1. Field of the Invention
The present invention relates to a light emitting apparatus using a luminescent element emitting fluorescence or phosphorescence by applying an electric field to an element having a film including an organic compound (hereinafter, described as “organic compound layer”) between a pair of electrodes and a method of fabricating the light emitting apparatus. Further, a light emitting apparatus in the specification includes an image display device, a light emitting device or a light source (including illuminating device). Further, a light emitting apparatus includes all of a module of a light emitting apparatus attached with a connector, for example, FPC (Flexible Printed Circuit) or TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package), a module provided with a printed circuit board at a front end of TAB tape or TCP and a module in which a luminescent element is directly mounted with IC (Integrated Circuit) by COG (Chip On Glass) system.
2. Description of the Related Art
There is expected application of a luminescent element using an organic compound characterized in thin shape, light weight, high response and direct current voltage drive as a light emitting body to a flat panel display of next generation. Particularly, a display apparatus arranged with luminescent elements in a matrix-like shape seems to be superior to a liquid crystal display apparatus of a related art in view of wide viewing angle and excellence in optical recognizing performance.
According to the light emitting mechanism of a luminescent element, it is said that by interposing an organic compound layer between a pair of electrodes and applying voltage, an electron injected from a cathode and a hole injected from an anode are recombined at a center of light emittance in the organic compound layer to form molecular exciton and when the molecular exciton returns to the ground state, energy is discharged to emit light. There are known singlet excitation and triplet excitation in an excited state and it seems that light can be emitted by way of either of the excited states.
It is possible to use driving methods of passive matrix drive (simple matrix type) and active matrix drive (active matrix type) for such a light emitting apparatus formed by arranging luminescent elements in a matrix-like shape. However, when a pixel density is increased, the active matrix type provided with a switch for each pixel (or dot) is advantageous since the active matrix type can be driven at low voltage.
Further, although a low molecular species material and a high molecular species (polymer species) material are respectively researched for an the organic compound for constituting the organic compound layer (strictly speaking, light emitting layer) regarded to be the core of a luminescent element, more attention is given to the high molecular species material facilitated to handle and having high heat resistance than the low molecular species material.
Further, although there are known methods such as vapor deposition method, spin coating method and ink jet method for a film forming method of the organic compounds, as a method for realizing full color formation by using the high molecular species material, spin coating method and ink jet method are particularly well known.
However, when the spin coating method is used, the organic compound is formed over an entire film forming surface and therefore, it is difficult to selectively form the film in which the organic compound is formed only at a portion intended to form the film and the film is not formed at a portion which is not necessary to form the film.
Further, the active matrix type light emitting apparatus is formed with a wiring for inputting an electric signal from an outside power source to a drive circuit formed over a substrate, and a wiring for electrically connecting a luminescent element comprising a cathode, an anode and the organic compound layer formed by the organic compound formed at a pixel portion and the outside power source and therefore, when the organic compound is formed at the portions of the wirings connected to the outside power source, there poses a problem that ohmic contact cannot be achieved with outside power source.
Meanwhile, according to the ink jet method known as a method of selectively forming an organic compound of a high molecular species, although organic compounds for emitting three kinds (R, G, B) of light can be coated to divide in one step, film forming accuracy is poor, the control is difficult and therefore, uniformity is not achieved and dispersion is liable to be brought about. As causes of the dispersion in the ink jet method, a dispersion in nozzle pitch, a dispersion in bending in ink flying, a dispersion in stage matching accuracy and a dispersion in timings of delivery of ink and movement of stage. For example, there are problems in conditions of execution in which a nozzle for ink jet is clogged by internal viscous resistance of ink prepared by dissolving the organic compound in a solvent and ink injected from the nozzle is not impacted to a desired position and a problem in practical use in which the need for an exclusive apparatus having a highly accurate stage, an automatic alignment mechanism and an ink head becomes costly. Further, ink spreads after impact and therefore, a margin to some degree is needed as an interval between contiguous pixels to thereby make highly fine formation difficult.