SiON Gradient Layers for LTPS TFT Optical Transmittance

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Solution Overview

Problem

The refractive index differential between adjacent layers in low-temperature polysilicon (LTPS) thin film transistors in LCD and OLED displays leads to reduced optical transmittance, limiting display resolution.

Innovation Solution

Incorporating transition stacks with graded refractive indices between inorganic layers, such as SiO and SiN layers, to minimize refractive index differentials and enhance optical transmittance by using sublayers with varying concentrations of SiO and SiN, deposited using plasma processing techniques.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If adjacent inorganic layers with different refractive indices are used in LTPS TFT, then device functionality is achieved, but optical transmittance is reduced

Engineering Contradiction:

Improveoptical transmittanceVSAvoidlayer structure complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

A transition stack comprising multiple inorganic sublayers (SiO2, SiN, and SiON layers) is introduced between the first inorganic layer (SiO2) and second inorganic layer (SiN). These intermediate layers have refractive indices that gradually transition from the first layer to the second layer, reducing optical reflection and improving light transmittance through the TFT structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The refractive index parameter is gradually changed across the transition stack by using sublayers with different compositions (SiO2 with n≈1.46, SiN with n≈2.0, and SiON with intermediate values). This gradual parameter change minimizes abrupt refractive index differences, thereby reducing reflective interference and enhancing optical transmittance.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If more transition layers are added to improve optical transmittance, then resolution is enhanced, but manufacturing complexity increases

Engineering Contradiction:

Improvedisplay resolutionVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The transition stack uses composite inorganic materials (SiO2, SiN, and SiON layers) with different optical properties. By combining these materials in a graded structure, the patent achieves improved optical transmittance and display resolution while maintaining compatibility with existing LTPS TFT manufacturing processes.

Inventive Principle:

Principle #40Composite materials

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 reduces reflective interference and improves optical transmittance, thereby enhancing display resolution with minimal cost increase.

Implementation Method 1

When adjacent layers have different refractive indices, optical transmittance is reduced

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

This approach reduces reflective interference and improves optical transmittance

Methodology Applied

Scientific EffectReflective interference: Interference

Implementation Method 3

deposited using plasma processing techniques

Methodology Applied

Scientific EffectPlasma deposition: Plasma Enhanced Chemical Vapour Deposition

Data Source

PatentUS9634039B2SiON gradient concept

Publication Date: 2017.04.25 APPLIED MATERIALS INC

AI summary

Embodiments of the present disclosure generally relate to methods and devices for use of low temperature polysilicon (LTPS) thin film transistors in liquid crystal display (LCD) and organic light-emitting diode (OLED) displays.