Amorphous Oxide Semiconductor Transistors for OLED Aperture Ratio
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Solution Overview
Problem
In organic electroluminescent display devices, the aperture ratio of light-emitting cells is reduced due to the large size of transistors, leading to insufficient luminous intensity and display unevenness, especially when using polysilicon transistors with high mobility, which makes it difficult to achieve high-definition displays at low power consumption.
Innovation Solution
The use of amorphous oxide semiconductors for both driving and switching transistors, with different electron carrier concentrations and gate insulating film properties, allows for a configuration where the driving transistor has lower mobility and a thicker gate insulating film than the switching transistor, enabling a higher aperture ratio and reducing display unevenness through UV or plasma irradiation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysilicon transistors with high mobility are used, then the transistor can control current effectively, but the transistor size increases reducing the aperture ratio
Solution Approach 1:
The patent applies local quality by using amorphous oxide semiconductor materials with different electron carrier concentrations in different transistor regions. The driving transistor uses a first amorphous oxide semiconductor layer with lower electron carrier concentration for lower mobility and longer channel length, while the switching transistor uses a second amorphous oxide semiconductor layer with higher electron carrier concentration for higher mobility and shorter channel length. This localized material property differentiation resolves the contradiction between current control reliability and aperture ratio.
Solution Approach 2:
The patent changes the electron carrier concentration parameter of the amorphous oxide semiconductor material to control transistor mobility. By adjusting the electron carrier concentration, the patent achieves different mobility levels in driving and switching transistors without changing the fundamental material type, thereby optimizing both current control capability and aperture ratio through parameter modification rather than material substitution.
2Reliability
If the transistor channel length is increased to restrict current, then current control improves, but the transistor occupies more cell area reducing aperture ratio
Solution Approach 1:
The patent implements local quality by creating spatial variation in semiconductor material properties across different transistor regions. The driving transistor region contains amorphous oxide semiconductor with lower electron carrier concentration providing longer effective channel length for current restriction, while the switching transistor region contains amorphous oxide semiconductor with higher electron carrier concentration providing shorter channel length. This local material property differentiation allows current restriction without excessive area occupation.
Solution Approach 2:
The patent applies preliminary action by forming the amorphous oxide semiconductor layers with controlled electron carrier concentrations before transistor fabrication. The semiconductor layers are prepared with specific electrical properties in advance, allowing subsequent transistor processing to achieve desired current control characteristics without requiring excessive channel length, thereby preserving aperture ratio.
3Reliability
If more transistors are added to each cell for better control, then driving capability improves, but the transistor size and number increase blocking more light
Solution Approach 1:
The patent changes the electron carrier concentration parameter of the amorphous oxide semiconductor to optimize transistor performance. By using materials with appropriate electron carrier concentrations, the patent achieves reliable driving capability with transistors of minimized size, thereby maximizing the light-emitting area and luminous intensity without requiring additional transistors.
4Illumination intensity
If the aperture ratio is increased to improve luminous intensity, then light emission improves, but transistor control capability may be compromised
Solution Approach 1:
The patent applies local quality by using amorphous oxide semiconductor materials with optimized electron carrier concentrations in different transistor regions. This allows transistors to maintain excellent control capability in minimal space, enabling high aperture ratio design that maximizes luminous intensity without compromising transistor control functionality.
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 enhances the aperture ratio of light-emitting cells, enabling bright and high-quality displays at low power consumption while minimizing characteristic variations and display unevenness across the device.
Implementation Method 1
irradiating the active layer of the second transistor with ultraviolet rays or plasma to make an electron carrier concentration of the active layer of the second transistor higher than an electron carrier concentration of the active layer of the first transistor
Implementation Method 2
irradiating the active layer of the second transistor with ultraviolet rays or plasma to make an electron carrier concentration of the active layer of the second transistor higher than an electron carrier concentration of the active layer of the first transistor
Implementation Method 3
The organic EL uses a phenomenon called injection electroluminescence in which light is emitted by recombination of an electron-hole pair
Data Source
AI summary
An organic electroluminescent display device in which a plurality of light-emitting cells each having an organic electroluminescent portion are arranged on a substrate, wherein, for each of the light-emitting cells, a first transistor which controls energization on the organic electroluminescent portion, and a second transistor which switches a signal to be given to an input of the first transistor are disposed, active layers of the first and second transistors are formed by an amorphous oxide semiconductor, and, the first and second transistors are formed so that, when the first and second transistors are driven under same conditions, an amount of an output current of the first transistor is smaller than an amount of an output current of the second transistor.