Driving Transistor with Composite Semiconductor for OLED Reliability

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Solution Overview

Problem

The existing organic light-emitting display devices face issues with the longevity of thin film transistors due to threshold voltage changes under stress, leading to reduced lifespan and compromised picture quality due to the need for multiple switching transistors per pixel, which also affects resolution and aperture ratio.

Innovation Solution

The implementation of a driving thin film transistor with a semiconductor layer comprising an n-type impurity layer, amorphous silicon, and an n+-type impurity layer, along with a negative threshold voltage, to minimize threshold voltage variations and reduce power consumption, thereby enhancing the transistor's lifespan and display reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple switching transistors are used per pixel to ensure proper operation, then reliability is improved, but device complexity increases and aperture ratio decreases

Engineering Contradiction:

Improvetransistor operation reliabilityVSAvoidnumber of switching transistors per pixel

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention combines multiple switching transistor functions into a single driving transistor by using multiple gate electrodes (first gate electrode and second gate electrode) that can independently control different aspects of transistor operation. This merging approach maintains the reliability of multi-transistor operation while reducing device complexity and increasing aperture ratio.

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If multiple switching transistors are used per pixel to ensure proper operation, then reliability is improved, but the area occupied by light-shielding portions increases, reducing aperture ratio

Engineering Contradiction:

Improvetransistor operation reliabilityVSAvoidaperture ratio

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The invention merges multiple transistor functions into one device, reducing the total area required for light-shielding portions. The single driving transistor with multiple gate electrodes occupies less space than multiple separate transistors, thereby increasing the aperture ratio and improving display quality.

Inventive Principle:

Principle #5Merging (Combining)

3Ease of manufacture

If conventional semiconductor layers are used in driving transistors, then manufacturing is simpler, but threshold voltage changes under stress, reducing lifespan

Engineering Contradiction:

Improvesemiconductor layer fabricationVSAvoidtransistor lifespan

Core Design Contradiction:

Ease of manufactureVSDuration of action of stationary object

Solution Approach 1:

The invention uses a composite semiconductor layer structure comprising an amorphous silicon layer and a microcrystalline silicon layer. This composite structure combines the advantages of both materials: amorphous silicon provides ease of manufacture while microcrystalline silicon provides superior electrical characteristics and stability. The combination resolves the contradiction between manufacturing simplicity and device lifespan by leveraging the complementary properties of the two materials.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The invention changes the crystalline parameters of the semiconductor layer by introducing a microcrystalline silicon layer with specific crystal structure characteristics. This parameter change (from fully amorphous to composite amorphous-microcrystalline) stabilizes the threshold voltage under stress conditions while maintaining manufacturability through established deposition techniques.

Inventive Principle:

Principle #35Parameter changes

4Power

If higher driving voltage is used to ensure proper transistor operation, then power consumption increases, but if lower voltage is used, then transistor control becomes less effective

Engineering Contradiction:

Improvedriving voltageVSAvoidpower consumption

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The invention introduces dynamic control capability through multiple gate electrodes that can be independently biased. The first gate electrode and second gate electrode can apply different voltages to optimize transistor operation at different stages, enabling effective control at lower overall power consumption levels. This dynamic control approach replaces the need for high static driving voltage with intelligent, staged voltage application.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS8304281B2Driving transistor of organic light-emitting, method for fabricating the transistor, and organic light-emitting device including the transistor

Publication Date: 2012.11.06 LG DISPLAY CO LTD

AI summary

A driving TFT for an organic light-emitting display device includes a gate electrode on a portion of a substrate, a gate insulation layer on an entire surface of the substrate including the gate electrode, a semiconductor layer on the gate insulation layer and covering the gate electrode, the semiconductor layer including an n-type impurity layer, and source and drain electrodes overlapping portions of the semiconductor layer at respective sides thereof.