(a) Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device in which a high voltage can be applied to an anode electrode by improving a pattern of apertures of a grid electrode.
(b) Description of the Related Art
Generally, electron emission devices can be classified into two types. A first type uses a hot (or thermoionic) cathode as an electron emission region (or source) and a second type uses a cold cathode as an electron emission region (or source).
Also, in the second type of 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 their type, they all basically have an electron emission unit placed within a vacuum vessel, and a light emission unit facing the electron emission unit in the vacuum vessel.
Generally, an FEA type electron emission device has a front substrate and a rear substrate. Electron emission regions, together with cathode electrodes and gate electrodes for emitting electrons (or electron beams) from the electron emission regions, are formed on the rear substrate. Phosphor layers, together with an anode electrode that receives high voltages for accelerating the electron beams, are formed on the surface of the front substrate facing the rear substrate.
In the FEA type electron emission device, as a high voltage is applied to the anode electrode (i.e., as the voltage applied to the anode goes up), a brightness of the electron emission device can be increased, and/or driving voltages of the electron emission device can be decreased such that the lifespan of electron emission regions of the electron emission device can be increased due to a low voltage drive condition.
However, when a high voltage is applied to the anode electrode, an arc discharge may be possible. An arc discharge can occur because a significant amount of gas is ionized in a moment of outgassing. As such, the electron emission regions and the exposed electrodes can be damaged due to the arc discharge.
Therefore, an electron emission device with a grid electrode of a mesh type has been proposed. The grid electrode is mounted between the front substrate and the rear substrate. The grid electrode has many apertures to pass electron beams and/or to focus electrons emitted from the electron emission regions. Additionally, the grid electrode helps in preventing elements from being damaged due to an arc discharge.
A conventional grid electrode has one aperture corresponding to one sub-pixel. In the context of the present invention, a sub-pixel is referred to as an intersection of one cathode electrode and one gate electrode. However, a high voltage applied to the anode electrode can still adversely affect electron emission regions of an electron emission device when the apertures of the grid electrode are too large. Thus, an outbreak of diode emission is possible. In the context of the present invention, a diode emission is referred to as an unwanted pixel illumination caused by electrons emitted at a specific sub-pixel due to a high voltage applied to the anode electrode. To prevent such diode emission, a conventional electron emission device has a limit on how high a voltage level can be applied to the anode electrode.