ALD Moisture Barrier Layer for Top-Gate TFT Substrates
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Solution Overview
Problem
Conventional top-gate type TFT substrates with aluminum oxide layers formed by sputtering have insufficient moisture barrier properties, leading to moisture penetration that can cause defects in organic EL display layers, such as dark spots or reduced brightness.
Innovation Solution
A top-gate type TFT substrate with a first moisture barrier layer formed by atomic layer deposition, covering the gate insulating layer, gate electrode, and contact regions of the oxide semiconductor layer, reducing resistance and enhancing moisture barrier properties, and optionally a second moisture barrier layer on a resin substrate for further enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an aluminum oxide layer is formed by sputtering to provide moisture barrier property, then the moisture barrier function is provided, but the water vapor transmission rate is insufficiently low
Solution Approach 1:
The patent changes the deposition method parameter from sputtering to atomic layer deposition (ALD). This parameter change results in a fundamentally different film structure with superior density and moisture barrier properties, achieving a water vapor transmission rate of less than 1×10^-6 g/m²/day, which is sufficiently low to prevent moisture-related defects in organic EL display layers.
2Reliability
If a moisture barrier layer is formed to prevent moisture penetration, then moisture barrier property is improved, but contact region resistance is not sufficiently reduced
Solution Approach 1:
The aluminum oxide layer formed by atomic layer deposition serves multiple functions simultaneously: (1) it provides excellent moisture barrier properties with extremely low water vapor transmission rate, and (2) it reduces contact region resistance through aluminum doping during the ALD process. This multi-functionality resolves the contradiction by achieving both moisture protection and electrical performance improvement with a single layer.
3Manufacturing precision
If aluminum doping is applied to reduce contact region resistance, then contact region resistance is reduced, but moisture barrier property is insufficient
Solution Approach 1:
The patent changes the deposition method parameter from sputtering to atomic layer deposition (ALD). This parameter change enables the aluminum oxide layer to achieve both low contact region resistance (through controlled aluminum doping) and superior moisture barrier properties (through the dense, pinhole-free film structure characteristic of ALD), simultaneously resolving both requirements.
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 substrate achieves significantly reduced water vapor transmission rates and lower contact region resistances, providing improved moisture barrier and electrical performance, thereby preventing defects in organic EL display layers.
Implementation Method 1
The first moisture barrier layer includes a metal oxide and is formed by atomic layer deposition
Implementation Method 2
The mere formation of the first moisture barrier layer can reduce the resistances of the contact regions of the oxide semiconductor layer being in contact with the first moisture barrier layer
Data Source
AI summary
The thin film transistor element substrate of the present disclosure includes a first moisture barrier layer covering the gate insulating layer and the gate electrode, covering the contact regions of the oxide semiconductor layer other than the connecting portion of the contact region connected to the source electrode and the connecting portion of the contact region connected to the drain electrode, and covering an surface of the substrate on which the oxide semiconductor layer is not disposed. The first moisture barrier layer includes a metal oxide and is formed by atomic layer deposition. The first moisture barrier layer formed by atomic layer deposition is in contact with a pair of contact regions.