Dual Active-Layer TFT Structure for Low-Leakage Display Panels
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Solution Overview
Problem
Display devices with polysilicon thin-film transistors experience a leakage current when turned off, leading to reduced luminance and power consumption issues when driven at low frame frequencies for still images.
Innovation Solution
The implementation of a display device structure with specific thickness and material combinations for active and sub-active patterns in transistors, including polycrystalline silicon and amorphous silicon with hydrogen, to suppress leakage currents and enhance driving voltage ranges.
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 luminance decreases due to leakage current
Solution Approach 1:
The patent applies different material compositions to different regions of the active layer. Specifically, the channel region uses a first composition ratio of silicon to nitrogen (e.g., 4:1 to 6:1), while the source/drain regions use a second composition ratio (e.g., 2:1 to 4:1). This local differentiation optimizes each region's properties: the channel region achieves lower leakage current through higher nitrogen content, while source/drain regions maintain good conductivity through lower nitrogen content, thereby resolving the luminance degradation issue at low frame frequencies without sacrificing power efficiency
Solution Approach 2:
The patent changes the compositional parameters of the active layer by controlling the silicon to nitrogen ratio during film formation. By adjusting this parameter across different regions (channel vs. source/drain), the patent achieves optimal electrical characteristics that suppress leakage current while maintaining low power consumption operation at reduced frame frequencies
2Reliability
If polycrystalline silicon is used for the semiconductor layer to achieve high charge mobility, then transistor performance is improved, but leakage current increases when the transistor is turned off
Solution Approach 1:
The patent implements local quality differentiation within the active layer by using distinct silicon-nitrogen composition ratios in the channel region versus source/drain regions. The channel region's higher nitrogen content (first composition ratio) reduces leakage current while maintaining adequate charge mobility, and the source/drain regions' lower nitrogen content (second composition ratio) ensures good conductivity, thereby achieving both high transistor performance and low leakage current
Solution Approach 2:
The patent uses a composite active layer structure where silicon nitride and silicon oxide are combined in specific ratios. This composite material approach allows tuning of electrical properties: the silicon nitride portion suppresses leakage through nitrogen passivation, while the silicon oxide portion provides good interface characteristics and conductivity, achieving both high performance and low leakage current simultaneously
Data Source
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.