Laser Crystallization Orientation for Display Transistor Uniformity
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Solution Overview
Problem
The existing active-matrix organic electroluminescence (EL) displays face issues with streaks and unevenness due to variations in transistor characteristics caused by inconsistent excimer laser power during the crystallization process, leading to differences in threshold voltage and mobility among transistors, which affect the drive timing and result in visual streaks and colored boundaries between pixel columns.
Innovation Solution
The solution involves forming transistors in the pixel circuits and buffers using a laser with a predetermined wavelength, where the channel length direction of transistors is set parallel or perpendicular to the scan direction of the laser, to average variations in crystal grain size and transistor characteristics, thereby minimizing differences in threshold voltage and mobility, and optimizing the arrangement of pixel subpixels to reduce visual recognition of streaks and color differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If excimer laser power is used during crystallization process, then transistor formation is achieved, but variations in laser power cause streaks and unevenness in display
Solution Approach 1:
The patent changes the physical parameters of the laser crystallization process by using a laser with a predetermined wavelength (e.g., green laser at 532nm) instead of conventional excimer laser (ultraviolet). This parameter change results in more stable laser power output during scanning, reducing variations in transistor characteristics and eliminating streaks and colored boundaries in the display.
2Manufacturing precision
If laser scanning is performed in conventional direction, then crystallization is achieved, but inconsistent laser power causes threshold voltage and mobility variations
Solution Approach 1:
The patent changes the wavelength parameter of the laser to a predetermined value (e.g., 532nm green laser) which provides more stable power output during scanning. This parameter change reduces variations in threshold voltage and mobility across transistors, improving uniformity without increasing device complexity.
3Reliability
If pixel circuits are formed with standard transistor arrangement, then display function is achieved, but visual streaks and colored boundaries appear between pixel columns
Solution Approach 1:
The patent changes the laser wavelength parameter to reduce transistor characteristic variations, which directly eliminates the causes of visual streaks and colored boundaries. This results in improved visual uniformity and display performance without requiring changes to the pixel circuit arrangement.
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 suppresses the occurrence of streaks and color unevenness by averaging transistor characteristic variations, resulting in improved image quality and reduced visual recognition of boundaries between pixel columns, enhancing the overall performance and appearance of active-matrix organic EL displays.
Implementation Method 1
The transistors in the pixel circuits and the transistors in the buffers are formed through irradiation with laser light that is moved for scanning in a predetermined direction and has a predetermined wavelength
Data Source
AI summary
A display includes a pixel array part with pixels that each have at least one transistor whose conduction state is controlled by a drive signal input to a control terminal, and a scanner including a plurality of buffers that are formed of transistors. The buffers correspond to a pixel arrangement and output a drive signal to the control terminals of the transistors of the pixels. The transistors of the pixels and the transistors of the buffers are formed through irradiation with laser light that is moved for scanning in a predetermined direction and has a predetermined wavelength. The transistors in the buffers are formed in such a way that the channel length direction of the transistors is set parallel to the scan direction of the laser light.