Image forming apparatus for forming image by electron irradiation

Abstract: In an image forming apparatus, a support member (50) for maintaining the distance between a face plate (30) and a rear plate (31) is interposed between the face plate (30) and the rear plate (31). An intermediate layer (52) is formed at a portion near the face plate (30). The intermediate layer (52) is a low-resistance film, and is set to have almost the same potential as that of the face plate (30). As a result, an electron beam from an electron-emitting portion near the support member (50) follows an orbit which steadily comes close to the support member near the face plate. By setting the interval between electron-emitting devices adjacent to each other via the support member to be larger than the interval between devices adjacent to each other without the mediacy of the support member, the electron beam is irradiated on a proper position on the face plate (30).

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus for forming an image by irradiating electrons emitted by an electron-emitting device on an image forming member, in which a support member (spacer) is arranged inside an envelope. DESCRIPTION OF THE RELATED ART Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction emission (SCE) type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter). A known example of the surface-conduction emission type electron-emitting devices is described in, e.g., M.I. Elinson, "Radio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later. The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, "Thin Solid Films", 9,317 (1972)], an In 2 O 3 /SnO 2 thin film [M. Hartwell and C.G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975)], a carbon thin film [Hisashi Araki et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO 2 thin film according to Elinson mentioned above. Fig. 17 is a plan view showing the surface-conduction emission type electron-emitting device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction emission type electron-emitting devices. Referring to Fig. 17, numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in Fig. 17. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in Fig. 17 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in Fig. 17 in a rectangular shape at almost the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion 3005. In the above surface-conduction emission type electron-emitting devices byM. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. That is, the forming processing is to form an electron-emitting portion by electrification. For example, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the two ends of the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the forming processing, electrons are emitted near the fissure. Known examples of the FE type electron-emitting devices are described in W.P. Dyke and W.W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C.A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenium cones", J. Appl. Phys., 47, 5248 (1976). Fig. 18 is a cross-sectional view showing a typical example of the FE type device structure (device by C.A. Spindt et al. described above) . Referring to Fig. 18, numeral 3010 denotes a substrate; 3011, an emitter wiring layer made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and the gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and a gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of Fig. 18. A known example of the MIM type electron-emitting devices is described in C.A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32,646 (1961). Fig. 19 shows a typical example of the MIM type device structure. Fig. 19 is a cross-sectional view of the MIM type electron-emitting device. Referring to Fig. 19, numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 10nm, (100 Å); and 3023, an upper electrode made of a metal and having a thickness of about 8 to 30nm (80 to 300 Å). In the MIM type electron-emitting device, an appropriate voltage is applied between the upper electrode 3023 and the lower electrode 3021 to emit electrons from the surface of the upper electrode 3023. Since the above-described cold cathode devices can emit electrons at a temperature lower than that for hot cathode devices, they do not require any heater. The cold cathode device therefore has a structure simpler than that of the hot cathode device and can be micropatterned. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the hot cathode device is low because it operates upon heating by a heater. For this reason, applications of the cold cathode devices have enthusiastically been studied. Of cold cathode devices, the above surface-conduction emission type electron-emitting devices are advantageous because they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied. Regarding applications of surface-conduction emission type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, electron-beam sources, and the like have been studied. As an application to image display apparatuses, in particular, as disclosed in the U.S. Patent No. 5,066,833 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using the combination of an surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon reception of an electron beam has been studied. This type of image display apparatus using the combination of the surface-conduction emission type electron-emitting device and the fluorescent substance is expected to have more excellent characteristics than other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight because it is of a self-emission type and that it has a wide view angle. A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Patent No. 4,904,895 filed by the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: "Recent Development on Microtips Display at LETI", Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)] An example of an application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present application. European Patent Application EP-A-0739029 describes an image forming apparatus comprising a front face and a plurality of electron emitting devices mounted on a rear substrate, the front face and rear substrate being separated by a plurality of supporting spacers, each provided with a conductive surface film. Of image display apparatuses using electron-emitting devices like the ones described above, a thin, flat display apparatus receives a great deal of attention as an alternative to a CRT (Cathode-Ray Tube) display apparatus because of a small space and light weight. Fig. 20 is a perspective view of an example of a display panel for a flat image display apparatus where a portion of the panel is removed for showing the internal structure of the panel. In Fig. 20, numeral 3115 denotes a rear plate; 3116, a side wall; and 3117, a face plate. The rear plate 3115, the side wall 3116, and the face plate 3117 form an envelope airtight container) for maintaining the inside of the display panel vacuum. The rear plate 3115 has a substrate 3111 fixed thereto, on which N x M cold cathode devices 3112 are provided (M, N = positive integer equal to "2" or greater, appropriately set in accordance with an object number of display pixels). As shown in Fig. 23, the N x M cold cathode devices 3112 are arranged with M row-direction wirings 3113 and N column-direction wirings 3114. The portion constituted with the substrate 3111, the cold cathode devices 3112, the row-direction wiring 3113, and the column-direction wiring 3114 will be referred to as "multi electron-beam source". At an intersection of the row-direction wiring 3113 and the column-direction wiring 3114, an insulating layer (not shown) is formed between the wirings, to maintain electrical insulation. Further, a fluorescent film 3118 made of a fluorescent substance is formed under the face plate 3117. The fluorescent film 3118 is colored with red, green and blue, three primary color fluorescent substances (not shown). Black conductive material (not shown) is provided between the fluorescent substances constituting the fluorescent film 3118. Further, a metal back 3119 made of Al or the like is provided on the surface of the fluorescent film 3118 on the rear plate 3115 side. In Fig. 20, symbols Dxl to Dxm, Dyl to Dyn, and Hv denote electric connection terminals for airtight structure provided for electrical connection of the display panel with an electric circuit (not shown). The terminals Dxl to Dxm are electrically connected to the row-direction wiring 3113 of the multi electron-beam source; Dyl to Dyn, to the column-direction wiring 3114; and Hv, to the metal back 3119 The inside of the airtight container is exhausted at about 10 -4 Pa (10 -6 Torr). As the display area of the image display apparatus becomes larger, the image display apparatus requires a means for preventing deformation or damage of the rear plate 3115 and the faceplate 3117 caused by a difference in pressure between the inside and outside of the airtight container. If the deformation or damage is prevented by heating the rear plate 3115 and the face plate 3117, not only the weight of the image display apparatus increases, but also image distortion and parallax are caused when the user views the image from an oblique direction. To the contrary, in Fig. 20, the display panel comprises a structure support member (called a spacer or rib) 3120 made of a relatively thin glass to resist the atmospheric pressure. With this structure, the interval between the substrate 3111 on which the multi beam-electron source is formed, and the face plate 3117 on which the fluorescent film 3118 is formed is normally kept at submillimeters to several millimeters. As described above, the inside of the airtight container is maintained at high vacuum. In the image display apparatus using the above-described display panel, when a voltage is applied to the cold cathode devices 3112 via the outer terminals Dx1 to Dxm and Dy1 to Dyn, electrons are emitted by the cold cathode devices 3112. At the same time, a high voltage of several hundreds V to several kV is applied to the metal back 3119 via the outer terminal Hv to accelerate the emitted electrons and cause them to collide with the inner surface of the face plate 3117. Consequently, the respective fluorescent substances constituting the fluorescent film 3118 are excited to emit light, thereby displaying an image. The above-mentioned electron beam apparatus of the image forming apparatus or the like comprises an envelope for maintaining vacuum inside the apparatus, an electron source arranged inside the envelope, a target on which an electron beam emitted by the electron source is irradiated, an acceleration electrode for accelerating the electron beam toward the target, and the like. In addition to them, a support member (spacer) for supporting the envelope from its inside against the atmospheric pressure applied to the envelope is arranged inside the envelope. The display panel of this image display apparatus suffers the following problem. Some of electrons emitted near the spacer strike the spacer, or ions produced by the action of emitted electrons attach to the spacer. Further, some of electrons which have reached the face plate are reflected and scattered, and some of the scattered electrons strike the spacer to charge the spacer. The orbits of electrons emitted by the cold cathode devices are changed by the charge-up of the spacer, and the electrons reach positions different from proper positions on the fluorescent substances. As a result, a distorted image is displayed near the spacer. To solve this problem, the charge-up of the spacer is eliminated (to be referred to as charge-up elimination hereinafter) by f lowing a small current through the spacer. In this case, a high-resistance film is formed on the surface of an insulating spacer to flow a small current through the surface of the spacer. As the amount of emitted electrons by cold cathode devices increases, the charge-up elimination ability becomes poorer, and the charge-up amount depends on the intensity of an electron beam. Along with this, an electron beam emitted by a device near the spacer shifts from a proper position on the target depending on the intensity (luminance) of the electron beam. For example, in displaying a moving image, the image fluctuates. SUMMARY OF THE INVENTION It is an object of the present invention as claimed to provide an image forming apparatus capable of forming an image while suppressing distortion and fluctuation in forming an image by irradiating electrons on an image forming member. The structures of a spacer and an electron-emitting device will be described with reference to Figs. 1A and 1B. Referring to Figs. 1A and 1B, numeral 30 denotes a face plate including fluorescent substances and a metal back; 31, a rear plate including an electron source substrate; 50, a spacer; 51, a high-resistance film on the surface of the spacer; 52, an electrode on the face plate side; 13, device driving wiring; 111, a device; 112, a typical electron beam orbit; and 25, an equipotential line. Symbol a denotes a length from the inner surface of the face plate to the lower end of the intermediate layer (low-resistance film) on the face plate side; and d, a distance between the electron source substrate and the face plate. The concepts of the present invention will be sequentially explained below. Some of electrons emitted near the spacer strike the spacer, or ions produced by the action of emitted electrons attach to the spacer, charging the spacer. The orbits of electrons emitted by the devices are changed by the charge-up of the spacer, the electrons reach positions different from proper positions, and thus a distorted image is displayed near the spacer. To solve this problem, the high-resistance film 51 is formed on the surface of the spacer 50 to relax the charge-up of the spacer. However, as the number of emitted electrons emitted by cold cathode devices increases, the charge-up elimination ability of the high-resistance film becomes poorer, and the charge-up amount depends on the number of emitted electrons. In this case, an electron beam undesirably fluctuates. Particularly when no electron directly strikes the spacer, charge-up by electrons reflected by the face plate is considered to mainly contribute to the charge-up of the spacer. The charge-up of the spacer by electrons reflected by the face plate has a distribution in which the charge-up amount is large on the face plate side, as shown in Fig. 2. From this, fluctuations in electron beam can be suppressed by covering the position having the largest charge-up amount in this charge-up distribution with an electrode. As the first requirement of the present invention, therefore, the electrode 52 (having the length a ) on the face plate side is extended to the rear plate side, as shown in Fig. 1A. However, the space near the spacer has an electric field indicated by the equipotential lines 52. An electron beam is expected to follow an orbit like the orbit 112 and steadily move toward the spacer 50 (including the parts 51 to 53). Accordingly, as the second requirement of the present invention, an electron beam can be caused to reach a proper position by shifting an electron-emitting device 111 near the spacer from a position corresponding to the reach position, on the face plate, of an electron emitted by this device in the direction away from the spacer. As a result, the landing position of the electron beam on the face plate scarcely depends on the electron emission amount to reduce distortion and fluctuation of an image in displaying a moving image. The first aspect of the image forming apparatus according to the present invention has the following arrangement. An image forming apparatus having a rear substrate with a plurality of electron-emitting devices arranged substantially linearly, a front substrate with an image forming member on which an image is formed by electrons emitted by the electron-emitting devices, and a support member for maintaining an interval between the rear substrate and the front substrate is characterized in that the support member comprises an electrode extending from an abutment portion between the front substrate and the support member to a predetermined position toward the rear substrate, the electrode is, when in use, maintained at a high potential, and intervals of the plurality of electron-emitting devices arranged substantially linearly are set to have an interval between two electron-emitting devices adjacent to each other via the support member larger than an interval between two electron-emitting devices adjacent to each other without mediacy of the support member. In this arrangement, with the electrode extending from the abutment portion of the support member against the front substrate, the influence of charge-up of the support member on the front substrate side on which the support member is particularly easily charged can be relaxed. Since this electrode is at a high potential, electrons emitted by the electron-emitting devices can be deflected toward the support member. However, the electron-emitting devices are arranged at different intervals, which relaxes nonuniformity of the irradiation points of electrons emitted by the respective electron-emitting devices on the image forming member owing to nonuniform orbit shapes of the electrons emitted by the respective electron-emitting devices upon the deflection. In this arrangement, the front substrate may comprise an acceleration electrode which when in use is applied with a voltage for accelerating electrons emitted by the electron-emitting devices, and the electrode arranged on the support member may be connected to the acceleration electrode. The electrode arranged on the support member is connected to the acceleration electrode to have a high potential. The second aspect of the image forming apparatus according to the present invention has the following arrangement. An image forming apparatus having a rear substrate with a plurality of electron-emitting devices arranged substantially linearly, a front substrate with an image forming member on which an image is formed by electrons emitted by the electron-emitting devices, a support member for maintaining an interval between the rear substrate and the front substrate, and an acceleration electrode which is arranged on or near the front substrate and applied, when in use, with a voltage for accelerating electrons emitted by the electron-emitting devices toward the front substrate is characterized in that the support member comprises an electrode which is connected to the acceleration electrode and extends to a predetermined position toward the rear substrate, and intervals of the plurality of electron-emitting devices arranged substantially linearly are set to have an interval between two electron-emitting devices adjacent to each other via the support member larger than an interval between two electron-emitting devices adjacent to each other without mediacy of the support member. In this arrangement, since the electrode arranged on the support member is formed near the front substrate, the influence of charge-up of the support member near the front substrate in which the support member is particularly easily charged can be relaxed. Since the electrode of the support member is connected to the acceleration electrode, electrons emitted by the electron-emitting devices are deflected toward the support member. However, the electron-emitting devices are arranged at different intervals, which relaxes nonuniformity of the irradiation points of electrons emitted by the respective electron-emitting devices on the image forming member owing to nonuniform orbit shapes of the electrons emitted by the respective electron-emitting devices upon the deflection. In the first and second aspects described above, the support member may comprise conductive means for giving conductivity for relaxing charge-up on the support member. More specifically, conductive means for establishing a conductive state between the abutment portion of the support member against the rear substrate and the abutment portion against the front substrate may be arranged. For example, the conductive means is a conductive film formed from the abutment portion of the support member against the rear substrate to the abutment portion against the front substrate. By flowing a current through this conductive means, charge-up can be effectively relaxed. As the current increases, however, the power consumption increases. For this reason, the resistance of the conductive means is desirably set higher than that of the electrode arranged on the support member. In preferred embodiments, to suppress unexpected discharge, a potential difference between a potential of the electrode arranged on the support member and a potential of an abutment portion of the support member against the rear substrate, and a length of a portion of the support member where no electrode is arranged desirably have a relationship of not more than 8 kV/mm, and more desirably have a relationship of not more than 4 kV/mm. That is, in the respective aspects described above, since the electrode arranged on the support member is at a high potential, discharge may occur. However, this discharge can be made difficult to occur by setting the above relationship between the potential difference and the length of the portion of the support member where no electrode is arranged. More specifically, discharge at the electrode arranged on the support member is considered to easily occur at a portion of the electrode near the rear plate, the potential difference between the potential of the electrode on the rear substrate side and the potential of the abutment portion of the support member against the rear substrate, and the length of the portion of the support member where no electrode is arranged are set to have the above relationship. For example, when the electrode arranged on the support member is connected to the acceleration electrode for applying a voltage for accelerating electrons, and a voltage drop at the electrode of the support member is smaller than the voltage applied to the acceleration electrode, the voltage applied to the acceleration electrode and the length of the portion of the support member where no electrode is arranged are set to have the above relationship. In the respective aspects described above, the electrode arranged on the support member preferably abuts against the front substrate and is also arranged on the abutment surface. Although the electrode arranged on the support member is formed as, e.g., a layer on the support member, this layer may also be formed on the abutment surface against the front substrate. When the front substrate has the electrode for setting the electrode arranged on the support member at a high potential (more specifically, e.g., the acceleration electrode also has this function), the conductive state between the electrode arranged on the support member and the electrode arranged on the front substrate can be improved. The electrode arranged on the support member desirably has a sheet resistance of 10 6 to 10 12 Ω/sq. The electrode arranged on the support member reaches a position corresponding to not less than 1/10 of a distance between the front substrate and the rear substrate when measured from a position where the support member abuts against the front substrate. With this structure, a high charge-up elimination ability can be attained at the position where the support member is most easily charged. In the respective aspects described above, the image forming apparatus may further comprise deflection means, arranged between a portion near an abutment portion of the support member against the rear substrate and the electron-emitting devices, for generating a force in a direction away from the support member for electrons emitted by the electron-emitting devices. With this deflection means, the interval between electron-emitting devices adjacent to each other via the support member need not be so larger than the interval between electron-emitting devices adjacent to each other without the mediacy of the support member. This deflection means is, e.g., an electrode arranged near the abutment portion of the support member against the rear substrate. This electrode is formed as, e.g., a layer. The electrode is preferably lower in resistance than the portion of the support member where no electrode is arranged. If the resistance is low, a voltage rise per unit length toward the front substrate can be suppressed in the support member, so that the normal line of the equipotential line changes to the direction away from the support member near the abutment portion of the support member against the rear substrate. As a result, the force in the direction away from the support member can be applied to electrons. When the support member is arranged on the wiring on the rear substrate, the electrode is preferably electrically connected to this wiring. In the respective aspects described above, an interval between adjacent electron-emitting devices of the plurality of electron-emitting devices may be set in accordance with a degree of deflection of each electron-emitting device toward the support member. More specifically, in the respective aspects described above, when the arrangement position of each electron-emitting device is shifted in the direction away from the support member from the position obtained by vertically projecting, on the rear substrate, each point where an electron emitted by each electron-emitting device is irradiated on the image forming member, the shift amount may be set in accordance with the degree of deflection. In the respective aspects described above, an interval between adjacent electron-emitting devices of the plurality of electron-emitting devices may be set in accordance with a degree of deflection of each electron-emitting device toward the support member so as to arrange irradiation points of electrons emitted by the electron-emitting devices on the image forming member at an almost equal interval. More specifically, in the respective aspects described above, when the arrangement position of each electron-emitting device is shifted in the direction away from the support member from the position obtained by vertically projecting, on the rear substrate, each point where an electron emitted by each electron-emitting device is irradiated on the image forming member, the shift amount may be set larger for a device nearer the support member and smaller for a device father from the support member. The image forming apparatus of the present invention has the following forms. (1) The cold cathode device is a cold cathode device having a conductive film including an electron-emitting portion between a pair of electrodes, and preferably a surface-conduction emission type electron-emitting device. (2) The electron source is an electron source having a simple matrix layout in which a plurality of cold cathode devices are wired in a matrix by a plurality of row-direction wirings and a plurality of column-direction wirings. (3) The electron source is an electron source having a ladder-shaped layout in which a plurality of rows (to be referred to as a row direction hereinafter) of a plurality of cold cathode devices arranged parallel and connected at two terminals of each device are arranged, and a control electrode (to be referred to as a grid hereinafter) arranged above the cold cathode devices along the direction (to be referred to as a column direction hereinafter) perpendicular to this wiring controls electrons emitted by the cold cathode devices. (4) According to the concepts of the present invention, the present invention is not limited to an image forming apparatus suitable for display. The above-mentioned image forming apparatus can also be used as a light-emitting source instead of a light-emitting diode for an optical printer made up of a photosensitive drum, the light-emitting diode, and the like. At this time, by properly selecting m row-direction wirings and n column-direction wirings, the image forming apparatus can be applied as not only a linear light-emitting source but also a two-dimensional light-emitting source. In this case, the image forming member is not limited to a substance which directly emits light, such as a fluorescent substance used in embodiments (to be described below), but may be a member on which a latent image is formed by charging of electrons. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are views showing the structure of a spacer and the traveling orbit of an electron in an embodiment; Fig. 2 is a graph showing a model of the charge-up of the spacer; Figs. 3A and 3B are schematic cross-sectional views of an image display apparatus in the embodiment; Figs. 4A and 4B are plan views showing examples of the alignment of fluorescent substances on the face plate of a display panel; Figs. 5A and 5B are a plan view and a cross-sectional view, respectively, of a flat surface-conduction emission type electron-emitting device used in the embodiment; Figs. 6A to 6E are views respectively showing the steps in manufacturing the flat surface-conduction emission type electron-emitting device; Fig. 7 is a graph showing the waveform of the application voltage in forming processing; Figs. 8A and 8B are graphs respectively showing the waveform of the application voltage and a change in emission current Ie in activation processing; Fig. 9 is a cross-sectional view of a step surface-conduction emission type electron-emitting device used in the embodiment; Figs. 10A to 10F are views respectively showing the steps in manufacturing the step surface-conduction emission type electron-emitting device; Fig. 11 is a graph showing typical characteristics of the surface-conduction emission type electron-emitting device used in the embodiment; Fig. 12 is a partially cutaway perspective view showing the display panel of the image display apparatus in the embodiment; Fig. 13 is a partial cross-sectional view of the substrate of a multi electron-beam source used in the embodiment. Fig. 14A is a partial plan view of the substrate of a multi electron-beam source. Fig. 14B is a partial plan view of the substrate of the multi electron-beam source used in the embodiment; Fig. 15 is a partial cross-sectional view of the electron-emitting portion of the multi electron-beam source ; Fig. 16 is a block diagram showing the schematic arrangement of a driving circuit for the image display apparatus of the embodiment; Fig. 17 is a view showing an example of the surface-conduction emission type electron-emitting device; Fig. 18 is a view showing an example of an FE type device; Fig. 19 is a view showing an example of an MIM type device; Fig. 20 is a partially cutaway perspective view of the display panel of the image display apparatus Fig. 21 is a partial plan view of the substrate of the multi electron-beam source used in the embodiment; Figs. 22A and 22B are a plan view and a cross-sectional view, respectively, of a spacer plate used in the embodiment; Figs. 23A and 23B are a plan view and a cross-sectional view, respectively, of another spacer plate used in the embodiment; and Fig. 24 is a view showing the structure of the spacer and the traveling orbit of an electron in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. <General Description of Image Display Apparatus> First, the construction of a display panel of an image display apparatus to which the present invention is applied and a method for manufacturing the display panel will be described below. Fig. 12 is a perspective view of the display panel where a portion of the panel is removed for showing the internal structure of the panel. In Fig. 12, numeral 1015 denotes a rear plate; 1016, a side wall; and 1017, a face plate. These parts form an airtight container for maintaining the inside of the display panel vacuum. To construct the airtight container, it is necessary to seal-connect the respective parts to obtain sufficient strength and maintain airtight condition. For example, a frit glass is applied to junction portions, and sintered at 400 to 500°C in air or nitrogen atmosphere, thus the parts are seal-connected. A method for exhausting air from the inside of the container will be described later. Since the inside of the airtight container is kept exhausted at about 10 -4 Pa (10 -6 Torr), a spacer 1020 including a low-resistance film 21 is arranged as a structure resistant to the atmospheric pressure in order to prevent damage of the airtight container caused by the atmospheric pressure or sudden shock. The rear plate 1005 has a substrate 1011 fixed there, on which N x M cold cathode devices 1012 are provided (M, N = positive integer equal to "2" or greater, appropriately set in accordance with an object number of display pixels. For example, in a display apparatus for high-quality television display, desirably N = 3000 or greater, M = 1000 or greater. In this embodiment, N = 3072, M = 1024.). The N x M cold cathode devices 3112 are arranged with M row-direction wirings 1013 and N column-direction wirings 1014. The portion constituted with these parts 1011 to 1014 will be referred to as "multi electron-beam source". In the multi electron-beam source used in the image display apparatus of the present invention, the material, shape, and manufacturing method of the cold cathode device are not limited as far as an electron source is prepared by wiring cold cathode devices in a simple matrix. Therefore, the multi electron-beam source can employ a surface-conduction emission (SCE) type electron-emitting device or an FE type or MIM type cold cathode device. The structure of the multi electron-beam source prepared by arranging SCE type electron-emitting devices (to be described later) as cold cathode devices on a substrate and wiring them in a simple matrix will be described. Figs. 14A and 14B are plan views of a multi electron-beam source of che type used in the display panel in Fig. 12. Fig. 14A is a plan view of a region where no spacer is arranged, and Fig. 14B is a plan of a region where the spacer is arranged. SCE type electron-emitting devices like the one shown in Figs. 5A and 5B (to be described later) are arranged on the substrate 1011. These devices are wired in a simple matrix by the row-direction wiring electrodes 1013 and the column-direction wiring electrodes 1014. At an intersection of each row-direction wiring electrode 1013 and the column-direction wiring electrode 1014, an insulating layer (not shown) is formed between the electrodes to maintain electrical insulation. Symbol a in Figs. 14A and 14B denotes a line having a position where a beam spot is formed. In the region in Fig. 14A where no spacer is formed, electron-emitting device portions are arranged at the same pitch. Near the spacer, as shown in Fig. 14B, electron-emitting device portions are formed at positions spaced apart from the spacer with respect to positions where beam spots are formed. At electron-emitting portions arranged parallel to the column-direction wiring electrodes 1014, when the positions of a plurality of electron-emitting portions are shifted from lines where beam spots are formed, the shift amount of each electron-emitting device from a corresponding line position where a beam spot is formed is set such that the shift amount, from the spacer, of each electron-emitting portion near the spacer becomes larger. Fig. 15 shows a cross-section cut out along the line B - B' in Fig. 14A. A multi electron-beam source having this structure is manufactured by forming the row-direction wiring electrodes 1013, the column-direction wiring electrodes 1014, an electrode insulating film (not shown), and device electrodes and conductive thin films of SCE type electron-emitting devices on the substrate in advance, and then supplying electricity to the devices via the row-direction wiring electrodes 1013 and the column-direction wiring electrodes 1014 to perform forming processing and activation processing (both of which will be described later). In this embodiment, the substrate 1011 of the multi electron-beam source is fixed to the rear plate 1015 of the airtight container. However, if the substrate 1011 has sufficient strength, the substrate 1011 of the multi electron-beam source itself may be used as the rear plate of the airtight container. Further, a fluorescent film 1018 is formed under the face plate 1017. As this embodiment is a color display apparatus, the fluorescent film 1018 is colored with red, green and blue three primary color fluorescent substances. The fluorescent substance portions are in stripes as shown in Fig. 4A, and black conductive material 1010 is provided between the stripes. The object of providing the black conductive material 1010 is to prevent shifting of display color even if electron-beam irradiation position is shifted to some extent, to prevent degradation of display contrast by shutting off reflection of external light, to prevent charge-up of the fluorescent film by electron beams, and the like. The black conductive material 1010 mainly comprises graphite, however, any other materials may be employed so far as the above object can be attained. Further, three-primary colors of the fluorescent film is not limited to the stripes as shown in Fig. 4A. For example, delta arrangement as shown in Fig. 4B or any other arrangement may be employed. Note that when a monochrome display panel is formed, a single-color fluorescent substance may be applied to the fluorescent film 1018, and the black conductive material may be omitted. Further, a metal back 1019, which is well-known in the CRT field, is provided on the rear plate side surface of the fluorescent film 1018. The object of providing the metal back 1019 is to improve light-utilization ratio by mirror-reflecting a part of light emitted from the fluorescent film 1018, to protect the fluorescent film 1018 from collision between negative ions, to use the metal back 1019 as an electrode for applying an electron-beam accelerating voltage, to use the metal back 1019 as a conductive path for electrons which excited the fluorescent film 1018, and the like. The metal back 1019 is formed by, after forming the fluorescent film 1018 on the face plate 1017, smoothing the fluorescent film front surface, and vacuum-evaporating A1 thereon. Note that in a case where the fluorescent film 1018 comprises fluorescent material for low voltage, the metal back 1019 is not used. Further, for application of accelerating voltage or improvement of conductivity of the fluorescent film, transparent electrodes made of an ITO material or the like may be provided between the face plate 1017 and the fluorescent film 1018, although the embodiment does not employ such electrodes. Fig. 13 is a schematic cross-sectional view cut out along the line A - A' in Fig. 12. Reference numerals of the respective parts are the same as those in Fig. 12. In this embodiment, the spacer 1020 comprises a high-resistance film 11 for relaxing charge-up on the surface of an insulating member 1, in addition to a low-resistance film 21 serving as an electrode for effectively relaxing charge-up near the face plate. The low-resistance film 21 is formed on the surfaces of the insulating member 1 to relax charge-up. Further, the low-resistance film 21 is formed on an abutment surface 3 of the spacer which faces the inner surface (metal back 1019 and the like) of the face plate 1017, and a side surface 5 of the spacer which contacts the inner surface of the face plate 1017. A necessary number of such spacers are fixed on the inner surface of the face plate and the surface of the substrate 1011 at necessary intervals with a joining material 1040 to attain the above purpose. In addition, the high-resistance films 11 are formed at least the surfaces, of the surfaces of the insulating member 1, which are exposed in a vacuum in the airtight container, and are electrically connected to the inner surface (metal back 1019 and the like) of the face plate 1017 and the surface of the substrate 1011 (row- or column-direction wiring 1013 or 1014) via the low-resistance film 21 and the joining material 1040 on the spacer 1020. In this embodiment, each spacer 1020 has a thin plate-like shape, extends along a corresponding row-direction wiring 1013, and is electrically connected thereto. The spacer 1020 has insulating properties good enough to stand a high voltage applied between the row- and column-direction wirings 1013 and 1014 on the substrate 1011 and the metal back 1019 on the inner surface of the face plate 1017, and conductivity enough to prevent the surface of the spacer 1020 from being charged. As the insulating member 1 of the spacer 1020, for example, a silica glass member, a glass member containing a small amount of an impurity such as Na, a soda-lime glass member, or a ceramic member consisting of alumina or the like is available. Note that the insulating member 1 preferably has a thermal expansion coefficient near the thermal expansion coefficients of the airtight container and the substrate 1011. The current obtained by dividing an accelerating voltage Va applied to the face plate 1017 (the metal back 1019 and the like) on the high potential side by a resistance Rs of the high-resistance film 11 for preventing charge-up flows in the high-resistance film 11 of the spacer 1020. The resistance Rs of the spacer is set in a desired range from the viewpoint of prevention of charge-up and consumption power. A sheet resistance R/sq is preferably set to 10 12 Ω/sq or less from the viewpoint of prevention of charge-up. To obtain a sufficient charge-up prevention effect, the sheet resistance R is preferably set to 10 11 Ω/sq or less . The lower limit of this sheet resistance depends on the shape of each spacer and the voltage applied between the spacers, and is preferably set to 10 5 Ω/sq or more. A thickness t of the high-resistance film 11 formed on the insulating material preferably falls within a range of 10 nm to 1 µm. A thin film having a thickness of 10 nm or less is generally formed into an island-like shape and exhibits unstable resistance depending on the surface energy of the material and the adhesion properties with the substrate, resulting in poor reproduction characteristics. In contrast to this, if the thickness t is 1 µm or more, the film stress increases to increase the possibility of peeling of the film. In addition, a longer period of time is required to form a film, resulting in poor productivity. The thickness preferably falls within a range of 50 to 500 nm. The sheet resistance R/sq is ρ/t, and a resistivity p of the high-resistance film preferably falls within a range of 0.1 Ωcm to 10 8 Ωcm in consideration of the preferable ranges of R/sq and t. To set the sheet resistance and the film thickness in more preferable ranges, the resistivity p is preferably set to 10 2 to 10 6 Ωcm. As described above, when a current flows in the high-resistance film formed on the spacer or the overall display generates heat during operation, the temperature of the spacer rises. If the resistance temperature coefficient of the high-resistance film is a large negative value, the resistance decreases with an increase in temperature. As a result, the current flowing in the spacer increases to raise the temperature. The current keeps increasing beyond the limit of the power source. It is empirically known that the resistance temperature coefficient which causes such an excessive increase in current is a negative value whose absolute value is 1% or more. That is, the resistance temperature coefficient of the high-resistance film is preferably set to less than -1%. As a material for the high-resistance film 11 having charge-up prevention properties, for example, a metal oxide can be used. Of metal oxides, a chromium oxide, nickel oxide, or copper oxide is preferably used. This is because, these oxides have relatively low secondary electron-emitting efficiency, and are not easily charged even if the electrons emitted by the cold cathode device 1012 collide with the spacer 1020. In addition to such metal oxides, a carbon material is preferably used because it has low secondary electron-emitting efficiency. Since an amorphous carbon material has a high resistance, the resistance of the spacer 1020 can be easily controlled to a desired value. The low-resistance film 21 of the spacer 1020 also functions to electrically connect the high-resistance film 11 to the face plate 1017 (metal back 1019 and the like) on the high potential side. The low-resistance film 21 will also be referred to as an intermediate electrode layer (intermediate layer) hereinafter. This intermediate electrode layer (intermediate layer) has a plurality of functions as described below. (1) The low-resistance film serves to electrically connect the high-resistance film 11 to the face plate 1017. As described above, the high-resistance film 11 is formed to relax the surface of the spacer 1020 from being charged. When, however, the high-resistance film 11 is connected to the face plate 1017 (metal back 1019 and the like) directly or via the joining material 1040, a large contact resistance is produced at the interface between the connecting portions. As a result, the charges produced on the surface of the spacer 1020 may not be quickly removed. This problem can be solved by forming the low-resistance intermediate layer on the abutment surface 3 and the side surface portion 5, of the spacer 1020, which are in contact with the face plate 1017 and the joining material 1040. (2) The low-resistance film serves to make the potential distribution of the high-resistance film 11 uniform. Electrons emitted by the cold cathode devices 1012 follow the orbits formed in accordance with the potential distribution formed between the face plate 1017 and the substrate 1011. To prevent the electron orbits from being disturbed near the spacer 1020, the entire potential distribution of the spacer 1020 must be controlled. When the high-resistance film 11 is connected to the face plate 1017 (metal back 1019 and the like) and the substrate 1011 (wiring 1013 or 1014 and the like) directly or via the joining material 1040, variations in the connected state occurs owing to the contact resistance of the interface between the connecting portions. As a result, the potential distribution of the high-resistance film 11 may deviate from a desired value. The overall potential of the high-resistance film 11 can be effectively controlled by forming the low-resistance intermediate layer throughout the entire length of the spacer end portion (abutment surface 3 or side surface portion 5), of the spacer 1020, which is in contact with the face plate 1017, and applying a desired potential to the intermediate layer portion. (3) The intermediate layer serves to control the orbits of emitted electrons. Electrons emitted by the cold cathode devices 1012 follow the orbits formed in accordance with the potential distribution formed between the face plate 1017 and the substrate 1011. Electrons emitted by the cold cathode devices 1012 near the spacer may be subjected to constrains (changes in the positions of the wirings and the devices) accompanying the structure of the spacer 1020. In this case, to form an image free from distortion and irregularity, the orbits of the electrons emitted by the cold cathode devices must be controlled to irradiate the electrons at desired positions on the face plate 1017. The formation of the low-resistance intermediate layer on the side surface portion 5 in contact with the face plate 1017 allows the potential distribution near the spacer 1020 to have desired characteristics, thereby controlling the orbits of emitted electrons. As a material for the low-resistance film 21, a material having a resistance sufficiently lower than that of the high-resistance film 11 can be selected. For example, such a material is properly selected from metals such as Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu, and Pd, alloys thereof, printed conductors constituted by metals such as Pd, Ag, Au, RuO 2 , and Pd-Ag or metal oxides and glass or the like, transparent conductors such as In 2 O 3 -SnO 2 , and semiconductor materials such as polysilicon. The joining material 1040 needs to have conductivity to electrically connect the spacer 1020 to the row-direction wiring 1013 and the metal back 1019. That is, a conductive adhesive or frit glass containing metal particles or conductive filler is suitably used. In Fig. 12, symbols Dxl to Dxm, Dyl to Dyn and Hv denote electric connection terminals for airtight structure provided for electrical connection of the display panel with an electric circuit (not shown). The terminals Dxl to Dxm are electrically connected to the row-direction wiring 1013 of the multi electron-beam source; Dyl to Dyn, to the column-direction wiring 1014 of the multi electron-beam source; and Hv, to the metal back 1019 of the face plate. To exhaust air from the inside of the airtight container and make the inside vacuum, after forming the airtight container, an exhaust pipe and a vacuum pump (neither is shown) are connected, and air is exhausted from the airtight container to vacuum at about 10 -5 Pa (10 -7 Torr). Thereafter, the exhaust pipe is sealed. To maintain the vacuum condition inside of the airtight container, a getter film (not shown) is formed at a predetermined position in the airtight container, immediately before/after the sealing. The getter film is a film formed by heating and evaporating getter material mainly including, e.g., Ba, by heating or highfrequency heating. The suction-attaching operation of the getter film maintains the vacuum condition in the container 10 -3 Pa or 10 -5 Pa (1 x 10 -5 or 1 x 10 -7 Torr). In the image display apparatus using the above display panel, when a voltage is applied to the cold cathode devices 1012 via the outer terminals Dxl to Dxm and Dyl to Dyn, electrons are emitted by the cold cathode devices 1012. At the same time, a high voltage of several hundreds V to several kV is applied to the metal back 1019 via the outer terminal Hv to accelerate the emitted electrons to cause them collide with the inner surface of the face plate 1017. With this operation, the respective color fluorescent substances constituting the fluorescent film 1018 are excited to emit light, thereby displaying an image. The voltage to be applied to each SCE type electron-emitting device 1012 as a cold cathode device in the present invention is normally set to about 12 to 16 V; a distance d between the metal back 1019 and the cold cathode device 1012, about 0.1 mm to 8 mm; and the voltage to be applied across the metal back 1019 and the cold cathode device 1012, about 0.1 kV to 10 kV. The basic structure and manufacturing method of the display panel, and the general description of the image display apparatus according to the embodiment of the present invention have been described. <Manufacturing Method of Multi Electron-Beam Source> Next, the manufacturing method of the multi electron-beam source used in the display panel according to the embodiment of the present invention will be described. As far as the multi electron-beam source used in the image display apparatus is obtained by arranging cold cathode devices in a simple matrix, the material, shape, and manufacturing method of the cold cathode device are not limited. As the cold cathode device, therefore, an SCE type electron-emitting device or an FE type or MIM type cold cathode device can be used. Under circumstances where inexpensive display apparatuses having large display screens are required, an SCE type electron-emitting device, of these cold cathode devices, is especially preferable. More specifically, the electron-emitting characteristic of an FE type device is greatly influenced by the relative positions and shapes of the emitter cone and the gate electrode, and hence a high-precision manufacturing technique is required to manufacture this device. This poses a disadvantageous factor in attaining a large display area and a low manufacturing cost. According to an MIM type device, the thicknesses of the insulating layer and the upper electrode must be decreased and made uniform. This also poses a disadvantageous factor in attaining a large display area and a low manufacturing cost. In contrast to this, an SCE type electron-emitting device can be manufactured by a relatively simple manufacturing method, and hence an increase in display area and a decrease in manufacturing cost can be attained. The present inventors have also found that among the SCE type electron-emitting devices, an electron-beam source where an electron-emitting portion or its peripheral portion comprises a fine particle film is excellent in electron-emitting characteristic and further, it can be easily manufactured. Accordingly, this type of electron-beam source is the most appropriate electron-beam source to be employed in a multi electron-beam source of a high luminance and large-screened image display apparatus. In the display panel of the embodiment, SCE type electron-emitting devices each having an electron-emitting portion or peripheral portion formed from a fine particle film are employed. First, the basic structure, manufacturing method and characteristic of the preferred SCE type electron-emitting device will be described, and the structure of the multi electron-beam source having simple-matrix wired SCE type electron-emitting devices will be described later. <Preferred Structure and Manufacturing Method of SCE Device> The typical structure of the SCE type electron-emitting device where an electron-emitting portion or its peripheral portion is formed from a fine particle film includes a flat type structure and a stepped type structure. <Flat SEC Type Electron-Emitting Device> First, the structure and manufacturing method of a flat SCE type electron-emitting device will be described. Fig. 5A is a plan view explaining the structure of the flat SCE type electron-emitting device; and Fig. 5B, a cross-sectional view of the device. In Figs. 5A and 5B, numeral 1101 denotes a substrate; 1102 and 1103, device electrodes; 1104, a conductive thin film; 1105, an electron-emitting portion formed by the forming processing; and 1113, a thin film formed by the activation processing. As the substrate 1101, various glass substrates of, e.g., quartz glass and soda-lime glass, various ceramic substrates of, e.g., alumina, or any of those substrates with an insulating layer formed of, e.g., SiO 2 thereon can be employed. The device electrodes 1102 and 1103, provided in parallel to the substrate 1101 and opposing to each other, comprise conductive material. For example, any material of metals such as Ni, Cr, Au, Mo, W, Pt, Ti, Cu, Pd and Ag, or alloys of these metals, otherwise metal oxides such as In 2 O 3 -SnO 2 , or semiconductive material such as polysilicon, can be employed. The electrode is easily formed by the combination of a film-forming technique such as vacuum-evaporation and a patterning technique such as photolithography or etching, however, any other method (e.g., printing technique) may be employed. The shape of the electrodes 1102 and 1103 is appropriately designed in accordance with an application object of the electron-emitting device. Generally, an interval L between electrodes is designed by selecting an appropriate value in a range from tens nm(hundreds Angstroms) to hundreds micrometers. Most preferable range for a display apparatus is from several micrometers to tens micrometers. As for electrode thickness d, an appropriate value is selected from a range from tens nm (hundreds Angstroms) to several micrometers. The conductive thin film 1104 comprises a fine particle film. The "fine particle film" is a film which contains a lot of fine particles (including masses of particles) as film-constituting members. In microscopic view, normally individual particles exist in the film at predetermined intervals, or in adjacent to each other, or overlapped with each other. One particle has a diameter within a range from several angstroms to thousands angstroms. Preferably, the diameter is within a range from 1 nm (10 Angstroms) to 20 nm (200 Angstroms). The thickness of the film is appropriately set in consideration of conditions as follows. That is, condition necessary for electrical connection to the device electrode 1102 or 1103, condition for the forming processing to be described later, condition for setting electric resistance of the fine particle film itself to an appropriate value to be described later etc. Specifically, the thickness of the film is set in a range from several tenths nm (Angstroms) to hundreds nm (thousands Angstroms), more preferably, 1 nm (10 Angstroms) to 50nm (500 Angstroms). Materials used for forming the fine particle film are, e.g., metals such as Pd, Pt, Ru, Ag, Au, Ti, In, Cu, Cr, Fe, Zn, Sn, Ta, W and Pb, oxides such as PdO, SnO 2 , In 2 O 3 , PbO and Sb 2 O 3 , borides such as HfB 2 , ZrB 2 , LaB 6 , CeB 6 , YB 4 and GdB 4 , carbides such as TiC, ZrC, HfC, TaC, SiC and WC, nitrides such as TiN, ZrN and HfN, semiconductors such as Si and Ge, and carbons. Any of appropriate material(s) is appropriately selected. As described above, the conductive thin film 1104 is formed with a fine particle film, and sheet resistance of the film is set to reside within a range from 10' to 10' (Ω/sq) As it is preferable that the conductive thin film 1104 is electrically connected to the device electrodes 1102 and 1103, they are arranged so as to overlap with each other at one portion. In Fig. 5B, the respective parts are overlapped in order of, the substrate, the device electrodes, and the conductive thin film, from the bottom. This overlapping order may be, the substrate, the conductive thin film, and the device electrodes, from the bottom. The electron-emitting portion 1105 is a fissured portion formed at a part of the conductive thin film 1104. The electron-emitting portion 1105 has a resistance characteristic higher than peripheral conductive thin film. The fissure is formed by the forming processing to be described later on the conductive thin film 1104. In some cases, particles, having a diameter of several tenths nm (Angstroms) to tens nm (huridreds Angstroms), are arranged within the fissured portion. As it is difficult to exactly illustrate actual position and shape of the electron-emitting portion, therefore, Figs. 5A and 5B show the fissured portion schematically. The thin film 1113, which comprises carbon or carbon compound material, covers the electron-emitting portion 1115 and its peripheral portion. The thin film 1113 is formed by the activation processing to be described later after the forming processing. The thin film 1113 is preferably graphite monocrystalline, graphite polycrystalline, amorphous carbon, or mixture thereof, and its thickness is 50nm (500 Angstroms.) or less, more preferably, 30 nm (300 Angstroms) or less. As it is difficult to exactly illustrate actual position or shape of the thin film 1113, Figs. 5A and 5B show the film schematically. Fig. 5A shows the device where a part of the thin film 1113 is removed. The preferred basic structure of SCE type electron-emitting device is as described above. In the embodiment, the device has the following constituents. That is, the substrate 1101 comprises a soda-lime glass, and the device electrodes 1102 and 1103, an Ni thin film. The electrode thickness d is 1000 angstroms and the electrode interval L is 2 micrometers. The main material of the fine particle film is Pd or PdO. The thickness of the fine particle film is about 100 angstroms, and its width W is 100 micrometers. Next, a method of manufacturing a preferred flat SCE type electron-emitting device will be described with reference to Figs. 6A to 6E which are cross-sectional views showing the manufacturing processes of the SCE type electron-emitting device. Note that reference numerals are the same as those in Figs. 5A and 5B. (1) First, as shown in Fig. 6A, the device electrodes 1102 and 1103 are formed on the substrate 1101. Upon formation of the electrodes 1102 and 1103, first, the substrate 1101 is fully washed with a detergent, pure water and an organic solvent, then, material of the device electrodes is deposited there (as a depositing method, a vacuum film-forming technique such as evaporation and sputtering may be used). Thereafter, patterning using a photolithography etching technique is performed on the deposited electrode material. Thus, the pair of device electrodes 1102 and 1103 shown in Fig. 6A are formed. (2) Next, as shown in Fig. 6B, the conductive thin film 1104 is formed. Upon formation of the conductive thin film 1104, first, an organic metal solvent is applied to the substrate 1101 in Fig. 6A, then the applied solvent is dried and sintered, thus forming a fine particle film. Thereafter, the fine particle film is patterned, in accordance with the photolithography etching method, into a predetermined shape. The organic metal solvent means a solvent of organic metal compound containing material of minute particles, used for forming the conductive thin film, as main component (i.e., Pd in this embodiment). In the embodiment, application of organic metal solvent is made by dipping, however, any other method such as a spinner method and spraying method may be employed.As a film-forming method of the conductive thin film made with the minute particles, the application of organic metal solvent used in the embodiment can be replaced with any other method such as a vacuum evaporation method, a sputtering method or a chemical vapor-phase accumulation method. (3) Then, as shown in Fig. 6C, appropriate voltage is applied between the device electrodes 1102 and 1103, from a power source 1110 for the forming processing, then the forming processing is performed, thus forming the electron-emitting portion 1105. The forming processing here is electric energization of a conductive thin film 1104 formed of a fine particle film, to appropriately destroy, deform, or deteriorate a part of the conductive thin film, thus changing the film to have a structure suitable for electron emission. In the conductive thin film, the portion changed for electron emission (i.e., electron-emitting portion 1105) has an appropriate fissure in the thin film. Comparing the thin film 1104 having the electron-emitting portion 1105 with the thin film before the forming processing, the electric resistance measured between the device electrodes 1102 and 1103 has greatly increased.The forming processing will be explained in detail with reference to Fig. 7 showing an example of waveform of appropriate voltage applied from the forming power source 1110. Preferably, in case of forming a conductive thin film of a fine particle film, a pulse-form voltage is employed. In this embodiment, a triangular-wave pulse having a pulse width T1 is continuously applied at pulse interval of T2, as shown in Fig. 7. Upon application, a wave peak value Vpf of the triangular-wave pulse is sequentially increased. Further, a monitor pulse Pm to monitor status of forming the electron-emitting portion 1105 is inserted between the triangular-wave pulses at appropriate intervals, and current that flows at the insertion is measured by a galvanometer 1111.In this example, in 10 -3 Pa (10 -5 Torr) vacuum atmosphere, the pulse width T1 is set to 1 msec; and the pulse interval T2, to 10 msec. The wave peak value Vpf is increased by 0.1 V, at each pulse. Each time the triangular-wave has been applied for five pulses, the monitor pulse Pm is inserted. To avoid ill-effecting the forming processing, a voltage Vpm of the monitor pulse is set to 0.1 V. When the electric resistance between the device electrodes 1102 and 1103 becomes 1 x 10 6 Ω, i.e., the current measured by the galvanometer 1111 upon application of monitor pulse becomes 1 x 10 -7 A or less, the electrification of the forming processing is terminated.Note that the above processing method is preferable to the SCE type electron-emitting device of this embodiment. In case of changing the design of the SCE type electron-emitting device concerning, e.g., the material or thickness of the fine particle film, or the device electrode interval L, the conditions for electrification are preferably changed in accordance with the change of device design. (4) Next, as shown in Fig. 6D, appropriate voltage is applied, from an activation power source 1112, between the device electrodes 1102 and 1103, and the activation processing is performed to improve electron-emitting characteristics obtained in the preceding step. The activation processing here is electrification of the electron-emitting portion 1105, formed by the forming processing, on appropriate condition(s), for depositing carbon or carbon compound around the electron-emitting portion 1105 (In Fig. 6D, the deposited material of carbon or carbon compound is shown as material 1113). Comparing the electron-emitting portion 1105 with that before the activation processing, the emission current at the same applied voltage has become, typically 100 times or greater. The activation is made by periodically applying a voltage pulse in 10 -2 or 10 -3 Pa (10 -4 or 10 -5 Torr) vacuum atmosphere, to accumulate carbon or carbon compound mainly derived from organic compound(s) existing in the vacuum atmosphere. The accumulated material 1113 is any of graphite monocrystalline, graphite polycrystalline, amorphous carbon or mixture thereof. The thickness of the accumulated material 1113 is 50 nm 500 Angstroms or less, more preferably, 30 nm (300 Angstroms) or less. The activation processing will be described in more detail with reference to Fig. 8A showing an example of waveform of appropriate voltage applied from the activation power source 1112. In this example, a rectangular wave at a predetermined voltage is applied to perform the activation processing. More specifically, a rectangular-wave voltage Vac is set to 14 V; a pulse width T3, to 1 msec; and a pulse interval T4, to 10 msec. Note that the above electrification conditions are preferable for the SCE type electron-emitting device of the embodiment. In a case where the design of the SCE type electron-emitting device is changed, the electrification conditions are preferably changed in accordance with the change of device design. In Fig. 6D, numeral 1114 denotes an anode electrode, connected to a direct-current (DC) high-voltage power source 1115 and a galvanometer 1116, for capturing emission current Ie emitted from the SCE type electron-emitting device (in a case where the substrate 1101 is incorporated into the display panel before the activation processing, the Al layer on the fluorescent surface of the display panel is used as the anode electrode 1114). While applying voltage from the activation power source 1112, the galvanometer 1116 measures the emission current Ie, thus monitors the progress of activation processing, to control the operation of the activation power source 1112. Fig. 8B shows an example of the emission current Ie measured by the galvanometer 1116. In this example, as application of pulse voltage from the activation power source 1112 is started, the emission current Ie increases with elapse of time, gradually comes into saturation, and almost never increases then. At the substantial saturation point, the voltage application from the activation power source 1112 is stopped, then the activation processing is terminated. Note that the above electrification conditions are preferable to the SCE type electron-emitting device of the embodiment. In case of changing the design of the SCE type electron-emitting device, the conditions are preferably changed in accordance with the change of device design. As described above, the SCE type electron-emitting device as shown in Fig. 6E is manufactured. <Step SCE Type Electron-Emitting Device> Next, another typical structure of the SCE type electron-emitting device where an electron-emitting portion or its peripheral portion is formed of a fine particle film, i.e., a stepped SCE type electron-emitting device will be described. Fig. 9 is a cross-sectional view schematically showing the basic construction of the step SCE type electron-emitting device. In Fig. 9, numeral 1201 denotes a substrate; 1202 and 1203, device electrodes; 1206, a step-forming member for making height difference between the electrodes 1202 and 1203; 1204, a conductive thin film using a fine particle film; 1205, an electron-emitting portion formed by the forming processing; and 1213, a thin film formed by the activation processing. Difference between the step device structure from the above-described flat device structure is that one of the device electrodes (1202 in this example) is provided on the step-forming member 1206 and the conductive thin film 1204 covers the side surface of the step-forming member 1206. The device interval L in Figs. 5A and 5B is set in this structure as a height difference Ls corresponding to the height of the step-forming member 1206. Note that the substrate 1201, the device electrodes 1202 and 1203, the conductive thin film 1204 using the fine particle film can comprise the materials given in the explanation of the flat SCE type electron-emitting device. Further, the step-forming member 1206 comprises electrically insulating material such as SiO 2 . Next, a method of manufacturing the stepped SCE type electron-emitting device will be described with reference Figs. 10A to 10F which are cross-sectional views showing the manufacturing processes. In these figures, reference numerals of the respective parts are the same as those in Fig. 9. (1) First, as shown in Fig. 10A, the device electrode 1203 is formed on the substrate 1201. (2) Next, as shown in Fig. 10B, an insulating layer for forming the step-forming member is deposited. The insulating layer may be formed by accumulating, e.g., SiO 2 by a sputtering method, however, the insulating layer may be formed by a film-forming method such as a vacuum evaporation method or a printing method. (3) Next, as shown in Fig. 10C, the device electrode 1202 is formed on the insulating layer. (4) Next, as shown in Fig. 10D, a part of the insulating layer is removed by using, e.g., an etching method, to expose the device electrode 1203. (5) Next, as shown in Fig. 10E, the conductive thin film 1204 using the fine particle film is formed. Upon formation, similar to the above-described flat device structure, a film-forming technique such as an applying method is used. (6) Next, similar to the flat device structure, the forming processing is performed to form the electron-emitting portion 1205 (the forming processing similar to that explained using Fig. 6C may be performed). (7) Next, similar to the flat device structure, the activation processing is performed to deposit carbon or carbon compound around the electron-emitting portion (activation processing similar to that explained using Fig. 6D may be performed). As described above, the stepped SCE type electron-emitting device shown in Fig. 10F is manufactured. <Characteristic of SCE Type Electron-Emitting Device Used in Display Apparatus> The structure and manufacturing method of the flat SCE type electron-emitting device and those of the stepped SCE type electron-emitting device are as described above. Next, the characteristic of the electron-emitting device used in the display apparatus will be described below. Fig. 11 shows a typical example of (emission current Ie) to (device voltage (i.e., voltage to be applied to the device) Vf) characteristic and (device current If) to (device application voltage Vf) characteristic of the device used in the display apparatus. Note that compared with the device current If, the emission current Ie is very small, therefore it is difficult to illustrate the emission current Ie by the same measure of that for the device current If. In addition, these characteristics change due to change of designing parameters such as the size or shape of the device. For these reasons, two lines in the graph of Fig. 11 are respectively given in arbitrary units. Regarding the emission current Ie, the device used in the display apparatus has three characteristics as follows: First, when voltage of a predetermined level (referred to as "threshold voltage Vth") or greater is applied to the device, the emission current Ie drastically increases, however, with voltage lower than the threshold voltage Vth, almost no emission current Ie is detected. That is, regarding the emission current Ie, the device has a nonlinear characteristic based on the clear threshold voltage Vth. Second, the emission current Ie changes in dependence upon the device application voltage Vf. Accordingly, the emission current Ie can be controlled by changing the device voltage Vf. Third, the emission current Ie is output quickly in response to application of the device voltage Vf. Accordingly, an electrical charge amount of electrons to be emitted from the device can be controlled by changing period of application of the device voltage Vf. The SCE type electron-emitting device with the above three characteristics is preferably applied to the display apparatus. For example, in a display apparatus having a large number of devices provided corresponding to the number of pixels of a display screen, if the first characteristic is utilized, display by sequential scanning of display screen is possible. This means that the threshold voltage Vth or greater is appropriately applied to a driven device, while voltage lower than the threshold voltage Vth is applied to an unselected device. In this manner, sequentially changing the driven devices enables display by sequential scanning of display screen. Further, emission luminance can be controlled by utilizing the second or third characteristic, which enables multi-gradation display. <Structure of Simple-Matrix Wired Multi Electron-Beam Source> Next, the structure of a multi electron-beam source where a large number of the above SCE type electron-emitting devices are arranged with the simple-matrix wiring will be described below. Fig. 14 is a plan view of the multi electron-beam source used in the display panel in Fig. 12. There are SCE type electron-emitting devices similar to those shown in Figs. 5A and 5B on the substrate. These devices are arranged in a simple matrix with the row-direction wiring 1013 and the column-direction wiring 1014. At an intersection of the wirings 1013 and 1014, an insulating layer (not shown) is formed between the wires, to maintain electrical insulation. Fig. 15 shows a cross-section cut out along the line A-A' in Fig. 14. Note that this type multi electron-beam source is manufactured by forming the row- and column-direction wirings 1013 and 1014, the insulating layers (not shown) at wires' intersections, the device electrodes and conductive thin films on the substrate, then supplying electricity to the respective devices via the row- and column-direction wirings 1013 and 1014, thus performing the forming processing and the activation processing. <Arrangement (and Driving Method) of Driving Circuit> Fig. 16 is a block diagram showing the schematic arrangement of a driving circuit for performing television display on the basis of a television signal of the NTSC scheme. Referring to Fig. 16, a display panel 1701 is manufactured and operates in the same manner described above. A scanning circuit 1702 scans display lines. A control circuit 1703 generates signals and the like to be input to the scanning circuit 1702. A shift register 1704 shifts data in units of lines. A line memory 1705 inputs 1-line data from the shift register 1704 to amodulated signal generator 1707. A sync signal separation circuit 1706 separates a sync signal from an NTSC signal. The function of each component in Fig. 16 will be described in detail below. The display panel 1701 is connected to an external electric circuit through terminals Dx1 to Dxm and Dy1 to Dyn and a high-voltage terminal Hv. Scanning signals for sequentially driving an electron source 1 in the display panel 1701, i.e., a group of electron-emitting devices 15 wired in a m x n matrix in units of lines (in units of n devices) are applied to the terminals Dxl to Dxm. Modulated signals for controlling the electron beams output from the electron-emitting devices 15 corresponding to one line, which are selected by the above scanning signals, are applied to the terminals Dy1 to Dyn. For example, a DC voltage of 5 kV is applied from a DC voltage source Va to the high-voltage terminal Hv. This voltage is an accelerating voltage for giving energy enough to excite the fluorescent substances to the electron beams output from the electron-emitting devices 15. The scanning circuit 1702 will be described next. This circuit incorporates m switching elements (denoted by reference symbols S1 to Sm in Fig. 16). Each switching element serves to select either an output voltage from a DC voltage source Vx or 0 V (ground level) and is electrically connected to a corresponding one of the terminals Dox1 to Doxm of the display panel 1701. The switching elements S1 to Sm operate on the basis of a control signal Tscan output from the control circuit 1703. In practice, this circuit can be easily formed in combination with switching elements such as FETs. The DC voltage source Vx is set on the basis of the characteristics of the electron-emitting device in Fig. 11 to output a constant voltage such that the driving voltage to be applied to a device which is not scanned is set to an electron emission threshold voltage Vth or lower. The control circuit 1703 serves to match the operations of the respective components with each other to perform proper display on the basis of an externally input image signal. The control circuit 1703 generates control signals Tscan, Tsft, and Tmry for the respective components on the basis of a sync signal Tsync sent from the sync signal separation circuit 1706 to be described next. The sync signal separation circuit 1706 is a circuit for separating a sync signal component and a luminance signal component from an externally input NTSC television signal. As is known well, this circuit can be easily formed by using a frequency separation (filter) circuit. The sync signal separated by the sync signal separation circuit 1706 is constituted by vertical and horizontal sync signals, as is known well. In this case, for the sake of descriptive convenience, the sync signal is shown as the signal Tsync. The luminance signal component of an image, which is separated from the television signal, is expressed as a signal DATA for the sake of descriptive convenience. This signal is input to the shift register 1704. The shift register 1704 performs serial/parallel conversion of the signal DATA, which is serially input in a time-series manner, in units of lines of an image. The shift register 1704 operates on the basis of the control signal Tsft sent from the control circuit 1703. In other words, the control signal Tsft is a shift clock for the shift register 1704. One-line data (corresponding to driving data for n electron-emitting devices) obtained by serial/parallel conversion is output as n signals ID1 to IDn from the shift register 1704. The line memory 1705 is a memory for storing 1-line data for a required period of time. The line memory 1705 properly stores the contents of the signals ID1 to IDn in accordance with the control signal Tmry sent from the control circuit 1703. The stored contents are output as data I'D1 to I'Dn to be input to a modulated signal generator 1707. The modulated signal generator 1707 is a signal source for performing proper driving/modulation with respect to each electron-emitting device 15 in accordance with each of the image data I'D1 to I'Dn. Output signals from the modulated signal generator 1707 are applied to the electron-emitting devices 15 in the display panel 1701 through the terminals Doy1 to Doyn. The electron-emitting device according to the present invention has the following basic characteristics with respect to an emission current Ie, as described above with reference to Fig. 11. A clear threshold voltage Vth (8 V in the surface-conduction emission type electron-emitting device of the embodiment described later) is set for electron emission. Each device emits electrons only when a voltage equal to or higher than the threshold voltage Vth is applied. In addition, the emission current Ie changes with a change in voltage equal to or higher than the electron emission threshold voltage Vth, as shown in Fig. 11. Obviously, when a pulse-like voltage is to be applied to this device, no electrons are emitted if the voltage is lower than the electron emission threshold voltage Vth. If, however, the voltage is equal to or higher than the electron emission threshold voltage Vth, the electron-emitting device emits an electron beam. In this case, the intensity of the output electron beam can be controlled by changing a peak value Vm of the pulse. In addition, the total amount of electron beam charges output from the device can be controlled by changing a width Pw of the pulse. As a scheme of modulating an output from each electron-emitting device in accordance with an input signal, therefore, a voltage modulation scheme, a pulse width modulation scheme, or the like can be used. In executing the voltage modulation scheme, a voltage modulation circuit for generating a voltage pulse with a constant length and modulating the peak value of the pulse in accordance with input data can be used as the modulated signal generator 1707. In executing the pulse width modulation scheme, a pulse width modulation circuit for generating a voltage pulse with a constant peak value and modulating the width of the voltage pulse in accordance with input data can be used as the modulated signal generator 1707. As the shift register 1704 and the line memory 1705 may be of the digital signal type or the analog signal type. That is, it suffices if an image signal is serial/parallel-converted and stored at predetermined speeds. When the above components are of the digital signal type, the output signal DATA from the sync signal separation circuit 1706 must be converted into a digital signal. For this purpose, an A/D converter may be connected to the output terminal of the sync signal separation circuit 1706. Slightly different circuits are used for the modulated signal generator depending on whether the line memory 1705 outputs a digital or analog signal. More specifically, in the case of the voltage modulation scheme using a digital signal, for example, a D/A conversion circuit is used as the modulated signal generator 1707, and an amplification circuit and the like are added thereto, as needed. In the case of the pulse width modulation scheme, for example, a circuit constituted by a combination of a high-speed oscillator, a counter for counting the wave number of the signal output from the oscillator, and a comparator for comparing the output value from the counter with the output value from the memory is used as the modulated signal generator 1707. This circuit may include, as needed, an amplifier for amplifying the voltage of the pulse-width-modulated signal output from the comparator to the driving voltage for the electron-emitting device. In the case of the voltage modulation scheme using an analog signal, for example, an amplification circuit using an operational amplifier and the like may be used as the modulated signal generator 1707, and a shift level circuit and the like may be added thereto, as needed. In the case of the pulse width modulation scheme, for example, a voltage-controlled oscillator (VCO) can be used, and an amplifier for amplifying an output from the oscillator to the driving voltage for the electron-emitting device can be added thereto, as needed. In the image display apparatus of this embodiment which can have one of the above arrangements, when voltages are applied to the respective electron-emitting devices through the outer terminals Dx1 to Dxm and Dy1 to Dyn, electrons are emitted. A high voltage is applied to the metal back 1019 or the transparent electrode (not shown) through the high-voltage terminal Hv to accelerate the electron beams. The accelerated electrons collide with the fluorescent film 1018 to cause it to emit light, thereby forming an image. The above arrangement of the image display apparatus is an example of an image forming apparatus to which the present invention can be applied. Various changes and modifications of this arrangement can be made within the scope of the present invention as claimed. Although a signal based on the NTSC scheme is used as an input signal, the input signal is not limited to this. For example, the PAL scheme and the SECAM scheme can be used. In addition, a TV signal (high-definition TV such as MUSE) scheme using a larger number of scanning lines than these schemes can be used. <Structures of Spacer and Electron-Emitting Device Near Spacer> The structures of the spacer and the electron-emitting device will be described with reference to Figs. 1A and 1B. Referring to Figs. 1A and 1B, numeral 30 denotes a face plate including fluorescent substances and a metal back; 31, a rear plate including an electron source substrate; 50, a spacer; 51, a high-resistance film on the surface of the spacer; 52, an electrode (intermediate layer) on the face plate side; 13, device driving wiring; 111, a device; 112, a typical electron beam orbit; and 25, an equipotential line. Symbol a denotes a length from the inner surface of the face plate to the lower end of the electrode (intermediate layer) on the face plate side; and d, a distance between the electron source substrate and the face plate. The concepts of the present invention will be sequentially explained again. Some of electrons emitted near the spacer strike the spacer, or ions produced by the action of emitted electrons attach to the spacer, charging the spacer. The orbits of electrons emitted by the devices are changed by the charge-up of the spacer, the electrons reach positions different from proper positions, and thus a distorted image is displayed near the spacer. To solve this problem, the high-resistance film 51 is formed on the surface of the spacer 50 to relax the charge-up of the spacer. However, as the amount of emitted electrons by cold cathode devices increases, the charge-up elimination ability of the high-resistance film becomes poorer, and the charge-up amount depends on the number of emitted electrons. In this case, an electron beam undesirably fluctuates. Particularly when no electron directly strikes the spacer, charging of electrons reflected by the face plate is considered to mainly contribute to the charge-up of the spacer. The charge-up of the spacer by electrons reflected by the face plate has a distribution in which the charge-up amount is large on the face plate side, as shown in Fig. 2. As shown in Fig. 2, the charge-up amount is the largest at a position corresponding to about 1/10 of the distance between the electron source substrate and the face plate from the face plate. As the first requirement of the present invention, therefore, the position having the largest charge-up amount is covered with an electrode in order to effectively suppress the fluctuation of an electron beam. For this purpose, the intermediate layer 52 (having the length a ) on the face plate side is extended to the rear plate side, as shown in Fig. 1A. An electron beam is expected to follow an orbit like the orbit 112 and steadily move toward the spacer 50 (including the parts 51 to 53). Accordingly, as the second requirement of the present invention, an electron beam can be caused to reach a proper position by shifting an electron-emitting device 111 near the spacer from a position corresponding to the landing position, on the face plate, of an electron emitted by this device in the direction away from the spacer. Since a device nearer the spacer is more easily influenced by the electrode of the spacer on the face plate side, the device must be spaced apart from the position corresponding to the landing position of an electron. If the intermediate layer of the spacer on the face plate side is made too long, a decrease in discharge breakdown voltage cannot be corrected even by shifting a device near the spacer. For this reason, the length of the intermediate layer of the spacer must be set such that the accelerating voltage and the exposure length of the high-resistance film of the spacer have a relationship of 8 kV/mm or less. To further increase the discharge breakdown voltage, the length of the intermediate layer of the spacer is preferably set such that the accelerating voltage and the exposure length of the high-resistance film have a relationship of 4 kV/mm or less. On the side surface of the spacer which contacts the electron source substrate and the abutment surface of the spacer which abuts against the electron source substrate, another electrode for keeping the spacer at the same potential as that of the electron source substrate may be arranged. In this case, the conductive state between the electron source substrate and the spacer is improved. In addition, an electron beam emitted by a device near the spacer is temporarily moved in the direction away from the spacer by arranging an electrode long to a certain degree on the side surface of the spacer, and then moved toward the spacer by the electrode on the face plate side. As a result, the beam can be caused to reach a proper position. At this time, if the electrode on the electron source substrate side is made too long, an electron beam temporarily moved away from the spacer cannot return even by the electrode on the face plate side. For this reason, the length of the electrode on the electron source substrate side must be set in correspondence with the distance between the electron source substrate and the face plate. In this manner, when the intermediate layer is arranged on the abutment and side surfaces of the spacer which face the electron source substrate, the device shift amount can be decreased, compared to the case wherein no electrode is arranged, and thus the margin for forming wiring and devices increases. The present invention will be described in more detail below with reference to embodiments. In each of the following embodiments, a multi electron-beam source is prepared by wiring N x M (N = 3, 072, M = 1,024) SCE type electron-emitting devices each having an electron-emitting portion on a conductive fine particle film between electrodes, by M row-direction wirings and N column-direction wirings in a matrix (see Figs. 12 and 14). An appropriate number of spacers are arranged to obtain the atmospheric pressure resistance of the image forming apparatus. <First Embodiment> The first embodiment will be described with reference to Figs. 1B to 3B. Numeral 30 denotes a face plate including fluorescent substances and a metal back; 31, a rear plate including an electron source substrate; 50, a spacer; 51, a conductive thin film on the surface of the spacer; 52, an intermediate layer on the face plate side; 53, an intermediate layer on the rear plate side; 13, column- or row-direction wiring; 111-1, a device on the nearest column or row to the spacer (to be referred to as the nearest line hereinafter); 111-2, a device on the second nearest column or row to the spacer (to be referred to as the second nearest line hereinafter; a subsequent column or row will be referred to as the nth nearest line hereinafter); 112-1, a typical electron beam orbit from the nearest line; 112-2, a typical electron beam orbit from the second nearest line; and 25, an equipotential line. Symbol a denotes a length from the inner surface of the face plate to the lower end of the intermediate layer on the face plate side; b, a length from the inner surface of the rear plate to the upper end of the intermediate layer on the rear plate side; and d, a distance between the electron source substrate and the face plate. The feature of the first embodiment is to electrically connect the electrode 52, in addition to shifting an electron-emitting device from a proper position, and to correct the orbit of an electron beam near the spacer, e.g., the orbits 112-1 and 112-2. The distance d between the electron source substrate and the face plate is set to 2 mm, and the thickness of the spacer is to 200 µm. The distance between the side surface of the spacer and the nearest line is set to 560 µm, the distance to the second nearest line is to 1,070 µm, the distance to the third nearest line is to 1,680 µm, and the distance to the fourth nearest line is to 2,350 µm. Subsequent lines are aligned at an interval of 700 µm. In the first embodiment, the device pitches are set to the above values in order to arrange positions where electrons emitted by respective electron-emitting devices are irradiated on the image forming member, at an interval of 700 µm. The spacer is located at the center between electron-emitting devices adjacent to each other via the spacer. Electrons emitted by the adjacent electron-emitting devices reach positions symmetrical about the center of the spacer. Therefore, the irradiation position of an electron emitted by the nearest device to the spacer is spaced apart from the side surface of the spacer by about 250 µm. The irradiation position of an electron emitted by the second nearest device is spaced apart from the side surface of the spacer by about 950 µm. Electrons emitted by subsequent electron-emitting devices are irradiated on positions spaced apart by 700 µm each. Electron-emitting devices in the first embodiment are located such that the nearest device is shifted from a position where an irradiation point is vertically projected on the rear substrate, by 310 µm in the direction away from the spacer, the second nearest device is shifted by 120 µm in the direction away from the spacer, and the third nearest device is shifted by 30 µm in the direction away from the spacer. The fourth nearest and subsequent devices are not shifted in the direction away from the spacer because they are hardly influenced by deflection caused by the electrode of the spacer. In this case, an SnO 2 film is used as the conductive film of the spacer, the sheet resistance of the SiO 2 film is set on the order of 10 10 Ω/sq, and the length of the electrode on the face plate side is set to 760 µm. Note that in the embodiment shown in Fig. 1B, no electrode 53 is arranged on the rear plate side. When a voltage of 3 kV was applied to the face plate 30 to drive devices, beams reached proper positions on the face plate 30 at an interval of about 700 µm for an electron emission amount Ie of 3 µA per device, and no position variation (fluctuation) occurred for an electron emission amount Ie of about 2 to 6 µA per device. The application voltage to the face plate was changed from 2 to 6 kV not to find any variations in landing position of the electron beam. This is because the electrode 53 is used only to establish a conductive state between the spacer and the face plate, like the conventional spacer. Beams reaching proper positions at the same interval though devices were farther from the spacer than in the case wherein the distance between the side surface of the spacer and the nearest line was 250 µm and the interval between lines was 700 µm. At this time, any device farther from the spacer than the fourth nearest line was hardly influenced by the spacer. When the electrode 53 having a length of about 50 µm was formed on the side surface of the spacer which contacted the electron source substrate in order to improve the conductive state between the spacer and the electron source substrate, as shown in Figs. 3A and 3B, and when an electrode was formed on the abutment surface of the spacer which faced the electron source substrate, as shown in Fig. 3B, devices were hardly influenced by deflection caused by the electrode on the electron source substrate, and the same results were obtained. An example using a flat field emission (FE) type electron-emitting device as an electron source in the first embodiment will be explained with reference to Fig. 21. Fig. 21 is a plan view of the flat FE type electron-emitting electron source. Numeral 3101 denotes each electron-emitting portion; 3102 and 3103, a pair of device electrodes for applying a potential to the electron-emitting portion 3101; 3104 and 3105, device electrodes; and 3113, row-direction wiring. A spacer is formed on the row-direction wiring 3113 connected to the device electrode 3105. Numeral 3114 denotes each column-direction wiring; and 1020, a spacer. Symbol a denotes each line on which the center of a spot is formed. A voltage is applied across the device electrodes 3102 and 3103 to cause a sharp distal end in the electron-emitting portion 3101 to emit an electron. The electron is drawn by an accelerating voltage (not shown) facing the electron source to collide with a fluorescent substance (not shown), and causes the fluorescent substance to emit light. In this example, by shifting the device electrodes 3104 and 3105 in the above-described manner, a high-quality image in which a beam shift is suppressed even near the spacer can be obtained. In this example, the beam spot formation period is set to 1,350 µm, and the position of only the nearest electron-emitting portion to the spacer is shifted. At this time, the distance between the side surface of the spacer and the nearest electron-emitting portion is set to 850 µm, the distance to the second nearest line is to 1,925 µm, and the distance to the third nearest line is to 3,275 µm. The present invention is also applicable to a Spindt type electron-emitting device, and the same effects as those described above can be obtained. In the first embodiment, a soda-lime glass is used as the material of the substrate of the spacer. However, if an insulating ceramic such as alumina or alumina nitride is used, the same effects as those described above can be obtained. <Second Embodiment> The second embodiment is different from the first embodiment in that an electrode extending from an abutment position between a spacer and an electron source substrate toward a front substrate by 180 µm is arranged, the distance between the side surface of the spacer and the nearest line is set to 440 µm, the distance to the second nearest line is to 1,050 µm, the distance to the third nearest line is to 1,680 µm, and the fourth nearest and subsequent lines are located at proper positions. Also in the second embodiment, the device pitches are set to the above values in order to arrange positions where electrons emitted by respective electron-emitting devices are irradiated on the image forming member, at an interval of 700 µm. The spacer is located at the center between electron-emitting devices adjacent to each other via the spacer. Electrons emitted by the adjacent electron-emitting devices reach positions symmetrical about the center of the spacer. Therefore, the irradiation position of an electron emitted by the nearest device to the spacer is spaced apart from the side surface of the spacer by about 250 µm. The irradiation position of an electron emitted by the second nearest device is spaced apart from the side surface of the spacer by about 950 µm. Electrons emitted by subsequent electron-emitting devices are irradiated on positions spaced apart by each 700 µm. Electron-emitting devices in the second embodiment are located such that the nearest device is shifted from a position where each irradiation point is vertically projected on the rear substrate, by 190 µm in the direction away from the spacer, the second nearest device is shifted by 100 µm in the direction away from the spacer, and the third nearest device is shifted by 30 µm in the direction away from the spacer. The fourth nearest and subsequent devices are not shifted in the direction away from the spacer because they are hardly influenced by deflection caused by the electrode of the spacer. In the second embodiment, since an electron is applied with a force in the direction away from the spacer by the electrode of the support member formed near the rear substrate, the shift amount of each device from the position where the irradiation point of an electron is vertically projected on the rear plate becomes smaller than that in the first embodiment. Consequently, the same effects as those in the first embodiment were obtained. The present inventors confirmed the effects obtained when a beam emitted by a device near the spacer was moved away from the spacer by the electrode of the support member formed on the electron source substrate side, and the device is arranged away from the spacer. <Third Embodiment> The third embodiment is different from the first embodiment in that the distance d between an electron source substrate and a face plate is set to 3 mm, the length of an electrode on the rear plate side is to 200 µm, the length of an electrode on the face plate side is to 1,000 µm, the nearest line to the fifth nearest line are sequentially arranged at positions spaced apart from the side surface of a spacer by 690, 1,210, 1,760, 2,420, and 3,070 µm, and subsequent lines are arranged at proper positions. As a result, electrons emitted by all the devices reached proper positions for an electron emission amount Ie of 3 µA, and did not fluctuate for an electron emission amount Ie of 3 to 6 µA. As described above, according to the third embodiment, an electron beam can reach a target without striking the spacer, and distortion of an image near the spacer can be reduced. Further, variations (fluctuations) in beam landing position depending on the luminance of a beam near the spacer can be reduced. <Fourth Embodiment> The fourth embodiment concerns the case wherein the structure of an intermediate layer is partially changed in an image forming apparatus having the same structure as that in the first embodiment. The fourth embodiment will be described with reference to Figs. 22A, 22B, 23A, and 23B. Figs. 22A and 22B are views for explaining a spacer in which an electrode is formed on an abutment surface on the face plate side, and an electrode is also formed on the rear plate side. Figs. 23A and 23B are views for explaining a spacer shown in Figs. 22A and 22B in which an electrode is further formed on an abutment surface on the rear plate side. Figs. 22B and 23B are cross-sectional views of the spacers, respectively, cut out along the lines A - A' in Figs. 22A and 22B. Referring to Figs. 22A, 22B, 23A, and 23B, numeral 52 denotes an electrode on the face plate side; 51a, a spacer substrate; and 53, an electrode on the rear plate side. In the fourth embodiment as well as the above embodiments, a high-resistance film (not shown) is formed on the surface of the spacer substrate 51a. The remaining structure is the same as that in the first embodiment. The length of the electrode on the face plate side was set to 760 µm, the length of the electrode on the rear plate side was to 50 µm, and each of the spacer in Figs. 22A and 22B and the spacer in Figs. 23A and 23B was applied to the image apparatus in the first embodiment to obtain a high-quality image in which a beam shift was suppressed even near the spacer, similar to the first embodiment. <Fifth Embodiment> The fifth embodiment exemplifies, with reference to Fig. 24, the structure of an electron-emitting device when a resistive material is used as a material for an intermediate layer in an image forming apparatus having the same structure as that in the first embodiment. Referring to Fig. 24, numeral 330 denotes a face plate including fluorescent substances and a metal back; 331, a rear plate including an electron source substrate; 350, a spacer; 351, a high-resistance film on the surface of the spacer; 352, a resistive film (intermediate layer) on the face plate side; 353, a resistive film (intermediate layer) on the rear plate side; 313, device driving wiring; 3111, a device; 3112, a typical electron beam orbit; and 325, an equipotential line. Symbol h denotes a distance between the electron source substrate and the face plate; a , a length of the resistive film on the face plate side; and b, a length of the resistive film on the rear plate side. In the fifth embodiment, the distance h between the electron source substrate and the face plate is set to 3 mm, the length a of the electrode on the face plate side is to 1,050 µm, and the length b of the electrode on the rear plate side is to 50 µm. In the fifth embodiment, the distance between spots is set to 650 µm, the distance between devices nearest to each other via the spacer is set to 710 µm, and the distance between the second nearest devices via the spacer is set to 1,330 µm. The third nearest and subsequent electron-emitting devices to the spacer are arranged at proper positions in Fig. 24. The sheet resistance value of each intermediate layer is 10 5 Ω/sv, and the sheet resistance of the high-resistance film is 10 9 Ω/sv. The image forming apparatus in the fifth embodiment was driven by the same method as in the first embodiment to similarly obtain a high-quality image in which a beam shift was suppressed even near the spacer. Note that in the fifth embodiment, a potential gradient is generated by a voltage drop even at the intermediate layer portion owing to the relationship between the resistances of the intermediate layer 352 on the face plate side and the intermediate layer 353 and the high-resistance film 351 on the rear plate side. Accordingly, a potential gradient between the intermediate layer and the high-resistance film 351 can suppress discharge from the stub of the intermediate layer that sometimes occurs in fabrication as compared with the case of using a low-resistance electrode because the field gradient at the interface between the intermediate layer and the high-resistance layer 351 is small. In the fifth embodiment, a tin oxide target containing antimony is used as a material for the intermediate layer, and sputtering is performed in the argon atmosphere to form a resistive tin oxide film. However, various materials can be selected as far as the resistance of the intermediate layer is lower than that of the high-resistance film. In the fifth embodiment, although the resistive film 352 on the face plate side and the resistive film 353 on the rear plate side are made of the same material, one of them can be formed of an electrode. If the intermediate layer is formed of an electrode, various structures described above can be employed. <Other Embodiments> The present invention can be applied to any cold cathode electron-emitting device except for an SCE type electron-emitting device. As a concrete example, there is a field emission type electron-emitting device in which a pair of electrodes facing each other are formed along a substrate surface serving as an electron source, like the one disclosed in Japanese Patent Laid-Open No. 63-274047 filed by the present applicant. The present invention is also applicable to an image forming apparatus using an electron source other than a simple matrix type electron source. For example, a support member like the one described above is used between an electron source and a control electrode in an image forming apparatus for selecting SCE type electron-emitting devices using the control electrode, like the one disclosed in Japanese Patent Laid-Open No. 2-257551 filed by the present applicant. According to the concepts of the present invention, the present invention is not limited to an image forming apparatus suitable for display. The above-mentioned image forming apparatus can also be used as a light-emitting source instead of a light-emitting diode for an optical printer made up of a photosensitive drum, the light-emitting diode, and the like. In this case, by properly selecting m row-direction wirings and n column-direction wirings, the image forming apparatus can be applied as not only a linear light-emitting source but also a two-dimensional light-emitting source. As has been described above, according to the present invention, an image almost free from distortion and fluctuation can be formed while a shift between a proper position on a front substrate having an image forming member formed thereon and the irradiation point of an electron is suppressed.

Claims: An image forming apparatus having a rear substrate (31, 1011, 331) with a plurality of electron-emitting devices (111, 3111) arranged substantially linearly; a front substrate (30, 1017, 330) with an image forming member (1018) on which an image is formed by electrons emitted by said electron-emitting devices, and a support member (50, 1020, 350) for maintaining an interval between said rear substrate and said front substrate, characterized in that said support member comprises an electrode (52, 21, 352) extending from an abutment portion between said front substrate and said support member to a predetermined position toward said rear substrate, said electrode is, when in use, maintained at a high potential, and intervals of said plurality of electron-emitting devices arranged substantially linearly are set to have an interval between two electron-emitting devices adjacent to each other via said support member larger than an interval between two electron-emitting devices adjacent to each other without mediacy of said support member. An apparatus according to claim 1, wherein said front substrate comprises an acceleration electrode (1019) which when in use is applied with a voltage for accelerating electrons emitted by said electron-emitting devices, and said electrode arranged on said support member is connected to said acceleration electrode. An image forming apparatus having a rear substrate (1011) with a plurality of electron-emitting devices (111, 3111) arranged substantially linearly; a front substrate (1017) with an image forming member (1018) on which an image is formed by electrons emitted by said electron-emitting devices; a support member (1020) for maintaining an interval between said rear substrate and said front substrate, and an acceleration electrode (1019) which is arranged on or near said front substrate and applied, when in use, with a voltage for accelerating electrons emitted by said electron-emitting devices toward said front substrate, characterized in that said support member comprises an electrode (21) which is connected to said acceleration electrode and extends to a predetermined position toward said rear substrate, and intervals of said plurality of electron-emitting devices arranged substantially linearly are set to have an interval between two electron-emitting devices adjacent to each other via said support member larger than an interval between two electron-emitting devices adjacent to each other without mediacy of said support member. An apparatus according to any one of claims 1 to 3, wherein said support member comprises conductive means (51, 11) for giving conductivity for relaxing charge-up on said support member. An apparatus according to claim 4, wherein said conductive means is a conductive member arranged from an abutment portion of said support member against said rear substrate to an abutment portion against said front substrate. An apparatus according to any one of claims 1 to 5, wherein the difference between the potential of said electrode arranged on said support member and the potential of an abutment portion of said support member against said rear substrate, and the length of the portion of said support member where no electrode is arranged have a relationship of not more than 8kV/mm. An apparatus according to claim 6, wherein the difference between the potential of said electrode arranged on said support member and the potential of the abutment portion of said support member against said rear substrate, and the length of the portion of said support member where no electrode is arranged have a relationship of not more than 4 kV/mm. An apparatus according to any one of claims 1 to 7, wherein said electrode arranged on said support member abuts against said front substrate and is also arranged on the abutment surface. An apparatus according to any one of claims 1 to 8, wherein said electrode arranged on said support member has a sheet resistance of 10 6 to 10 12 Ω/sq. An apparatus according to any one of claims 1 to 8, wherein said electrode arranged on said support member reaches a position corresponding to not less than 1/10 of a distance between said front substrate and said rear substrate when measured from a position where said support member abuts against said front substrate. An apparatus according to any one of claims 1 to 10, further comprising deflection means, arranged between a portion near an abutment portion of said support member against said rear plate and said electron-emitting devices, for generating a force in a direction away from said support member for electrons emitted by said electron-emitting devices. An apparatus according to any one of claims 1 to 11, wherein an interval between adjacent electron-emitting devices of said plurality of electron-emitting devices is set in accordance with the degree of deflection of electrons emitted by each electron-emitting device toward said support member. An apparatus according to any one of claims 1 to 12, wherein an interval between adjacent electron-emitting devices of said plurality of electron-emitting devices is set in accordance with the degree of deflection of electrons emitted by each electron-emitting device toward said support member so as to arrange irradiation points of electrons emitted by said electron-emitting devices on said image forming member at a substantially equal interval.

Inventors: FUSHIMI MASAHIRO, MITSUTAKE HIDEAKI, YAMAZAKI KOJI, FUSHIMI, MASAHIRO, MITSUTAKE, HIDEAKI, YAMAZAKI, KOJI, FUSHIMI, MASAHIRO, C/O CANON KABUSHIKI KAISHA, MITSUTAKE, HIDEAKI, C/O CANON KABUSHIKI KAISHA, Yamazaki, Koji,Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1998
Main classification: H01J29
IPC codes: H01J29, H01J31