Amorphous Silicon TFT Structure for Low Photoexcited Current
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Solution Overview
Problem
Amorphous silicon (a-Si) thin-film transistors (TFTs) face challenges in reducing the channel length to aperture ratio due to photoexcited current issues, which increase ON resistance and limit the threshold voltage, making it difficult to enhance the aperture ratio and visual recognition characteristics in display apparatus.
Innovation Solution
The design incorporates a substrate with a gate electrode, a gate insulation layer, a body layer segmented into a first region, a second region, and a channel region, with channel stoppers and contact layers containing impurities in a-Si, allowing for controlled impurity concentration to suppress photoexcited current and reduce ON resistance, enabling shorter channel lengths without decreasing threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the channel length is reduced to improve aperture ratio, then the aperture ratio is improved, but the threshold voltage decreases due to increased photoexcited current
Solution Approach 1:
The body layer is divided into three regions with different impurity concentrations: the channel region maintains low impurity concentration to suppress photoexcited current and maintain threshold voltage, while the first and second regions adjacent to source/drain electrodes have higher impurity concentrations to reduce contact resistance. This local differentiation resolves the contradiction by allowing short channel length for high aperture ratio while maintaining adequate threshold voltage through selective impurity distribution.
Solution Approach 2:
The body layer is segmented into distinct regions (channel region, first region, second region) with different electrical characteristics. The channel region is separated from the source/drain contact regions, allowing independent optimization of each region's impurity concentration to simultaneously achieve low threshold voltage and low contact resistance.
2Area of stationary object
If the channel length is shortened to improve aperture ratio, then the aperture ratio is improved, but the ON resistance increases due to threshold voltage degradation
Solution Approach 1:
The body layer is divided into regions with different impurity concentrations optimized for their specific functions. The channel region maintains low impurity concentration to suppress photoexcited current and maintain threshold voltage, enabling short channel length for high aperture ratio. Simultaneously, the first and second regions adjacent to source/drain electrodes have higher impurity concentrations to reduce contact resistance, compensating for any ON resistance increase from shortened channel length.
Solution Approach 2:
The body layer is segmented into channel region and contact regions, allowing the channel length to be minimized for high aperture ratio while the contact regions provide low resistance paths. This segmentation enables independent optimization of channel dimensions for aperture ratio and contact region properties for ON resistance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses photoexcited current, allows for a shorter channel length, reduces ON resistance, and significantly improves the aperture ratio, enhancing visual recognition characteristics and light shielding efficiency in display apparatus.
Implementation Method 1
each of the first contact layer and the second contact layer comprises an impurities-containing first amorphous silicon layer which is in direct contact to the source electrode or the drain electrode
Implementation Method 2
it is known that a-Si produces a photoexcited current, causing a short channel effect. Therefore, there is a problem that it is difficult to reduce a ratio L/W of a channel length L to a channel width W
Data Source
AI summary
A body layer formed of a semiconductor layer, the body layer comprising, a first region, a second region, and a channel region positioned therebetween; a channel stopper formed on the channel region; source and drain electrodes electrically connected to the first and second regions via first and second contact layers respectively are provided. Each of the first and second contact layers comprises an impurities-containing first amorphous silicon layer; a thickness of each of the first and second regions is less than a thickness of the channel region; and the first and second regions comprise a second amorphous silicon layer containing impurities in a concentration being less than a concentration of impurities contained in the first amorphous silicon layer. This makes it possible to suppress a photoexcited current and improve the aperture ratio in a case that a display apparatus is configured.