Electron emitting device and process for producing the same

Abstract: An electron emitting device causes electron emission by a current supply in a coarse resistor film. The coarse thin resistor film is composed at least of a coarse thin silicon film.

Description: The present invention relates to a electron emitting device for causing electron emission according to the preamble of claim 1 or claim 2 and to a process for producing the same. A surface conduction electron emitting device is provided with a coarse resistor film in which the film-constituting material is discontinuous as an island structure or has defects, and emits electrons by supplying a current to such resistor film. Conventionally such coarse resistor film has been obtained by forming, on a insulating substrate, a thin film of metal, metal oxide or semi-metal by chemical vapor deposition or sputtering, and applying a current to thus formed film of several ohms to several hundred ohms to cause local destructions of the film by Joule's heat, thereby obtaining a resistance of several killoohms to several hundred megaohms. However, because of such forming process, the electron-emitting device cannot be formed on another semiconductor device but has to be formed as a separate device. The manufacturing process is therefore inevitably complex, and it has been difficult to achieve compactization through integration with a driving circuit. Besides, in the conventional coarse resistor film utilizing metal, metal oxide or semi-metal, the quantity of electron emission is increased by forming, on the surface of said film, a layer of a material for reducing the work function such as a Cs or CsO layer, stable electron emission cannot be expected since the alkali metal such as cesium is unstable. Such unstability can be prevented by forming a silicide of such alkali metal, but the formation of a silicide or oxide layer on the conventional thin film of metal, metal oxide or semi-metal complicates the manufacturing process. Also such conventional forming process is unstable, so that the produced electron emitting devices show fluctuation in the efficiency of electron emission and are associated with a short service life. US-A-3 611 077 discloses a cold cathode vacuum tube comprising a substrate, a thin continuous film of a semiconductive material and electrodes mechanically attached to the substrate. During the fabrication of this device a high electric field is established across the cathode thereby producing a fairly uniform break. According to a second embodiment of the aforesaid device the cold cathode vacuum tube may comprise a plurality of noncontiguous droplets of undefined size. An object of the present invention is to provide an electron emitting device not associated with the above-mentioned drawbacks associated with the prior technology. Another object of the present invention is to provide an electron emitting device allowing easy manufacture and compactization, through the use of a coarse silicon thin film as the resistor film for electron emission by current supply. Still another object of the present invention is to provide an electron emitting device provided with a high electron emission efficiency, a limited device-to-device fluctuation of the characteristics, and a long service life. In case of a generic electron emitting device these objects are achieved by the features according to the characterizing portions of claim 1 or claim 2. Figs. 1 is a schematic view showing the first embodiment of the electron emitting device of the present invention; Fig. 2A is a schematic cross-sectional view of an example of the coarse high resistance film in said embodiment; Fig. 2B is a schematic cross-sectional view of the coarse high resistance film in the second embodiment; Figs. 3A to 3D are schematic views showing process steps for producing the coarse high resistance film. Referring to Fig. 1, on an insulating member 101 such as a glass plate, there are provided electrodes 102, 103 for current supply, between which formed is a coarse high resistance film 104 composed of fine particles. Fig. 2A is a schematic cross-sectional view of an example of the coarse high resistance film 104 in the present embodiment, and Fig. 2B is a schematic cross-sectional view showing another embodiment of the coarse high resistance film 104 in the present invention. In Fig. 5A, metal particles (105) of a size of 0.1 to 10 µm are formed with a distance of 1 to 10 nm (10 - 100 Å) on the insulating member 101 to constitute a coarse high resistance film 104 having discontinuous areas of regular distribution in the sense that the size and gap of the particles are relatively uniform. In Fig. 2B, metal particles 106 of a size of 0.1 to 10 µm, having a surfacial oxide layer 107 of a thickness of zero point several to several tens nm, are formed on the insulating member 101 to constitute a coarse high resistance film 104 having discontinuous areas of regular distribution, across said oxide layers 107. In comparison with the conventional process employing current supply at a high temperature, the above-explained process provides a coarse high resistance film of a stable characteristic with reduced fluctuation. Besides said film can be easily formed even when it is integrated with another semiconductor device, as the current supply at a high temperature is unnecessary. In the following there will be explained a process for producing the coarse high resistance film 104 shown in Fig. 2B. Figs. 3A to 3D are schematic views showing process steps for producing the coarse high resistance film 104. At first, as shown in Fig. 3A, metal particles of a size of 0.1 - 10 µm, composed of copper in this case, are deposited by ordinary evaporation on the insulating member 110 on which electrodes 102, 103 are formed in advance. The metal particles 106 can be formed in a fine particulate structure by setting the insulating member 101 at a relatively high temperature, and the particle size can be controlled by the rate and time of evaporation, and the temperature of substrate. The metal is not limited to Cu but can be Pb, Al or other metals. Then, as shown in Fig. 3B, the metal particles 106 are oxidized or nitrogenated to obtain a thin oxide or nitride layer 107 of a thickness of zero point several. to several tens nm on the surface of said particles. Subsequently, as shown in Fig. 3C, metal particles 106 are again deposited by ordinary evaporation and are oxidized or nitrogenated. The above-explained evaporation and oxidization are repeated by a number of desired times to obtain, as shown in Fig. 3D, a coarse high resistance film 104 in which the metal particles 106 are separated by the oxide or nitride layer 107, thus having regular discontinuous areas. In this manner it is rendered possible to easily form a coarse high resistance film 104 in which minute and regular discontinuities are uniformly distributed. Also the stability of the process allows to provide electron emitting devices with low fluctuation in performance and with a long service life, at a high production yield. The electron emitting device of the present invention is optimized in structure and has an improved electron emitting efficiency, as the discontinuities are regularly distributed in the coarse high resistance film. Also the regular formation of the film reduces the device-to-device fluctuation in case of mass production, and allows to obtain the electron emitting devices of uniform characteristic. Also the above-explained process, not involving conventional forming process, do not contain unstable parameters and can provide electron emitting devices of a long service life and a stable characteristic.

Claims: An electron emitting device for causing electron emission from a coarse high resistance film by a current supply therein, wherein said coarse high resistance film is composed of an agglomerate of fine metal particles having small gaps therebetween, characterized in that the size of said particles and the size of the gaps therebetween are relatively uniform, said particles having a size of 0.1 to 10 µm and the gaps between said particles showing a size of 1 to 10 nm. An electron emitting device for causing electron emission from a coarse high resistance film by a current supply therein, wherein said coarse high resistance film is composed of an agglomerate of fine metal particles having regular discontinuous areas, characterized in that the size of said particles is 0.1 to 10 µm and said particles are separated from each other by a superficial oxide or nitride layer which form said regular discontinuous areas, said oxide or nitride layer showing a thickness of zero point several to several tens nm. An electron emitting device according to claim 1 or 2, characterized in that said coarse high resistance film is provided between electrodes placed side by side on a substrate. An electron emitting device according to claim 3, characterized in that said substrate is a planar one. Method for forming an electron emitting device according to claim 2 wherein said agglomerate of fine metal particles provided with said oxide or nitride layer is obtained by repeatingly performing the process steps of evaporation of the metal material of said particles and conversion of the surface thereof into a high resistance state.

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, H01J9