Scan Driver Back-Biasing for Oxide TFT Off-Current Reduction
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Solution Overview
Problem
Display devices with oxide thin film transistors suffer from off-current phenomena, leading to inefficiencies and increased complexity in scan driver designs due to the need for compensation voltages and complex structures to manage threshold voltages.
Innovation Solution
The implementation of a scan driver with back-biasing voltage application on driving and buffer transistors, using NMOS oxide thin film transistors, to adjust threshold voltages based on clock signals and scan input signals, thereby reducing off-current and simplifying the circuit structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide thin film transistors operate in depletion mode with negative threshold voltage, then reliability is improved, but off-current phenomenon occurs
Solution Approach 1:
The patent applies back-biasing voltage to dynamically adjust the threshold voltage of oxide thin film transistors. By changing the biasing condition, the transistor operates in enhancement mode with positive threshold voltage during active periods, eliminating off-current while maintaining reliability through controlled parameter adjustment.
2Object-generated harmful factors
If compensation voltage is stored in internal capacitor and applied to gate terminal, then off-current phenomenon is prevented, but device complexity increases
Solution Approach 1:
The patent extracts the threshold voltage control function from complex internal compensation circuits and implements it through simple back-biasing voltage application. This eliminates the need for internal capacitors and complex compensation structures while effectively preventing off-current phenomenon.
3Object-generated harmful factors
If back-biasing voltage is applied to adjust threshold voltage, then off-current is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements dynamic threshold voltage control through back-biasing that automatically adjusts with operating conditions. The threshold voltage is not fixed but dynamically optimized based on real-time biasing conditions, reducing the need for precise manufacturing tolerances while eliminating off-current.
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 minimizes off-current in oxide thin film transistors, enhancing the operating margin and reliability of the scan driver while reducing the complexity of the scan signal outputting circuits, resulting in improved performance and efficiency.
Implementation Method 1
the at least one of the scan signal outputting circuits may perform a back-biasing voltage applying operation on at least one of the driving transistors and the buffer transistors when the driving transistors and the buffer transistors are turned on or off
Data Source
AI summary
A scan driver includes scan signal outputting circuits, at least one of the scan signal outputting circuits includes a driving circuit and a buffer circuit. The driving circuit includes driving transistors. The driving circuit provides first and second driving signals to first and second driving nodes, respectively by turning on or off the driving transistors in response to clock signals and a scan input signal. The buffer circuit includes buffer transistors. The buffer circuit outputs a scan signal at an output node by turning on or off the buffer transistors in response to the first and second driving signals. The at least one of the scan signal outputting circuits performs a back-biasing voltage applying operation on at least one of the driving transistors and the buffer transistors when the driving transistors and the buffer transistors are turned on or off.