1. Field of the Invention
This invention relates to an improved design of field emission display (FED) and more particularly to an FED in which the inorganic fluorescent screen is replaced by an organic EL light emitting layer, forming an innovative field emission organic light emitting diode (FEOLED) with improved luminance and lower power consumption.
2. Description of the Related Art
The CRT (cathode-ray tube) is widely employed in TVs and computer terminals. There are three main parts of a CRT: (1) a cathode electrode for hot electron source, (2) a deflection system for deflecting hot electrons injecting from the cathode electrode in perpendicular and horizontal directions to the inorganic phosphor on a fluorescent screen, and (3) an indium tin oxide (ITO) anode electrode on a transparent glass substrate, which ITO anode electrode is coated with inorganic fluorescent screen. Hot electrons generated by applying a high voltage between the cathode and the ITO anode electrode impact the inorganic phosphor on a fluorescent screen to give rise to light. Such device is called a CRT or a Braun tube.
Conventionally, the flat panel display such as FED or SED (surface emission display) is similar to the traditional CRT. Its basic principle of operations is similar to that of CRT. Basically, the emitted electrons bombard the inorganic phosphor of a fluorescent screen, to cause the light emission. However, FED and SED differ from CRT in two main aspects: (1) electrons are emitted from cold cathode electrode; and (2) it is not necessary to have a deflection system for deflecting hot electrons in perpendicular and horizontal directions to the inorganic phosphor. However, the inorganic fluorescent screen for the anode electrode is the same as for CRT display.
Another prior art flat panel display is the OLED (organic light emitting diode) display. The typical structure of OLED comprises (1) an anode electrode of indium tin oxides (ITO) coated on glass substrate, (2) cathode electrode made of low work function metal, and organic multiple layers between the anode and the cathode. Generally, the organic films are deposited by evaporation in a vacuum chamber. When D.C. voltage is applied between the transparent ITO electrode (anode electrode) and the cathode electrode, holes from the anode electrode flow into the hole transport layer (HTL), electrons from the cathode electrode flow into the electron transport layer (ETL). Both carriers (holes and electrons) move toward the interface between the two transport layers (HTL and ETL) and recombine to form excitons. Then these excitons emit light through the transparent electrode (ITO coated on glass substrate). Therefore, the light emitting process for OLED is completed in solid state phase.
For FED and SED, when electric voltage is applied, neither the injection and transport of carriers nor light emission is completed in solid state phase. The light emitting principle of FED and SED is that the electrons are excited and accelerated by the high electric field under vacuum so as to become sufficiently energized to bombard the inorganic phosphor to emit light. Such process is called CL (cathode luminescence).
The inventor has previously applied for patent in an electron multiplier (Dynode) for FED innovation, described in Japan Pat. Pub. No. 2004-227801. The invention discloses a design in which FED luminosity was enhanced by adding secondary electron material-coated holes to the dynode.
Moreover, the inventor has also previously applied for patent in a white light organic electroluminescence (EL) innovation, described in Japan Pat. Pub. No. 2005-150078. The essence of that innovation was that a highly purified white light organic EL can be constructed by stacking three organic emitting layers of different colors (red, green and blue) to an ITO coated glass substrate.