Oxide Semiconductor Transistor Gate Insulator Thickness Control
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Solution Overview
Problem
Transistors using oxide semiconductor layers in organic electroluminescence display devices face reliability issues due to changes in threshold voltage over time, particularly in bottom gate and dual gate structures, leading to display unevenness and reduced reliability.
Innovation Solution
The implementation of a display device structure that includes a bottom gate driving transistor and a dual gate writing transistor, with varying gate insulating film thicknesses to control ON current and sub-threshold swing, allowing for improved switching characteristics and reduced thermal degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a bottom gate or dual gate structure is used for oxide semiconductor transistors, then device integration is improved, but threshold voltage changes over time occur leading to display unevenness
Solution Approach 1:
The patent applies different gate insulating film thicknesses to different transistors within the same pixel circuit. The bottom gate driving transistor has a thicker gate insulating film (200-500 nm) compared to the dual gate writing transistor (100-300 nm), creating localized quality differences that compensate for threshold voltage shifts and improve display uniformity
Solution Approach 2:
The patent changes the gate insulating film thickness parameter to control transistor characteristics. By adjusting this physical parameter differently across transistor types, the invention achieves improved ON current accuracy and suppressed thermal degradation without changing the fundamental device structure
2Power
If gate insulating film thickness is reduced, then ON current increases, but thermal degradation increases
Solution Approach 1:
The patent implements local quality by assigning different gate insulating film thicknesses to different transistor functions. The writing transistor uses a thinner film (100-300 nm) for high ON current, while the driving transistor uses a thicker film (200-500 nm) for thermal stability, optimizing each local region for its specific function
Solution Approach 2:
The patent creates dynamic control by using the thinner gate insulating film in the writing transistor to achieve steep sub-threshold swing for fast switching, while the thicker film in the driving transistor provides thermal stability during continuous operation, allowing the system to adapt to different operational requirements
3Ease of manufacture
If uniform gate insulating film thickness is used, then manufacturing is simplified, but display unevenness occurs
Solution Approach 1:
The patent implements local quality by assigning different gate insulating film thicknesses to different transistor functions. The bottom gate driving transistor has a thicker gate insulating film (200-500 nm) compared to the dual gate writing transistor (100-300 nm), creating localized quality differences that compensate for threshold voltage shifts and improve display uniformity
Solution Approach 2:
The patent segments the gate insulating film into different thickness regions corresponding to different transistor types. This segmentation allows independent optimization of each transistor's electrical characteristics while maintaining a manageable manufacturing process through selective deposition
Data Source
AI summary
A display device includes a light-emitting element, a first transistor controlling a current value flowing from a driving power supply line to the light-emitting element, and a second transistor applying a voltage corresponding to a luminance of the light-emitting element to a first gate electrode of the first transistor, the first transistor including the first gate electrode, a first insulating film, a first oxide semiconductor layer, a second insulating film, and a first conductive layer, the second transistor including the first insulating film, a second oxide semiconductor layer, a second insulating film, and a second gate electrode.