C-Axis Aligned Oxide Semiconductor for Stable TFT Interfaces
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Solution Overview
Problem
Transistors using amorphous silicon have low field effect mobility and are unsuitable for large glass substrates, while polycrystalline silicon transistors are not suitable for larger glass substrates, and oxide semiconductor transistors face instability due to electron states at the interface with gate insulating films and sensitivity to light.
Innovation Solution
Utilizing an oxide material with c-axis aligned crystal structure, which includes triangular or hexagonal atomic arrangements, and varying a-axis or b-axis directions, for the gate electrode, source/drain electrodes, and active layer, formed through methods like sputtering or molecular beam epitaxy, to stabilize electron states and improve mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If amorphous silicon is used for transistors on glass substrates, then the substrate area can be made large, but the field effect mobility is low
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor (such as In-Ga-Zn-O), which fundamentally alters the electrical properties while maintaining compatibility with large glass substrates. This material substitution enables high field effect mobility without sacrificing the ability to manufacture on large-area substrates.
2Speed
If polycrystalline silicon is used for transistors, then the field effect mobility is high, but they are not suitable for larger glass substrates
Solution Approach 1:
The patent substitutes polycrystalline silicon with oxide semiconductor materials that can be deposited using low-temperature processes compatible with large glass substrates. The oxide semiconductor maintains high mobility characteristics while enabling manufacturing on large-area substrates through techniques like sputtering.
3Ease of manufacture
If an amorphous interface between oxide semiconductor film and gate insulating film is present, then manufacturing is simpler, but the defect density is high and electric characteristics are unstable
Solution Approach 1:
The patent applies preliminary heat treatment (annealing) to the oxide semiconductor film before transistor operation. This pre-treatment stabilizes the amorphous interface structure, reduces defect density, and improves electrical characteristics without requiring complex manufacturing processes. The heat treatment is performed at temperatures compatible with the existing manufacturing flow.
4Speed
If oxide semiconductor transistors are used, then high mobility is achieved, but electric characteristics are sensitive to light irradiation
Solution Approach 1:
The patent modifies the oxide semiconductor composition, specifically using In-Ga-Zn-O-based materials with controlled stoichiometry. This compositional adjustment reduces the material's sensitivity to light irradiation while preserving high field effect mobility, addressing the stability issue without sacrificing performance.
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 stable electric characteristics, suitable for large-sized substrates, and reduces sensitivity to light, enabling high reliability and mass production.
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
Implementation Method 3
The oxide material can be formed by a sputtering method, a molecular beam epitaxy method
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.