Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2000-01-13
2002-07-30
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S491000, C313S311000
Reexamination Certificate
active
06426590
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a planar color lamp for illuminating a flat panel display and more particularly, relates to a planar color lamp that utilizes field emission light source of nanotube emitters that are arranged in serpentine shape for use in the illumination of LCD or other flat panel displays and a method for fabricating such color lamp.
BACKGROUND OF THE INVENTION
In the construction of liquid crystal display (LCD) panels, a method of illumination must be utilized since the liquid crystal itself does not illuminate. The illumination is also important when the available lighting for viewing a LCD is insufficient. In order to make large LCD panels, and specifically colored LCD panels, a high efficiency light source must be used for illumination in order to achieve the requirements of small panel thickness, lightweight and low power consumption. The capability of achieving high brightness at a low power consumption is essential for obtaining a long battery life between recharging in portable applications for LCD's. In recent years, the improvements made in the other parts of a LCD display, i.e., the color filter arrays, the thin film transistors, and other performance enhancement layers reduce the overall transmittance of a liquid crystal display panel. As a result, any improvement that can be made in the brightness/power ratio must be obtained from the improvement in the backlighting efficiency of a panel.
In the conventional backlighting technology for flat panel displays, cathode fluorescent lamps are used to illuminate the flat panel display. The cathode fluorescent lamps provide the benefits of high luminous efficiency, long service life, lightweight and rugged structure. The lamps are normally installed in pairs along the sides of a display panel, e.g., a display panel in a notebook computer, with a light tube arrangement for creating uniform lighting across a diffuser screen. More recently, improvements in backlighting have been provided which include a flat fluorescent backlight and a wedge-shaped light tube which distributes the light from a single bulb evenly over the entire display surface. The wedge-shaped construction allows a single lamp to illuminate the entire liquid crystal display panel. A plastic molded light tube which contains prismatic specular reflectors helps to spread the light uniformly across a front plane of the device.
Flat fluorescent lamps have also been recently developed to directly illuminate a display panel. A typical construction of a flat fluorescent lamp device measures only 3 mm thick. Panel sizes ranging from diagonal lengths between 25 mm and 350 mm have been made by using the conventional cold cathode technology. The lamp housing can be constructed by using a formed plate and a flat plate laminated together. For instance, a typical lamp can be constructed of a serpentine channel of four intervals equipped with an electrode at each end. A typical design of the flat fluorescent lamp includes a phosphor coating on both a top and a bottom plate, while a reflective coating is placed only on the bottom plate. A high voltage of between 1 kV and 3 kV (depending on the panel size and cathode type) is normally required to operate a flat fluorescent lamp.
For a color liquid crystal display device, color filters in three basic colors of red, green and blue must be utilized. The manufacturing process for color filters involves a number of steps such as chemical vapor deposition, spin coating of insulators and metals, and the planarization and orientation film coatings. Color filters can be formed on glass substrates by complicated processing steps which include glass finishing and preparation of both the front and the back of a substrate, the polishing and lapping process, the washing and cleaning of the substrate, the coating, curing and other steps which must be performed on the substrate.
The formation of color filters requires a repetitive process to be carried out for forming the three primary color elements. Inbetween the color elements, a black border or a black matrix is needed for providing the necessary contrast. To prepare the color filters, either an organic dye or a pigment can be used as long as it is suitable as a light absorbing color filter material. For instance, a gelatin can be deposited and dyed in successive photolithographic operations by using proximity printing equipment and standard photoresist materials. A pigment dispersion method can also be used which eliminates the gelatin layer and is capable of higher temperature stability. Other methods for forming color filters include electrodeposition and printing.
FIG. 1A
shows a conventional color filter device
110
consisting of three primary color filters, i.e., red filter
112
, green filter
114
and blue filter
116
. A white light source
120
is used for backlighting the single pixel
110
. In this conventional color filter/backlighting arrangement, a large area is occupied by a single pixel and as a result, the resolution achieved on a liquid crystal display panel is relatively poor.
In another conventional color filter/backlighting device as shown in
FIG. 1B
, in the same area that was occupied by a single pixel where a white light backlighting is used, three pixels are arranged wherein each pixel can be one of the three primary colors by utilizing three different light sources
124
,
126
and
128
for each pixel. Significant improvement in resolution is therefore possible due to the greatly reduced sizes of the pixels. The color filters used in this arrangement,
130
,
132
and
134
are essentially transparent for accepting a color from the color sources
124
,
126
and
128
. This arrangement is known as a sequential color display. In the sequential color display arrangement, a cathode-ray tube is normally employed as a light source that emits light at a plurality of wavelengths. Since there is an inherent light loss created by the polarization of the emitted light and the duty cycle of the liquid crystal cell, the maximum efficiency for the transmitted white light is reduced to as low as 25%. The display brightness in a field sequential color display is therefore a major concern.
In recent years, flat panel display devices have been developed and widely used in electronic applications such as personal computers. One of the popularly used flat panel display device is an active matrix liquid crystal display which provides improved resolution. However, the liquid crystal display device has many inherent limitations that render it unsuitable for a number of applications. For instance, liquid crystal displays have numerous fabrication limitations including a slow deposition process for coating a glass panel with amorphous silicon, high manufacturing complexity and low yield for the fabrication process. Moreover, the liquid crystal display devices require a fluorescent backlight which draws high power while most of the light generated is wasted. A liquid crystal display image is also difficult to see under bright light conditions or at wide viewing angles which further limit its use in many applications.
Other flat panel display devices have been developed in recent years to replace the liquid crystal display panels. One of such devices is a field emission display device that overcomes some of the limitations of LCD and provides significant advantages over the traditional LCD devices. For instance, the field emission display devices have higher contrast ratio, larger viewing angle, higher maximum brightness, lower power consumption and a wider operating temperature range when compared to a conventional thin film transistor (TFT) liquid crystal display panel.
A most drastic difference between a FED and a LCD is that, unlike the LCD, FED produces its own light source utilizing. colored phosphors. The FEDs do not require complicated, power-consuming backlights and filters and as a result, almost all the light generated by a FED is visible to the user. Furthermore, the FEDs do not require large arrays of thin film
Chung Feng-Yu
Tsai Kuang-Lung
Wang Wen-Chun
Guharay Karabi
Industrial Technology Research Institute
Patel Nimeshkumar D.
Tung Randy W.
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