OLED Driving TFT Bent Semiconductor Layout for Gray Level Control

Solution Overview

Problem

Existing organic light emitting diode (OLED) displays face challenges in controlling the magnitude of the gate voltage for driving thin film transistors, which limits the number of gray levels that can be displayed.

Innovation Solution

The OLED display incorporates a driving semiconductor layer with bent portions, allowing for a broader driving range of the gate voltage. This is achieved by forming a storage capacitor that overlaps the driving semiconductor layer, ensuring sufficient storage capacitance even at high resolutions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a thin gate insulating layer is formed in the driving thin film transistor to enable rapid switching operation, then switching speed is improved, but the driving range of gate voltage becomes narrow making it difficult to control gray levels

Engineering Contradiction:

Improveswitching speedVSAvoidgate voltage control range

Core Design Contradiction:

SpeedVSEase of operation

Solution Approach 1:

The pixel circuit is divided into two separate thin film transistors: a switching TFT with a thin gate insulating layer for rapid switching operation, and a driving TFT with a thick gate insulating layer for broad gate voltage driving range and precise gray level control. This segmentation allows each transistor to be optimized for its specific function without compromise

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different gate insulating layer thicknesses are applied to different transistors within the same pixel circuit based on their specific functional requirements. The switching TFT receives a thin gate insulating layer (50-150 nm) for fast switching, while the driving TFT receives a thick gate insulating layer (200-500 nm) for voltage control stability

Inventive Principle:

Principle #3Local quality

2Productivity

If the gate insulating layer thickness is reduced for rapid switching, then switching performance is improved, but the number of displayable gray levels decreases

Engineering Contradiction:

Improveswitching operation speedVSAvoidgray level precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The pixel circuit is divided into two separate thin film transistors: a switching TFT with a thin gate insulating layer for rapid switching operation, and a driving TFT with a thick gate insulating layer for broad gate voltage driving range and precise gray level control. This segmentation allows each transistor to be optimized for its specific function without compromise

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different gate insulating layer thicknesses are applied to different transistors within the same pixel circuit based on their specific functional requirements. The switching TFT receives a thin gate insulating layer (50-150 nm) for fast switching, while the driving TFT receives a thick gate insulating layer (200-500 nm) for voltage control stability

Inventive Principle:

Principle #3Local quality

3Measurement precision

If display resolution is increased, then image quality is improved, but storage capacitance becomes insufficient leading to low gray level stains

Engineering Contradiction:

Improvedisplay resolutionVSAvoidstorage capacitance sufficiency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The storage capacitor is formed by utilizing the overlap region between the driving gate electrode and the driving semiconductor layer, merging the transistor structure with the capacitor structure. This eliminates the need for a separate dedicated capacitor area, allowing sufficient storage capacitance even in high-resolution displays with limited pixel area

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The thick gate insulating layer of the driving TFT serves dual functions: as the gate dielectric for voltage control and as the capacitor dielectric for charge storage. The driving gate electrode and driving semiconductor layer also serve dual roles as both transistor components and capacitor electrodes, maximizing space utilization

Inventive Principle:

Principle #6Universality (Multi-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

The solution enables more precise control of gray levels, increasing the resolution and improving display quality of the OLED display while preventing low gray level stains.

Implementation Method 1

electrons injected from one electrode and holes injected from the other electrode are combined with each other in the organic emission layer to form an exciton, and light is emitted while the exciton discharges energy

Methodology Applied

Scientific EffectElectroluminescence: Electroluminescence

Data Source

PatentUS12213358B2Organic light emitting diode display with bent semiconductor layer

Publication Date: 2025.01.28 SAMSUNG DISPLAY CO LTD

AI summary

An organic light emitting diode display includes a substrate, a scan line on the substrate for transferring a scan signal, a data line crossing the scan line and for transferring a data signal, a driving voltage line crossing the scan line and for transferring a driving voltage, a switching thin film transistor coupled to the scan line and the data line, a driving thin film transistor coupled to a switching drain electrode of the switching thin film transistor, and an organic light emitting diode (OLED) coupled to a driving drain electrode of the driving thin film transistor, wherein a driving semiconductor layer of the driving thin film transistor is bent and in a plane substantially parallel to the substrate.