed to a rear plate  41 . A light-emitting member  44  formed of, for example, phosphor, that emits light when irradiated with electrons emitted from the electron-emitting devices and a metal back  45  corresponding to the anode  11  described above are stacked on the inner surface of a glass substrate  43  to form a face plate  46 . The rear plate  41  and the face plate  46  are hermetically joined together via a support frame  42  provided between the rear plate  41  and the face plate  46  and a joint member, such as frit glass, to form a display panel  47 . The display panel  47  is constituted of the face plate  46 , the support frame  42 , and the rear plate  41 , as described above. Since the rear plate  41  is mainly provided to reinforce the strength of the electron source substrate  31 , the separate rear plate  41  can be omitted if the electron source substrate  31  itself has sufficient strength. In other words, the support frame  42  may be directly sealed on the electron source substrate  31 , so that the display panel  47  is formed of the face plate  46 , the support frame  42 , and the electron source substrate  31 . Alternatively, a support member called a spacer may be disposed between the face plate  46  and the rear plate  41  to provide sufficient strength against air pressure. 
     Next, a display  25  equipped with the display panel  47 , described above, and a television set  27  will be described using the block diagram of  FIG. 11B . 
     A receiving circuit  20  includes a tuner and a decoder, receives TV signals of satellite broadcasting, terrestrial broadcasting, etc. and various signals of data broadcasting via networks, and outputs decoded image data to an image-processing unit  21 . The “signals” can translate into “input signals”. The image-processing unit  21  includes a γ compensating circuit, a resolution converting circuit, and an interface circuit. The image-processing unit  21  converts processed image data to the display format of the display (image display unit)  25  and outputs the image data to the display  25  as image signals. 
     The display  25  includes at least the above-described display panel  47  and further includes a driving circuit  108  and a control circuit  22  that controls the driving circuit  108 . The control circuit  22  performs signal processing, such as a compensating process, on input image signals and outputs the image signals and various control signals to the driving circuit  108 . The control circuit  22  includes a synchronizing-signal separating circuit, an RGB converting circuit, a luminance-signal converting section, and a timing control circuit. The driving circuit  108  outputs driving signals to the electron-emitting devices in the display panel  47  in response to input image signals, so that TV pictures are displayed on the basis of the driving signals. The driving circuit  108  includes a scanning circuit, a modulating circuit, and a high-voltage supply circuit that supplies anode potential. The receiving circuit  20  and the image-processing circuit  21  may be accommodated in a housing, as a set top box (STB  26 ), separate from the display  25 , or alternatively, may be accommodated in a housing integrated with the display  25 . Here, an example in which the television set  27  displays TV pictures is described. However, assuming that the receiving circuit  20  is a circuit that receives images distributed via the Internet etc., the television set  27  functions as an image display apparatus capable of displaying not only TV pictures but also various images. 
     EXAMPLES 
     More concrete examples based on the foregoing embodiment will be described hereinbelow. 
     Example 1 
     In this example, the electron-emitting device shown in  FIGS. 1A to 1D  was manufactured according to the process in  FIGS. 6A to 6H . 
     The substrate  1  is made from PD200 that is low-sodium glass developed for plasma displays, on which the insulating layer  23  made from SiN(Si x N y ) with a thickness of 500 nm was formed by sputtering. Next, the insulating layer  24  made from SiO 2  with a thickness of 25 nm was formed thereon by sputtering. Furthermore, the conductive layer  25  made from TaN with a thickness of 30 nm was stacked on the insulating layer  24  by sputtering ( FIG. 6A ). 
     Next, a resist pattern was formed on the conductive layer  25  using a photolithographic technology. Thereafter, the conductive layer  25 , the insulating layer  24 , and the insulating layer  23  were processed in sequence using a dry etching technique to form the gate  5  and the insulating member  3  constituted of the first insulating layer  3   a  and the second insulating layer  3   b  ( FIG. 6B ). Since a material that produces fluoride in the insulating layers  23  and  24  and the conductive layer  25  was selected, a CF 4 -based gas was used as processing gas to be used at that time. As a result of RIE using the gas, the side surface  3   f  of the insulating layer  3   a,  the side surface  3   d  of the insulating layer  3   b,  and the side surface  5   a  of the gate  5  after etching formed about 80° with respect to the horizontal surface of the substrate  1 . 
     Next, after the resist was released, protrusions are formed on the side surface of the gate  5  and the side surface of the insulating member  3  using FIB, as shown in  FIG. 6C . In the FIB processing, the side surfaces were cut off so that the amplitude A 1  of the protrusions  15  of the gate  5  reaches 6 nm, and the period T 1  reaches 12 nm, and the width W 1  of the protrusions  15  reaches 6 nm. 
     Next, the side surface  3   d  of the insulating layer  3   b  was etched using BHF (hydrofluoric acid/ammonium fluoride solution) into a depth of about 70 nm to form the depressions  7  in the insulating member  3  ( FIG. 6D ). 
     Next, Ni was educed on the surface of the gate  5  by electrolytic plating to form the release layer  20  ( FIG. 6E ). 
     Next, molybdenum (Mo) serving as a cathode material was deposited on the release layer  20 , the side surface of the insulating member  3 , and the surface of the substrate  1  to form molybdenum films ( 6  and  6 C). A directional sputtering method was used to form the films. With this film forming method, the angle of the substrate  1  was set so that the substrate  1  is horizontal to the sputter target. This sputtering technique employed a shield plate so that sputtered particles are incident on the substrate surface at limited angles. The peaks of the incident angle were set at 90° and 60° with respect to the horizontal direction using the shield plate. Argon plasma was generated at an output of 3.0 kW and a degree of vacuum of 0.1 Pa, the substrate  1  was disposed so that the distance between the substrate  1  and the Mo target is 100 mm or less, and a molybdenum film with a thickness of 20 nm was formed on the substrate  1  ( FIG. 6F ). 
     After the molybdenum film was formed, a resist pattern was formed by the photolithography technology so that the cathode  6  has a width of 3 μm in the Y-direction. Thereafter, the molybdenum film was processed using a dry etching technique to form the cathode  6 . A CF 4 -based gas was used as a processing gas at that time. Thereafter, the Ni release layer  20  educed on the gate  5  was removed using an etchant containing iodine and potassium iodide to release the molybdenum film  6 C on the gate  5  ( FIG. 6G ). 
     Lastly, Cu with a thickness of 500 nm was deposited by sputtering and is patterned to form the cathode electrode  2 , thus producing the electron-emitting device of this example ( FIG. 6H ). 
     The characteristics of the electron-emitting device of this example were evaluated with the configuration in  FIG. 3A . Evaluation conditions were as follows: the driving voltage (Vf) was set at 21 V; the anode apply voltage (Va) was set at 11.8 kV; and the interval between the anode and the electron-emitting device was set at 1.7 mm. As a result, the mean device current If was 127 μA, the electron emission current Ie was 28 μA, and the mean electron emission efficiency η was 18%, so that an electron-emitting device with sufficient emission current and high efficiency was provided. 
     After the electron emission characteristics were determined, observation of the electron-emitting device using a scanning electron microscope (SEM) showed that the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  was 5.0 nm. As shown in  FIGS. 1D and 2 , the plurality of protrusions  16  of the cathode  6  were provided along the corner  32  of the insulating member  3  (in the Y-direction), and the individual protrusions  16  were provided in one-to-one correspondence with the plurality of protrusions  15  of the gate  5 . As shown in  FIG. 2  and  FIGS. 7A and 7B , the cathode  6  covered, of the corner  32  of the insulating member  3 , portions between the protrusions  16 . The cathode  6  also covered, of the side surface of the insulating member  3 , portions between the protrusions  16 . The portions  6   b  of the cathode  6  in  FIG. 7B  were thinner and had higher resistance than the portions  6   a  of the cathode  6 . The distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  and the period T 1  and the amplitude A 1  of the protrusions  15  of the gate  5  satisfied the relationships, A 1 ≧0.5×d 1  and 10×d 1 ≧T 1 . 
     Table 1 shows the evaluation results of the electron emission characteristics of electron-emitting devices formed in the same procedure, with the amplitude A 1  and the period T 1  of the protrusions  15  of the gate  5  varied. The width W 1  of the protrusions  15  of the gate  5  was set at half of the period T 1 . In any case, electron-emitting devices having higher efficiency η than an electron-emitting device of comparative example 1, described later, were obtained. 
     In this example, the relationship among A 1 , T 1 , and d 1  satisfied A 1 ≧0.5×d 1  and 10×d 1 ≧T 1 , so that electron-emitting devices having high efficiency η were obtained. 
     Comparative Example 1 
     An electron-emitting device in which the gate  5  has not the protrusions  15  was manufactured as Comparative Example 1. Since the basic manufacturing method is the same as in Example 1, only differences from Example 1 will be described here. In this example, the gate  5  was manufactured without the process using FIB shown in  FIG. 6C . 
     The characteristics of the electron-emitting device of this comparative example were evaluated under the same conditions as for the electron-emitting devices of Example 1, as in Example 1, the mean device current If was 30 μA, the electron emission current Ie was 4 μA, and the mean electron emission efficiency η was 11%. 
     After the electron emission characteristics were determined, observation of the electron-emitting device using an SEM showed that the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  was 5.0 nm. The distance d 1  between the protrusions  16  and the gate  5  was constant along the corner  32 , and the plurality of protrusions  16  dotted along the corner  32  (in the Y-direction) as in  FIG. 1D  were not formed. The electron-emitting device of Comparative Example 1 could not obtain a sufficient electron emission efficiency η as compared with the electron-emitting devices of Example 1. This seems to be because the emitted electrons collided with the gate  5 , so that they could not reach the anode  11 . Another reason why a sufficient electron emission efficiency η could not be obtained seems to be because the cathode  6  has not the depressions and protrusions along the corner  32  as in  FIG. 1D . Temporal changes in emission current of the electron-emitting device of this comparative example were larger than those of the electron-emitting device of Example 1. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                 Efficiency 
               
               
                   
                 A1(nm) 
                 T1(nm) 
                 d1(nm) 
                 If(μA) 
                 Ie(μA) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 1 
                 6.0 
                 12.0 
                 5.0 
                 127 
                 28 
                 18 
               
               
                   
                 6.0 
                 50.0 
                 5.0 
                 60 
                 9 
                 13 
               
               
                   
                 15.0 
                 12.0 
                 5.0 
                 96 
                 26 
                 21 
               
               
                 Comparative 
                   
                   
                 5.0 
                 30 
                 4 
                 11 
               
               
                 example 
               
               
                   
               
            
           
         
       
     
     Example 2 
     Next, an example in which an electron-emitting device in which the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  was set larger than the electron-emitting device of Example 1 was manufactured will be shown. Since the basic manufacturing method is the same as in Example 1, only differences from Example 1 will be described here. 
     In this example, the growth of the protrusions  16  of the cathode  6  was inhibited by reducing the amount of molybdenum deposited as a cathode material. In this example, the molybdenum film was deposited on the surface of the substrate  1  into a thickness of 10 nm. The reduction of the amount of molybdenum deposited corresponds to an increase in distance d 1 . 
     As a result of evaluation of the electron emission characteristics of the electron-emitting device of this example under the same conditions in Example 1, the mean device current If was 2 nA, the electron emission current Ie was 0.4 nA, and the mean electron-emitting device was 18%. Although the efficiency η was hither than that of the electron-emitting device of Comparative Example 1, a sufficient emission current like the electron-emitting device of Example 1 could not obtained. 
     When the gap  8  was observed using an SEM, as in Example 1, after determination of the electron emission characteristics, the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  was 15.3 nm. The major reason that the current Ie and the device current If were lower than those of the electron-emitting device of Example 1 seems to be because the value of d 1  was significantly larger than the value of d 1  of the electron-emitting device of Example 1. 
     As shown in  FIGS. 1D and 2 , the protrusions  16  of the cathode  6  were provided along the corner  32  of the insulating member  3  (in the Y-direction), and the protrusions  16  of the cathode  6  and the protrusions  15  of the gate  5  faced each other in one-to-one correspondence. However, the protrusions and depressions along the corner  32 , shown in  FIG. 1D , are smaller than those of the electron-emitting device of Example 1. This also seems to be the reason that the current Ie and the device current If were lower than those of the electron-emitting device of Example 1. 
     In this example, the period T 1  of the protrusions  15  of the gate  5  satisfied 10×d 1 ≧T 1 , and the amplitude A 1  of the protrusions  15  of the gate  5  satisfied A 1 ≧0.5×d 1 , but the distance d 1  did not satisfy 10≧d 1 ≧1. The reason why sufficient emission current could not be obtained seems to be because the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  exceeds 10 nm. 
     Example 3 
     Next, Example 3 in which the phases of the protrusions  15  of the gate  5  and the protrusions  16  of the cathode  6  are shifted by half period will be described. 
     In this example, the electron-emitting device with the configuration that is schematically shown in  FIG. 8  was manufactured. Since the basic manufacturing method is the same as that of Example 1, only differences from Example 1 will be described here. 
     In this example, protrusions were manufactured on the side surface  5   a  of the gate  5  but were not manufactured on the side surface  3   d  of the insulating layer  3   b  using FIB in the process described using  FIG. 6C  ( FIG. 9 ). The FIB process was performed so that the amplitude A 1  of the protrusions  15  of the gate  5  reaches 6.3 nm and the interval W 2  between two adjacent protrusions  15  reaches 12.5 nm. The other processes for manufacturing the electron-emitting device are the same as in Example 1. 
     After the electron-emitting device was formed by the above method, the electron emission characteristics were evaluated under the same conditions as in Example 1. As a result, the mean device current If was 10 μA, the electron emission current Ie was 16 μA, and the mean electron emission efficiency η was 61%, thus providing an electron-emitting device with sufficient emission current and high efficiency η. The reason that the electron emission efficiency η of the electron-emitting device of this example was higher than the efficiency η of the electron-emitting devices of Examples 1 and 2 seems to be as follows: electric flux lines directly above the protrusions  16  of the cathode  6  did not directly travel to the gate  5 , but traveled upward perpendicularly to the substrate (toward the anode  11 ), thus increasing nonscattered electrons that do not collide with the gate  5 . 
     Observation using an SEM after the characteristics were determined showed that the distance d 1  between the protrusions  16  of the cathode  6  and the gate  5  was 5.5 nm. Thus, the major reason that the current Ie and the device current If were lower than those of the electron-emitting device of Example 1 seems to be because the value of d 1  was larger than the value of d 1  of the electron-emitting device of Example 1. 
     As shown in  FIG. 1D , the plurality of protrusions  16  of the cathode  6  were provided along the corner  32  of the insulating member  3  (in the Y-direction), and as shown in  FIG. 8 , the individual protrusions  16  of the cathode  6  were disposed between two adjacent protrusions  15  of the gate  5 . The relationship among A 1 , W 2 , and d 1  satisfied d 1 ≦W 2 ≦3×d 1  and A 1 ≧d 1 . 
     Table 2 shows the evaluation results of the electron emission characteristics with the sizes W 2  and A 1  varied by the FIB process in the same procedure. 
     In any case, electron-emitting devices with higher electron emission efficiency η than that in Comparative Example 1 could be obtained. The relationship among W 2 , A 1 , and d 1  satisfied d 1 ≦W 2 ≦3×d 1  and A 1 ≧d 1 . 
     Example 4 
     Example 4 in which the value W 2  is higher than that of Example 3 is shown. Since the basic manufacturing method is the same as that of Example 3, only differences from Example 3 will be described here. In this example, the FIB process was performed so that the amplitude A 1  of the protrusions  15  of the gate  5  reaches 6 nm, and the interval W 2  reaches 30 nm. The other processes for manufacturing the electron-emitting device are the same as in Example 3. 
     After the electron-emitting device was formed by the above method, the electron emission characteristics of the electron-emitting device of this example were evaluated under the same conditions as in Example 1. As a result, the device current If was 2 μA, the electron emission current Ie was 1 μA, and the mean electron emission efficiency η was 36%. The electron emission efficiency η was lower than that of the electron-emitting device of Example 3 but is higher than that of the electron-emitting device of Example 1. 
     Observation using an SEM after the characteristics were determined showed that the mean interval d 1  between the protrusions  16  and the gate  5  was 5.5 nm. As shown in  FIG. 1D , the plurality of protrusions  16  of the cathode  6  were disposed along the corner  32  of the insulating member  3  (in the Y-direction), and as shown in  FIG. 8 , the individual protrusions  16  of the cathode  6  were disposed between two adjacent protrusions  15  of the gate  5 . In this example, the relationship among W 2 , A 1 , and d 1  satisfies A 1 ≧d 1  but does not satisfy d 1 ≦W 2 ≦3×d 1 . In this example, the reason that the electron emission efficiency η was lower than that of the electron-emitting device of Example 3 seems to be because the effect of the protrusions  15  was decreased due to the large value of W 2 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                 Efficiency 
               
               
                   
                 A1(nm) 
                 T1(nm) 
                 d1(nm) 
                 If(μA) 
                 Ie(μA) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Example 3 
                 5.5 
                 11.0 
                 5.4 
                 11 
                 16 
                 59 
               
               
                   
                 6.3 
                 12.5 
                 5.5 
                 10 
                 16 
                 61 
               
               
                   
                 6.9 
                 13.7 
                 5.9 
                 3 
                 7 
                 71 
               
               
                 Example 4 
                 6.0 
                 33.0 
                 5.5 
                 2 
                 1 
                 36 
               
               
                   
               
            
           
         
       
     
     Comparative Example 2 
     In this comparative example, the portions  6   b  of the cathode  6  of the electron-emitting device manufactured in Example 1, shown in  FIG. 7B , were removed using FIB. Measurement of the electron emission characteristics as in Example 1 showed that the initial electron emission current Ie was the same as in Example 1. However, temporal changes in electron emission current Ie were larger than the electron-emitting device of Example 1. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2009-222513, filed on Sep. 28, 2009, which is hereby incorporated by reference herein in its entirety.