Shift Register TFT Duty Cycle Reduction for Display Reliability
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Solution Overview
Problem
Existing display devices face challenges in maintaining driving performance and display quality due to fluctuations in characteristics of thin film transistors (TFTs) caused by bias stress, especially when TFTs are in the ON state for long periods, leading to decreased reliability and display quality, particularly in non-rectangular and environmentally diverse applications.
Innovation Solution
The implementation of shift registers with multiple linked units, each comprising thin film transistors of a first conductivity type connected in parallel, which output sequential selection pulses to selection lines and are turned ON/OFF by clock signals in different phases, reducing the duty cycle of the ON period to 12.5% or less, thereby mitigating fluctuations in TFT characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If thin film transistors are kept in the ON state for long periods to maintain continuous driving capability, then the driving continuity is improved, but the characteristics of TFTs fluctuate due to bias stress, worsening reliability and display quality
Solution Approach 1:
The patent implements periodic switching of TFTs between ON and OFF states using a shift register circuit that sequentially activates different TFT groups. Each TFT is driven in periodic pulses rather than continuous operation, allowing characteristics to stabilize during OFF periods while maintaining overall driving continuity through the sequential activation of multiple TFTs in the shift register sequence.
2Productivity
If the duty cycle of TFT ON period is increased to improve driving efficiency, then the productivity is improved, but the fluctuations in TFT characteristics increase, worsening display quality
Solution Approach 1:
The patent divides the driving function into multiple segments by implementing a shift register circuit with multiple stages, where each stage controls a different TFT or TFT group. This segmentation allows the overall driving efficiency to be maintained while each individual TFT operates at a lower duty cycle, reducing characteristic fluctuations and improving display quality.
3Device complexity
If shift register units are designed with simple structures to reduce device complexity, then the manufacturing precision is improved, but the ability to control TFT duty cycle and mitigate characteristic fluctuations is reduced
Solution Approach 1:
The patent combines multiple functional elements within each shift register unit, including TFTs connected in parallel, clock signal generation, and selection pulse output, into an integrated structure. This merging approach maintains relatively simple device complexity while achieving effective control over TFT duty cycles and characteristic fluctuations through the coordinated operation of combined elements.
Data Source
AI summary
A display device includes pixel circuit rows, selection lines connected to the pixel circuit rows, and a shift register including linked shift register units. The shift register units output sequential selection pulses to the selection lines. Each of the shift register units outputs the selection pulse to a corresponding selection line among the selection lines. Each of the shift register units includes thin film transistors of a first conductivity type that are connected in parallel, and that, during an ON state, connect the corresponding selection lines to a fixed potential wiring line for applying a non-selection level for the selection pulse. During each frame period, the thin film transistors are turned ON/OFF by clock signals in different phases. The duty cycle of the ON period of each of the thin film transistors during each said frame period is 12.5% or less.