Polysilicon TFT Streak Reduction via Ion Implantation
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Solution Overview
Problem
Organic electroluminescent display devices suffer from display unevenness in the form of horizontal and vertical streaks due to variations in drive current, caused by energy variations in excimer laser irradiation during the crystallization of amorphous silicon films used in thin film transistors.
Innovation Solution
A method involving the deposition of an amorphous silicon film on a substrate, followed by excimer laser irradiation to form a polysilicon film, and subsequent impurity ion-implantation, particularly with p-type and n-type impurities like boron and phosphorus, to equalize channel current and reduce streak unevenness by adjusting the potential barriers in the channel region of the thin film transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If excimer laser irradiation is used to crystallize amorphous silicon film, then polysilicon film is formed efficiently, but energy variation in laser irradiation causes drive current variation and display streaks
Solution Approach 1:
The patent applies local quality by implanting impurities at specific locations in the channel region to compensate for spatial variations in laser energy. By creating localized impurity regions, the invention addresses non-uniformities in the crystallized polysilicon film caused by energy variation across the laser irradiation area, thereby equalizing drive current across different pixels while maintaining efficient crystallization.
2Manufacturing precision
If impurity ion-implantation is performed to equalize channel current, then display streak unevenness is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by performing impurity ion-implantation on the amorphous silicon film before laser crystallization. This preliminary impurity introduction allows the impurities to be uniformly distributed in the amorphous phase, and then uniformly incorporated into the polysilicon structure during crystallization, achieving display uniformity while avoiding the need for complex post-crystallization processing steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method significantly reduces horizontal and vertical streak unevenness, with boron and phosphorus ion-implantation demonstrating improvement effects of up to 50% and 48.07% respectively, while maintaining proper operation of the organic EL display panel.
Implementation Method 1
performing a laser irradiation to the amorphous silicon film so the amorphous film is melted and crystallized to form a polysilicon film
Implementation Method 2
the amorphous film is melted and crystallized
Implementation Method 3
the amorphous film is melted and crystallized to form a polysilicon film
Implementation Method 4
implanting impurities in the polysilicon film
Data Source
AI summary
The invention reduces display unevenness of a horizontal streak and a vertical streak of an organic EL display device to improve display quality. A silicon oxide film is deposited on a glass substrate by a plasma CVD method, and an amorphous silicon film is further deposited on the silicon oxide film by the plasma CVD method. Next, an excimer laser is irradiated to the amorphous silicon film for heating the film until the film melts and the film is crystallized to form a polysilicon film. Then, this polysilicon film is etched in a predetermined pattern. After then, a p-type impurity, for example, boron is ion-implanted in the polysilicon film. Then, a gate insulation film formed of a silicon oxide film is deposited by a CVD method, covering the polysilicon film. Next, a gate electrode is formed on the gate insulation film.