(a) Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device with a grid electrode which focuses the electron beams emitted from the electron emission regions, and prevents the electron emission regions from being adversely influenced by the anode electric field.
(b) Description of Related Art
Generally, electron emission devices can be classified into two types. A first type uses a hot cathode as an electron emission source, and a second type uses a cold cathode as the electron emission source.
Also, in the second type electron emission devices, there are a field emitter array (FEA) type, a surface conduction emitter (SCE) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a ballistic electron surface emitting (BSE) type.
Although the electron emission devices are differentiated in their specific structure depending upon the types thereof, they all basically have a vacuum structure formed by first and second substrates. Electron emission regions and driving electrodes are formed on the first substrate to emit electrons from the electron emission regions. Phosphor layers are formed on the second substrate together with an anode electrode for accelerating the electrons emitted from the electron emission regions toward the second substrate to emit light or display the desired images.
Assuming a case where the voltages applied to the driving electrodes on the first substrate are the same, the higher the voltage applied to the anode electrode, the more the screen brightness is enhanced. However, as the voltage applied to the anode electrode is elevated, the electron emission regions are influenced by the anode electric field, and electrons are emitted from the electron emission regions even at the off-state pixels where the electron emission should not be made, thereby causing mis-emission of light. Because of this, it has been proposed that a mesh-shaped grid electrode be provided between the first and second substrates with a plurality of beam-guide holes. The grid electrode functions both to shield the electron emission regions from the anode electric field, and to focus the electron beams emitted from the electron emission regions.
Typically, the grid electrode has one electron beam passage hole that corresponds to each of the respective pixel regions on the first substrate. However, with such a structure, it is very difficult to align the grid electrode between the first and second substrates in accordance with the alignment state of the first and second substrates such that the electron beam passage holes are located at their proper positions, and to assemble them with each other. Because of this, the method for assembling an electron emission device with the above described grid electrode is complicated and expensive.
Furthermore, the grid electrode primarily influences the trajectory of the electron beams depending upon its positional relation to the first and second substrates, and the voltages applied thereto. However, although the typical grid electrode may effectively shield the electron emission regions from the anode electric field, the electron beams passing through the typical grid electrode may be over-focused because the typical grid electrode is not optimized based upon its positional relation to the first and second substrates, and the voltages applied thereto, thereby deteriorating the screen image quality.