Stacked Poly-Si TFT Channel Layout for High-Resolution Displays
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Solution Overview
Problem
As the resolution of display devices increases, the size of pixels decreases, leading to a problem where driving TFTs do not have a channel long enough to secure stable driving characteristics, which affects the performance of light emitting display devices.
Innovation Solution
A TFT substrate with a vertically stacked and bent channel structure using polycrystalline silicon semiconductor layers, where the first and second semiconductor layers are electrically connected in series, and at least one channel portion has a bent structure in a plan view, increasing the channel length and enhancing stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of display devices increases, then the display quality is improved, but the pixel size decreases leading to insufficient channel length in driving TFTs
Solution Approach 1:
The patent applies vertical stacking to extend the channel length in the thickness direction (z-axis) rather than only in the planar direction (x-y plane). By forming first and second semiconductor layers stacked vertically with respective channel portions, the effective channel length is increased without occupying additional pixel area, thus resolving the contradiction between high resolution and sufficient channel length.
Solution Approach 2:
The patent introduces bent channel structures where at least one channel portion is configured to extend in different directions (e.g., first channel portion extends in first direction, second channel portion extends in second direction). This curved/bent path increases the effective channel length within the limited pixel area without requiring a larger pixel size.
2Measurement precision
If the pixel size decreases to increase resolution, then the display detail is improved, but the channel length of driving TFT becomes insufficient affecting driving stability
Solution Approach 1:
By utilizing the vertical dimension through stacked semiconductor layers, the patent increases channel length without increasing pixel area. This maintains driving stability (reliability) while enabling higher pixel resolution, as the extended channel provides sufficient control for the light emitting diode even in smaller pixels.
Solution Approach 2:
The patent divides the single channel into multiple channel portions formed in different semiconductor layers (first channel portion in first semiconductor layer, second channel portion in second semiconductor layer). These segmented channel portions are electrically connected in series to form the complete channel, allowing the channel to be distributed across multiple layers to achieve sufficient total length in limited space.
3Reliability
If a longer channel is formed in the planar direction to increase channel length, then the driving stability is improved, but the pixel area increases reducing the number of pixels
Solution Approach 1:
Instead of extending the channel in the planar direction which would increase pixel area, the patent extends the channel in the vertical direction through stacked semiconductor layers. This allows achieving sufficient channel length for driving stability while maintaining compact pixel area, enabling higher pixel density.
Solution Approach 2:
The channel is segmented into multiple channel portions located in different vertical layers. This segmentation allows the channel to achieve sufficient total length through vertical stacking rather than horizontal extension, thus maintaining small pixel area while ensuring driving stability.
Data Source
AI summary
A thin film transistor (TFT) substrate comprises a TFT located on a substrate and including a gate electrode, a first semiconductor layer and a second semiconductor layer, wherein the first semiconductor layer, the gate electrode and the second semiconductor layer vertically stacked, and the first and second semiconductor layers are made of polycrystalline silicon, and wherein the first and second semiconductor layers are electrically connected to each other in series and respectively include first and second channel portions, and at least one of the first and second channel portions has a bent structure in a plan view.