C-Axis Aligned Oxide Semiconductor Films for Stable Gate Interfaces
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Solution Overview
Problem
Transistors using oxide semiconductors face instability in electric characteristics due to high defect density at the interface between the oxide semiconductor film and the gate insulating film, especially when in an amorphous state, and are sensitive to light irradiation, making them unsuitable for large-scale production.
Innovation Solution
A semiconductor device is developed using an oxide material with c-axis aligned crystal structure, which has a triangular or hexagonal atomic arrangement, allowing for stable electron states and reduced defect density, and can be formed using methods like sputtering or molecular beam epitaxy, suitable for use in transistors as a gate electrode, source/drain electrodes, or active layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If an amorphous oxide semiconductor film is used, then the transistor can be formed over a larger glass substrate, but the defect density at the interface is high and electric characteristics are unstable
Solution Approach 1:
The invention changes the structural parameter of the oxide semiconductor film from amorphous to crystalline state. By forming a crystalline oxide semiconductor film with specific crystal orientation (c-axis alignment), the defect density at the interface is reduced and electric characteristics are stabilized while maintaining compatibility with large substrate manufacturing
Solution Approach 2:
The invention uses a composite structure consisting of a crystalline oxide semiconductor film layer formed over a gate insulating film. This layered composite structure combines the advantages of crystalline materials (low defect density, stable electric characteristics) with the manufacturing scalability of film-based processes on large substrates
2Reliability
If a polycrystalline silicon transistor is used, then high field effect mobility is achieved, but it is not suitable for being formed over a larger glass substrate
Solution Approach 1:
The invention changes the material parameter from polycrystalline silicon to crystalline oxide semiconductor. This material substitution maintains high field effect mobility characteristics while enabling formation over large glass substrates through film deposition techniques that are scalable to large areas
Solution Approach 2:
The invention replaces the mechanical grain structure of polycrystalline silicon with a crystalline structure in an oxide semiconductor system. This substitution allows achieving high mobility through crystal orientation (c-axis alignment) rather than through grain structure control, enabling large-area fabrication
3Ease of manufacture
If the interface between oxide semiconductor film and gate insulating film is in an amorphous state, then manufacturing is simplified, but the defect density is high and transistor electric characteristics become unstable
Solution Approach 1:
The invention changes the structural parameter of the interface from amorphous to crystalline state. By forming a crystalline oxide semiconductor film with c-axis alignment, the interface defect density is reduced while maintaining manufacturing feasibility through controlled crystallization processes
Solution Approach 2:
The invention performs preliminary crystallization treatment to form a crystalline oxide semiconductor film before final transistor fabrication. This preliminary action of crystallizing the film reduces interface defect density in advance, ensuring stable electric characteristics throughout the manufacturing process
4Ease of manufacture
If conventional oxide semiconductor materials are used, then transistors can be manufactured, but light irradiation changes the electric characteristics and reduces reliability
Solution Approach 1:
The invention uses a composite material system with specific crystal orientation (c-axis aligned crystalline oxide semiconductor). This structured composite material exhibits stability against light irradiation while maintaining manufacturability through established film deposition and crystallization techniques
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 provides semiconductor devices with improved electric characteristics and reliability, enabling mass production on large substrates with reduced sensitivity to light, thus enhancing the performance and stability of transistors.
Implementation Method 1
an oxide material including crystal with c-axis alignment, which has a triangular or hexagonal atomic arrangement when seen from the direction of the a-b plane, a surface, or an interface
Implementation Method 2
The oxide material can be formed by a sputtering method, a molecular beam epitaxy method, an atomic layer deposition method, a pulsed laser deposition method, or the like
Implementation Method 3
The oxide material can be formed by a sputtering method, a molecular beam epitaxy method, an atomic layer deposition method, a pulsed laser deposition method, or the like
Data Source
AI summary
An object is to provide a material suitably used for a semiconductor included in a transistor, a diode, or the like. Another object is to provide a semiconductor device including a transistor in which the condition of an electron state at an interface between an oxide semiconductor film and a gate insulating film in contact with the oxide semiconductor film is favorable. Further, another object is to manufacture a highly reliable semiconductor device by giving stable electric characteristics to a transistor in which an oxide semiconductor film is used for a channel. A semiconductor device is formed using an oxide material which includes crystal with c-axis alignment, which has a triangular or hexagonal atomic arrangement when seen from the direction of a surface or an interface and rotates around the c-axis.