Thin Film Transistor Substrate Polycrystallization Direction Control
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Solution Overview
Problem
The polycrystallization process for thin film transistors often results in damaged characteristics due to irregular crystal orientations, particularly when laser light is scanned in one direction and then irradiated in another, making it difficult to maintain desired transistor properties, especially in peripheral circuit areas of liquid crystal display devices.
Innovation Solution
A method involving a transparent insulating substrate with pixel transistors aligned in a specific direction for high mobility and peripheral circuits aligned perpendicular to that direction, where the channel length of high-speed transistors is positioned outside the extended portions of stripe areas to minimize the impact of crystal orientation disorders, and polycrystallization is performed in a manner that ensures high mobility in the desired direction without overlapping with the display area's crystal orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If excimer laser light scans in a short-side direction to polycrystallize amorphous silicon film, then polycrystallization efficiency is improved, but crystal grain size becomes uneven in scanning direction causing mobility reduction
Solution Approach 1:
The patent divides the polycrystallization process into two separate scanning directions. First, laser light scans in the short-side direction to achieve efficient polycrystallization. Then, a second scanning in the long-side direction is performed to even out the crystal grain sizes in the scanning direction, thereby resolving the contradiction between polycrystallization efficiency and crystal grain uniformity.
2Reliability
If gate length direction is parallel to scanning direction for high mobility, then carrier mobility is improved, but crystal orientation disorders in peripheral circuit areas damage transistor characteristics
Solution Approach 1:
The patent applies different scanning strategies to different areas of the substrate. In the display area, the gate length direction is aligned parallel to the scanning direction to achieve high mobility. In the peripheral circuit area, a second scanning in the long-side direction is performed to correct crystal orientation disorders, thereby maintaining high-speed transistor characteristics without being affected by the harmful crystal orientation disorders.
3Area of stationary object
If laser light is scanned in one direction then irradiated in another direction, then polycrystallization coverage is improved, but crystal characteristic disorders increase damaging transistor properties
Solution Approach 1:
The patent employs periodic action by performing two sequential scanning operations. The first scan in the short-side direction provides initial polycrystallization coverage. The second scan in the long-side direction periodically intervenes to correct and even out the crystal grain sizes, thereby achieving both comprehensive coverage and uniform crystal characteristics without damaging transistor properties.
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
This approach effectively reduces the influence of crystal characteristic disorders, maintaining high mobility and performance in thin film transistors, particularly in high-speed driving circuits, while allowing for precise control over transistor channel orientations to prevent damage from repeated laser irradiation.
Implementation Method 1
excimer laser light having a long-slit shape scans and polycrystallizes an amorphous silicon film
Implementation Method 2
polycrystallizing the amorphous silicon film
Data Source
AI summary
A method for producing a thin film transistor substrate includes the steps of: (i) depositing an amorphous semiconductor film on a transparent insulating substrate; (ii) patterning the amorphous semiconductor film so as to form insular amorphous semiconductor films, the step (ii) including a process (I) for forming, in respective stripe areas each of which is elongate in a first direction in a display area, a plurality of insular semiconductor films whose channel length is in line with the first direction, and a process (II) for forming, in an area including extended portions of the striped areas in a peripheral circuit area, a plurality of insular semiconductor films; (iii) polycrystallizing the insular semiconductor films in the peripheral circuit area so that the insular semiconductor films have high mobility in a second direction and polycrystallizing the insular semiconductor films in the display area so that the insular semiconductor films have high mobility in the first direction; and (iv) forming TFTs by using polycrystalline insular semiconductor films. In at least one peripheral circuit, a channel of a high speed TFT is positioned on a portion other than the extended portions of the stripe areas.