Electron emitting device, method for producing the same, and display apparatus and electron scribing apparatus utilizing same.

Abstract: An electron emitting device comprises a substrate; an insulating layer formed thereon and having a hollow part therein; a substantially conical electrode formed in the hollow part; and a conductive layer formed on the insulating layer and having an aperture on the hollow part; the hollow part is formed by etching utilizing an ion beam.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an electron emitting device, a method for producing the same, and a display apparatus and an electron scribing apparatus utilizing said electron emitting device. Related Background Art Conventionally used electron emitting devices are mostly those utilizing a hot cathode, but the electron emission by the hot cathode has been associated with drawbacks such as a large energy loss by heating and the necessity for preliminary heating. For resolving these drawbacks there have been proposed various electron emitting devices of cold cathode type, including a field effect type electron emitting device in which a high electric field is locally generated and the electron emission is realized by field emission. Fig. 1 is a schematic partial cross-sectional view showing an example of such field effect electron emitting device, and Figs. 2A to 2D are schematic views showing the steps for producing said device. As shown in Fig. 1, said field effect electron emitting device is composed of a substrate 101 composed for example of Si; a point-shaped electron emitting part 108 composed for example of molybdenum (Mo) and formed on said substrate; an insulating layer 102 composed for example of SiO₂ and having an aperture around said point-shaped electron emitting part 108; and an electrode 109 of which end is positioned close to the pointed part of the conical shape. In such electron emitting device, electrons are emitted from the pointed part where the intensity of electric field is strong, when a voltage is applied between the substrate 101 and the electrode 109. Such field effect electron emitting device utilizing microfabrication technology is for example reported by C. A. Spindt et al. in Journal of Applied Physics, Vol. 47, No. 12, 1976, p5246. Said electron emitting device is obtained by forming a hole of a diameter of about 1.5 µm in a thin film of SiO₂ and a gate electrode formed in succession on a Si substrate, and further forming, by metal deposition, a conical emitter electrode with a diameter of the pointed end not exceeding 1000 Å for field emission. The above-mentioned electron emitting device is generally prepared by the following process; (1) At first, as shown in Fig. 2A, an insulating layer 102 for example of a SiO₂ film of a thickness of 1 - 1.2 µm is formed on the substrate 101 composed for example of Si. (2) Then, on said insulating layer 102, a Mo layer 109 of a thickness for example of about 0.4 µm is formed for example by electron beam evaporation. (3) An electron beam resist, composed for example of PMMA (polymethylmethacrylate) is applied by spin coating on said Mo layer 109. (4) Said electron beam resist is irradiated with an electron beam in a desired pattern, and is then partially removed for example with isopropyl alcohol according to said desired pattern. (5) The Mo layer 109 is selectively etched according to the resist pattern, to form a first aperture 103. (6) Then the remaining electron beam resist is completely removed, and the insulating layer 102 is etched with hydrofluoric acid to form a second aperture 704 (Fig. 2A). (7) Then the substrate 101 is rotated about an axis X with an inclination by a predetermined angle , and aluminum is deposited by evaporation onto the Mo layer 109, thereby forming an Al layer 105. Since aluminum is deposited also on the lateral face of the Mo layer 109, the diameter of the first aperture 103 can be arbitrarily reduced by the control of amount of evaporation (Fig. 2B). Subsequently Mo is deposited for example by electron beam evaporation perpendicularly to the substrate 101. Since Mo is deposited not only on the Al layer 105 and the substrate 101 but also on the lateral face of the Al layer 105, the diameter of the first aperture 103 decreases gradually with the deposition of a Mo layer 106. As the area of deposition of Mo on the Si substrate decreases according to the decrease in the diameter of said first aperture 103, there is formed a substantially conical electrode 108 on the substrate 101 (Fig. 2C). Finally the field effect electron emitting device is obtained by removing the Mo layer 106 and the Al layer 105, as shown in Fig. 8D. It is however difficult, in the above-explained process, to prepare a smaller field effect electron emitting device, for example the device smaller than 3 µm, with a high production yield, since the formation of the field forming space and the electron emitting part involves complicated technology such as oblique evaporation. Also in the above-explained process for producing the electron emitting device, since the formation of the conical emitter electrode 108 is achieved by metal deposition, utilizing the shape of the aperture 103 in the Al layer 109, the reproducibility of the shape (height, angle, bottom diameter etc.) of said emitter electrode 108 is low, leading to poor production yield and unsatisfactory uniformity of the shape or performance of the device. The production yield is particularly poor when plural electron emitting devices are formed at the same time on a Si substrate, leading to a high cost. Since this tendency becomes more marked as the size of the electron emitting device becomes smaller, it has been difficult to obtain finer electron emitting devices. Besides the manufacturing process of the above-explained conventional electron emitting device is very complex, leading to the high cost of the device. SAMMARY OF THE INVENTION In consideration of the foregoing, an object of the present invention is to provide an electron emitting device allowing manufacture in a smaller size and with a high yield. Another object of the present invention is to provide an electron emitting device allowing manufacture with a lower cost. Still another object of the present invention is to provide a display apparatus and an electron scribing apparatus utilizing electron emitting devices enabling manufacture in a smaller size and arrangement with a higher density with a lower cost. Still another object of the present invention is to provide an electron emitting device excellent in the reproducibility of the shape of the emitter electrode (in the following also referred to as "protruding electrode") and enabling manufacture in a simple process, and a display apparatus and an electron scribing apparatus utilizing said electron emitting device. Still another object of the present invention is to provide an electron emitting device comprising a substrate; an insulating layer formed thereon and having a hollow part therein; a substantially conical electrode being the protruding electrode formed in said hollow part; and a conductive layer (electrode) formed on said insulating layer and having an aperture corresponding to said hollow part, wherein said hollow part is formed by ion beam etching. Still another object of the present invention is to provide a field emission type electron emitting device formed by: irradiating the surface of a substrate of an insulating material with a focused ion beam along an arbitrary circle defined on said surface, thereby forming an ion implanted area in said substrate; chemically etching said substrate to eliminate said ion implanted area thereby forming an electric field forming space having a projection at the bottom thereof; covering said projection with a conductive material to form a point-shaped protruding electrode ; and covering the surface of said substrate, excluding said electric field forming space, with a conductive material thereby forming an electrode for forming an electric field in cooperation with said point-shaped protruding electrode. Still another object of the present invention is to provide a field emission type electron emitting device formed by: irradiating the surface of a substrate composed of a semiconductive or conductive material having a surfacial insulating layer with a focused ion beam along an arbitrary circle defined on said surface, thereby forming an ion implanted area in said substrate; chemically etching said substrate to eliminate said ion implanted area thereby forming an electric field forming space having a projection at the bottom thereof; covering said projection with a conductive material to form a point-shaped protruding electrode ; and covering the surface of said substrate, excluding said electric field forming space, with a conductive material thereby forming an electrode for forming an electric field in cooperation with said point-shaped protruding electrode. Still another object of the present invention is to provide a field emission type electron emitting device formed by: irradiating the surface of a substrate composed of an insulating material with a focused ion beam along an arbitrary race track-shaped trajectory defined on said surface, thereby forming an ion implanted area in said substrate; chemically etching said substrate to eliminate said ion implanted area thereby forming an electric field forming space having a line-shaped projection at the bottom thereof; covering said line-shaped projection with a conductive material to form a line-shaped protruding electrode ; and covering the surface of said substrate, excluding said electric field forming space, with a conductive material thereby forming an electrode for forming an electric field in cooperation with said line-shaped protruding electrode. Still another object of the present invention is to provide a method for producing an electron emitting device, comprising steps of: irradiating the surface of a substrate composed of a semiconductive or conductive material having a surfacial insulating layer with a focused ion beam along an arbitrary race track-shaped trajectory defined on said surface, thereby forming an ion implanted area in said substrate; chemically etching said substrate to eliminate said ion implanted area thereby forming an electric field forming space having a line-shaped projection at the bottom thereof; covering said line-shaped projection with a conductive material to form a line-shaped protruding electrode; and covering the surface of said substrate, excluding said electric field forming space, with a conductive material thereby forming an electrode for forming an electric field in cooperation with said line-shaped protruding electrode. irradiating an insulating or semiconductor substrate with an ion beam at a desired pattern; etching said substrate subjected to the ion beam irradiation to remove the portion thereof irradiated with the ion beam so as to form a hollow part in the substrate, said hollow part having a water-drop-like shape at least in a section along the electron emitting direction, forming a protruding electrode (304) on the bottom of the hollow part, forming a conductive layer (303) on said substrate, said layer having an aperture corresponding to the hollow part. The foregoing objects can be attained, by the features of the claims 1 to 28. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic partial cross-sectional view of an example of the conventional field emission type electron emitting device; Figs. 2A to 2D are schematic views showing steps of a method for producing the field emission type electron emitting device shown in Fig. 1; Fig. 3 is a schematic cross-sectional view of an electron emitting device constituting a first embodiment of the present invention; Figs. 4A to 4C are schematic cross-sectional views showing steps of a method for producing the electron emitting device shown in Fig. 3; Fig. 5 is a schematic perspective view of an electron emitting device constituting a second embodiment of the present invention; Fig. 6 is a schematic perspective view of an electron emitting device constituting a third embodiment of the present invention; Figs. 7A to 7H are schematic cross-sectional and perspective views of a field emission type electron emitting device constituting a fourth embodiment of the present invention; Fig. 8 is a schematic view of a concentrated ion beam scanning apparatus employed in the preparation of the device of the present invention; Figs. 9 and 10 are charts showing the etch depth as a function of the amount of ion implantation. Figs. 11A to 11E are schematic cross-sectional views showing the method for producing the electron emitting device of fifth and eighth embodiments; Fig. 12 is a schematic perspective view of a multiple device constituting a sixth embodiment of the present invention; Figs. 13A to 13H are schematic cross-sectional and perspective views of a field emission type electron emitting device constituting a seventh embodiment of the present invention; and Fig. 14 is a schematic perspective view of a multiple device constituting a ninth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The aforementioned objects can be attained, according to a preferred embodiment of the present invention, by an electron emitting device at least comprising an insulating or semiconductive substrate having a hollow part therein; a protruding electrode in the hollow part and a conductive layer provided on said substrate and having an aperture corresponding to said hollow part; said hollow part having a water drop like-shape at least in a first section along the electron emission direction. In said electron emitting device, a plurality of said hollow parts respectively provided with said protruding electrodes is formed in said substrate, and said conductive layer may be provided with plural apertures respectively corresponding to said plural hollow parts. Said ion beam is preferably a focused ion beam (FIB). Also said protruding electrode and said conductive layer are preferably formed at the same time. The above-mentioned electron emitting device is naturally applicable to a display apparatus or an electron scribing apparatus. Furthermore, there is preferably applied a treatment for reducing the work function of said protruding electrode. Furthermore, the work function of said protruding electrode is reduced preferably by covering the surface of said protruding electrode with a material of a lower work function than that of said substrate Said hollow part (also referred to as electric field forming space) and said protruding electrode may be formed in plural numbers on a single substrate. The electron emitting device according to the present invention may have a substrate formed of a semiconductor substrate (301) and an insulating layer (302) on said substrate, said electrode (304) being formed on said semiconductor substrate. Further, said protruding electrode may be made of the same material of said conductive layer (303). According to another embodiment of the electron emitting device of the present invention said hollow part has a line-shape (1403) in a second section perpendicular to the first section. Further, said protruding electrode may have a line-shape (1403) in said second section. Said insulating layer may be formed by vacuum evaporation. Also said line-shaped protruding electrode may be formed by vacuum evaporation. Furthermore, said conductive layer may be formed by vacuum evaporation. Naturally said line-shaped protruding electrode and said conductive layer may be formed by vacuum evaporation at the same time. Furthermore, the depth and shape of said hollow part can be controlled by the accelerating voltage of said focused ion beam, amount of implanted ions and/or kind of implanted ions. Also as explained in the foregoing, there is preferably applied a treatment for reducing the work function of said line-shaped protruding electrode. Likewise, the work function of said line-shaped protruding electrode is reduced preferably by covering the surface of said line-shaped protruding electrode with a material of a lower work function than that of said substrate. Also in these devices, said hollow part and said line-shaped protruding electrode may be formed in plural number on a single substrate. Furthermore the aforementioned objects can be attained, according to the present invention, by a method for producing an electron emitting device comprising steps of: irradiating an insulating or semiconductive substrate with an ion beam at a desired pattern; etching said substrate subjected to the ion beam irradiation to remove the portion thereof irradiated with said ion beam; so as to form a hollow part in the substrate, said hollow part having a water-drop-like shape at least in a section along the electron emitting direction, forming a protruding electrode (304) on the bottom of the hollow part, forming a conductive layer (303) on said substrate, said layer having an aperture corresponding to the hollow part. In the above-mentioned method, said substrate may be a semiconductive substrate having an insulating layer formed thereon. In such case, said semiconductive substrate is preferably composed of GaAs or Si. Furthermore, the above-mentioned semiconductive substrate may be composed of an insulating substrate having a semiconductive layer formed thereon. Said insulating layer is preferably composed of a material selected from SiO₂, semiconductive Si, Si₃N₄ and AlS. Also said conductive material is preferably selected from W, Mo, Ta, Ti and Pt. The above-mentioned method preferably contains an additional step for depositing a material of a low work function. Said material of low work function is preferably at least a boride or a carbide. Said boride is preferably selected from LaB₆ and SmB₆. Also said carbide is preferably selected from TiC and ZrC. Also the substrate in the above-mentioned method preferably comprises a crystalline material, which is preferably a monocrystalline or polycrystalline material. Said crystalline material is advantageously selected from Si, Ge, yttrium aluminum garnet (YAG), yttrium iron garnet (YIG) and GaAs. Also in the above-mentioned method, the irradiation with said ion beam may be conducted along a circle having the center at a desired position, or along a rack track including a straight line between two circles having centers at desired positions. Thus the present invention allows to produce an electron emitting device by irradiating a predetermined position of a crystalline material with a focused ion beam thereby forming an ion implanted area, and chemically etching said material to eliminate a predetermined portion of said ion implanted area thereby forming said hollow part. Also the present invention extremely simplifies the method for producing the electron emitting device and drastically improves the reproducibility of the shape of the emitter (protruding electrode), by forming an aperture in the substrate by means of maskless etching utilizing the ion beam. The present invention will be clarified in greater detail in the following description. It is already known that irradiation of a Si or GaAs single crystal with an ion beam of Be, Si or Au with an intensity of 10¹⁴ ions/cm² or higher varies said single crystal into amorphous state, whereby the irradiated portion shows an increased etching rate and can be selectively etched after the ion implantation. Such etching method is usable also on SiO₂ crystal. Such etching method combined with focused ion beam technology allows to form a fine hole with a high precision. The cross-sectional shape of the hole formed by such etching is determined by the scattered distribution of the implanted ions, and assumes the form of a water drop as shown in Fig. 3. The present invention utilizes the hole of such water drop form obtained by scattering of the implanted ions, for the preparation of a field emission type electron emitting device. [1st embodiment] Fig. 3 is a schematic cross-sectional view showing an electron emitting device constituting a preferred embodiment of the present invention. There are shown an n-GaAs (semiconductive) substrate 301; an epitaxially grown SiO₂ layer 302, serving as an insulating layer, of a thickness of 0.5 µm; a tungsten gate electrode 303 (conductive layer) of a thickness of 0.4 µm; an emitter 304 (protruding electrode); and a hole 305 formed by etching utilizing the focused ion beam technology. The emitter 304 has a diameter of several hundred Angstroms at the pointed end, and is capable of emit a current of about 1 nA by the application of a voltage of 20 V or higher between the substrate 301 and the gate electrode 303. In the following there will be explained the process for producing the electron emitting device of the present invention. Figs. 4A - 4C are schematic cross-sectional views showing the steps of a process for producing the electron emitting device shown in Fig. 3. (1) At first, on the n-GaAs substrate 301, the SiO₂ insulating layer 302 of a thickness of 0.5 µm was formed by epitaxial growth. (2) Then, the SiO₂ layer 302 was irradiated with an ion beam of 200 keV with a dose of 10¹⁶ ions/cm², focused to a diameter of 0.1 µm, as shown in Fig. 4A. (3) Subsequently the SiO₂ layer 302 was treated with heated acid to selectively etch the area implanted with the ion beam in the step (2), thereby obtaining a hole 305 of water drop form as shown in Fig. 4B. (4) Then, on the SiO₂ layer 302, tungsten was deposited with a thickness of 0.4 µm by sputtering to form the gate electrode 303 and the emitter 304 as shown in Fig. 4C, whereby the electron emitting device as shown in Fig. 3 was completed. Thus the electron emitting device of the present embodiment can be prepared by an extremely simple process, in comparison with the process for the conventional device. Also the yield can be improved since the reproducibility of the shape of the emitter 304 is improved in comparison with the conventional process. Also since the precision of the shape of the emitter 304 can be improved, it becomes easier to form the emitter 304 in a smaller size than in the conventional technology, and it is rendered possible to obtain an electron emitting device capable of electron emission with a voltage lower than in the conventional devices. The substrate 301, which is composed of GaAs in the present embodiment, may also be composed of Si. Furthermore the substrate 301 may be composed for example of a glass substrate and amorphous silicon formed thereon, or an insulating substrate and a semiconductor epitaxially grown thereon, for example by SOI (silicon on insulator) technology. Also the SiO₂ layer may be replaced by a layer of semiconductive Si, Si₃N₄ or AlS. Also the gate electrode may be composed of Mo, Ta, Ti, Pt etc. instead of W. [2nd embodiment] Fig. 5 is a perspective view of an electron emitting device constituting another preferred embodiment of the present invention, wherein plural electron emitting devices are linearly arranged on a single substrate. The present invention, being capable of improving the production yield of each electron emitting device, is particularly effective when plural electron emitting devices are formed on a single substrate as in the present embodiment. [3rd embodiment] Fig. 6 is a perspective view of an electron emitting device constituting another preferred embodiment of the present invention, wherein plural electron emitting devices are arranged in a matrix on a single substrate. The electron emitting device of the present embodiment is prepared by forming, on an insulating substrate 309, a Ni metal film of a thickness of 1 µm in a linear form as a substrate electrode 310, then forming an insulating layer 302 for example of SiO₂ on said substrate electrode 310, and forming a linear gate electrode 303 perpendicularly to the substrate electrode 310. The present invention, being easily capable of improving the precision of the shape of the emitter 304, allows to reduce the dimension of the electron emitting device and to arrange such devices in a higher density. More specifically, since the hole 305 can be formed with a size of 0.5 µm or smaller, the electron emitting devices can be arranged in a matrix with a pitch as small as about 1 µm. In the present embodiment each element is provided with an emitter, but it is also possible to form plural emitters in each element, and such structure allows to obtain a two-dimensional electron beam of a large current. As explained in the foregoing, the present embodiment provides an electron emitting device of a simple structure with a larger freedom in size, which can be widely employed in appliances utilizing electron beam. For example, in the field of display, it can be utilized as an electron source for a cathode ray tube or a flat panel display, or as an electron emitting device for a flat image pickup tube. Industrially, it can be utilized as the electron emitting device for an electron scribing apparatus for semiconductor device manufacture, utilizing the features of the present invention such as a large current and a high device density. For example, the electron emitting device of the present invention may be employed instead of the LaB₆ conventionally used in such apparatus. Also utilizing the feature of high density arrangement of the present invention, the device may be provided with emitters arranged one-dimensionally or two-dimensionally and may be positioned parallel to the wafer, thereby achieving a high speed pattern drawing. [4th embodiment] Figs. 7A to 7D are schematic cross-sectional view while Figs. 7E to 7H are schematic perspective views, showing the method for producing the field emission type electron emitting device of the present embodiment. The cross-sectional views in Figs. 7A to 7D respectively correspond to lines A-A in Figs. 7E to 7H. A substrate 701 can be composed of an insulating single crystal such as yttrium-iron garnet (YIG) or yttrium-aluminum garnet (YAG), but YIG with crystal orientation (111) is employed in the present embodiment. (1) At first the YIG substrate was subjected to ion implantation with a Be²⁺ ion beam of 160 keV focused to a spot of 0.1 µm or smaller as shown in Figs. 7A and 7E. The ion dose was 4 x 10¹⁶ ions/cm² in an area for forming the wiring electrode space (703), and 2 x 10¹⁶ ions/cm² in an area for forming the electric field forming space (704) (hollow part). The ion implantation for forming the electric field forming space was conducted along a circle of 0.4 µm around a desired position. The implanted Be ions were scattered in the substrate 701, thus forming a water drop-shaped implanted area 705 as shown in Fig. 7A. (2) Then the substrate was immersed in phosphoric acid of room temperature to selectively etch off said implanted area, thereby forming, as shown in Figs. 7B and 7F, an electric field forming space 706, an electrode wiring space 707 and a pointed projection 708 at a depth of 0.5 µm from said desired position on the surface of the substrate. (3) Subsequently tungsten was perpendicularly deposited by vacuum evaporation in a thickness of 0.2 µm on the surface of the substrate, thereby simultaneously forming an electrode 709, a wiring 710 and a point-shaped protruding electrode 711 as shown in Figs. 7C and 7G. In this state an electron emission of 50 µA of higher was obtained by a voltage application of 30 V between the wiring 710 and the electrode 709. (4) For improving the electron emitting cahracteristics of this device, LaB₆ 712, as a material of low work function, was perpendicularly deposited by vacuum evaporation in a thickness of 200 Å on the surface of the substrate 701, as shown in Figs. 7D and 7H. The field emission type electron emitting device thus completed showed electron emission of 100 µA or higher form the point-shaped protruding electrode , by a voltage application of 25 V between the electrode wiring and the electrode. Thus the surface coverage with a material of low work function reduced the required voltage or increased the emission current at a same voltage. In addition to LaB₆, said material of low work function can for example be borides such as SmB₆ or carbides such as TiC or ZrC. Fig. 8 schematically shows an ion beam scanning apparatus employed in the ion beam irradiation mentioned above. In the following there will be explained the operating method of ion beam with said apparatus. (1) An ion beam which is field emitted from an Au-Si-Be liquid metal ion source 801 is focused by an electric condenser lens 802, and a necessary specy is separated by an E × B mass separator 803. (2) Then the beam is again focused by an objective lens 804, and is deflected toward a target 807 under computer control. (3) The target 807 is set at a desired position by movement in the X-Y plane, by a stage 806 moved by a stage unit 806. In Fig. 8 there are also shown a SEI 808 and a Faraday cup 809. The ion implantation with the apparatus shown in Fig. 8 can be conducted with an accelerating voltage of 40 - 80 kV and a beam diameter of 0.1 µm, for example in case of implanting Si or Be ions perpendicularly into the (111) plane of YIG substrate. Figs. 9 and 10 show the etch depth obtained by implanting Be or Si ions with different doses or accelerating voltages and etching a predetermined portion of the implanted area with phosphoric acid of room temperature. As will be understood from these charts, the size of the electric field forming space and the electrode wiring space can be arbitrarily selected by the accelerating voltage of the focused ion beam, dose of ions and specy of ions. [5th embodiment] Figs. 11A to 11E are schematic cross-sectional views showing the method for producing a field emission type electron emitting device employing N-GaAs semiconductor single crystal doped with Si at 3 × 10¹⁸ ions/cm² as the substrate. (1) At first, a SiO₂ film 1102 of a thickness of 0.2 µm, formed by vacuum evaporation on a substrate 1101 as shown in Fig. 11A, was irradiated with an Au²⁺ ion beam 1103 of 80 keV with a dose of 8 × 10¹⁸ ions/cm², focused to a diameter of 0.1 µm, inside a circle of 0.4 µm around a desired position, and was thus removed by sputter-etching. (2) Then, as shown in Fig. 11B, the substrate was irradiated with a Si²⁺ ion beam 1104 of 160 keV focused to a diameter of 0.1 µm along a circle of 0.35 µm around said desired position with a dose of 2 × 10¹⁶ ions/cm² to form a water drop-shaped implanted area 1105. (3) Then the substrate was immersed in hydrochloric acid heated to 70°C to selectively etch off the ion implanted area, thereby forming an electric field forming space 1106 and a pointed projection 1107 as shown in Fig. 11C. (4) Subsequently a metal, such as Au-Ge alloy, constituting an ohmic contact with N-GaAs was perpendicularly deposited onto the substrate by vacuum evaporation with a thickness of 0.2 µm, and alloy was formed by a heat treatment for 3 minutes at 400°C. Thus an electrode 1108 and a point-shaped protruding electrode 1109 were formed as shown in Fig. 11D. In this state electron emission of 50 µA or higher was obtained from the point-shaped protruding electrode 1109 by a voltage application of 40 V between the GaAs substrate 1101 and the electrode 1108. (5) For improving the electron emitting characteristics of this device, LaB₆ 1110, as a material of low work function, was perpendicularly deposited by vacuum evaporation with a thickness of 200 Å, as shown in Fig. 11E. The field emission type electron emitting device thus completed showed electron emission of 100 µA or higher from the point-shaped protruding electrode by a voltage application of 30 V between the GaAs substrate and the electrode. [6th embodiment] Fig. 12 is a schematic perspective view of a part of the surface of a field emission type electron emitting device with a multiple structure of the 4th embodiment. The materials and conditions employed are same as those shown in Figs. 7A, 7E - 7C and 7G. In the present embodiment, the protruding electrodes were arranged with a pitch of 1.2 µm, and 4 lines by 15 columns in a unit, and 64 units were formed in a square of 250 x 250 µm. An emission current density of 300 A/cm² could be obtained by a voltage application of 45 V between the electrodes 1202 and all the protruding electrodes 1203. In the present embodiment, the electrode is integrally constructed while the protruding electrodes are electrically independent, but the electrode may be constructed independently for each protruding electrode, and the protruding electrodes may be connected in common. [7th embodiment] Figs. 13A - 13D are schematic cross-sectional views, and Figs. 13E - 13H are schematic perspective views, showing the method of producing a field emission type electron emitting device of the present embodiment. The cross-sectional views in Figs. 13A - 13D respectively correspond to lines B-B in Figs. 13E - 13H. A substrate 1301 can be composed of an insulating single crystal such as yttrium-iron garnet (YIG) or yttrium-aluminum garnet (YAG), but YIG with crystal orientation (111) is employed in the present embodiment. (1) At first the YIG substrate was subjected to ion implantation with a Be²⁺ ion beam of 160 keV focused to a spot of 0.1 µm or smaller as shown in Figs. 13A and 13E. The ion dose was 4 x 10¹⁶ ions/cm² in an area for forming the electrode wiring space (1303), and 2 x 10¹⁶ ions/cm² in an area for forming the electric field forming space (1304). The ion implantation for forming the electric field forming space was conducted along a race track having linear portions of 1 µm between semi-circles of a radius of 0.2 µm at a predetermined position. The implanted Be ions were scattered in the substrate 1301, thus forming a water drop-shaped implanted area 1305 as shown in Fig. 13A. (2) Then the substrate was immersed in phosphoric acid of room temperature to selectively etch off said implanted area, thereby forming, as shown in Figs. 13B and 13F, an electric field forming space 1306, an electrode wiring space 1307 and a pointed projection 1308 at a depth of 0.5 µm from the surface of the substrate in said position. (3) Subsequently tungsten was perpendicularly deposited by vacuum evaporation in a thickness of 0.2 µm on the surface of the substrate, thereby simultaneously forming an electrode 1309, a wiring 1310 and a line-shaped protruding electrode 1311. In this state an electron emission of 5 mA or higher was obtained by a voltage application of 30 V between the wiring 1310 and the electrode 1309. (4) For improving the electron emitting characteristics of this device, LaB₆ 1312, as a material of low work function, was perpendicularly deposited by vacuum evaporation in a thickness of 200 Å on the surface of the substrate 1301, as shown in Figs. 13D and 13H. The field emission type electron emitting device thus completed showed electron emission of 10 mA or higher from the line-shaped protruding electrode , by a voltage application of 25 V between the electrode wiring and the electrode. Thus the surface covering with a material of low work function reduced the required voltage or increased the emission current at a same voltage. In addition to LaB₆, said material of low work function can for example be borides such as SmB₆ or carbides such as TiC or ZrC. The present embodiment is basically same as the 4th embodiment, except the difference in the shape of the electric field forming space 1306. However, because of said difference in shape, the present embodiment provides a considerably stronger electron emission in comparison with the 4th embodiment. The electron emitting device of the present embodiment can also be prepared by the ion beam scanning apparatus explained above. [8th embodiment] Also in the present 8th embodiment, the electric field forming space, seen from above, is oblong as in the 7th embodiment, but the cross section in each step, along the line B-B in Fig. 13H is same as in the 5th embodiment. Consequently the present embodiment will be explained in the following with reference to Fig. 11. Figs. 11A to 11E are schematic cross-sectional views showing the method for producing a field emission type electron emitting device employing N-GaAs semiconductor single crystal doped with Si at 3 x 10¹⁸ ions/cm² as the substrate. (1) At first, a SiO₂ film 1102 of a thickness of 0.2 µm, formed by vacuum evaporation on a substrate 1101 as shown in Fig. 11A, was irradiated with an Au²⁺ ion beam 1103 of 80 keV with a dose of 8 x 10¹⁸ ions/cm², focused to a diameter of 0.1 µm, inside a race track having linear portions of 1 µm between semi-circles of a radius of 0.2 µm and placed in a predetermined position, and said film was thus removed by sputter-etching. (2) Then, as shown in Fig. 11B, the substrate was irradiated with a Si²⁺ ion beam 1104 of 160 keV focused to a diameter of 0.1 µm along a trajectory which is 0.05 µm inside said race track with a dose of 2 x 10¹⁶ ions/cm² to form a water drop-shaped implanted area 1105. (3) Then the substrate was immersed in hydrochloric acid heated to 70°C to selectively etch off the ion implanted area, thereby forming an electric field forming space 1106 and a pointed projection 1107 as shown in Fig. 11C. (4) Subsequently a metal, such as Au-Ge alloy, constituting an ohmic contact with N-GaAs was deposited onto the substrate by perpendicular vacuum evaporation with a thickness of 0.2 µm, and alloy was formed by a heat treatment for 3 minutes at 400°C. Thus an electrode 1108 and a line-shaped protruding electrode 1109 were formed as shown in Fig. 11D. In this state electron emission of 5 mA or higher was obtained from the line-shaped protruding electrode 1109 by a voltage application of 40 V between the GaAs substrate 1101 and the electrode 1108. (5) For improving the electron emitting characteristics of this device, LaB₆ 1110, as a material of low work function, was deposited by perpendicular vacuum evaporation with a thickness of 200 Å, as shown in Fig. 11E. The field emission type electron emitting device thus completed showed electron emission of 10 mA or higher from the line-shaped protruding electrode by a voltage application of 30 V between the GaAs substrate and the electrode. This value is considerably higher than in the 5th embodiment. [9th embodiment] Fig. 14 is a schematic perspective view of a part of the surface of a field emission type electron emitting device with a multiple structure of the 7th embodiment. The materials and conditions employed are same as those shown in Figs. 13A, 13E - 13C and 13G. In the present embodiment, the protruding electrodes were arranged with a line pitch of 2.0 µm and a column pitch of 1.2 µm, and 2 lines by 8 columns in a unit, and 64 units were formed in a square of 250 x 250 µm. An emission current density as high as 8000 A/cm² could be obtained by a voltage application of 45 V between the electrode 1402 and all the protruding electrodes 1403. In the present embodiment, the electrodes are integrally constructed while the protruding electrodes electrically independent, but the electrodes may be constructed independently for the protruding electrodes , and the protruding electrodes may be constructed in common. The electron emitting device of the present invention may be applied to a display device, as the electron source of a cathode ray tube, in such a manner that the fluorescent material can be irradiated by the electrons emitted by said device. Also a multiple electron emitting device having elements in a number of pixels can provide so-called flat panel display not requiring deflecting means. As explained in the foregoing, the electron emitting device of the present invention, being manufacturable with a simple process, can reduce the production cost. Also the present invention, capable of improving the precision and reproducibility of the size, position, emitter shape etc. of the electron emitting device, can improve the production yield of the device and the uniformity of characteristics thereof, and allows further compactization of the device. Furthermore, the electron emitting device of the present invention can be arranged with a high density, and can easily provide a large emission current. Consequently, the device of the present invention can be utilized for producing the display apparatus or electron scribing apparatus of improved performance. Furthermore, the present invention allows to obtain a field emission type electron emitting device of an extremely small size, for example less than 3 microns, by irradiating a crystalline material with a focused ion beam and chemically removing the ion implanted area only.

Claims: An electron emitting device comprising: an insulating or semiconductor substrate having a hollow part therein; a protruding electrode (304) in the hollow part; and a conductive layer (303) provided on said substrate, and having an aperture corresponding to the hollow part, said device characterized in that the hollow part has a water-drop-like shape at least in a first section along the electron emission direction. An electron emitting device according to claim 1, characterized in that a plurality of said hollow parts is formed in said substrate. An electron emitting device according to claim 1 or 2, characterized in that said substrate is formed of a semiconductor substrate (301) and an insulating layer (302) on said substrate, said electrode (304) being formed on said semiconductor substrate. An electron emitting device according, to claims 1 to 3, characterized in that said protruding electrode is made of the same material of said conductive layer (303). An electron emitting device according to any of claims 1 to 4, characterized in that said hollow part has a line-shape (1403) in a second section perpendicular to the first section. An electron emitting device according to claim 5, characterized in that said protruding electrode has a line-shape (1403) in said second section. An electron emitting device according to any of claims 1 to 7, characterized in that said hollow part has a protrusion at a bottom therein. An electron emitting device according to claim 7, characterized in that said protruding electrode is made of a conductive material on said protrusion on the bottom of said hollow part. An electron emitting device according to claim 1, characterized in that a work function lowering material (712) is provided on said protruding electrode. An electron emitting device according to claim 3, characterized in that said protruding electrode is covered with a work function lowering material (712), the work function of which is lower than that of said semiconductor substrate (301). An electron emitting device according to claim 9, characterized in that said work function lowering material is selected from boride and carbide. An electron emitting device according to claim 11, characterized in that said boride is LaB₆, or SmB₆. An electron emitting device according to claim 11, characterized in that said carbide is TiC or ZrC. An electron emitting device according to claim 1, characterized in that said substrate is made of a crystalline material. An electron emitting device according to claim 14, characterized in that said crystalline material is single crystalline or polycrystalline. An electron emitting device according to claim 14, characterized in that said crystalline material is selected from Si, Ge, Y, AlS, yttrium aluminum garnet, yttrium iron garnet and GaAs. An electron emitting device according to claim 3, characterized in that said semiconductor substrate is made of GaAs or Si. An electron emitting device according to claim 3, characterized in that said insulating layer is made of SiO₂, semi-insulating Si, Si₃N₄ or AlS. An electron emitting device according to claim 1, characterized in that said protruding electrode is made of W, Mo, Ta, Ti or Pt. A display apparatus comprising the electron emitting device according to claims 1 to 19. An electron scribing apparatus comprising the electron emitting device according to claim 1 to 19. A method for producing an electron emitting device as claimed in any of the claims 1 to 19, said method comprising the steps of: irradiating an insulating or semiconductor substrate with an ion beam at a desired pattern; etching said substrate subjected to the ion beam irradiation to remove the portion thereof irradiated with the ion beam so as to form a hollow part in the substrate, said hollow part having a water-drop-like shape at least in a section along the electron emitting direction, forming a protruding electrode (304) on the bottom of the hollow part, forming a conductive layer (303) on said substrate, said layer having an aperture corresponding to the hollow part. A method according to claim 22, further comprising steps of vapor deposition for forming an insulating layer (302) on a semiconductor layer (301) for forming the substrate, for forming the protruding electrode and/or for forming the conductive layer. A method according to claim 22, characterized in that the ion beam acceleration voltage and the injected ion quantity and/or the injected species is regulated to control the depth and shape of the removed portion. A method according to claim 22, characterized in that said ion beam is a focused ion beam (FIB). A method according to claim 22, characterized in that said step for forming the electron emitting electrode (304) and said step for forming the conductive layer (303) are simultaneously performed. A method according to claim 22, characterized in that said ion beam irradiation is performed along a circle, the center of which is on a desired position. A method according to claim 22, characterized in that said ion beam is irradiated along a race track including a straight line between two circles, the centers of which are on desired positions.

Inventors: OKUNUKI MASAHIKO, TSUKAMOTO TAKEO, WATANABE NOBUO, OKUNUKI, MASAHIKO, TSUKAMOTO, TAKEO, WATANABE, NOBUO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: H01J1
IPC codes: H01J1, H01J9