Multi-Layer Semiconductor Channel for High Mobility TFTs
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Solution Overview
Problem
Thin-film transistors (TFTs) face limitations in achieving high mobility and positive threshold voltage due to low channel mobilities, leading to insufficient on current, high off-leakage current, and increased power consumption, which affects the performance and reliability of high-resolution and large-screen displays.
Innovation Solution
The implementation of multi-layer semiconductor channel stacks with alternating electron mobilities, where one layer has a mobility less than 20 cm2/V s and another greater than 20 cm2/V s, enhancing the overall electron mobility and reducing off-leakage current while maintaining a positive threshold voltage, thereby improving the speed and efficiency of TFTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high carrier concentration is used in the semiconductor channel to achieve high mobility, then the response speed increases, but the off-leakage current increases and threshold voltage becomes negative
Solution Approach 1:
The semiconductor channel is divided into multiple layers with different carrier concentrations. The first layer (in contact with gate insulator) has lower carrier concentration to reduce off-leakage current, while the second layer has higher carrier concentration to maintain high mobility and response speed. This segmentation allows each layer to optimize for its specific function.
Solution Approach 2:
Different regions of the channel have different carrier concentrations tailored to local requirements. The region near the gate insulator interface has lower carrier concentration to minimize leakage, while the region farther from the interface has higher carrier concentration to enhance conductivity and response speed.
2Speed
If high carrier concentration is used in the semiconductor channel to achieve high mobility, then the response speed increases, but the threshold voltage becomes negative instead of positive
Solution Approach 1:
The channel is segmented into layers with different carrier concentrations. The first layer's lower carrier concentration helps establish a positive threshold voltage by reducing unwanted carrier accumulation at the gate interface, while the second layer's higher carrier concentration ensures fast response speed is maintained.
3Reliability
If low mobility channel is used in TFTs, then the threshold voltage remains positive and off-leakage current is reduced, but the on current becomes insufficient
Solution Approach 1:
The channel is divided into functional layers: the first layer provides stable threshold voltage and low leakage, while the second layer provides high conductivity for sufficient on current.
Solution Approach 2:
The patent combines layers with different mobility characteristics into a single multi-layer channel structure, merging the advantages of low-mobility layers (stable threshold voltage, low leakage) with high-mobility layers (high on current).
4Speed
If high mobility channel is used in TFTs, then the response speed increases, but the off-leakage current becomes unacceptably high
Solution Approach 1:
The channel is segmented so that only the necessary portion has high carrier concentration for fast response, while other portions maintain lower carrier concentration to minimize leakage current.
Data Source
AI summary
Embodiments herein include thin-film transistors (TFTs) including channel layer stacks with layers having differing mobilities. The TFTs disclosed herein transport higher total current through both the low mobility and the high mobility channel layers due to higher carrier density in high mobility channel layer and/or the high mobility channel layers, which increases the speed of response of the TFTs. The TFTs further include a gate structure disposed over the channel layer stack. The gate structure includes one or more gate electrodes, and thus the TFTs are top-gate (TG), double-gate (DG), or bottom-gate (BG) TFTs. The channel layer stack includes a plurality of layers with differing mobilities. The layers with differing mobilities confer various benefits to the TFT. The high mobility layer increases the speed of response of the TFT.