Patent ID: 7348722

Claim:
A field emission device comprising: a substrate; a cathode electrode formed on the substrate; a focusing control insulating layer formed on the cathode electrode, and having a first cavity that exposes a portion of the cathode electrode; an electron emission source disposed on the cathode electrode, said electron emission source being exposed by the first cavity; a focusing control electrode formed on the focusing control insulating layer and including a focusing control hole aligned with the first cavity; and means for applying to the focusing control electrode a voltage that is lower than the potential of the cathode electrode so as to control the focus of an electron beam emitted from the electron emission source; a gate insulating layer formed on the focusing control electrode, and having a second cavity aligned with the first cavity; and a gate electrode formed on the gate insulating layer, and having a gate hole aligned with the second cavity, wherein an edge of the focusing control electrode facing the electron emission source is formed at a relative position, (x, y) calculated by the following equations, with respect to an upper edge of the electron emission source: C/ 2 <x< 2 C − E/ 2 <y< 2 F/ 3, wherein C denotes a radius of the electron emission source, E denotes a height of the electron emission source, and F denotes a height from the upper portion of the electron emission source to the gate electrode.