In general, flat panel displays (FPDs) may be classified into emissive displays and non-emissive displays.
The emissive displays may be cathode ray tubes (CRTs), plasma display panels (PDPs), and field emission displays (FEDs), and the non-emissive displays may be liquid crystal displays (LCDs).
Although an LCD is lightweight and consumes low power, the LCD is a non-emissive display that cannot be self-luminescent but receives external light to form an image so that an object cannot be observed using the LCD in a dark place. In order to solve this problem, a backlight unit (BLU) is installed on a rear surface of the LCD.
Conventional BLUs may employ cold cathode fluorescent lamps (CCFLs) functioning as linear light sources and light emitting diodes (LEDs) functioning as point light sources.
However, complicated constructions of BLUs have led to a rise in fabrication costs. Also, since a light source is disposed on a side of a BLU, power consumption increases due to reflection and transmission of light. Above all, it is difficult to ensure uniformity of luminance due to on-going scaling-up of LCDs.
In recent years, field emission BLUs having planar emissive structures have been developed in order to solve the above-described problems. Compared with conventional BLUs using CCFLs, the field emission BLUs consume low power and exhibit comparatively uniform luminance over large emission regions.
Conventionally, a field emission BLU includes a cathode substrate having a field emitter and an anode substrate having a fluorescent material, which are disposed a pre-determined distance apart from each other and opposite to each other and vacuum-packaged, so that electrons emitted from the field emitter collide with the fluorescent material of the anode substrate to cause cathode luminescence of the fluorescent material.
The above-described conventional FED will now be described in more detail with reference to FIG. 1.
FIG. 1 illustrates a conventional FED.
Referring to FIG. 1, an anode electrode 110 is disposed on one surface of an anode substrate 100, and a fluorescent material 120 is disposed on one surface of the anode electrode 110. A cathode electrode 210 is disposed on one surface of a cathode substrate 200, and field emitters 220 are disposed on a first substrate of the cathode electrode 210. A gate electrode 400 is disposed over the cathode substrate 200 on which the cathode electrode 210 and the field emitters 220 are disposed. Each of the field emitters 220 is exposed through an inclined opening 400a of the gate electrode 400 opposite to the fluorescent material 120. Also, a plurality of first spacers 310 are disposed between the gate electrode 400 and the anode electrode 110, and a plurality of second spacers 320 are disposed between the gate electrode 400 and the cathode electrode 210.
When a predetermined drive voltage is applied to the cathode electrode 210, the gate electrode 400, and the anode electrode 110, electron beams are radially emitted from the field emitter 220. As a result, the electron beams emitted from the field emitter 220 reach a portion of the fluorescent material 120 corresponding to the corresponding pixel to emit light.
On the other hand, a CCFL having the above-described construction operates at low speed, thus precluding partial dimming or pulse driving. Furthermore, there is a specific limit for increasing a contrast ratio or eliminating a residual image from a dynamic picture.
In order to overcome the above-described drawbacks, a BLU using an LED controls luminance or drives pulses according to an image displayed on a picture so as to obtain a high contrast ratio and a clear moving image. However, the BLU using the LED requires a high fabrication cost and complicated driver circuits. In addition, the BLU using the LED has a relatively short lifetime and hinders surface emission.
Therefore, a vast amount of research has been conducted on field emission lamps capable of local dimming in which a plurality of cathode electrodes are embodied as cathode blocks. However, when the number of the cathode blocks is increased to enable fine local dimming, interconnections between the cathode blocks and external electrodes become complicated.
Owing to the above-described problems, a field emission lamp capable of standard local dimming has only a limited number of cathode blocks, thereby hindering fine local dimming.