Oxide TFT Gate Insulating Stack for Low Off-Leakage
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Solution Overview
Problem
Oxide semiconductors used in transistors are sensitive to hydrogen, leading to uneven hydrogen distribution and increased off-leakage current when silicon nitride is used as a gate insulating layer, while silicon oxide layers have insufficient dielectric constant, resulting in poor coverage and breakdown resistance.
Innovation Solution
A dual gate structure with a silicon nitride first gate insulating layer and a thicker silicon oxide hydrogen block layer is implemented, where the silicon oxide layer prevents hydrogen diffusion from the silicon nitride layer, maintaining a higher dielectric constant and reducing off-leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If silicon nitride is used as a gate insulating layer, then the dielectric constant is increased, but hydrogen diffuses into the oxide semiconductor layer causing increased off-leakage current
Solution Approach 1:
A hydrogen block layer is introduced as an intermediary between the silicon nitride gate insulating layer and the oxide semiconductor layer. This intermediate layer prevents hydrogen from diffusing into the oxide semiconductor while allowing the silicon nitride layer to maintain its high dielectric constant for effective transistor operation.
Solution Approach 2:
The gate insulating layer structure is segmented into multiple layers: a lower silicon nitride layer for high dielectric constant and an upper hydrogen block layer for preventing hydrogen diffusion. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between dielectric performance and hydrogen barrier requirements.
2Object-affected harmful factors
If silicon oxide is used as a gate insulating layer to block hydrogen, then hydrogen diffusion is prevented, but the dielectric constant is insufficient leading to poor coverage and breakdown resistance
Solution Approach 1:
The gate insulating layer uses a composite structure combining silicon nitride (high dielectric constant) and silicon oxide (hydrogen barrier properties). This composite approach allows the system to simultaneously achieve high dielectric constant for reliability and effective hydrogen blocking, overcoming the limitations of using either material alone.
3Object-affected harmful factors
If the gate insulating layer is formed thicker to prevent hydrogen diffusion, then hydrogen blocking is improved, but the dielectric breakdown resistance decreases
Solution Approach 1:
The gate insulating layer is segmented into functional sub-layers: a thinner silicon nitride layer providing dielectric strength and a thicker silicon oxide layer providing hydrogen blocking. This segmentation allows the total thickness to be optimized for hydrogen blocking while the silicon nitride portion maintains sufficient dielectric breakdown resistance.
Solution Approach 2:
The composite structure of silicon nitride and silicon oxide layers allows different thickness optimizations for different functions. The silicon nitride layer can be kept thinner to maintain dielectric strength, while the silicon oxide layer can be thicker to provide hydrogen blocking, achieving both goals simultaneously.
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 configuration effectively reduces off-leakage current, ensures uniform transistor characteristics, and minimizes manufacturing complexity by controlling hydrogen diffusion and maintaining sufficient dielectric strength.
Implementation Method 1
hydrogen derived from ammonia gas used in the film forming process remains in the silicon nitride and is diffused
Implementation Method 2
a second gate insulating layer, which is a hydrogen block layer, disposed between the active layer and the gate electrode on the active layer side
Data Source
AI summary
A thin film transistor including: an active layer formed of an oxide semiconductor including at least indium and gallium; a gate electrode; a first gate insulating layer disposed between the active layer and the gate electrode on the gate electrode side; and a second gate insulating layer, which is a hydrogen block layer, disposed between the active layer and the gate electrode on the active layer side.