Concentric Circular Electrode TFT for Leakage Current Reduction
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Solution Overview
Problem
Existing thin film transistors (TFTs) in liquid crystal display devices face issues with leakage current and level shift of electric potential due to parasitic capacitance, which affect image quality and require simultaneous reduction of leakage current, increase of ON current, and minimization of stray capacitance.
Innovation Solution
The TFT design features source and drain electrodes with concentric circular shapes, formed by sequentially depositing a gate insulating film, intrinsic amorphous silicon, and n+amorphous silicon layers, optimizing the channel width-to-length ratio and effective stray capacitance area to reduce leakage current and level shift while increasing ON current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional TFT structures with protruding amorphous silicon ends are used, then manufacturing is simpler, but leakage current increases due to parasitic TFT capacitance and contaminants
Solution Approach 1:
The patent applies circular electrode shapes instead of conventional rectangular patterns. The source electrode (501) and drain electrode (505) are formed as concentric circles, eliminating sharp corners and protruding ends where contaminants accumulate. This curvature-based design reduces parasitic capacitance and prevents leakage current while maintaining manufacturing feasibility through standard photolithography processes.
2Object-generated harmful factors
If electrodes with concentric circular shapes are used, then leakage current is reduced, but device complexity increases
Solution Approach 1:
The patent implements a nested concentric circular structure where the source electrode (501) is positioned at the center and the drain electrode (505) surrounds it. Both electrodes are formed in the same layer, creating a compact nested configuration that reduces parasitic capacitance between gate and source/drain while simplifying the overall device structure compared to multi-layer approaches.
3Power
If stray capacitance area is increased, then ON current is optimized, but level shift of electric potential increases
Solution Approach 1:
The patent transitions from conventional planar electrode layouts to a concentric circular configuration, effectively utilizing radial dimensionality. This dimensional change allows the source and drain electrodes to be arranged in the same layer with optimized spacing, reducing stray capacitance area while maintaining sufficient channel width for adequate ON current, thereby minimizing level shift.
Data Source
AI summary
A TFT, in which source and drain electrodes having concentric circular shapes are formed, reduces an OFF current caused by a leakage current and optimizes an ON current and a stray capacitance between gate and source electrodes. The TFT includes a gate electrode formed on a substrate; and source and drain electrodes obtained by sequentially forming a gate insulating film, an intrinsic amorphous silicon layer, and an n+ amorphous silicon layer on the gate electrode, wherein the source and drain electrodes have circular shapes. One of the source and drain electrodes is disposed at the center, and the other one of the source and drain electrodes having a concentric circular shape surrounds the former. A channel region may be formed between the source and drain electrodes; and an area of an effective stray capacitance may be less than 150 μm2. A ratio of a width of a channel to a length of the channel may be more than 4.5 and a filling capacity index to the effective stray capacitance may be less than 50.