Polysilicon TFT Nonlinear Channel Leakage Reduction
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Solution Overview
Problem
Polycrystalline silicon (p-Si) thin film transistors (TFTs) suffer from high current leakage due to grain boundary traps in the depletion region, which complicates the doping process and increases manufacturing costs, especially in organic light-emitting displays (OLEDs), where additional circuits are required to reduce leakage current.
Innovation Solution
A polycrystalline silicon TFT with a nonlinear electron-moving path is designed, featuring bent or stepped channel structures that reduce electron mobility and extend the channel length, thereby reducing current leakage without the need for additional masks or complex doping processes, and incorporating a narrower drain width to further minimize leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional linear channel structure is used in p-Si TFT, then electron mobility is high, but current leakage increases due to grain boundary traps in the depletion region
Solution Approach 1:
The channel structure is transformed from a linear path to a bent/curved path extending from source to drain. This curvature increases the effective channel length and reduces the electric field strength at grain boundaries, thereby reducing current leakage while maintaining sufficient electron mobility for device operation
Solution Approach 2:
The bent channel structure creates non-uniform electric field distribution along the channel path, with reduced field strength at critical grain boundary regions. This local modification of electric field characteristics reduces leakage current at grain boundaries without significantly impacting overall electron transport
2Reliability
If an offset structure (LDD) is introduced to reduce leakage current, then current leakage decreases, but device complexity and manufacturing complexity increase due to additional masks and differential doping processes
Solution Approach 1:
The invention extracts and eliminates the need for complex offset structures and differential doping processes. By using a bent channel geometry, the leakage reduction function is achieved through structural design rather than additional doping steps, simplifying the manufacturing process
Solution Approach 2:
The channel geometry parameter is changed from linear to bent, which fundamentally alters the electric field distribution and carrier transport characteristics. This parameter change achieves leakage reduction without requiring additional process steps or structural components
3Reliability
If a larger gate is used to reduce leakage current, then current leakage decreases, but the area of the light-emitting region decreases, reducing luminous efficiency
Solution Approach 1:
The bent channel allows for a more compact transistor footprint, enabling the light-emitting region to maintain its area while the channel provides sufficient length for leakage reduction. The curved path achieves longer effective channel length without increasing the linear dimensions of the device
Data Source
AI summary
A thin film transistor comprises an Si-based channel having a nonlinear electron-moving path, a source and a drain disposed at both sides of the channel, a gate disposed above the channel, an insulator interposed between the channel and the gate, and a substrate supporting the channel and the source and the drain disposed at either side of the channel respectively.