Field emission cathode device and field emission display using the same

The field emission cathode device includes an insulating substrate with a number of cathodes mounted thereon. A number of field emission units are mounted on the cathodes. A dielectric layer is disposed on the insulating substrate and defines a number of voids corresponding to the field emission units. The dielectric layer has an upper and lower section and disposed on the insulating substrate. The dielectric layer defining a plurality of voids corresponding to the field emission units. A number of grids disposed between the upper and lower sections, and wherein each grid are secured by the upper and lower sections of the dielectric layer.

BACKGROUND

1. Technical Field

The disclosure relates to field emission displays and, specifically, to a field emission cathode device and display using the device.

2. Discussion of Related Art

Field emission displays (FEDs) are a new, rapidly developing flat panel display technology. Compared to conventional technologies, such as cathode-ray tube (CRT) and liquid crystal display (LCD) technologies, FEDs are superior in providing a wider viewing angle, lower energy consumption, smaller size, and higher quality. In particular, carbon nanotube-based FEDs (CNTFEDs) have attracted much attention in recent years.

Generally, FEDs can be roughly classified into diode and triode structures. Diode structures have only one cathode electrode and only one anode electrode, and are only suitable for displaying characters, not for applications requiring high resolution. The diode structures require high voltage, produce relatively non-uniform electron emissions, and require relatively costly driving circuits. Triode structures were developed from diode structures by adding a gate electrode for controlling electron emission. Triode structures can emit electrons at relatively lower voltages.

Referring toFIGS. 4 and 5, a triode field emission cathode device100, according to the prior art, is disclosed. The field emission cathode device100includes an insulating substrate102, a number of longitudinal cathodes104attached on the substrate102, a number of field emission units110distributed on the cathodes104, a dielectric layer106, and a number of gate electrodes108directly mounted on the top of the dielectric layer106. The cathodes104are spaced and parallel. The field emission units110are arranged in series on the cathodes104. The field emission units110are electrically connected to the cathodes104and have a number of field emitters mounted thereon. The dielectric layer106includes a number of through holes116exposing the cathodes104and the field emission units110. An axis of the gate electrode108is perpendicular to that of the cathodes104. Due to detachability between the gate electrodes108and the dielectric layer106, the gate electrodes108are prone to sliding and deformation relative to the dielectric layer106during packaging of the field emission cathode device100. In addition, during operation of the field emission cathode device100, the gate electrodes108are easily distorted by the electric field, which results in a short circuit between the cathodes104and the gate electrodes108. Therefore, the distance between the cathodes104and the gate electrodes108cannot be too short, and preferably exceed 20 microns (μm). However, as the distance between the cathodes104and the gate electrodes108increases, working voltage of the gate electrodes108must increase accordingly. The high working voltage affects the field emission performance of the field emission cathode device100.

What is needed, therefore, is a field emission cathode device and a field emission display with lower working voltage and a higher field emission performance.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present field emission cathode device and field emission display using the same, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION

Reference will now be made to the drawings to describe one embodiment of the present field emission cathode device and a field emission display using the same, in detail.

Referring toFIG. 1andFIG. 2, a field emission cathode device10includes an insulating substrate12, a number of parallel longitudinal cathodes14, spaced and mounted on the insulating substrate12, a number of field emission units32electrically mounted on the cathodes14, a bottom dielectric layer portion26attached on the insulating substrate12, a number of strip shaped grids22perpendicular to the cathodes14in a different plane and distributed on the bottom dielectric layer portion26, and an upper dielectric layer portion28mounted on the grids.

In the present embodiment, the insulating substrate12is glass. However other insulating materials, such as silicon dioxide or ceramic, can be used.

The cathodes14can be copper, aluminum, gold, silver, indium tin oxide (ITO), or a combination thereof. In the present embodiment, the cathodes14are silver.

Each emission unit32includes a number of field emitters mounted thereon. While the field emitters can be metal or silicon having sharp tips or carbon nanotubes, in the present embodiment, carbon nanotubes are used. The field emission units32are located on the cathodes14.

The dielectric layer26is latticed, consisting of a plurality of perpendicularly intersected strips to define a plurality of voids262therein. The dielectric layer26is deposed on the insulating substrate12and extends across a part of the cathodes14, such that some parallel strips of the dielectric layer26are sandwiched between adjacent cathodes14and other strips perpendicular thereto extend across the cathodes14. Each void262corresponds to one field emission unit32. The dielectric layer is insulating material, such as glass, silicon dioxide, or ceramic. The dielectric layer comprises of a bottom dielectric layer portion26and an upper dielectric layer portion28. The dielectric layer is thicker than 15 μm, in the present embodiment being 20 μm.

The grids22are parallel and distributed on the bottom dielectric layer portion26, separating the bottom dielectric layer portion26and upper dielectric layer portion28mounted on the grids22. The bottom dielectric layer portion26mounted below the grids22. The grids22are perpendicular to the cathodes14in a different plane. Each of the grids22covers a number of voids262of the bottom dielectric layer portion26. There can be a plurality of grids22that cover corresponding voids262of the bottom dielectric layer portion26. The bottom dielectric layer portion26supports the grids22. The upper dielectric layer portion26can fix the grids22. The grid22has a metal mesh with holes structure. The holes have an effective diameter that is equal largest round particle that can pass through. The holes can have an effective diameter that is from 3 μm to 1000 μm with distance between the grids22and the cathodes14exceeding or equaling 10 μm. In the present embodiment, the grids22are stainless steel, with the distance between the grids22and the cathodes14of about 15 μm.

In operation, different voltages are applied to the cathodes14and the grids22. Generally, the voltage of the cathodes14is zero or connected to ground. The voltage of the gate electrodes22ranges from ten to several hundred volts (V). The electrons emitted by the field emitter of the field emission units32move towards the grids22under the influence of the applied electric field induced by the grids22, and are then emitted through the holes of the mesh. The cathodes14are insulated from each other, as are the grids22. Thus, the field emission currents at different field emission units32can easily be modulated by selectively changing the voltages of the grids22and the cathodes14. It is to be understood that the number of cathodes14and grids22can be set as desired to achieve the proper modulation.

In the field emission cathode device10, the grids22firmly fixed by the dielectric layer portions26,28such that risk of distortion of the grids22creating an uneven distance between the grids22and the cathodes14(resulting uneven emission of the electrons) is prevented. Thus, the electron emission current of the field emission cathode device10is uniform. Even if the distance between the grids22and the cathodes14is relatively short, the grids22will not touch the cathodes14. Therefore, short circuit between the cathodes14and the grids22is prevented, allowing work voltage of the field emission cathode device10to be easily controlled.

FIG. 3shows a field emission display200using field emission cathode device10. The field emission display200includes an anode electrode device212facing field emission cathode device10.

The distance between the grids22and the cathodes14exceeds or equals 10 μm.

The anode electrode device212of the present embodiment includes a glass substrate214, a transparent anode216disposed on the glass substrate241, and a phosphor layer218spread on the transparent anode216. An insulated spacer220is disposed between the anode electrode device212and the substrate12to maintain a vacuum seal. The edges of the grids22are fixed to the spacer220. The transparent anode216can be an indium tin oxide (ITO) thin film.

In operation, different voltages are applied to the cathodes14, the grids22and the anode216. Generally, the voltage of the cathodes14is zero or connected to ground. The voltage of the gate electrodes22is ten to several hundred volts. The electrons emitted by the field emitter of the field emission units32move towards the grids22under the influence of the applied electric field induced by the grids22, and are then emitted through the meshes of the grids22. Finally the electrons reach the anode216under the electric field induced by the anode216and collide with the phosphor layer218located on the transparent anode216. The phosphor layer218then emits visible light to accomplish display function of the field emission display200. The cathodes14are insulated from each other, as are grids22. Thus, field emission currents at different field emission units32can be easily modulated by selectively changing the voltages of the grids22and the cathodes14.