Amorphous Oxide Semiconductor TFT for Flexible Displays
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Solution Overview
Problem
Thin film field effect transistors (TFTs) using amorphous oxide semiconductors face challenges in achieving low OFF current, high ON-OFF ratio, and stability across varying environmental conditions, particularly when used on flexible resin substrates, due to high temperature processing requirements and sensitivity to temperature and humidity changes.
Innovation Solution
A TFT structure with a mean square interface roughness between the gate insulating layer and the active layer less than 2 nm, a carrier concentration of the active layer between 1 × 10^15 cm^-3 and 1 × 10^19 cm^-3, and a film thickness of 0.5 nm to 20 nm, using an amorphous oxide semiconductor with In, Ga, and Zn, and a low carrier concentration layer to maintain stability and reduce environmental dependency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal treatment process at relatively high temperature is used to fabricate transistors using silicon thin films, then the transistor performance is improved, but it becomes difficult to form transistors directly on resin substrates which are low in heat resistance
Solution Approach 1:
The invention changes the material parameter from crystalline metal oxides to amorphous oxide semiconductors, which can be processed at lower temperatures while maintaining transistor performance. This allows direct formation of transistors on resin substrates without requiring high-temperature thermal treatment processes
Solution Approach 2:
The invention uses composite structures including amorphous oxide semiconductor active layers combined with specific gate insulating layer configurations. This composite approach enables low-temperature processing while achieving the desired transistor characteristics and compatibility with resin substrates
2Temperature
If an amorphous oxide semiconductor is used in an active layer of a TFT, then low temperature processing is enabled, but the OFF current becomes high and the ON/OFF ratio becomes low
Solution Approach 1:
The invention optimizes the carrier concentration parameter of the amorphous oxide semiconductor to a specific range (1×10^15 to 1×10^19 cm^-3), which simultaneously achieves low OFF current, high ON/OFF ratio, and maintains compatibility with low-temperature processing on resin substrates
Solution Approach 2:
The invention applies different quality characteristics to different regions: the active layer uses amorphous oxide semiconductor with optimized carrier concentration for low-temperature processing, while the gate insulating layer structure is specifically designed to compensate and achieve the desired electrical characteristics
3Reliability
If the carrier concentration of an amorphous oxide semiconductor is reduced to achieve low OFF current, then the ON/OFF ratio improves, but the characteristics vary under continuous driving and environmental conditions
Solution Approach 1:
The invention identifies and optimizes multiple parameters simultaneously: carrier concentration (1×10^15 to 1×10^19 cm^-3), interface roughness (less than 2 nm), and film thickness (0.5 nm to 20 nm). This multi-parameter optimization achieves both low OFF current with high ON/OFF ratio and stable characteristics under continuous driving and environmental variations
Solution Approach 2:
The invention incorporates feedback mechanisms through the gate insulating layer structure design, which compensates for variations in the amorphous oxide semiconductor properties, thereby stabilizing the transistor characteristics during continuous operation and across environmental conditions
Data Source
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AI summary
A TFT is provided which includes on a substrate, at least a gate electrode, a gate insulating layer, an active layer containing an amorphous oxide semiconductor, a source electrode, and a drain electrode, wherein a mean square interface roughness between the gate insulating layer and the active layer is less than 2 nm, a carrier concentration of the active layer is 1 × 1015 cm-3 or more, and a film thickness of the active layer is 0.5 nm or more and less than 20 nm. A TFT is provided which has high field effect mobility and a high ON-OFF ratio, and is improved in environmental temperature dependency. Also, a display using the TFT is provided.