Dual Switching Element Pixel Circuit for Vth Shift Suppression
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Solution Overview
Problem
Active-matrix-type organic EL display devices face issues with Vth shift in drive switching elements, leading to irregular brightness and reduced electron mobility, particularly when using amorphous silicon for semiconductor layers, which affects the emission of desired light quantities.
Innovation Solution
The display device employs a configuration with two switching elements per pixel, where one assumes a positive bias state and the other a reverse bias state alternately, with data signals and scanning signals being sequentially inverted to minimize Vth shift and enhance electron mobility, using N-channel-type MIS transistors and amorphous silicon semiconductor layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single drive switching element is used per pixel, then the device complexity is reduced, but Vth shift occurs leading to brightness irregularities
Solution Approach 1:
The drive switching element is divided into two separate switching elements (first drive switching element and second drive switching element) that operate alternately. This segmentation allows one element to be active while the other resets, preventing cumulative Vth shift and maintaining brightness uniformity across all pixels.
2Manufacturing precision
If amorphous silicon is used for semiconductor layer, then the manufacturing precision is improved, but electron mobility is reduced affecting current flow
Solution Approach 1:
The patent changes the operational parameters of the switching elements by implementing alternating activation patterns and adjusting bias conditions. This allows amorphous silicon-based devices to achieve sufficient effective mobility through optimized driving schemes, compensating for the inherently lower material mobility.
3Productivity
If drive switching elements are always driven during operation, then the productivity is improved, but Vth shift accumulates causing brightness degradation
Solution Approach 1:
The patent implements periodic action by alternately activating the first and second drive switching elements. While one element is driven to maintain pixel operation, the other element is reset during its inactive period. This periodic alternation prevents Vth shift accumulation while maintaining continuous display operation.
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 configuration effectively suppresses Vth shift, ensures consistent light emission across the screen, and enhances electron mobility, allowing for sufficient current flow and improved brightness uniformity.
Implementation Method 1
one switching element assumes a positive bias state and the other switching element assumes a reverse bias state, and the bias states are alternately changed over between the first switching element and the second switching element
Implementation Method 2
a power source is supplied to an organic EL element through the drive switching element
Data Source
AI summary
The present invention enhances a display quality of a display device as a task. As means for solving such a task, the present invention provides a display device including a light emitting element and a switching element in a pixel, wherein the switching element is provided for supplying a power source to the light emitting element and is constituted of a first switching element and a second switching element. The first switching element and the second switching element are configured to be operated, in response to inputting of data signals into the inside of the pixel, one switching element assumes a positive bias state and another switching element assumes a reverse bias state, and the bias states are alternately changed over between the first switching element and the second switching element in response to time-sequential inputting of the data signals, and the supply of the power source to the light emitting element is performed by way of either one of the first switching element and the second switching element.