OLED Driving Transistor Layout to Reduce Afterimages and Thickness
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Solution Overview
Problem
Existing organic light emitting diode displays face issues with thickness and display defects such as instantaneous afterimages due to protrusions in the polycrystalline semiconductor layer.
Innovation Solution
The display device incorporates a driving transistor with a gate electrode disposed under the polycrystalline semiconductor layer, reducing the thickness of the gate insulating layer and minimizing the impact of protrusions, while using a compensation transistor to compensate for variations in transistor characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a gate electrode is disposed on the polycrystalline semiconductor layer (top gate configuration), then the transistor can be manufactured with standard processes, but the thickness of the display device increases and protrusions in the semiconductor layer cause instantaneous afterimages
Solution Approach 1:
The patent inverts the conventional top-gate configuration by placing the gate electrode beneath the polycrystalline semiconductor layer, creating a bottom-gate structure. This inversion resolves the thickness issue by eliminating the need for thick gate insulating layers above the semiconductor, while still achieving functional transistors through the bottom gate control mechanism.
2Ease of manufacture
If a gate electrode is disposed on the polycrystalline semiconductor layer, then transistor manufacturing is simplified, but protrusions in the semiconductor layer cause display defects such as instantaneous afterimages
Solution Approach 1:
By inverting the gate configuration to bottom-gate, the patent eliminates the interaction between protrusions and the gate structure, preventing the formation of instantaneous afterimages while maintaining transistor functionality through the bottom gate's electrical control of the channel.
3Reliability
If the gate insulating layer thickness is reduced to minimize protrusion impact, then display defects are reduced, but the transistor's electrical characteristics deteriorate
Solution Approach 1:
The bottom-gate configuration allows the gate insulating layer to be positioned where it provides effective electrical control without being compromised by protrusions. This inversion enables the use of optimized insulating layer thickness that maintains both display quality and transistor electrical characteristics, as the gate control is exerted from below rather than being disrupted by surface irregularities.
4Reliability
If a compensation transistor is added to compensate for transistor characteristic variations, then display uniformity is improved, but the device complexity increases
Solution Approach 1:
The compensation transistor is configured to automatically compensate for threshold voltage variations and other characteristic deviations in the driving transistor. By using the same bottom-gate structure and material layers, the compensation mechanism operates autonomously without requiring additional complex control circuits or external calibration, thus improving display uniformity while minimizing the increase in device complexity.
Data Source
AI summary
An organic light emitting diode display includes a driving transistor and a compensation transistor. The driving transistor includes a first gate electrode disposed on a substrate, a polycrystalline semiconductor layer disposed on the first gate electrode of the driving transistor and including a first electrode, a second electrode, and a channel, and a second gate electrode disposed on the polycrystalline semiconductor layer of the driving transistor. The compensation transistor includes a polycrystalline semiconductor layer including a first electrode, a second electrode, and a channel, and a gate electrode disposed on the polycrystalline semiconductor layer of the compensation transistor.