OLED Driving TFT Light-Blocking Layout for Low-Leakage Grayscale Control

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Solution Overview

Problem

The existing organic light emitting display devices using hybrid thin film transistors with polycrystalline and oxide semiconductor layers face process complexity due to separate formation requirements and high current fluctuation rates, leading to large current variation and low grayscale expression.

Innovation Solution

The display device incorporates a driving transistor with a first oxide semiconductor pattern and a switching transistor with a second oxide semiconductor pattern, utilizing a first and second light blocking layer configuration to minimize parasitic capacitance and current variation, and includes a storage capacitor for precise grayscale control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a polycrystalline semiconductor layer is used for the driving thin film transistor to achieve fast driving speed, then the driving speed is improved, but the current fluctuation rate increases and grayscale expression deteriorates

Engineering Contradiction:

Improvedriving speedVSAvoidcurrent fluctuation rate

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent changes the material parameter of the semiconductor layer from polycrystalline to oxide semiconductor, which fundamentally alters the electrical characteristics. This parameter change reduces the current fluctuation rate and improves grayscale expression while maintaining adequate driving speed for the application

Inventive Principle:

Principle #35Parameter changes

2Reliability

If hybrid thin film transistors with different semiconductor layers (polycrystalline and oxide) are used, then leakage current is reduced, but the process complexity increases

Engineering Contradiction:

Improveleakage current blockingVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent uses the same oxide semiconductor material for both the driving transistor and switching transistors, creating homogeneity in the semiconductor layer material throughout the device. This eliminates the need for separate formation processes for different semiconductor types while maintaining effective leakage current blocking

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The oxide semiconductor layer serves multiple functions simultaneously: it acts as the active layer for both driving and switching transistors, provides leakage current blocking, and enables grayscale control. This multi-functionality reduces process complexity by eliminating the need for separate polycrystalline semiconductor formation processes

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12477899B2Organic light emitting display device for reducing leakage current in off state

Publication Date: 2025.11.18 LG DISPLAY CO LTD

AI summary

The present invention relates to a hybrid organic light emitting display device including a driving thin film transistor having an oxide semiconductor pattern and a switching thin film transistor having an oxide semiconductor pattern or a polycrystalline semiconductor pattern in a driving device unit for driving a unit pixel, in which a light blocking layer below an active layer is electrically connected to a source electrode to form the driving thin film transistor with wide control range at low gradation and the light blocking layer is disposed as close as possible to the active layer to broaden the control range of the driving thin film transistor.