The present invention relates to flat panel displays of the field emission cathode type and, in particular, to the use of a spacer between a cathode and an anode to take advantage of the pin hole imaging effect and an electric field to produce high resolution full color image display. In the preferred embodiment, the spacer is made of a glass-ceramic material.
The cathode ray tube (CRT) technology, with its many attractive attributes such as high brightness, good color quality, high resolution, long operating life time, is still the main stream display technology nowadays. It is its bulk that overshadows a lot of its merits and encourages the emerging flat panel technologies to challenge its place. Through the last twenty years, various types of flat panel technologies have emerged but have succeeded only in making a dent on the vast display market by creating a small form factor display panel for the portable computer industry. The huge consumer television (TV) market, which is emerging towards high definition television (HDTV) format, is still unchallenged by the current available flat panel technologies, such as: liquid crystal display (LCD); electroluminescent display (EL); plasma display panel (PDP); vacuum fluorescent display (VFD); field emission display (FED) and light emitting diode (LED).
The problem of these current flat panel technologies is that they in principle only have a few, but not all of the above mentioned attributes that the CRT technology inherently enjoys. The LCD does not emit light. The PDP cannot generate quality color efficiently and is in association with very complicated drive circuitry. The EL and LED are deficient in blue color. The VFD is deficient in color. The FED in principle should have all the good attributes but lacks a structure to embrace them. In order to break these barriers, some approaches have resorted to brute force by spending billions of dollar on a particular flat panel technology. The 10 inch active matrix liquid crystal display (AMLCD), a color display, is a result of such an effort, but one can also tell from the difficulty of this effort that a 40 inch AMLCD will be extremely difficult to achieve.
In the FED, its cathode is based on the field emission cold cathode principle, as proposed by Spindt in 1968. In this design, the anode is made based on the common CRT anode principle, such as using an electrical conductor coated with phosphor material emitting light in response to the bombardment of electrons from the cathode. In principle, this type of device has the potential of providing many nice features, such as high emission efficiency, high and stable emission current, good color quality, high resolution, small form factor and simple control mechanism. The main problems that it is facing today is lacking a structure which can provide:
(1) uniform spacing between Cathode and Anode; PA1 (2) adequate spacing to allow sufficient anode voltage to be applied in order to realize the good quality of the CRT phosphor; PA1 (3) means to guarantee minimum cross-talk between phosphor dots to achieve high resolution; PA1 (4) means to provide strong support between anode and cathode so that both conditions as mentioned in above items 1, 2 and 3 can be met and thus a thin and large display device can be realized; and PA1 (5) easy to manufacture.
Many structures have been proposed by various people before in order to satisfy these criteria. None of them have succeeded completely. These structures can be basically grouped into the following three categories:
1. Polyimide Type Spacer Structure
The U.S. Pat. Nos. 5,063,327, 4,923,421 and 4,857,161, are typical in this approach. It uses a supporting mechanism made from polyimide spacers or pillars using techniques commonly known in the integrated circuit industry, to separate the emitting surface and the display face of the flat panel display.
2. Rigid Elongated Thin and Pointed Spacer Structure
The U.S. Pat. No. 4,857,799, and 5,015,912 illustrate this type of display. The supporting mechanism is composed of elongated, thin and pointed parallel spacer plates integrally connected between the face plate and back plate, to be interspersed between adjacent rows of pixels on the anode.
3. Small Discrete Type Device with Limited Peripheral Wall Support Structure
The U.S. Pat. No. 3,855,499 is a typical example of this type of display where the whole device relies on the peripheral wall support to create a small vacuum environment for the display device to function.
In the three types of displays described above, the first type, while providing a structure that satisfies the first, third and fifth but fails to satisfies the second and fourth of the above mentioned criteria. In other words, for the first type of displays, the thin pillars used as the support between the face plate and back plate can only be made to allow a very small spacing between these two plates. Within this spacing, only low anode voltage can be used and thus only bluish green ZnO:Zn type low voltage phosphor of the VFD type can be used. Phosphors of other color operating in this low voltage will exhibit low efficiency, low brightness and short life time. This technique is also incapable of providing larger spacing between these two plates.
The design in the second type, while providing a structure that satisfies the second (i.e. larger spacing), fails somewhat in satisfying the first, third, fourth and fifth of the above mentioned criteria.
The third type, while it can provide character or graphic generator type of display application, is only applicable to a limited small size device of a few inches only.
The present invention intends to address these problems by introducing a new shield plate structure, whereof an electric field will be applied between the anode and cathodes using the pin hole image effect to create a new kind of FED, such that all of the above mentioned criteria can be satisfied to produce a high resolution, high brightness, high efficiency, full color flat panel display device with very thin profile and very simple structure.