TFT Circuit Leakage Current Suppression via Node Potential Holding
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Solution Overview
Problem
Depression-type TFTs in circuits face issues with leakage current, leading to potential gate output defects and deterioration of output characteristics, particularly when the gate potential equals the source potential, causing leakage current flow and affecting the TFT's ability to turn off properly.
Innovation Solution
A TFT circuit design incorporating a node potential holding circuit with depression-type TFTs, where a first low potential is supplied to a first node, and a second low potential is supplied to a second node, with a sub-circuit that sets the potential of the second node to be lower than the second low potential and higher than the first low potential, effectively managing the leakage current and maintaining the TFT in an off state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If depression-type TFTs are used in drive circuits, then floating charges can be discharged rapidly, but leakage current causes deterioration of output characteristics and gate output defects
Solution Approach 1:
The drive circuit is divided into multiple stages with different TFT types. Enhancement-type TFTs are used in stages where leakage current would affect output characteristics (signal transmission stages), while depression-type TFTs are used in stages where rapid charge discharge is needed (floating node discharge stages). This segmentation allows each TFT type to be used in its optimal application context.
Solution Approach 2:
Different regions of the drive circuit are assigned different TFT characteristics based on local functional requirements. The circuit structure selectively applies enhancement-type TFTs in positions requiring low leakage current and depression-type TFTs in positions requiring rapid switching and charge discharge, optimizing local performance for each specific function.
2Reliability
If enhancement-type TFTs are used, then leakage current is suppressed, but floating charges cannot be discharged promptly
Solution Approach 1:
The drive circuit is segmented to assign different TFT types to different functional stages. Enhancement-type TFTs handle signal transmission where leakage suppression is critical, while depression-type TFTs handle floating node discharge where speed is critical. This functional segmentation resolves the contradiction by matching TFT characteristics to stage requirements.
Solution Approach 2:
The threshold voltage parameter of the TFT is changed based on the functional requirements of different circuit stages. Enhancement-type TFTs (positive threshold voltage) are used where low leakage is needed, while depression-type TFTs (negative threshold voltage) are used where rapid charge discharge is needed, optimizing performance for each specific function.
3Speed
If depression-type TFTs are used, then floating nodes are discharged rapidly, but leakage current flows when gate potential equals source potential
Solution Approach 1:
The harmful leakage current effect is extracted and isolated to specific circuit stages where it can be tolerated or managed. Depression-type TFTs are placed in stages where their leakage current does not affect output quality (such as stages connected to fixed potential nodes), while enhancement-type TFTs are used in stages where leakage would degrade performance (signal output stages).
Solution Approach 2:
Different stages of the drive circuit are assigned different TFT types based on local functional requirements and tolerance for leakage current. The circuit structure ensures that depression-type TFTs with higher leakage are placed in positions where leakage does not generate harmful effects, while enhancement-type TFTs are used where leakage would be problematic.
Data Source
AI summary
A TFT circuit (101) includes a first node (N1) to which a first low potential (Vc) is supplied, a depression-type first TFT (21) which is arranged between the first node (N1) and low-potential wiring (11) for supplying a second low potential (Va) higher than the first low potential (Vc), and in which a drain terminal is connected to the first node, and a depression-type second TFT (22) which is arranged between the first TFT (21) and the low potential wiring (11) and in which a source terminal is connected to a source terminal of the first TFT, in which the first low potential (Vc) is supplied to a gate terminal of the second TFT, a second node (N2) enterable a floating state is formed between the source terminal of the first TFT and the source terminal of the second TFT, and the second node (N2) is connected to a sub-circuit (SC1) which is settable a potential of the second node (N2) to be lower than the second low potential (Va) and higher than the first low potential (Vc).