1. Field of the Invention
The present invention relates to a method for manufacturing an electron emission element, an electron source having a plurality of the electron emission elements arranged therein, and an image forming apparatus such as a display that is configured using the electron source.
2. Related Background Art
Known electron-emission elements are roughly classified into two types: thermionic-emission elements and cold-emission elements. Cold-emission elements include a field emission type (hereafter referred to as an "FE" type), a metal/insulating layer/metal type (hereafter referred to as an "MIM" type), and surface conduction electron emission elements.
An example of the FE type is disclosed in W. P. Dyke and W. W. Dolan, "Field Emission", Advances in Electronics and Electron Physics, 8, 89 (1956) or C. A. Spindt, "Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones", J. Appl. Phys., 47, 5248 (1976).
An example of the MIM type is disclosed in C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 (1961).
An example of the surface conduction electron emission elements is disclosed in M. I. Elinson, "The Emission of Hot Electrons and the Field Emission of Electrons from Tin Oxide," Radio Eng. and Electron Phys., 10, 1290 (1965).
The surface conduction electron emission element uses a phenomenon in which electron emission occurs when a current flows through a thin and small film formed on an insulating substrate, parallel with the film surface. In a typical example of a configuration of the surface conduction electron emission element, conduction processing called forming and subsequent activation are used to form an electron emission section in a conductive thin film that links a pair of element electrodes provided on an insulating substrate.
The forming is accomplished by applying a voltage to both ends of the thin film used to form the electron emission section to locally destroy, deform, or modify this film in order to form a crack having a high electric resistance.
The activation applies a voltage to both ends of the thin film in a vacuum atmosphere having an organic compound to form a carbon film near the crack. Electrons are emitted from near the crack.
Since the surface conduction electron emission element has a simple structure and is easy to manufacture, a large number of such elements are arranged over a large area. Thus, various applications have been researched to utilize this characteristic. This element has been applied to, for example, charging beam sources or image forming apparatuses such as displays.
An example of an arrangement of a large number of surface conduction electron emission elements is an electron source in which such elements are arranged in parallel in such a way that a large number of rows are formed by connecting both ends of the individual elements (for example, Japanese Patent Application Laid-Open No. 1-031332 specification of the applicant).
In particular, for image forming apparatuses such as displays, planar displays using liquid crystals have become popular in recent years in place of CRTs. Disadvantageously, these displays do not emit light spontaneously, they must have a back light. Thus, the development of displays that emit light spontaneously has been desired. An image forming apparatus that is a display comprising a combination of an electron source having a large number of surface conduction electron emission elements arranged therein and a fluorescent body that emits visible radiation using electrons emitted from the electron source is an excellent spontaneously-light-emitting display that is relatively easy to manufacture even with a large screen and that has a high display grade (for example, U.S. Pat. No. 5,066,883 specification of the applicant).
For electron emission elements used for the electron source or the image forming apparatus, the further provision of a stable controlled electron emission characteristic and the improvement of electron emission efficiency are desired in order to provide bright display images stably.
For image forming apparatuses using a fluorescent body as an image forming member, such apparatuses using a low current and forming bright high-grade images, for example, flat televisions, are obtained by providing a stable controlled electron emission characteristic and further improving electron emission efficiency. The use of a low current is also expected to reduce the cost of a driving circuit constituting the image forming apparatus.