Gate Floating TFT for Flicker Reduction in LTPS Displays
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Solution Overview
Problem
Low frequency driving mode and intermittent driving mode in display devices using low temperature poly-silicon (LTPS) TFTs suffer from flicker issues due to poor OFF characteristics, leading to luminance changes and charge loss during the hold period.
Innovation Solution
Implementing a gate floating form where the gate electrode is disconnected from the power supply during the dwell period, and optimizing the source potential in the dwell period to minimize leakage currents and maintain constant pixel potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If LTPS or α-Si TFTs are used in low frequency driving mode, then device complexity is reduced, but flicker occurs due to poor OFF characteristics
Solution Approach 1:
The gate electrode is preliminarily set to a floating state before the dwell period begins. This preliminary action prevents charge accumulation at the gate during the dwell period, thereby preventing luminance fluctuation and flicker in the subsequent scan period.
Solution Approach 2:
The gate electrode's electrical state is changed from connected to disconnected (floating) during the dwell period. This parameter change in the gate's electrical configuration allows the TFT to maintain better OFF characteristics and reduce leakage current, thereby suppressing flicker.
2Ease of operation
If the gate is connected to power supply during dwell period, then TFT control is maintained, but charge loss occurs leading to luminance changes
Solution Approach 1:
The gate is preliminarily set to floating state before the dwell period to prevent charge accumulation. This preliminary configuration prevents the need for complex charge management during the dwell period while maintaining TFT control through the switch mechanism.
Solution Approach 2:
The gate connection is periodically switched between connected state (during scan period) and floating state (during dwell period). This periodic action optimizes the balance between TFT control and charge loss prevention by adapting the gate state to the operational requirements of each period.
3Reliability
If dwell period is extended to reduce flicker, then display stability improves, but scan frequency decreases
Solution Approach 1:
The gate's electrical state parameter is changed to floating during the dwell period, which improves OFF characteristics and reduces leakage current. This parameter change allows for better display stability even when the dwell period is extended, as the floating gate prevents charge accumulation that would otherwise require a longer dwell period to dissipate.
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
The gate floating form effectively suppresses flicker by maintaining constant hold voltage and luminance, reducing luminance change rates and improving display stability.
Implementation Method 1
the gate electrode is disconnected from the power supply during the dwell period
Implementation Method 2
a pixel capacitance connected to the drain
Data Source
AI summary
When an intermittent driving mode is carried out in a TFT using LIPS andα-Si for a pixel transistor, a flicker easily occurs. A display device includes a TFT including a gate, a source, and a drain; a signal line connected to the source; a pixel capacitance connected to the drain; a first power supply configured to supply a potential that breaks electricity conducted between the source and the drain to the gate; and a switch configured to supply a potential of the first power supply to the gate. The display device includes a scan period and a dwell period. The switch is turned on in the scan period, and the switch is turned off in the dwell period.