Electron emission device

Abstract: An electron emission device has a first metal layer (4), an insulation layer (6) formed on the first metal layer, a second metal layer (8) formed on the insulation layer, and means for applying a voltage across the first and second metal layers to cause the second metal layer to emit electrons. The insulation layer includes an organic insulation layer.

Description: The present invention relates to a multi-emitter device for emitting electrons (an electron emission device), and more particularly to an electron emission device which induces electron emission upon application of a voltage. Such an electron emission device is suitably used as an electron source of an electron beam apparatus. As an electron source of an electron beam apparatus such as a cathode ray tube, thermal electron emission from a thermal cathode has been used. Such an electron emission device which uses the thermal cathode has a large energy loss due to heating, needs heating means and takes a long time for pre-heating and hence cannot be active simultaneously with the switch-on. A study of electron emission device which do not need heating has been made and several devices have been proposed. For example, a reverse bias is applied to PN junction to cause electron avalanche break-down to emit electrons out of the device, a voltage is applied across two metals of a metal-insulation layer-metal layer structure to emit electrons passed through the insulation layer by a tunneling effect out of the device through the metal layer (MIM type), a voltage is applied to a high resistance thin film orthogonally to a direction of film thickness to emit electrons from the surface of the thin film externally of the device (surface conduction (SCE) type), or a voltage is applied to a metal having a shape which is easy to create electric field concentration to generate a locally high density electric field so that electrons are emitted from the metal externally of the device (field effect (FE) type). Of those, the MIM type electron emission device needs a relatively low application voltage and does not need a very high vacuum. In the proposed MIM type device, a lower (non-electron emission) metal is Al or Be, an insulation layer is a surface oxidation layer of that metal (for example, Al₂O₃ (as in DE-A-3 432 877) or BeO layer formed by thermal oxidation, air oxidation or anode oxidation), and an upper metal is Au, Pt or Al. Since the insulation layer of the prior art MIM type device is an inorganic thin film, a pinhole is easily formed during the manufacture. Accordingly, it is difficult to manufacture the device having a good performance or the characteristic of the device varies from device to device. Sci. Prog. Oxf., vol.69(1985) pp.533-550; J.R. Peterson et al. "Langmuir-Blodgett-films" suggests the possible use of Langmuir-Blodgett-films as insulating and tunneling layers. It is an object of the present invention to provide an electron emission device which resolves the above problems and has no structural defect such as pinhole in an insulation layer. The object is solved by a multi-emitter device for emitting electrons according to the characterising part of claim 1. Figs. 1 and 2 show partial sectional views of electron emission devices for illustrating the structure, Fig. 3(a) shows a partial plan view of the electron emission device in accordance with present invention, and Figs. 3(b) and 3(c) show B-B and C-C sectional views of Fig. 3(a). Fig. 1 shows a partial sectional view of an electron emission device. In Fig. 1, numeral 2 denotes a substrate which is made of insulative material including ceramics such as glass, alumina, saphire, mica and magnecia, and crystals such as GaAs, GaSb, InAs, GaP and spinel (MgAl₂O₄) Numeral 4 denotes a first metal layer, numeral 6 denotes an insulation layer and numeral 8 denotes a second metal layer. Those layers form an MIM structure. The first metal layer 4 may be made of Al, Be, Mo, Pt, Ta, Au, Pd, Ag, W, Cr, Mg or Ni-Cr. The metal layer 4 may be an alloy or silicide of some of those metals. The thickness of the metal layer 4 is not restrictive and it may be 0.01 - 5 µm. The insulation layer 6 may be made of organic insulation material such as stearic acid, arachidic acid, palmitic acid, n-paraffin, hexatriacontan and polyparaxylylene. The insulation layer 6 is preferably as thin as possible so long as insulation breakdown does not occur. The thickness is properly selected in accordance with the type of insulator used for the layer 6 and the type of metal used for the second metal layer 8. For example, it is 10 - 2000 Å. The second metal layer 8 may be made of Au, Pt, Al and Ag. The metal layer 8 may be alloy or silicide of some of those metals. The thickness of the metal layer 8 is as thin as possible to get a higher electron emission efficiency. For example, it is 10 - 500 Å. As shown in Fig. 1, means 10 for applying a voltage with the second metal layer 8 being positive is connected to the first metal layer 4 and the second metal layer 8. The means 10 include a power supply and a switch not shown. The electron emission device may be manufactured in the following manner. The surface of the material for the substrate 2 is polished by mechanical polishing or chemical polishing to have high degree of flatness and surface roughness, and the first metal layer 4 is formed on the substrate 2 by vapor deposition, sputtering, CVD, plasma CVD, ion implating or cluster ion beam method. The insulation layer 6 is then formed on the first metal layer 4. It may be formed by single molecule accumulation method (so-called Langmuir-Blodgett method), vapor deposition, or CVD. In the single molecule accumulation method, a single molecule layer of a surface active organic material is formed on liquid surface, and the substrate surface is moved across the liquid surface to shift the single molecule layer of the surface active organic material onto the substrate surface. The movement of the substrate is repeated as required so that the single crystal layer is accumulated to form the organic material film of a desired thickness. The molecules of the single molecule film or accumulated film should have a hydrophobic portion and a hydrophibic portion in the same chemical constitution. Most typical hydrophobic portion is a long chain alkyl group which usually has 5 - 30 carbons and preferably 10 - 25 carbons. If the length of the alkyl chain is appropriate, straight chain alkyl group or branched alkyl group may be used. Other hydrophobic groups are olefin hydrocarbon group such as vinylene, vinylidene and acetylene, condensated polycyclic phenyl group such as phenyl, naphthyl and anthranil and chained polycyclic phenyl group such as biphenyl and terphenyl. They may be used single or in combination, and may be located at an end or an intermediate position of the alkyl group. Most typical hydrophilic portions are carboxyl group, its metal salt and amine salt, sulfon amide group, amide group, amino group, imino group, hydroxyl group, class 4 amino group, oxyamino group, oxyimino group, diazonium group, quanidine group, hydrazine group, phosphoric acid group, silicic acid group and aluminic acid group. The organic insulation layer 6 formed by the single molecule accumulation method may be a fatty acid such as stearic acid, arachidic acid, palmitic acid, azulene squarilium dye and deviation of diacetylene. By the single molecule accumulation method, the organic insulation layer 6 having a uniformily thin thickness and substantially no defect such as pinhole is provided. The organic insulation layer 6 formed by the vapor deposition may be n-paraffin, hexatriacontan and stearic acid. The organic insulation layer 6 formed by the CVD method by a plasma polymerized film formed from polyparaxylylene and hydro-carbon. The second metal layer 8 is formed on the organic insulation layer 6. It is formed in the same manner as the first metal layer 4. Then, the voltage application means 10 is connected to the first metal layer 4 and the second metal layer 8. The device of the present embodiment is driven by closing the switch of the voltage application means 10. The voltage of the means 10 is appropriately selected in accordance with the structure of the MIM device and the desired electron emission characteristic. For example, it is 3 - 20 volts. By applying such a voltage across the first metal layer 4 and the second metal layer 8, electrons are emitted from the surface of the second metal layer 8. Fig. 2 shows a partial sectional view of an another electron emission device. In Fig. 2, the like elements to those shown in Fig. 1 are designated by the like numerals. The present embodiment is different from the first device only in that a lamination of an organic insulation layer 6 and an inorganic insulation layer 5 is used as the insulation layer. The inorganic insulation layer 5 may be made of an oxide of the metal used for the first metal layer 4. It may be formed by converting the surface of the first metal layer 4 to an insulation layer consisting of a metal oxide by means of thermal oxidation, air oxidation or anode oxidation. When the single molecule accumulation method is used to form the organic insulation layer 6, the surface of the first metal layer 4 may sometimes be automatically oxidized by dipping into liquid, and it may be used as the inorganic insulation layer 5. In the present embodiment, since the insulation layer is the lamination of the inorganic insulation layer and the organic insulation layer, a sufficient strength is provided by the inorganic insulation layer, and the defect such as pinhole in the inorganic insulation layer is covered by the organic insulation layer and the performance is improved. Figs. 3(a) to 3(c) show an embodiment of the electron emission device having a number of electron emission devices explained above arranged. Fig. 3(a) shows a partial plan view, and Figs. 3(b) and 3(c) show B-B and C-C sectional views. In the present embodiment, numeral 2 denote a substrate on which a plurality of first metal layers 4 of predetermined width are arranged in parallel along a direction C-C. Numeral 6 denotes an organic insulation layer which is applied over the entire surface to cover the substrate 2 and the first metal layer 4. Numeral 8 denotes second metal layers having a predetermined width and extending along a direction B-B. They are arranged parallelly at a constant pitch on the organic insulation layer 6. The substrate 2, first metal layers 4, organic insulation layer 6 and second metal layers 8 are made of the materials explained in the first embodiment. The device of the present embodiment is manufactured in the same manner as that explained in the first embodiment. In the present embodiment, however, the first metal layers 4 and second metal layers 8 must be patterned. The patterning may be done by conventional photolithography technique. While not shown in Fig. 3, means for applying a voltage with the second metal layers being positive is connected to the first metal layers 4 and the second metal layers 8. In the present embodiment, the MIM structure of the first embodiment is constructed at each of the crosspoints of the first metal layers 4 and the second metal layers 8. A desired MIM structure may be driven by a matrix drive. In accordance with the present embodiment, since the insulation layer of the MIM structure includes the organic insulation layer, the structural defect such as pinhole is substantially prevented and the electron emission device having a uniform characteristic is provided.

Claims: A multi-emitter device for emitting electrons comprising a substrate (2), a plurality of stripes of a first metal (4) arranged in parallel within a constant interval on said substrate, an insulator layer (6) on said first metal stripes, a plurality of stripes of a second metal (8) arranged in parallel with a constant interval on said insulator layer so as to form a matrix structure, and voltage applying means (10) for applying a voltage between said first and second metal stripes, characterized in that said insulator is an organic insulator comprising a multi-layer structure of mono-molecular layers. A multi-emitter device according to claim 1, wherein in addition an inorganic insulator layer (5) is provided between said organic insulator and at least one of said first and second metals. A multi-emitter device according to claim 1, wherein said voltage applying means comprises a power source and a switch. A multi-emitter device according to claim 1, wherein said organic insulator is a Langmuir-Blodgett film.

Inventors: OKUNUKI MASAHIKO, SHIMIZU AKIRA, SHIMODA ISAMU, SUGATA MASAO, SUZUKI AKIRA, TSUKAMOTO TAKEO, OKUNUKI, MASAHIKO, SHIMIZU, AKIRA, SHIMODA, ISAMU, SUGATA, MASAO, SUZUKI, AKIRA, TSUKAMOTO, TAKEO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1987
Main classification: H01J1
IPC codes: H01J1