Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2000-09-21
2002-05-28
Sikes, William I. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C438S486000, C438S487000, C372S024000, C372S040000, C117S904000
Reexamination Certificate
active
06396560
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P11-268803 filed Sep. 22, 1999, which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing a flat panel display (FPD) such as a liquid crystal display panel or O-ELD (organic electroluminescence display), and particularly to a method capable of producing, at a high throughput, a large-area liquid crystal display panel having a horizontal scanning circuit portion including a TFT characteristic having a high drive current (high mobility), and a pixel portion and a vertical scanning circuit portion each of which contains crystal grains excellent in uniformity.
In recent years, FPDs, in particular, liquid crystal display panels have been extensively used as display units for various kinds of electronic equipment. Currently, an active matrix type in which switching of pixels is performed by turning-on/turning-off switching elements formed at respective pixels of a display portion currently ranks as the dominant liquid crystal display panel.
With respect to such an active matrix type FPD such as a liquid crystal display panel, TFTs formed by an amorphous silicon thin film has come to be used as pixel switching elements because the amorphous silicon thin film having a good quality can be uniformly formed on the base of the panel over a large area.
The use of TFTs formed by an amorphous silicon thin film, however, has a problem. Since scanning portions such as a horizontal scanning circuit portion and a vertical scanning circuit portion of a liquid crystal display panel require high speed operation, TFTs used therefor require a TFT characteristic having a high drive current (high mobility). Accordingly, it is undesirable to use TFTs formed by an amorphous silicon thin film, which are low in operational speed, as TFTs of scanning portions of a liquid crystal display panel. To solve such a problem, liquid crystal display panels of a type of making use of an amorphous silicon thin film have been generally configured such that TFTs formed by the amorphous silicon thin film are used as pixel switching elements of a pixel portion, and a horizontal scanning portion and a vertical scanning portion, which are formed by exclusive use ICs, are externally connected to the pixel portion.
On the other hand, TFTs formed by a polycrystalline silicon thin film are higher in operational speed than TFTs formed by an amorphous silicon thin film. In this regard, there have been proposed FPDs such as liquid crystal display panels of a type in which scanning portions such as a horizontal scanning circuit portion and a vertical scanning circuit portion are formed by using TFTs formed by a polycrystalline silicon thin film and also a pixel portion is formed by using TFTs formed by the polycrystalline silicon thin film. With respect to the manufacture of liquid crystal display panels using TFTs formed by a polycrystalline silicon thin film as switching elements, there has been developed a technique of annealing an amorphous silicon thin film by irradiation of a pulse laser having an ultraviolet wavelength region such as an excimer laser, thereby crystallizing the amorphous silicon thin film.
Such a known laser annealing method generally involves irradiating an amorphous silicon thin film with a linear laser beam having a width less than 800 &mgr;m by several shots at each location by moving the laser beam relative to the amorphous silicon thin film, to anneal overall the amorphous silicon thin film, thereby crystallizing the amorphous silicon thin film.
This laser annealing method, however, has a problem that since the linear laser beam having a width less than 800 &mgr;m is used, not only the throughput is low but also crystal grains become uneven at adjacent laser irradiation portions.
To solve the problem caused by using a linear laser beam, there have been proposed methods of annealing overall an amorphous silicon thin film by using a large-area laser beam, thereby crystallizing the amorphous silicon thin film (for example, “Comparison of Effects Between Large-Area-Beam ELA and SPC on TFT Characteristics”, 1996 IEEE p1454~, and “1 Hz/15 Joules-excimer laser development for flat display applications”, SID '99 Conference). However, it has been actually impossible to crystallize, using a large-area laser beam, a large-area amorphous silicon thin film having a size of 10 inches or more by annealing from the viewpoints of energy density required for crystallization and load of an optical system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of capable of producing, at a high throughput, a large-area liquid crystal display panel having a horizontal scanning circuit portion including a TFT characteristic having a high drive current (high mobility), and a pixel portion and a vertical scanning circuit portion each of which contains crystal grains excellent in uniformity.
To achieve the above object, according to the present invention, there is provided a method of producing a FPD such as a liquid crystal display panel or O-ELD, including the steps of: irradiating a location, in which a horizontal scanning circuit portion is to be formed, of an amorphous silicon thin film panel to be crystallized with a specific number of shots of a laser beam having a uniform energy density distribution and having a rectangular shape of a long-side larger than a width of the amorphous silicon thin film panel and a short-side larger than a short-side of the horizontal scanning circuit portion, in a state in which a relative positional relationship between the amorphous silicon thin film panel and the laser beam is fixed; and irradiating a location, in which a vertical scanning circuit portion and a pixel portion are to be formed, of the amorphous silicon thin film panel with the laser beam while moving the laser beam relative to the amorphous silicon thin film panel along the length direction of the amorphous silicon thin film panel.
With this configuration, since laser annealing is performed by using the laser beam having a uniform energy density distribution and having a rectangular shape of a long-side larger than a width of the amorphous silicon thin film panel to be crystallized and a short-side larger than a short-side of the horizontal scanning circuit portion, it is possible to anneal the horizontal scanning circuit portion by the laser beam without the need of moving the laser beam relative to the horizontal scanning circuit portion, and hence to prevent crystal grains in the horizontal scanning circuit portion from becoming uneven. Also, since the location, in which the horizontal scanning circuit portion is to be formed, of the amorphous silicon thin film panel is annealed by irradiating the location with the specific number of shots of the laser beam in the state in which the relative positional relationship between the amorphous silicon thin film portion and the laser beam is fixed, it is possible to produce crystal grains having large grain sizes in the horizontal scanning circuit portion, and hence to form TFTs having a high mobility in the horizontal scanning circuit portion. Further, since the pixel portion and the vertical scanning circuit portion, which do not require a TFT characteristic having a high mobility comparable to that required for the horizontal scanning circuit portion, are formed by irradiating the amorphous silicon thin film panel with the laser beam while moving the laser beam relative to the amorphous silicon thin film along the length direction of the amorphous silicon thin film panel, it is possible to produce crystal grains having grain sizes which are small and less varied while preventing the crystal grains from becoming uneven in the transverse direction of the amorphous silicon thin film panel, and hence to form TFTs having uniform threshold values in the pixel portion and vertical scanning circuit portion.
In one preferred mode of the present inven
Nakajima Hideharu
Noguchi Takashi
Usui Setsuo
Chowdhury Tarifur R.
Sikes William I.
Sonnenschein Nath & Rosenthal
Sony Corporation
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