Flat Panel Display Active Layer Polishing for Brightness Uniformity

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Solution Overview

Problem

The formation of crystallization protrusions in the active layer of thin-film transistors (TFTs) during the sequential lateral solidification process leads to unwanted brightness deviations in flat panel displays, affecting the stability and uniformity of the display's brightness characteristics.

Innovation Solution

A method involving the formation of a step difference layer on the substrate, followed by the crystallization of an amorphous silicon layer using the sequential lateral solidification method, and subsequent polishing using chemical mechanical polishing (CMP) to remove crystallization protrusions, ensuring the active layer is formed only on the lower step region, thereby maintaining a planarized surface without height differences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If sequential lateral solidification method is used to crystallize amorphous silicon layer, then crystalline silicon layer is formed, but crystallization protrusions are generated causing brightness deviation

Engineering Contradiction:

Improvecrystalline silicon layer formationVSAvoidbrightness uniformity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent extracts and removes the harmful crystallization protrusions from the crystalline silicon layer through chemical mechanical polishing (CMP). This separates the useful crystalline structure from the harmful protrusions, achieving both crystalline silicon layer formation and brightness uniformity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the surface topology parameter by using CMP to reduce the height of crystallization protrusions to substantially the same level as the surrounding crystalline silicon layer. This parameter change eliminates brightness deviation while preserving the crystalline structure.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If amorphous silicon layer is crystallized without step difference layer, then crystallization is simpler, but crystallization protrusions form on the active layer

Engineering Contradiction:

Improvecrystallization processVSAvoidactive layer planarity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent performs preliminary action by forming a step difference layer structure before crystallizing the amorphous silicon layer. This pre-arranged structure guides the crystallization process and prevents protrusions from forming on the active layer, maintaining both ease of manufacture and active layer planarity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies local quality by creating different step levels (first step and second step) in the step difference layer. The amorphous silicon layer is selectively positioned on the lower second step, ensuring crystallization occurs only where needed while maintaining active layer planarity.

Inventive Principle:

Principle #3Local quality

3Productivity

If crystallization protrusions are not removed, then manufacturing process is shorter, but brightness characteristics are unstable

Engineering Contradiction:

Improvemanufacturing cycle timeVSAvoidbrightness stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent converts the harmful crystallization protrusions into a manageable intermediate state. By using CMP, the protrusions are transformed from defects into a controlled polishing process that achieves uniform surface level, turning a manufacturing challenge into a reliable process step.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

This approach effectively removes crystallization protrusions, ensuring stable and uniform brightness across the flat panel display, reducing product failures and maintaining consistent display quality.

Implementation Method 1

crystallizing the amorphous silicon layer into a crystalline silicon layer

Methodology Applied

Scientific EffectSequential lateral solidification: Phase Change

Implementation Method 2

polishing the crystalline silicon layer to form a planarized surface of the crystalline silicon layer having no height differences

Methodology Applied

Scientific EffectChemical mechanical polishing: Abrasion

Data Source

PatentUS8703589B2Flat panel display and method of manufacturing the same

Publication Date: 2014.04.22 SAMSUNG DISPLAY CO LTD

AI summary

A flat panel display having a thin-film transistor (TFT) and a pixel unit and a method of manufacturing the same are disclosed. In one embodiment, the method includes forming a step difference layer having a relatively high step and a relatively low step on a substrate and forming an amorphous silicon layer on the step difference layer along a height shape of the step difference layer. The method further includes crystallizing the amorphous silicon layer into a crystalline silicon layer and polishing the crystalline silicon layer to form a planarized surface of the crystalline silicon layer having no height differences so that the crystalline silicon layer remains on a region corresponding to the low step and an active layer is formed. According to this method, crystallization protrusions are effectively removed from the active layer, and thus, stable brightness characteristics of the display apparatus are guaranteed.