Multilayer Oxide Semiconductor Thin Film Transistor for High Mobility
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Solution Overview
Problem
Current thin film transistors using silicon materials for channel layers face limitations in achieving both high carrier mobility and large display size due to low mobility in amorphous Si and in-plane variation in polycrystalline Si, while oxide semiconductors like InGaZnO4 offer improved mobility but require further enhancement.
Innovation Solution
A thin film transistor design featuring an oxide semiconductor layer with a multilayer structure, including a carrier travel layer and a carrier supply layer, where the conduction band minimum or valence band maximum level of the carrier supply layer is higher in energy than that of the carrier travel layer, allowing carriers to be supplied and accumulated near the interface, reducing scattering and increasing mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If amorphous Si is used for the channel layer, then the display can be increased in size, but carrier mobility remains low (about 1 cm2/V*s or less)
Solution Approach 1:
The patent employs a composite oxide semiconductor structure consisting of multiple layers with different compositions and properties. The carrier supply layer (higher carrier concentration) and carrier travel layer (lower carrier concentration) work together to provide both sufficient carrier supply and high mobility transport, resolving the contradiction between achieving large display area and maintaining high carrier mobility.
2Reliability
If polycrystalline Si is used for the channel layer, then carrier mobility is high (about 30 to 300 cm2/V*s), but in-plane variation of transistor characteristics increases, making it hard to increase display size
Solution Approach 1:
The patent applies local quality by creating distinct regions within the oxide semiconductor layer with different carrier concentrations. The carrier supply layer has higher carrier concentration to ensure sufficient carriers, while the carrier travel layer has lower carrier concentration to minimize scattering and maximize mobility. This local differentiation allows high mobility while maintaining uniformity across the large display area.
3Device complexity
If a single-layer oxide semiconductor is used, then the structure is simple, but carrier mobility cannot be sufficiently increased due to travel scattering
Solution Approach 1:
The patent segments the oxide semiconductor layer into multiple functional layers: a carrier supply layer and a carrier travel layer. This segmentation allows the carrier supply layer to provide sufficient carriers while the carrier travel layer minimizes scattering effects. The energy band structure is designed so that the conduction band minimum of the carrier supply layer is higher than that of the carrier travel layer, enabling efficient carrier supply while maintaining high mobility in the travel layer.
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 enhances carrier mobility by suppressing scattering and allowing for controlled carrier concentration, leading to improved performance and manufacturing yield while maintaining the benefits of oxide semiconductor materials.
Implementation Method 1
A conduction band minimum level or a valence band maximum level corresponding to a carrier supply source of the carrier supply layer is higher in energy than a conduction band minimum level or a valence band maximum level corresponding to a carrier supply destination of the carrier travel layer
Implementation Method 2
carriers are accumulated in a region near an interface with the carrier supply layer of the carrier travel layer. Therefore, when the carrier travel layer acts as a channel, carriers travel in the region substantially two-dimensionally, and therefore travel scattering to carriers is suppressed
Data Source
AI summary
A thin film transistor, which is capable of improving carrier mobility, and a display device and an electronic device, each of which uses the thin film transistor, are provided. The thin film transistor includes: a gate electrode; an oxide semiconductor layer including a multilayer film including a carrier travel layer configuring a channel and a carrier supply layer for supplying carriers to the carrier travel layer; a gate insulating film provided between the gate electrode and the oxide semiconductor layer; and a pair of electrodes as a source and a drain. A conduction band minimum level or a valence band maximum level corresponding to a carrier supply source of the carrier supply layer is higher in energy than a conduction band minimum level or a valence band maximum level corresponding to a carrier supply destination of the carrier travel layer.