Dual Active-Layer TFT Display Structure for Low-Frequency Luminance Stability
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Solution Overview
Problem
Display devices with polysilicon thin-film transistors experience luminance decrease due to leakage current when driven at low frame frequencies to reduce power consumption, leading to potential flickering issues.
Innovation Solution
The implementation of a display device structure with specific thickness and material combinations in active and sub-active patterns, including polycrystalline silicon and amorphous silicon with hydrogen, to suppress leakage current and enhance driving voltage range, thereby preventing luminance decrease and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the display device is driven at a low frame frequency to reduce power consumption, then power consumption is reduced, but leakage current causes luminance decrease and potential flickering
Solution Approach 1:
The patent applies local quality by creating a sub-active pattern with different material composition (amorphous silicon with hydrogen) and different thickness (thinner than the main active pattern) specifically in regions where leakage current occurs. This localized modification suppresses leakage current in the channel region while preserving the overall transistor functionality, thereby maintaining luminance stability during low frame frequency operation without affecting power consumption benefits
2Reliability
If a thicker active layer is used to improve transistor performance, then charge mobility increases, but leakage current between source/drain regions increases
Solution Approach 1:
The patent employs composite materials by combining polycrystalline silicon (in the main active pattern) with amorphous silicon containing hydrogen (in the sub-active pattern). This composite structure allows the thicker polycrystalline silicon layer to provide high charge mobility while the thinner amorphous silicon layer with hydrogen suppresses leakage current, thus resolving the contradiction between mobility and leakage
3Use of energy by stationary object
If the emission time of pixels is increased to reduce power consumption, then power consumption decreases, but leakage current causes luminance lowering
Solution Approach 1:
The sub-active pattern acts as an intermediary layer that mediates between the source and drain regions. By introducing this intermediate amorphous silicon layer with hydrogen, the patent suppresses the harmful electric field interaction between source and drain that causes leakage current, thereby preventing luminance degradation during extended emission periods while allowing reduced frame frequency operation
Data Source
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AI summary
A display device includes a substrate, a first active layer including a driving active pattern of a driving transistor disposed on the substrate and a first active pattern of a first transistor disposed on the substrate, a second active layer including a driving sub-active pattern disposed on the driving active pattern of the first active layer, a first insulating film disposed on the first active layer and the second active layer, a driving gate electrode disposed on the first insulating film and overlapping the driving sub-active pattern, and a first gate electrode disposed on the first insulating film and overlapping the first active pattern, where a thickness of the driving active pattern is greater than a thickness of the driving sub-active pattern.