Oxide TFT Dual Gate Insulator for Low Off-Leakage Current
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Solution Overview
Problem
Oxide semiconductor transistors have high sensitivity to hydrogen, leading to uneven hydrogen distribution and increased off-leakage current when using silicon nitride as a gate insulating layer, while silicon oxide layers result in insufficient dielectric breakdown resistance due to their low relative dielectric constant.
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 high 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 relative dielectric constant is increased (about 8), but hydrogen diffusion occurs from ammonia gas during film formation, causing uneven hydrogen distribution and increased off-leakage current
Solution Approach 1:
The gate insulating layer is divided into two separate layers: a first gate insulating layer (silicon nitride) and a second gate insulating layer (silicon oxide). This segmentation allows each layer to perform its specialized function - the silicon nitride layer provides high dielectric constant while the silicon oxide layer acts as a hydrogen barrier, thus resolving the contradiction between achieving high dielectric constant and preventing hydrogen diffusion.
Solution Approach 2:
The silicon oxide layer serves as an intermediary hydrogen barrier between the oxide semiconductor active layer and the silicon nitride layer. This intermediary layer prevents hydrogen from the silicon nitride layer from diffusing into the sensitive oxide semiconductor, while still allowing the overall gate insulating structure to maintain sufficient dielectric constant for proper transistor operation.
2Object-affected harmful factors
If silicon oxide is used as a gate insulating layer to avoid hydrogen incorporation, then hydrogen block is achieved, but the relative dielectric constant is reduced (about 4), requiring reduced thickness which may cause poor step coverage or decreased dielectric breakdown resistance
Solution Approach 1:
The gate insulating layer is segmented into two functional layers where the silicon oxide layer (second gate insulating layer) specifically provides hydrogen blocking with sufficient thickness, while the silicon nitride layer (first gate insulating layer) compensates for the lower dielectric constant by providing additional dielectric strength. This segmentation allows each layer to be optimized for its specific function without compromising overall reliability.
Solution Approach 2:
The gate insulating structure uses a composite of silicon oxide and silicon nitride layers. The silicon oxide component provides excellent hydrogen barrier properties, while the silicon nitride component enhances the overall dielectric constant and breakdown resistance. This composite structure achieves both hydrogen blocking and sufficient dielectric performance that neither material could achieve alone.
3Object-affected harmful factors
If the gate insulating layer is formed to have sufficient thickness to block hydrogen, then hydrogen diffusion is prevented, but the manufacturing process complexity increases
Solution Approach 1:
Rather than forming a single extremely thick gate insulating layer to block hydrogen, the structure segments the function into two thinner layers with different material properties. This segmentation achieves effective hydrogen blocking through the silicon oxide layer while keeping each individual layer thickness within standard manufacturing ranges, thus preventing the need for excessively thick single layers that would complicate the manufacturing process.
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 breakdown resistance.
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.