Thin-Film Transistor OFF-Current Reduction Using AC Drain Bias
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Solution Overview
Problem
The existing methods for applying an OFF-state offset to P-type polycrystalline thin film transistors in liquid crystal display devices require additional processes and circuits, which increase complexity and risk of static electricity-induced deterioration, while also necessitating expensive driving circuits and complex lead connections.
Innovation Solution
A method involving the application of a ground voltage to the source electrode and a gate voltage to turn off the thin film transistor, with an alternating current voltage applied to the drain electrode, eliminating the need for additional circuits and pads, thereby stabilizing the transistor without increasing processing steps or introducing static electricity risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an OFF-state offset is applied using additional circuits and pads, then the OFF-current is reduced, but the device complexity increases and static electricity risks arise
Solution Approach 1:
The patent merges the OFF-state offset function with existing driving circuits by applying AC voltage to the data line that already connects to the drain electrode. This eliminates the need for separate offset application circuits and pads, reducing device complexity while maintaining the ability to reduce OFF-current through the combined action of the driving circuit and AC voltage application.
Solution Approach 2:
The data line and driving circuit are made multi-functional: they serve both as signal transmission paths for display data and as pathways for applying AC voltage to generate the OFF-state offset. This universal usage eliminates dedicated offset circuits, reducing the number of components and connection points that could be vulnerable to static electricity damage.
2Reliability
If additional pads are formed on the substrate, then the OFF-state offset can be applied, but the risk of static electricity-induced deterioration increases
Solution Approach 1:
The patent extracts the AC voltage application function from separate physical pads and integrates it into the existing data line connection. By removing the need for additional pads and using only the already-present data line connection points, the invention eliminates extra vulnerable interfaces that could be damaged by static electricity while preserving the OFF-state offset capability.
3Ease of manufacture
If polycrystalline silicon TFTs are used to reduce lead connections, then the manufacturing complexity is reduced, but OFF-current issues arise requiring stabilizing processes
Solution Approach 1:
The patent applies AC voltage periodically to the data line to generate the OFF-state offset in P-type polycrystalline silicon TFTs. This periodic voltage application creates the necessary electrical conditions to suppress carrier generation at P-N junctions during the OFF state, thereby reducing OFF-current and preventing residual images without requiring changes to the polycrystalline silicon manufacturing process itself.
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 reduces OFF-current and improves mobility of the thin film transistors, simplifies the manufacturing process, and prevents static electricity issues, while being applicable to both liquid crystal and organic electroluminescent display devices without increasing production costs.
Implementation Method 1
supplying an alternating current voltage to a drain electrode of the thin film transistor
Data Source
AI summary
A method of applying an OFF-state offset to a display device includes: supplying a ground voltage from a data driving circuit; to a source electrode of a thin film transistor supplying a gate voltage from a gate driving circuit to a gate electrode of the thin film transistor, the gate voltage turning off the thin film transistor; and supplying an AC voltage to a drain electrode of the thin film transistor.