Oxide Semiconductor TFT Stability via Hydrogen-Blocking Passivation
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Solution Overview
Problem
There is a demand for improving the stability and reliability of thin film transistor (TFT) devices with a channel layer made of an oxide semiconductor, as existing devices face challenges in maintaining high performance and resistance over time.
Innovation Solution
A TFT device structure is developed, including a substrate, gate electrode, channel layer, channel protection layer, electrode pair, and passivation layer, where the channel layer is made of an oxide semiconductor, and the channel protection and passivation layers are composed of silicon nitride and silicon oxynitride sub-layers with controlled hydrogen density to suppress active hydrogen species and enhance stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional protection film made of amorphous oxide semiconductor is used, then oxygen defects in the channel layer are suppressed, but active hydrogen species still enter the channel layer causing instability
Solution Approach 1:
The protection film is constructed as a composite structure with a first region containing silicon nitride and a second region containing silicon oxide. This composite material configuration allows the silicon nitride region to effectively block active hydrogen species while the silicon oxide region provides additional protective functions, thereby resolving the contradiction between preventing hydrogen entry and maintaining device stability.
Solution Approach 2:
The protection film is divided into regions with different material compositions - a first region with silicon nitride specifically positioned to block hydrogen species, and a second region with silicon oxide. This local differentiation of material properties allows targeted protection against hydrogen entry while maintaining overall device stability.
2Reliability
If the channel layer is made of oxide semiconductor for high electron mobility, then on/off ratio is improved, but stability and reliability deteriorate due to sensitivity to hydrogen and moisture
Solution Approach 1:
The protection film acts as an intermediary barrier between the oxide semiconductor channel layer and the external environment. The silicon nitride-containing first region specifically mediates the blocking of active hydrogen species, while the structure as a whole protects against moisture, thereby preserving the high electron mobility and on/off ratio characteristics of the oxide semiconductor while improving stability.
Solution Approach 2:
The multi-region protection film structure with different material compositions provides comprehensive environmental protection to the oxide semiconductor channel layer, allowing it to maintain its excellent electrical characteristics (high electron mobility and on/off ratio) while becoming resistant to hydrogen and moisture degradation.
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 results in a TFT device with high stability, reliability, and excellent electric characteristics, maintaining high electron mobility and resistance regardless of temperature, while also preventing degradation from moisture and hydrogen entry.
Implementation Method 1
a first sub-layer which is made of one of silicon nitride and silicon oxynitride and in which a density of H atoms bonded with Si atoms is no greater than 2.3×1021 cm−3
Data Source
AI summary
A TFT device including: a gate electrode; a channel layer above the gate electrode; a channel protection layer on the channel layer; an electrode pair on the channel protection layer composed of a source electrode and a drain electrode that are spaced away from one another, a part of each of the source electrode and the drain electrode in contact with the channel layer through the channel protection layer; and a passivation layer extending over the gate electrode, the channel layer, the electrode pair, and the channel protection layer. The channel layer is made of an oxide semiconductor. The TFT device has a first sub-layer made of one of silicon nitride and silicon oxynitride and in which Si—H density is no greater than 2.3×1021 cm−3. The first sub-layer is included in at least one of the channel protection layer and the passivation layer.