LTPS TFT Substrate with U-Shaped Gate for Symmetric Current Paths
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Solution Overview
Problem
The Low Temperature Poly-Silicon Thin Film Transistor (LTPS TFT) in AMOLED displays experiences higher off-state current due to grain defects, which can be reduced by using a Lightly Doped Offset structure, but this decreases the on-state current, and the asymmetry in TFT structure affects current flow when source and drain are exchanged.
Innovation Solution
Designing a TFT substrate with a U-shaped gate and source/drain structure that requires both current paths to pass through two offset and two overlapping structures, ensuring symmetry and reducing off-state current while maintaining or increasing on-state current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a Lightly Doped Offset structure is used to reduce off-state current, then off-state current is reduced, but on-state current decreases
Solution Approach 1:
The source and drain are divided into multiple segments (first source, second source, drain) with distinct functional regions. Each segment has specific doping characteristics, creating multiple offset structures that collectively reduce off-state current while maintaining adequate on-state current through distributed charge control.
Solution Approach 2:
Different regions of the active layer are doped with different concentrations and types (N-type or P-type). The offset regions have lighter doping than the contact regions, creating localized electrical properties that reduce leakage current in specific areas without affecting the overall conductivity needed for on-state operation.
2Object-generated harmful factors
If offset structure is added to reduce off-state current, then off-state current is reduced, but device complexity increases
Solution Approach 1:
The offset structures are merged with the source and drain contact regions rather than being separate components. The first source, second source, and drain are integrated into a single continuous structure with varying doping profiles, eliminating the need for additional fabrication steps while achieving the offset effect.
Solution Approach 2:
The doping concentration and type are varied continuously across the source-drain structure to create the offset effect. By changing the electrical parameters (doping level, doping type) across different regions rather than adding physical structures, the off-state current is reduced without increasing structural complexity.
3Reliability
If U-shaped gate and source/drain structure with symmetry is designed, then current path symmetry is achieved and electrical performance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The gate is designed with a U-shape that is intentionally asymmetric in its geometric form but creates symmetric electrical fields through specific doping arrangements. The first and second sources are positioned asymmetrically relative to the gate geometry, but their doping characteristics are configured to produce symmetric current paths electrically.
Solution Approach 2:
The doping configuration ensures that electrically equivalent points in the structure have the same potential characteristics. The first source and second source are doped to create equipotential conditions that ensure symmetric current distribution through the active layer, regardless of minor geometric variations in the U-shaped gate.
Data Source
AI summary
The present invention provides a manufacture method of a TFT substrate and a manufactured TFT substrate. By locating the first channel region and the first lightly doped offset region between the first source and the drain, and locating the second channel region and the second lightly doped offset region between the second source and the drain, and forming the first overlapping region and the second overlapping region respectively between the drain and the gate and between the second source and the gate, thus, the paths of the current flowing from the first, the second sources to the drain and the current flowing from the drain to the first, the second sources are the same. Namely, the current path from source to the drain and the current path from the drain to the source are the same. According, the symmetry of the TFT structure is realized.