Light-emitting Device Gate Potential Initialization
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Solution Overview
Problem
Light-emitting devices using oxide semiconductors face issues with after-images appearing after power is turned on due to potential being held in the gate electrode of the driver transistor, causing previous images to be displayed again.
Innovation Solution
Initializing the gate electrode potential of the transistor by decreasing the potential difference for n-channel transistors below the threshold voltage or increasing it above the threshold voltage for p-channel transistors before power is cut, ensuring the transistor is completely turned off and preventing current flow to the light-emitting element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor with extremely small off-state current using oxide semiconductor is used, then luminance stability is improved, but after-image appears after power on
Solution Approach 1:
The gate electrode potential is initialized before power supply is cut to ensure the transistor is completely turned off. This preliminary action prevents residual potential from causing after-images when power is restored, while maintaining the benefits of oxide semiconductor transistors with extremely small off-state currents for luminance stability during normal operation.
2Device complexity
If gate electrode potential is not initialized, then device complexity is reduced, but after-image appears after power on
Solution Approach 1:
The existing transistor switching mechanism is utilized to initialize the gate electrode potential. By controlling the switching transistor to set the gate potential to a predetermined state before power cutoff, the system uses its own components to achieve initialization without adding separate dedicated initialization circuits, thus minimizing complexity increase.
3Loss of energy
If power supply is cut without initializing gate potential, then power consumption is reduced, but image integrity is lost due to after-image
Solution Approach 1:
The gate electrode potential is initialized before power supply is cut to ensure complete transistor turn-off. This preliminary action preserves image integrity by preventing after-images when power is restored, while the brief initialization period costs minimal energy compared to maintaining continuous power supply without initialization.
Data Source
AI summary
Provided is a light-emitting device which can prevent appearance of an after-image after power on. Before or after supply of a power voltage applied to a light-emitting element is cut, a potential of a gate electrode of a transistor controlling the supply of the power voltage to the light-emitting element is initialized. Specifically, in the case where the transistor is n-channel type, the potential of the gate electrode is initialized so that a gate voltage is equal to or lower than a threshold voltage. In the case where the transistor is p-channel type, the potential of the gate electrode is initialized so that the gate voltage is equal to or higher than the threshold voltage.