Method of manufacturing an electron-emitting device as well as an electron source and an image forming apparatus comprising such electron-emitting devices

Abstract: A method of manufacturing an electron emitting device (104) of the type having, on a substrate 1, an electroconductive thin film (3) with an electron-emitting region (2), connected to respective electrodes (4,5). The electroconductive film (3) is formed by spraying through a nozzle (33;131) a solution containing component elements of the electroconductive thin film (3) which is to be formed. Spraying is performed whilst an electrical potential difference (V) is produced between the electrodes (4,5), between the nozzle (131) and the substrate (1), or both. The effect is to improve adherence of the film (3) to the substrate (1) or substrate and electrodes (1,4,5). This method may be extended to the manufacture of an electron source (1,102-104) having an array of electron-emitting devices (104).

Description: This invention relates to a method of producing an electron-emitting device, and also to methods of producing an electron source and an image forming apparatus both comprising such electron-emitting devices. There have been known two types of electron-emitting device; the thermionic cathode device and the cold cathode device. Cold cathode devices refer to the field emission type (hereinafter referred to as the FE type), the metal/insulation layer/metal type (hereinafter referred to as the MIM type), the surface conduction type, etc. Examples of FE type device include those proposed by W. P. Dyke & 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 molybdenum cones", J. Appl. Phys., 47, 5248 (1976). Examples of MIM device are disclosed in papers including C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961). Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965). A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO 2 thin film for a device of this type, the use of Au thin film is proposed in [G. Dittmer: "Thin Solid Films", 9, 317 (1972)] whereas the use of In 2 O 3 /SnO 2 and that of carbon thin film are disclosed respectively in [M. Hartwell and C. G. Fonstad: "IEEE Trans. ED Conf.", 519 (1975)] and [H. Araki et al.: "Vacuum", Vol. 26, No. 1, p. 22 (1983)]. Fig. 17 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In Fig. 17, reference numeral 1 denotes a substrate. Reference numeral 3 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 2 when it is subjected to an electrically energizing process referred to as "energization forming" as will be described hereinafter. In Fig. 17, a pair of device electrodes are separated by a length L of 0.5 to 1[mm] and a width W' is 0.1[mm]. Conventionally, an electron emitting region 2 is produced in a surface conduction electron-emitting device by subjecting the electroconductive thin film 3 of the device to an electrically energizing process, which is referred to as energization forming. In the energization forming process, a DC voltage or a slowly rising voltage that rises typically at, for instance, a very slow rate of 1V/min. is applied to given opposite ends of the electroconductive thin film 3 to locally destroy, deform or structurally modify the film and produce an electron-emitting region 2 which is electrically highly resistive. Thus, the electron-emitting region 2 is part of the electroconductive thin film 3 that typically contains fissures therein so that electrons may be emitted from the fissures and their neighboring areas. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron emitting region 2 whenever an appropriate voltage is applied to the electroconductive thin film 3 to make an electric current flow through the device. In an image display apparatus realized by arranging a large number of surface conduction electron-emitting devices of the above described type on a substrate and an anode electrode disposed above the substrate, a voltage is applied to the device electrodes of selected electron-emitting devices to cause their electron-emitting regions to emit electrons, while another voltage is applied to the anode electrode of the apparatus to attract electron beams emitted from the electron-emitting regions of the selected surface conduction electron-emitting devices. Under this condition, electrons emitted from the electron-emitting region of a surface conduction electron-emitting device form an electron beam, which move from the low potential side to the high potential side of the device electrode and, at the same time, toward the anode along a parabolic trajectory that is gradually spread before they finally get to the anode electrode. The trajectory of the electron beam is defined as a function of the potential difference of the voltages applied to the device electrodes of each device, the voltage applied to the anode electrode and the distance between the anode electrode and the electron-emitting devices. The image display apparatus is further provided with fluorescent members arranged on the anode electrode as so many pixels that emit light as emitted electrons collide with them. With this arrangement, the electron beam is required to have a profile that corresponds to the size of the pixel, or the target of the electron beam, but this requirement is not necessarily met in conventional image display apparatuses particularly in the case of high definition television sets comprising a large number of fine pixels. If such is the case, the electron beam can eventually hit adjacent pixels to produce unwanted colors on the screen to consequently degrade the quality of the display image. In addition, if the image display apparatus is very flat and has a large display screen that is tens of several inches (1 inch = 2.54 cm) wide as in the case of a so-called wall televisions set, it may be accompanied by another problem as described below. The surface conduction electron-emitting devices of such an image display apparatus is typically prepared by way of a patterning process using an aligner comprising a deep UV type light source, if the device electrodes of each surface conduction electron-emitting device is separated from other by less than 2 to 3µm, or a regular UV type light source, if the device electrodes are separated by more than 3µm, from the viewpoint of the performance of the aligner and the manufacturing yield. However, any known aligners have a relatively small exposure area that is several inches (1 inch = 2.54 cm) wide at most if they are of the deep UV type and are intrinsically not suited for a large exposure area because they are of the direct contact exposure type. The exposure area of aligners of the regular UV type does not generously exceed ten inches in the dimension and therefore they are by no means good for the manufacture of large screen apparatuses. In view of the above identified problem of aligners, the distance separating the device electrodes of each surface conduction electron-emitting device is preferably greater than 3µm and more preferably greater than tens of several µm in an electron source comprising a large number of such surface conduction electron-emitting devices or an image forming apparatus using such an electron source. On the other hand, as a result of the above described energization forming process, the produced electron-emitting region of the surface conduction electron-emitting device can become swerved particularly when the device electrodes are separated by a large distance to reduce the convergence of the electron beam emitted from there. Then, the energization forming process in the manufacture of surface conduction electron-emitting devices may lose accuracy in terms of the location and the profile of the electron-emitting region to produce devices that operate poorly. Thus, in an electron source comprising a large number of surface conduction electron-emitting devices having a large distance separating the device electrodes and an image forming apparatus using such an electron source, the electron-emitting devices do not operate uniformly for electron emission to consequently give rise to an uneven distribution of brightness nor the electron beams they emit converge in a desired way. The image displaying performance of such an apparatus is inevitably poor as it can provide only blurred images. Additionally, in the energization forming process for producing an electron-emitting region in the surface conduction electron-emitting device, each device consumes power normally between tens of several mW to several hundred mW, requiring a huge quantity of power for an electron source comprising a large number of surface conduction electron-emitting devices or an image forming apparatus using such an electron source. Then, in the energization forming process, there occurs a significant drop in the voltage applied to each device to additionally damage the uniformity in the performance of the produced devices. In certain cases, the substrate can be cracked during the energization forming process as a result of such lack of uniformity. In view of the above identified problems, the applicant has sought to provide an electron-emitting device that emits electrons at a sufficiently high efficiency and produces a finely defined electron beam and an image forming apparatus comprising such electron-emitting devices and hence capable of producing highly defined, clear and bright images with high quality. The applicant has also sought to provide an image forming apparatus having a large display screen that can produce highly defined, clear and bright images even if the device electrodes of each electron-emitting device comprised therein is separated from each other by more than 3µm and preferably more than tens of several µm. The applicant has also sought to provide a method of manufacturing an image forming apparatus that can produce finely defined, clear and bright images by using an electron source that comprises a large number of surface conduction electron-emitting devices that are free from the above identified problems. In short, the present invention is intended to provide a method of manufacturing a surface conduction electron-emitting device that is free from the above identified problems of the prior art and can be used for producing a large and high quality electron source and an image forming apparatus using such an electron source. The present invention is also intended to provide methods of manufacturing an electron source comprising a large number of such surface conduction electron-emitting devices and an image forming apparatus using such an electron source. The present invention concerns a method of manufacturing a surface conduction electron-emitting device comprising an electroconductive thin film including an electron-emitting region disposed between a pair of electrodes on a substrate. In the method described in European Patent Application EP-A-0536732 a solution containing component elements of the electroconductive thin film is applied onto the substrate - e.g. organic palladium solution is applied and heated to form a palladium or palladium oxide particulate thin film. By contrast to the foregoing method, the method in accordance with one aspect of the present invention, is one in which at least one of the electrodes has an electrode step at the surface of the substrate and wherein the method comprises a step of spraying a solution containing component elements of the electroconductive thin film through a nozzle onto the substrate, wherein during the step of spraying, an electric potential difference is produced between the pair of electrodes. In a preferred embodiment of the method in accordance with this one aspect of the present invention, during the step of spraying an electric potential difference is produced between the nozzle and the substrate. In a method in accordance with an alternative aspect of the present invention, the method comprises a step of spraying a solution containing component elements of the electroconductive thin film through a nozzle onto the substrate wherein during the step of spraying an electric potential difference is produced between the nozzle and the substrate. The aforesaid methods according to the one and the other aspects of the present invention can be applied to the manufacture of an electron source and of an image-forming apparatus, as set forth in the appended claims, claims 4 and 5, respectively. In the accompanying drawings: Figs. 1A and 1B are schematic views of an embodiment of surface conduction electron-emitting device according to the invention, showing a first basic structure; Figs. 2A through 2C are schematic sectional views of the surface conduction electron-emitting device of Figs.1A and 1B in different manufacturing steps; Fig. 3A is a schematic view of a surface conduction electron-emitting device according to the invention, illustrating a first method of manufacturing the same; Fig. 3B is a schematic view of a surface conduction electron-emitting device according to the invention, illustrating a second method of manufacturing the same; Figs. 4A and 4B are graphs schematically showing voltage waveforms that can be used for an energisation forming process; Fig. 5 is a schematic sectional view of the surface conduction electron-emitting device of Example 12 in a manufacturing step; Figs. 6A and 6B are schematic views of still another embodiment of surface conduction electron-emitting device according to the invention obtained by a first mode of manufacturing method according to the invention; Fig. 7 is a schematic view of an electron source having a simple matrix arrangement; Fig. 8 is a partially cut away schematic perspective view of a display panel comprising an electron source having a simple matrix arrangement; Figs. 9A and 9B are schematic views, illustrating two possible configurations of fluorescent film of display panel of an image forming apparatus; Fig. 10 is a block diagram of a drive circuit of an image forming apparatus for displaying images according to NTSC system television signals; Figs. 11AA through 11AC and 11BA through 11BC are schematic sectional views of the surface conduction electron-emitting device of Example 1 in different manufacturing steps; Fig. 12 is a block diagram of a gauging system for determining the electron emitting performance of a surface conduction electron-emitting device having the first basic structure; Figs. 13A and 13B are schematic plan views of the surface conduction electron-emitting device of Example 1, showing in particular its electron emitting region; Figs. 14A through 14C are schematic sectional views of the surface conduction electron-emitting device of Example 2 in different manufacturing steps; Figs. 15AA through 15AC and 15BA through 15BC are schematic sectional views of the surface conduction electron-emitting device of Example 3 in different manufacturing steps; Figs. 16A-16B are schematic plan views of the surface conduction electron-emitting device of Example 2, showing in particular its electron emitting region; and Fig. 17 is a schematic view of a conventional surface conduction electron-emitting device, showing its basic structure. A detailed description of a preferred embodiment will now be given by way of example. In this embodiment, the electroconductive film is made to have an area that poorly covers either one of the step portions formed by a pair of device electrodes at a location close to that step portion, preferably also close to the surface of the substrate so that fissures may be generated preferentially in that area to produce an electron-emitting region. Consequently, the electron-emitting region is located close to the device electrode of that step portion so that the electron beam emitted from the electron-emitting device is directly affected by the electric potential of that device electrode until it gets to the target with improved convergence. The convergence of the electron beam emitted from the electron-emitting region is greatly improved if the device electrode located close to the electron-emitting region is held to a low electric potential. Additionally, since the electron-emitting region is formed along the related device electrode and hence can be well controlled for its location and profile, it is not swerved unlike its counterpart of a conventional device and the electron beam emitted therefrom is similarly convergent as the electron beam emitted from a conventional electron-emitting device having a short distance between the device electrodes. Still additionally, since an area that poorly covers the related step portion is arranged in the electroconductive thin film to preferentially generate fissures and produce an electron-emitting region there, the level of power required for energization forming is remarkably reduced as compared with a conventional device so that consequently the produced electron-emitting device operates much better than any comparable conventional devices. The electron-emitting device can be operated better for electron emission and the electron beam emitted from the device can be controlled better if a control electrode for operating the electron-emitting device is arranged on the device electrodes or close to the device itself. If a control electrode is arranged on the substrate, the trajectory of the electron beam can be made free from distortions attributable to a charged-up state of the substrate. In the following method of manufacturing an electron-emitting device, an electroconductive thin film is formed by spraying a solution containing component elements of the electroconductive film. Such a method is safe and particularly suitable for producing a large display screen. The solution,containing component elements of the electroconductive thin film, is electrically charged and/or the device electrodes are held to different electric potentials during the step of spraying the solution in order to produce an area that poorly covers the related step portion so that fissures may be preferentially generated there to produce an electron-emitting region there because, with such an arrangement, the electron-emitting region may be formed along the related device electrode regardless of the profiles of the device electrodes and the electroconductive thin film and the electroconductive thin film may be strongly bonded to the substrate to produce a highly stable electron-emitting device. Thus, electron-emitting devices manufactured by the following method are highly uniform particularly in terms of the location and the profile of the electron-emitting region and hence operate uniformly. An electron source comprising a large number of electron-emitting devices each produced by the following method also operate uniformly and stably because the electron-emitting devices are manufactured by the above method. Additionally, since the power required for energization forming for the electron-emitting devices is not high, no significant voltage drop occurs in the process of energization forming so that consequently, the electron-emitting devices operate even more uniformly and stably. As the location and the profile of the electron-emitting region can be controlled well if the distance separating the device electrodes is greater than several µm or several hundred µm, the electron-emitting region is completely free from the problem of swerving and poor convergence of electron beam and hence electron-emitting devices according to the invention can be manufactured at a high yield. Consequently, an electron source that can generate highly convergent electron beams can be manufactured at low cost and a high yield. Additionally, in an image forming apparatus including such electron-emitting devices, electron beams are highly converged as they collide with the image-forming member of the apparatus so that it can produce fine and clear images that are free from blurs particularly in terms of color. Since the electron-emitting devices comprised in the apparatus operate uniformly and efficiently, it is suited for a large display screen. Now, the present invention will be described in greater detail by referring to preferred embodiments of electron-emitting device, of electron source comprising a large number of such electron-emitting devices and of image forming apparatus realized by using such an electron source. Preferred Embodiment This embodiment is configured to show a first basic structure as schematically illustrated in Figs. 1A and 1B. Note that, in Figs. 1A and 1B, reference numerals 1, 2 and 3 respectively denote a substrate, an electron-emitting region and an electroconductive thin film including an electron-emitting region, whereas reference numerals 4 and 5 denote device electrodes. Materials that can be used for the substrate 1 include quartz glass, glass containing impurities such as Na to a reduced concentration level, soda lime glass, glass substrate realized by forming an SiO 2 layer on soda lime glass by means of sputtering, ceramic substances such as alumina as well as Si. While the oppositely arranged device electrodes 4 and 5 may be made of any highly conducting material, preferred candidate materials include metals such as Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu and Pd and their alloys, printable conducting materials made of a metal or a metal oxide selected from Pd, Ag, RuO 2 , Pd-Ag and glass, transparent conducting materials such as In 2 O 3 -SnO 2 and semiconductor materials such as polysilicon. The distance L separating the device electrodes, the length W1 of the device electrodes, the contour of the electroconductive film 3 and other factors for designing a surface conduction electron-emitting device according to the invention may be determined depending on the application of the device. The distance L separating the device electrodes 4 and 5 is normally between several tens nm (hundred Å) and several hundred µm, although it is determined as a function of the performance of the aligner and the specific etching technique used in the photolithography process for the purpose of the invention as well as the voltage to be applied to the device electrodes, although a distance between several to several hundred µm is preferable because such a distance matches the exposing technique and the printing technique to be used for preparing a large display screen. While the length W1 and the film thicknesses d1, d2 of the device electrodes 4 and 5 are typically determined as a function of the electric resistances of the electrodes and other factors that may be involved when a large number of such electron-emitting devices are used, the length W1 is preferably between several µm and hundreds of several µm and the film thicknesses d1, d2 of the device electrodes 2 and 3 are between several tens nm (hundreds of several Å) and several µm. The surface conduction electron-emitting device has an electron-emitting region 2 located close to one of the device electrodes ( the device electrode 5 in Figs. 1A and 1B). As will be described in greater detail hereinafter, such an electron-emitting region 2 can be formed by differentiating the heights of the step portions of the device electrodes. Such differentiation between the step portions can be achieved by using films having different thicknesses d1 and d2 for the device electrodes 5 and 4 respectively or, alternatively, by forming an insulation layer typically made of SiO 2 film under either one of the device electrodes. The height of the step portion of each of the device electrodes is selected, taking the method of preparing the electroconductive thin film 3 and the morphology of the film 3 into consideration, in such way that the electroconductive thin film 3 shows a relatively high electric resistance and therefore a relatively reduced thickness due to poor step coverage or, if the electroconductive thin film is made of fine particles as will be described hereinafter, a relatively low density of fine particles in an area located close to the step portion of the device electrode having a greater thickness (or the step portion of the device electrode 5 in Figs. 1A and 1B) if compared with the remaining area of the electroconductive thin film. The step portion of the higher device electrode has a height typically more than five times, preferably more than ten times, as large as the thickness of the electroconductive thin film 3. The electroconductive thin film 3 is preferably a fine particle film in order to provide excellent electron-emitting characteristics. The thickness of the electroconductive thin film 3 is determined as a function of the electric resistance between the device electrodes 4 and 5 and the parameters for the forming operation that will be described hereinafter as well as other factors and preferably between several tenths and several hundred nm (several and several thousand Å), preferably between 1 and 50 nm (10 and 500 Å). The electroconductive thin film 4 normally shows a resistance per unit surface area between 10 2 and 10 7 Ω/cm 2 . The term a "fine particle film" as used herein refers to a thin film constituted of a large number of fine particles that may be loosely dispersed, tightly arranged or mutually and randomly overlapping (to form an island structure under certain conditions). If a fine particle film is used, the particle size is preferably between several tenths and several tens nm (several and several hundred Å), preferably between 1 and 20 nm (10 and 200 Å). By forming device electrodes having respective step portions whose heights are different from each other, the electroconductive thin film 3 that is prepared in a subsequent step comes to show a good step coverage relative to the device electrode 4 having a low step portion and a poor step coverage relative to the device electrode 5 having a high step portion. Note that the area of the electroconductive thin film 3 that poorly covers the step portion is preferably located close to the surface of the substrate. The electroconductive thin film 3 is made of a material selected from metals such as Pd, 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 carbon. The electron-emitting region 2 contains fissures and electrons are emitted from these fissures. The electron-emitting region 2 containing such fissures and the fissures themselves are produced as a function of the thickness, the state and the material of the electroconductive thin film 3 and the parameters for carrying out an energization forming process for the electron-emitting region 2. As described above, an area of the electroconductive thin film 3 is made to poorly covers the step portion of one of the device electrodes having a greater thickness at a position located close to the surface of the substrate by selecting an appropriate technique for preparing the electroconductive thin film in a subsequent step. With this arrangement, fissures can be generated preferentially in that area in the process of energization forming, which will be described hereinafter, to produce an electron-emitting region. As shown in Figs. 1A and 1B, a substantially linear electron-emitting region 2 is formed along the straight step portion of the device electrode having a greater thickness at a position close to the surface of the substrate, although the location of the electron-emitting region 2 is not limited to that of Fig. 1A or 1B. The fissures may contain electroconductive fine particles having a diameter of several tenths to several tens nm (several to hundreds of several Å.) The fine particles are part of some or all of the elements constituting the electroconductive thin film 3. Additionally, the electron-emitting region 2 containing fissures and the neighboring areas of the electroconductive thin film 3 may contain carbon and carbon compounds. Now, a preferred method of manufacturing the surface conduction electron-emitting device illustrated in Figs. 1A and 1B will be described by referring to Figs. 2A through 2C. 1) After thoroughly cleansing a substrate 1 with detergent and pure water, a material is deposited on the substrate 1 by means of vacuum deposition, sputtering or some other appropriate technique for a pair of device electrodes 4 and 5, which are then produced by photolithography. Then, the material of the electrodes is further deposited only on the device electrode 5, masking the other device electrode 4, to make the step portion of the device electrode 5 higher than that of the device electrode 4 (Fig. 2A). 2) An organic metal thin film is formed on the insulating substrate by spraying an organic metal solution through a nozzle 33 with a mask member 32 interposed therebetween as shown in Fig. 3A. The organic metal solution contains organic metal compounds of the metals that are principal components of the electroconductive thin film 3 to be formed there. Thereafter, the organic metal thin film is heated and baked to produce a patterned electroconductive thin film 3 (Fig. 2B). Note that the components in Fig. 3A that are same or similar to those of Figs. 1A and 1B are denoted by the same reference symbols. In Fig. 3A, reference numeral 31 denotes an area where organic metal solution fine particles are applied and reference numeral 34 denotes organic metal solution fine particles. While the organic metal solution is sprayed with a mask member 32 interposed between the nozzle 33 and the substrate 1 in order to omit an independent patterning step in the above description, an electroconductive thin film 3 may alternatively be formed without such a mask member 32 by using an appropriate photolithography technique such as lift-off or etching. 3) Thereafter, the device electrodes 4 and 5 are subjected to a process referred to as "energization forming". More specifically, the device electrodes 4 and 5 are electrically energized by means of a power source (not shown) until a substantially linear electron-emitting region 3 is produced at a position of the electroconductive thin film 3 near the step portion of the device electrode 5 (Fig. 2C) as an area where the electroconductive thin film is structurally modified. In other words, the electron-emitting region 2 is a portion of the electroconductive thin film 3 that is locally destroyed, deformed or transformed as a result of energization forming to have a modified structure. Figs. 4A and 4B show two different pulse voltages that can be used for energization forming.The voltage to be used for energization forming preferably has a pulse waveform. A pulse voltage having a constant height or a constant peak voltage may be applied continuously as shown in Fig. 4A or, alternatively, a pulse voltage having an increasing height or an increasing peak voltage may be applied as shown in Fig. 4B.Firstly, a pulse voltage having a constant height will be described. In Fig. 4A, the pulse voltage has a pulse width T1 and a pulse interval T2, which are typically between 1 µsec. and 10 msec. and between 10 µsec. and 100 msec. respectively. The height of the triangular wave (the peak voltage for the energization forming operation) may be appropriately selected depending on the profile of the surface conduction electron-emitting device. The voltage is typically applied for tens of several minutes in vacuum of an appropriate degree. Note, however, that the pulse waveform is not limited to triangular and a rectangular or some other waveform may alternatively be used.Now, a pulse voltage having an increasing height will be described. Fig. 4B shows a pulse voltage whose pulse height increases with time. In Fig. 4B, the pulse voltage has an width T1 and a pulse interval T2 that are substantially similar to those of Fig. 4A. The height of the triangular wave (the peak voltage for the energization forming operation) is increased at a rate of, for instance, 0.1V per step. Note again that the pulse waveform is not limited to triangular and a rectangular or some other waveform may alternatively be used.The energization forming operation will be terminated as appropriately judged by measuring the current running through the device electrodes when a voltage that is sufficiently low and cannot locally destroy or deform the electroconductive thin film 3 is applied to the device during an interval T2 of the pulse voltage. Typically the energization forming operation is terminated when a resistance greater than 1M ohms is observed for the device current running through the electroconductive thin film 3 while applying a voltage of approximately 0.1V to the device electrodes. 4) After the energization forming operation, the device is preferably subjected to an activation process. An activation process is a process to be carried out in order to dramatically change the device current (film current) If and the emission current Ie. In an activation process, a pulse voltage may be repeatedly applied to the device in a vacuum atmosphere. In this process, a pulse voltage is repeatedly applied as in the case of energization forming in an organic gas containing atmosphere. Such an atmosphere may be produced by utilizing the organic gas remaining in a vacuum chamber after evacuating the chamber by means of an oil diffusion pump or a rotary pump or by sufficiently evacuating a vacuum chamber by means of an ion pump and thereafter introducing the gas of an organic substance into the vacuum. The gas pressure of the organic substance is determined as a function of the profile of the electron-emitting device to be treated, the profile of the vacuum chamber, the type of the organic substance and other factors. The organic substances that can be suitably used for the purpose of the activation process include aliphatic hydrocarbons such as alkanes, alkenes and alkynes, aromatic hydrocarbons, alcohols, aldehydes, ketones, amines, organic acids such as, phenol, carbonic acids and sulfonic acids. Specific examples include saturated hydrocarbons expressed by general formula C n H 2n+2 such as methane, ethane and propane, unsaturated hydrocarbons expressed by general formula C n H 2n such as ethylene and propylene, benzene, toluene, methanol, ethanol, formaldehyde, acetaldehyde, acetone, methylethylketone, methylamine, ethylamine, phenol, formic acid, acetic acid and propionic acid. As a result of this process, carbon and carbon compounds contained in the atmosphere are deposited on the device to remarkably change the device current If and the emission current Ic.The activation process is terminated whenever appropriate, observing the device current If and the emission current Ie. The pulse width, the pulse interval and the pulse wave height are appropriately selected.For the purpose of the invention, carbon and carbon compounds typically refer to graphite (including so-called highly oriented pyrolytic graphite (HOPG), pyrolitic graphite (PG) and glassy carbon (GC), of which HOPG has a nearly perfect crystal structure of graphite and PG contains crystal grains having a size of about 20 nm (200 Å) and has a somewhat disturbed crystal structure, while GC contains crystal grains having a size as small as 2 nm (20 Å) and has a crystal structure that is remarkably in disarray) and non-crystalline carbon (including amorphous carbon and a mixture of amorphous carbon and fine crystals of graphite) and the thickness of film formed by deposition is preferably less than 50 nm (500 Å) and more preferably less than 30 nm (300 Å). 5) The surface conduction electron-emitting device is then subjected to a stabilizing step. This step is designed to evacuate vacuum container arranged for manufacturing the device to eliminate organic substances therefrom. Preferably, an oil free vacuum apparatus is used to evacuate the vacuum container so that it may not produce any oil that can adversely affect the performance of the electron-emitting device. Specific examples of oil free vacuum apparatus that can be used for the purpose of the invention include a sorption pump and an ion pump. If an oil diffusion pump of a rotary pump is used to evacuate the container to utilize the organic gas generated from one or more than one ingredients the oil of such a pump in the preceding activation step, the partial pressure of the oil ingredients has to be held as low as possible. The partial pressure of the organic gas within the vacuum container is preferably less than 1x10 -6 Pa (1x10 -8 Torr) and more preferably less than 1x10 -8 Pa (1x10 -10 Torr) under the condition where carbon and carbon compounds are no longer deposited on the electron-emitting device. For evacuating the vacuum container, it is preferable that the entire container is heated so that the molecules of the organic substances adsorbed to the inner walls of the container and the electron-emitting device may easily move away therefrom and become removed from the container. The heating operation may preferably be conducted at 80 to 200°C for more than five hours, although values for these parameters should be appropriately selected depending on the size and shape of the vacuum container, the configuration of the electron-emitting device and other considerations. High temperature is advantageous for causing the adsorbed molecules to move away. While the temperature range of 80 to 200°C is selected to minimize the possible damage by heat to the electron source to be prepared in the container, a higher temperature may be recommended if the electron source is resistant against heat. It is also necessary to keep the overall pressure in the vacuum container as low as possible. It is preferably less than 1 to 4x10 -5 Pa (1 to 3x10 -7 Torr) and more preferably less than 1x10 -6 Pa (1x10 -8 Torr). After completing the stabilizing step, the electron-emitting device is preferably driven in an atmosphere same as that in which said stabilizing process is terminated, although a different atmosphere may also be used. So long as the organic substances are satisfactorily removed, a lower degree of vacuum may be permissible for a stabilized operation of the device. With the use of such a vacuum condition, any additional deposition of carbon and carbon compounds is effectively prevented to stabilize both the device current If and the emission current Ie. In the foregoing method, a pair of device electrodes 4 and 5 are so formed that their step portions show different heights and a solution containing component elements of the electroconductive thin film 3 is sprayed onto them through a nozzle. As the step portions of the device electrodes are formed with different heights manufacturing method, the electroconductive thin film 3 formed thereafter is made to have a good step coverage for the device electrode 4 having a low step portion and a poor step coverage for the device electrode 5 having a high step portion. Thus, in the above described energization forming step, fissures can be preferentially generated in the poor step coverage area of the electroconductive thin film 3 to produce there an electron-emitting region 2, which is substantially linear and located close to the step portion of the device electrode 5 as shown in Figs. 1A and 1B. The electroconductive thin film, instead may be formed so as to show a good step coverage for one of the device electrodes and a poor step coverage for the other device electrode by tilting the substrate 1 (or the nozzle 33) of Fig. 3A as shown in Fig. 5 without differentiating the heights of the step portions of the device electrodes 4 and 5 unlike those of the device electrodes 4 and 5 of the electron-emitting device of Figs. 1A and 1B. Note that the components in Fig. 5 that are similar to those of Fig. 3A are denoted by the same reference symbols. Thus, with such a manufacturing method, since the electron-emitting device is prepared by means of a process exactly same as that of preparing a device comprising device electrodes whose step portions have different heights, a substantially linear electron-emitting region is formed in the energization forming step at a position close to the step portion of one of the device electrodes without differentiating the heights of the step portions of the device electrodes to consequently reduce the number of steps necessary for preparing the device electrodes and make the method advantageous. Now, electrostatic spraying to be used for the purpose of the invention will be described by referring to Fig. 3B. Fig. 3B schematically illustrates the principle of electrostatic spraying. An electrostatic spraying system that can be used for the purpose of the invention comprises a nozzle 131 for spraying an organic metal solution, a generator for atomizing an organic metal solution 132, a tank 133 for storing an organic metal solution, a high voltage DC power source for electrically charging fine particles of organic metal atomized in the generator 134 to a level of -10 to -100kV and a table 135 for carrying a substrate 1. The nozzle 131 can be so operated as to two-dimensionally scan the upper surface of the substrate 1 at a constant rate. The substrate 1 is grounded. With the above arrangement, negatively charged fine organic metal solution particles are sprayed through the nozzle 131 and move with an accelerated speed until they collide with the grounded substrate 1 and become deposited there to produce an organic metal film that is more cohesive than a film produced by any other spray method. The electroconductive thin film can be subjected to a patterning operation by means of photolithography as described above by referring to Fig. 3A and, if a mask member 32 as shown in Fig. 3A is used with electrostatic spraying, a highly cohesive, tight and uniform film can be produced by applying a voltage between the nozzle 33 and the mask member 32 to electrically charge fine particles of organic metal solution 34 sprayed from the nozzle 33 to a level of 10 to 100kV to accelerate them before they collide with the substrate 1. The surface conduction electron-emitting device can be prepared by a second method of spraying a solution containing component elements of the electroconductive thin film through a nozzle, applying a voltage to a pair of device electrodes formed on a substrate. More specifically, with the second method, unlike the first basic arrangement of forming a pair of device electrodes that are arranged asymmetrically, the pair of device electrodes physically appear identical as shown in Figs. 5A and 5B and differentiated only by the electric potentials of the electrodes so that the electroconductive thin film formed from an organic metal solution sprayed through a nozzle is made more cohesive and tight for the device electrode with a lower electric potential than for the device electrode with a higher electric potential and provides a poor step coverage for the device electrode with a higher electric potential. Consequently, a substantially linear electron-emitting region 2 is formed at a position close to the step portion of the device electrode with a lower electrode as shown in Figs. 6A and 6B. For spraying a solution containing component elements of the electroconductive thin film from a nozzle with the second manufacturing method, it is preferable to provide an electric potential difference between the nozzle and the substrate to enhance the adhesion between the substrate and the device electrodes and the electroconductive thin film to make the prepared surface conduction electron-emitting device operate more stably. As described above, a substantially linear electron-emitting region is formed along one of the device electrodes of a surface conduction electron-emitting device at a position close to the step portion of the electrode and the surface of the substrate if the device electrodes are separated by a large distance so that the electron-emitting region can be prepared uniformly in terms of position and profile and the surface conduction electron-emitting device operates excellently as will be described hereinafter. Additionally, since a nozzle is used to spray an organic metal solution onto the substrate to produce an electroconductive thin film, the substrate is not rotated as is the case when a spinner is used with a conventional manufacturing method. It is advantageous and effective when a large number of such surface conduction electron-emitting devices are arranged to produce an electron source because otherwise a large substrate carrying a number of surface conduction electron-emitting device would have been made to rotate with a risk of damage. An electron source and an image forming apparatus incorporating such an electron source can be manufactured with relatively simple equipment. An electron source can be realized by arranging surface conduction electron-emitting devices, which will be described below. For instance, a number of electron-emitting devices may be arranged in a ladder-like arrangement to realize an electron source as described earlier by referring to the prior art. Alternatively, an electron source may be realized by arranging n Y-directional wires on m X-directional wires with an interlayer insulation layer interposed therebetween and placing a surface conduction electron-emitting device close to each crossing of the wires, the pair of electrodes of device being connected to the corresponding X- and Y-directional wires respectively. This arrangement is referred to as simple matrix wiring arrangement, which will be described hereinafter in detail. Because of the basic characteristics of a surface conduction electron-emitting device as described above, the rate at which the device emit electrons can be controlled for by controlling the wave height and the wave width of the pulse voltage applied to the opposite electrodes of the device above the threshold voltage level if the applied device voltage Vf exceeds the threshold voltage Vth. On the other hand, the device does not practically emit any electron below the threshold voltage Vth. Therefore, regardless of the number of electron-emitting devices arranged in an apparatus, desired surface conduction electron-emitting devices can be selected and controlled for electron emission in response to an input signal by applying a pulse voltage to each of the selected devices if a simple matrix wiring arrangement is employed. An electron source having a simple matrix wiring arrangement is realized on the basis of the above simple principle. Fig. 7 is a schematic plan view of an electron source according to the invention and having a simple matrix wiring arrangement. In Fig. 7, the electron source comprises a substrate 1 which is typically made of a glass panel and has a profile that depends on the number and the application of the surface conduction electron-emitting devices 104 arranged thereon. There are provided a total of m X-directional wires 102, which are donated by Dx1, Dx2, ..., Dxm and made of an electroconductive metal produced by vacuum deposition, printing or sputtering. These wires are so designed in terms of material, thickness and width that, if necessary, a substantially equal voltage may be applied to the surface conduction electron-emitting devices. A total of n Y-directional wires are arranged and donated by Dy1, Dy2, ..., Dyn, which are similar to the X-directional wires in terms of material, thickness and width. An interlayer insulation layer (not shown) is disposed between the m X-directional wires and the n Y-directional wires to electrically isolate them from each other. Both m and n are integers. The interlayer insulation layer (not shown) is typically made of SiO 2 and formed on the entire surface or part of the surface of the insulating substrate 1 to show a desired contour by means of vacuum deposition, printing or sputtering. The thickness, material and manufacturing method of the interlayer insulation layer are so selected as to make it withstand the potential difference between any of the X-directional wires 102 and any of the Y-directional wires 103 observable at the crossing thereof. Each of the X-directional wires 102 and the Y-directional wires 103 is drawn out to form an external terminal. The oppositely arranged electrodes (not shown) of each of the surface conduction electron-emitting devices 104 are connected to related one of the m X-directional wire 102 and related one of the n Y-directional wires 103 by respective connecting wires 105 which are made of an electroconductive metal and formed by means of an appropriate technique such as vacuum deposition, printing or sputtering. In view of the method used for driving the electron source, which will be described hereinafter, the electron-emitting region of each surface conduction electron-emitting device is preferably formed close to the device electrode that is connected to the corresponding X-directional wire 102. The electroconductive metal material of the device electrodes and that of the m X-directional wires 102, the n Y-directional wires 103 and the connecting wires 105 may be same or contain a common element as an ingredient. Alternatively, they may be different from each other. These materials may be appropriately selected typically from the candidate materials listed above for the device electrodes. If the device electrodes and the connecting wires are made of a same material, they may be collectively called device electrodes without discriminating the connecting wires. The surface conduction electron-emitting devices 104 may be formed either on the substrate 1 or on the interlayer insulation layer (not shown). As will be described in detail hereinafter, the X-directional wires 102 are electrically connected to a scan signal application means (not shown) for applying a scan signal to a selected row of surface conduction electron-emitting devices 104. On the other hand, the Y-directional wires 103 are electrically connected to a modulation signal generation means (not shown) for applying a modulation signal to a selected column of surface conduction electron-emitting devices 104 and modulating the selected column according to an input signal. Note that the drive signal to be applied to each surface conduction electron-emitting device is expressed as the voltage difference of the scan signal and the modulation signal applied to the device. Now, an image forming apparatus comprising an electron source with a simple matrix wiring arrangement according to the invention will be described by referring to Figs. 8 through 10, of which Fig. 8 is a schematic perspective view of the display panel 201 of the image forming apparatus and Figs. 9A and 9B are two possible configurations of the fluorescent film 114 of the display panel, whereas Fig. 10 is a block diagram of a drive circuit for displaying television images according to NTSC television signals. In Fig. 8, reference numeral 1 denotes an electron source substrate carrying thereon a plurality of surface conduction electron-emitting devices according to the invention. Otherwise, the display panel comprises a rear plate 111 rigidly holding the electron source substrate 1, a face plate 116 prepared by laying a fluorescent film 114 that operates as an image forming member and a metal back 115 on the inner surface of a glass substrate 113 and a support frame 112. The rear plate 111, the support frame 112 and the face plate 116 are bonded together by applying frit glass to the junctions of the these components and baked to 400 to 500°C for more than 10 minutes in the atmosphere or in nitrogen and hermetically and airtightly sealed to produce an envelope 118. In Fig. 8, reference numeral 104 denotes an electron-emitting device and reference numerals 102 and 103 respectively denote the X-directional wiring and the Y-directional wiring connected to the respective device electrodes 4 and 5 of each electron-emitting device (Figs. 1A and 1B). While the envelope 118 is formed of the face plate 116, the support frame 112 and the rear plate 111 in the above described embodiment, the rear plate 31 may be omitted if the substrate 1 is strong enough by itself because the rear plate 111 is provided mainly for reinforcing the substrate 1. If such is the case, an independent rear plate 111 may not be required and the substrate 1 may be directly bonded to the support frame 112 so that the envelope 118 is constituted of a face plate 116, a support frame 112 and a substrate 1. The overall strength of the envelope 118 may be increased by arranging a number of support members called spacers (not shown) between the face plate 116 and the rear plate 111. Figs. 9A and 9B schematically illustrate two possible arrangements of fluorescent film. While the fluorescent film 114 comprises only a single fluorescent body 122 if the display panel is used for showing black and white pictures, it needs to comprise for displaying color pictures black conductive members 121 and fluorescent bodies 122, of which the former are referred to as black stripes (Fig. 9A) or members of a black matrix (Fig. 9B) depending on the arrangement of the fluorescent bodies. Black stripes or members of a black matrix are arranged for a color display panel so that the fluorescent bodies 122 of three different primary colors are made less discriminable and the adverse effect of reducing the contrast of displayed images of external light is minimized in the fluorescent film 114 by blackening the surrounding areas. While graphite is normally used as a principal ingredient of the black stripes, other conductive material having low light transmissivity and reflectivity may alternatively be used. A precipitation or printing technique may suitably be used for applying a fluorescent material to form fluorescent bodies 122 on the glass substrate 113 regardless of black and white or color display. An ordinary metal back 115 is arranged on the inner surface of the fluorescent film 114 as shown in Fig. 8. The metal back 115 is provided in order to enhance the luminance of the display panel by causing the rays of light emitted from the fluorescent bodies 122 (Fig. 9A or 9B) and directed to the inside of the envelope to mirror-reflect toward the face plate 116, to use it as a high voltage electrode Hv for applying an accelerating voltage to electron beams and to protect the fluorescent bodies 122 against damages that may be caused when negative ions generated inside the envelope 118 collide with them. It is prepared by smoothing the inner surface of the fluorescent film 114 (in an operation normally called "filming") and forming an Al film thereon by vacuum deposition after forming the fluorescent film 114. A transparent electrode (not shown) may be formed on the face plate 116 facing the outer surface of the fluorescent film 114 in order to raise the conductivity of the fluorescent film 34. Care should be taken to accurately align each set of color fluorescent bodies 122 and an electron-emitting device 104, if a color display is involved, before the above listed components of the envelope are bonded together. The envelope 118 is evacuated to a degree of vacuum of 10 -4 to 10 -5 Pa (10 -6 to 10 -7 Torr) or higher degree via an evacuation pipe (not shown) and hermetically sealed. More specifically, the inside of the envelope 118 is evacuated by means of an ordinary vacuum system typically comprising a rotary pump or a turbo pump to a degree of vacuum of about 10 -4 Pa (10 -6 Torr) and the surface conduction electron-emitting devices in the inside are subjected to an energization forming step and an activation step to produce electron-emitting regions 2 as described earlier by applying a voltage to the device electrodes 4 and 5 via the external terminals Dx1 through Dxm and Dy1 through Dyn. Thereafter, the vacuum system is switched to an ultra-high vacuum system typically comprising an ion pump, while baking the apparatus at 80 to 200°C. A getter process may be conducted in order to maintain the achieved degree of vacuum in the inside of the envelope 118 immediately before or after it is hermetically sealed. In a getter process, a getter arranged at a predetermined position in the envelope 118 is heated by means of a resistance heater or a high frequency heater to form a film by vapor deposition. A getter typically contains Ba as a principal ingredient and can maintain a high degree of vacuum by the adsorption effect of the vapor deposition film. The above described display panel 201 can be driven by a drive circuits as shown in Fig. 10. In Fig. 10, reference numeral 201 denotes a display panel. Otherwise, the circuit comprises a scan circuit 202, a control circuit 203, a shift register 204, a line memory 205, a synchronizing signal separation circuit 206 and a modulation signal generator 207. Vx and Va in Fig. 10 denote DC voltage sources. As shown in Fig. 10, the display panel 201 is connected to external circuits via external terminals Dx1 through Dxm, Dy1 through Dyn and high voltage terminal Hv, of which terminals Dx1 through Dxm are designed to receive scan signals for sequentially driving on a one-by-one basis the rows (of n devices) of an electron source in the apparatus comprising a number of surface-conduction type electron-emitting devices arranged in the form of a matrix having m rows and n columns. On the other hand, external terminals Dy1 through Dyn are designed to receive a modulation signal for controlling the output electron beam of each of the surface-conduction type electron-emitting devices of a row selected by a scan signal. High voltage terminal Hv is fed by the DC voltage source Va with a DC voltage of a level typically around 10kV, which is sufficiently high to energize the fluorescent bodies of the selected surface-conduction type electron-emitting devices. The scan circuit 202 operates in a manner as follows. The circuit comprises M switching devices (of which only devices S1 and Sm are specifically indicated in Fig. 10), each of which takes either the output voltage of the DC voltage source Vx or 0[V] (the ground potential level) and comes to be connected with one of the terminals Dx1 through Dxm of the display panel 201. Each of the switching devices Sl through Sm operates in accordance with control signal Tscan fed from the control circuit 203 and can be easily prepared by combining transistors such as FETs. The DC voltage source Vx of this circuit is designed to output a constant voltage such that any drive voltage applied to devices that are not being scanned due to the performance of the surface conduction electron-emitting devices (or the threshold voltage for electron emission) is reduced to less than threshold voltage. The control circuit 203 coordinates the operations of related components so that images may be appropriately displayed in accordance with externally fed video signals. It generates control signals Tscan, Tsft and Tmry in response to synchronizing signal Tsync fed from the synchronizing signal separation circuit 206, which will be described below. The synchronizing signal separation circuit 206 separates the synchronizing signal component and the luminance signal component form an externally fed NTSC television signal and can be easily realized using a popularly known frequency separation (filter) circuit. Although a synchronizing signal extracted from a television signal by the synchronizing signal separation circuit 206 is constituted, as well known, of a vertical synchronizing signal and a horizontal synchronizing signal, it is simply designated as Tsync signal here for convenience sake, disregarding its component signals. On the other hand, a luminance signal drawn from a television signal, which is fed to the shift register 204, is designed as DATA signal. The shift register 204 carries out for each line a serial/parallel conversion on DATA signals that are serially fed on a time series basis in accordance with control signal Tsft fed from the control circuit 203. (In other words, a control signal Tsft operates as a shift clock for the shift register 204.) A set of data for a line that have undergone a serial/parallel conversion (and correspond to a set of drive data for N electron-emitting devices) are sent out of the shift register 204 as n parallel signals Idl through Idn. The line memory 205 is a memory for storing a set of data for a line, which are signals Id1 through Idn, for a required period of time according to control signal Tmry coming from the control circuit 203. The stored data are sent out as I'd1 through I'dn and fed to modulation signal generator 207. Said modulation signal generator 207 is in fact a signal line that appropriately drives and modulates the operation of each of the surface-conduction type electron-emitting devices according to each of the image data I'd1 through I'dn and output signals of this device are fed to the surface-conduction type electron-emitting devices in the display panel 201 via terminals Dy1 through Dyn. The electron-emitting device described above has the following features in terms of emission current Ie. Firstly, there exists a clear threshold voltage Vth and the device emit electrons only a voltage exceeding Vth is applied thereto. Secondly, the level of emission current Ie changes as a function of the change in the applied voltage above the threshold level Vth, although the value of Vth and the relationship between the applied voltage and the emission current may vary depending on the materials, the configuration and the manufacturing method of the electron-emitting device. More specifically, when a pulse-shaped voltage is applied to an electron-emitting device according to the invention, practically no emission current is generated so far as the applied voltage remains under the threshold level, whereas an electron beam is emitted once the applied voltage rises above the threshold level. It should be noted here that the intensity of an output electron beam can be controlled by changing the peak level of the pulse-shaped voltage. Additionally, the total amount of electric charge of an electron beam can be controlled by varying the pulse width. Thus, either modulation method or pulse width modulation may be used for modulating an electron-emitting device in response to an input signal. With voltage modulation, a voltage modulation type circuit is used for the modulation signal generator 207 so that the peak level of the pulse shaped voltage is modulated according to input data, while the pulse width is held constant. With pulse width modulation, on the other hand, a pulse width modulation type circuit is used for the modulation signal generator 207 so that the pulse width of the applied voltage may be modulated according to input data, while the peak level of the applied voltage is held constant. Although it is not particularly mentioned above, the shift register 204 and the line memory 205 may be either of digital or of analog signal type so long as serial/parallel conversions and storage of video signals are conducted at a given rate. If digital signal type devices are used, output signal DATA of the synchronizing signal separation circuit 206 needs to be digitized. However, such conversion can be easily carried out by arranging an A/D converter at the output of the synchronizing signal separation circuit 206. It may be needless to say that different circuits may be used for the modulation signal generator 207 depending on if output signals of the line memory 205 are digital signals or analog signals. If digital signals are used, a D/A converter circuit of a known type may be used for the modulation signal generator 207 and an amplifier circuit may additionally be used, if necessary. As for pulse width modulation, the modulation signal generator 207 can be realized by using a circuit that combines a high speed oscillator, a counter for counting the number of waves generated by said oscillator and a comparator for comparing the output of the counter and that of the memory. If necessary, an amplifier may be added to amplify the voltage of the output signal of the comparator having a modulated pulse width to the level of the drive voltage of a surface-conduction type electron-emitting device according to the invention. If, on the other hand, analog signals are used with voltage modulation, an amplifier circuit comprising a known operational amplifier may suitably be used for the modulation signal generator 207 and a level shift circuit may be added thereto if necessary. As for pulse width modulation, a known voltage control type oscillation circuit (VCO) may be used with, if necessary, an additional amplifier to be used for voltage amplification up to the drive voltage of' surface-conduction type electron-emitting device. With an image forming apparatus having a configuration as described above, to which the present invention is applicable, the electron-emitting devices 104 emit electrons as a voltage is applied thereto by way of the external terminals Dx1 through Dxm and Dy1 through Dyn. Then, the generated electron beams are accelerated by applying a high voltage to the metal back 115 or a transparent electrode (not shown) by way of the high voltage terminal Hv. The accelerated electrons eventually collide with the fluorescent film 114, which by turn glows to produce images. The above described configuration of image forming apparatus is only an example to which the present invention is applicable and may be subjected to various modifications. The TV signal system to be used with such an apparatus is not limited to a particular one and any system such as NTSC, PAL or SECAM may feasibly be used with it. It is particularly suited for TV signals involving a larger number of scanning lines (typically of a high definition TV system such as the MUSE system) because it can be used for a large display panel comprising a large number of pixels. Specific examples will now be described in detail. Example 1 In this example, a number of surface conduction electron-emitting devices having a configuration illustrated in Figs. 1A and 1B were prepared along with a number of surface conduction electron-emitting devices for the purpose of comparison and they were tested for performance. Fig. 1A is a plan view and Fig. 1B is a cross sectional side view of a surface conduction electron-emitting device according to the invention and used in this example. Referring to Figs. 1A and 1B, W1 denotes the width of the device electrodes 4 and 5 and W2 denotes the width of the electroconductive thin film 3, while L denotes the distance separating the device electrodes 4 and 5 and d1 and d2 respectively denotes the height of the device electrode 4 and that of the device electrode 5. Figs. 11AA through 11AC show a surface conduction electron-emitting device arranged on substrate A in different manufacturing steps whereas Figs. 11BA through 11BC shows another surface conduction electron-emitting device also in different manufacturing steps, the latter being prepared for the purpose of comparison and arranged on substrate B. Four identical electron-emitting devices were produced on each of the substrates A and B. 1) After thoroughly cleansing a quartz glass plate with a detergent, pure water and an organic solvent for each of the substrates A and B, a Pt film was formed thereon by sputtering to a thickness of 30 nm (300Å) for a pair of device electrodes for each device, using a mask. For the substrate A, Pt was deposited to a further thickness of 80 nm (800Å) for one of the device electrodes, device electrode 4 (cf. Figs. 11AA and 11BA). Both of the device electrodes 4 and 5 on the substrate B had a thickness of 30 nm (300Å), whereas the device electrodes 4 and 5 on the substrate A had respective thicknesses of 30 and 110 nm (300Å and 1,100Å). The device electrodes were separated by a distance L of 100µm for both the substrate A and the substrate B.Thereafter, a Cr film (not shown) to be used for lift-off is formed by vacuum deposition to a thickness of 100nm (1,000Å) on each of the substrates A and B for the purpose of patterning the electroconductive thin film 3. At the same time, an opening of 100µm corresponding to the width W2 of the electroconductive thin film 3 was formed in the Cr film.The subsequent steps were identical for both the substrate A and the substrate B. 2) Thereafter, a solution of organic palladium (ccp-4230: available from Okuno Pharmaceutical Co., Ltd.) was sprayed onto the substrate 1 with the device electrodes 4 and 5 formed thereon. In the course of this operation, a voltage of 5kV was applied between the nozzle and the device electrodes to charge and accelerate the fine liquid particles of organic palladium solution. Thereafter, the organic Pd thin film was heated and baked at 300°C for 10 minutes in the atmosphere to produce an electroconductive thin film 3 mainly constituted by fine PdO particles. The film had a thickness of about 10 nm (100Å) and an electric resistance of Rs=5x10 3 Ω/□. Subsequently, the Cr film and the electroconductive thin film 3 were wet etched to produce an electroconductive thin film 3 having a desired pattern by means of an acidic wet etchant. (Figs. 11AB and 11BB) 3) Then, the substrates A and B were moved into the vacuum apparatus 55 of a gauging system as illustrated in Fig. 12 and heated in vacuum to chemically reduce the PdO to Pd in the electroconductive thin film 3 of each sample device. Then, the sample devices were subjected to an energization forming process to produce an electron-emitting region 2 by applying a device voltage Vf between the device electrodes 4 and 5 of each device (Figs. 11AC and 11BC). The applied voltage was a pulse voltage as shown in Fig. 4B (which was, however, not triangular but rectangularly parallelepipedic). Referring to Fig. 4B, the pulse width of T1=1msec and the pulse interval of T2=10msec were used. The wave height of the rectangularly parallelepipedic wave was increased gradually. 4) Subsequently, the substrates A and B were subjected to an activation process, maintaining the inside pressure of the vacuum apparatus 55 to about 10 -3 Pa (10 -5 Torr). A pulse voltage (which was, however, not triangular but rectangularly parallelepipedic) was applied to each sample device to drive it. The pulse width of T1=1msec and the pulse interval of T2=10msec were used and the drive voltage (wave height) was 15V. The activation process was terminated in 30 minutes. 5) Then, each sample surface conduction electron-emitting device on the substrates A and B was driven to operate within the vacuum apparatus 55 of about 10 -4 Pa (10 -6 Torr) in order to see the device current If and the emission current Ie. After the measurement, the electron-emitting regions 2 of the devices on the substrates A and B were microscopically observed. As for the parameters of the measurement, the distance H between the anode 54 and the electron-emitting device was 5mm and the anode voltage and the device voltage Vf were respectively 1kV and 18V. As a result of the measurement, the device current If and the emission current of each device on the substrate B were 1.2mA±25% and 1.0µA±30% respectively. On the other hand, the device current If and the emission current of each device on the substrate A were 1.0mA±5% and 0.95µA±4.5% to show a remarkably reduced deviation among the devices. At the same time, a fluorescent member was arranged on the anode 54 to see the bright spot on the fluorescent member produced by an electron beam emitted from each sample electron-emitting device surface and it was observed that the bright spot produced by a device on the substrate A was smaller than its counterpart produced by a device on the substrate B by about 30µm. Figs. 13A and 13B schematically illustrate what was observed for the electron-emitting region 2 of the electroconductive thin film 3 of each device on the substrate A and B. As seen from Figs. 13A and 13B, a substantially linear electron-emitting region 2 was observed near the device electrode 5 having a higher step portion (having a larger thickness) in each of the four devices on the substrate A, whereas a swerved electron-emitting region 2 was observed in the electroconductive thin film 3 of each of the four devices on the substrate B prepared for comparison. The electron-emitting region 2 was swerved by about 50pm at the middle point. As described above, the surface conduction electron-emitting device comprising a substantially linear electron-emitting region 2 located close to one of the device electrodes operates remarkably well to emit highly convergent electron beams without showing any substantial deviation in the performance. It was also found that the surface conduction electron-emitting device produces a relatively large bright spot on the fluorescent member if the electric potential of the device electrode 5 is made higher than that of the device electrode 4. Example 2 In this example, the second method of manufacturing the surface conduction electron-emitting device was used as will be described below by referring to Figs. 14A through 14C. 1) After thoroughly cleansing a quartz glass plate with a detergent, pure water and an organic solvent for a substrates 1, a Pt film was formed thereon by sputtering to a thickness of 30 nm (300Å) for a pair of device electrodes (Fig. 34A). The device electrodes were separated by a distance L of 100µm. 2) Thereafter, a solution of organic palladium (ccp-4230: available from Okuno Pharmaceutical Co., Ltd.) was sprayed onto the substrate 1 from a nozzle, while applying a voltage of 5kV to the device electrodes 4 and 5 from a power source 11. As in the case of Example 1, a voltage of 5kV was also applied between the device electrodes and the nozzle in order to charge the fine drops of the sprayed organic palladium solution with electricity and accelerate their speed before they got to the substrate 1. As a result, a dense film was formed on the device electrode 4 having a lower electric potential, whereas a less dense film was formed on the other device electrode 5 having a higher electric potential to produce a poorly covered area on the step portion of the device electrode 5. Thereafter, the organic Pd thin film was heated and baked at 300°C for 10 minutes in the atmosphere to produce an electroconductive thin film 3 mainly constituted by fine PdO particles. The film had a thickness of about 10 nm (100Å) and an electric resistance of Rs=5x10 3 Ω/□. Subsequently, any unnecessary areas of the Cr film were removed by patterning to produce an electroconductive thin film 3 having a desired profile (Fig. 14B). 3) Then, the substrates A and B were moved into the vacuum apparatus 55 of a gauging systemtem as illustrated in Fig. 12 and heated in vacuum to chemically reduce the PdO to Pd in the electroconductive thin film 3 of each sample device. Then, the sample device was subjected to an energization forming process to produce an electron-emitting region 2 by applying a device voltage Vf between the device electrodes 4 and 5 of each device (Fig. 14C). The applied voltage was a pulse voltage as shown in Fig. 4B (which was, however, not triangular but rectangularly parallelepipedic). The peak value of the wave height of the rectangularly parallelepipedic pulse voltage was gradually increased with time as shown in Fig. 4B. The pulse width of T1=1msec and the pulse interval of T2=10msec were used. Thereafter, as in case of Example 1, the sample device was subjected to an activation process and then tested for performance. It was found that the device performed well for electron emission like the devices of Example 1. When viewed through a microspcope, a substantially linear electron-emitting region 2 was observed along and near the device electrode 5 that had been held to a higher electric potential for spraying an organic palladium solution through a nozzle. Example 3 In this example, surface conduction electron-emitting devices according to the invention and having a configuration illustrated in Figs. 6A and 6B were prepared along with surface conduction electron-emitting devices for the purpose of comparison and they were tested for performance. The electron emission performance of these devices will be described below. Fig. 6A is a plan view of a surface conduction electron-emitting device according to the invention and used in this example and Fig. 6B is a cross sectional view thereof. Figs. 15AA through 15AC show a surface conduction electron-emitting device arranged on substrate A in different manufacturing steps, whereas Figs. 15BA through 15BC show another surface conduction electron-emitting device also in different manufacturing steps, the latter being prepared for the purpose of comparison and arranged on substrate B. Four identical electron-emitting devices were produced on each of the substrates A and B. 1) The both substrates A and B were made of quartz glass. After thoroughly cleansing them with a detergent, pure water and an organic solvent, a Pt film was formed thereon by sputtering for device electrodes 4 and 5 to a thickness of 60 nm (600Å) for the substrate A and 30 nm (300Å) for the substrate B (Figs. 15AA and 15BA). The device electrodes 4 and 5 had a thickness of 50 nm (500Å) on the substrate A and 30 nm (300Å) on the substrate B. The device electrodes of each device were separated by a distance of 60µm on the substrate A, whereas they were separated by 2µm on the substrate B. 2) Subsequently, a Cr film (not shown) to be used for lift-off is formed by vacuum deposition to a thickness of 60 nm (600Å) for the purpose of patterning the electroconductive thin film 3 on both the substrate A and the substrate B. At the same time, an opening of 100µm corresponding to the width W2 of the electroconductive thin film 3 was formed in the Cr film for each device on both the substrate A and substrate B. Thereafter, a solution of organic palladium (ccp-4230: available from Okuno Pharmaceutical Co., Ltd.) was sprayed onto the substrate A by means of an apparatus as shown in Fig. 3B to form an organic palladium thin film. At this time, unlike the case of Example 1, the substrate A carrying device electrodes was tilted by 30° relative to the normal line of Example 1 (Fig. 43). As a result of using the arrangement of tilting the substrate by 30° relative to the normal line of Example 1 for spraying the solution, a dense film was formed on and securely held to the device electrode 4 of each device, whereas a less dense film was formed on the device electrode 5 of each device and the device electrode 5 showed an area in the step portion that is poorly covered by the film.On the other hand, the solution of organic palladium (ccp-4230: available from Okuno Pharmaceutical Co., Ltd.) was applied to the substrate B carrying device electrodes 4 and 5 by means of a spinner and left there to produce an organic Pd thin film.Thereafter, the organic Pd thin film was heated and baked at 300°C for 10 minutes in the atmosphere to produce an electroconductive thin film 3 mainly constituted by fine PdO particles for both the substrate A and the substrate B. The film had a thickness of about 12 nm (120Å) and an electric resistance of 5x10 4 Ω/□ for both the substrate A and the substrate B.Subsequently, the Cr film and the electroconductive thin film 3 were wet etched to produce an electroconductive thin film 3 having a desired pattern by means of an acidic wet etchant (Figs. 15AB and 15BB). 3) Then, the substrates A and B were moved into the vacuum apparatus 55 of a gauging system as illustrated in Fig. 12. Thereafter, the sample devices were subjected to an energization forming process to produce an electron-emitting region 2 for each device by applying a voltage between the device electrodes 4 and 5 of each device from a power source 51 (Figs. 15AC and 15BC). The applied voltage was a pulse voltage as shown in Fig. 4B (although it was not triangular but rectangularly parallelepipedic). The peak value of the wave height of the pulse voltage was increased stepwise. The pulse width of T1=1msec and the pulse interval of T2=10msec were used. During the energization forming process, an extra pulse voltage of 0.1V (not shown) was inserted into intervals of the forming pulse voltage in order to determine the resistance of the electron emitting region, constantly monitoring the resistance, and the energization forming process was terminated when the resistance exceeded 1MΩ.If the product of the pulse wave height and the device current If at the end of the energization forming process is defined as forming power (P form ), the forming power P form of the substrate A was seven times as small as the forming power P form of the substrate B. 4) Subsequently, the inside of the vacuum apparatus 55 of the gauging system of Fig. 11 was further evacuated to about 10 -5 Pa (10 -7 Torr), leaving the substrates A and B within the vacuum apparatus 55 and then acetone was introduced into the vacuum apparatus 55 as an organic substance. The partial pressure of acetone was set to 3x10 -2 Pa (2x10 -4 Torr). A pulse voltage was applied to each sample device on the substrates A and B to drive it for an activation process. Referring to Fig. 3A (although the pulse was not triangular but rectangularly parallelepipedic), the pulse width of T1=1msec and the pulse interval of T2=10msec were used and the drive voltage (wave height) was 15V. A voltage of 1kV was also applied to the anode 54 of the vacuum apparatus, while observing the emission current (Ie) of each electron-emitting device. The activation process was terminated when Ie got to a saturated state. 5) Then, after further evacuating the inside of the vacuum apparatus to about 10 -5 Pa (1x10 -7 Torr), the ion pump used for evacuation was switched to an oil-free pump to produce an ultrahigh vacuum condition and the electron source was baked at 150°C for 2 hours. After the baking operation, the inside of the vacuum apparatus was held to a degree of vacuum of 10 -5 Pa (1x10 -7 Torr). Subsequently, each sample surface conduction electron-emitting device on the substrates A and B was driven to operate within the vacuum apparatus 55 in order to see the device current (If) and the emission current (Ie). The voltage applied to the anode 54 was 1kV and the device voltage (Vf) was 15V. The electric potential of the device electrode 4 was held higher than of the device electrode 5 for each device. As a result of the measurement, the device current (If) and the emission current (Ie) of each device on the substrate B were 0.90mA±6% and 0.7µA±5% respectively. On the other hand, the device current (If) and the emission current (Ie) of each device on the substrate A were 0.8mA±5% and 0.7µA±4% respectively to show a level of deviation substantially equal to all the devices. At the same time, a fluorescent member was arranged on the anode 54 to observe bright spots produced on the fluorescent member as electron beams emitted from the electron-emitting devices collide with it. The size and profile of the bright spots were substantially same for all the devices. After the measurement, the electron-emitting regions 2 of the devices on the substrates A and B were microscopically observed. Figs. 16A and 16B schematically illustrate what was observed for the electron-emitting region 2 of the electroconductive thin film 3 of each device on the substrates A and B. As seen from Figs. 16A and 16B, a substantially linear electron-emitting region 2 was observed near the device electrode 5 having a higher step portion in each of the four devices on the substrate A, while a similarly linear electron-emitting region 2 was observed at the middle point of the device electrodes in the electroconductive thin film 3 of each of the four devices on the substrate B prepared for comparison. As described above, the surface conduction electron-emitting device comprising a substantially linear electron-emitting region 2 located close to one of the device electrodes operates to emit highly convergent electron beams without showing any substantial deviation in the performance like a surface conduction electron-emitting device for comparison wherein the device electrodes are separated by only 2µm. Thus, the distance separating the device electrodes of the surface conduction electron-emitting device can be made as large as 60µm or 30 times larger than that of a surface conduction electron-emitting device for comparison.

Claims: A method of manufacturing a surface conduction electron-emitting device comprising an electroconductive thin film (3) including an electron-emitting region (2) disposed between a pair of electrodes (4,5) on a substrate (1), at least one (5) of the electrodes having an electrode step at the surface of the substrate, wherein said method comprises a step of spraying a solution (34) containing component elements of said electroconductive thin film (3) through a nozzle (33) onto said substrate (1), wherein during the step of spraying an electric potential difference is produced between the pair of electrodes (4,5). A method of manufacturing a surface conduction electron-emitting device comprising an electroconductive thin film (3) including an electron-emitting region (2) disposed between a pair of electrodes (4,5) on a substrate (1), wherein said method comprises a step of spraying a solution (34) containing component elements of said electroconductive thin film (3) through a nozzle (131) onto said substrate (1) wherein during the step of spraying, an electric potential difference (V) is produced between the nozzle and the substrate. A method according to claim 1, wherein said step of spraying a solution containing component elements of said electroconductive thin film (3) includes producing an electric potential difference (V) between the nozzle (33) and the substrate (1). A method of manufacturing an electron source (1, 102-105) comprising a plurality of surface conduction electron-emitting devices (104) on a substrate (1), wherein each of said plurality of surface conduction electron emitting devices (104) is manufactured by the method defined in any one of the preceding claims. A method of manufacturing an image-forming apparatus comprising an electron source (1, 102-105) and an image-forming member (114) for forming an image upon irradiation with electron beams emitted from said electron source (1,102-105), wherein the electron source (1, 102-105) is manufactured by the method as defined in claim 4.

Inventors: HAMAMOTO YASUHIRO, TSUKAMOTO TAKEO, YAMAMOTO KEISUKE, YAMANOBE MASATO, HAMAMOTO, YASUHIRO, TSUKAMOTO, TAKEO, YAMAMOTO, KEISUKE, YAMANOBE, MASATO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: H01J9
IPC codes: H01J9