Oxide Semiconductor Transistor C-Axis Alignment
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Solution Overview
Problem
Conventional transistors using oxide semiconductors face limitations in field-effect mobility, making them unsuitable for large-sized display devices and high-performance semiconductor applications, particularly as driver devices due to low crystallinity and limited substrate compatibility.
Innovation Solution
A method involving the crystallization of oxide semiconductor layers through annealing and crystal growth, combined with oxygen purification and hydrogen introduction to enhance field-effect mobility, allowing for the formation of c-axis-aligned crystal structures and improved interface states, thereby increasing transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If amorphous silicon is used to form transistors over glass substrates, then the transistors can be formed over larger glass substrates, but the field-effect mobility is low
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, and further changes the crystalline structure parameter by forming c-axis-aligned crystal structures. This transforms the material properties to achieve high field-effect mobility (exceeding 10 cm²/Vs) while maintaining compatibility with large glass substrates, thereby resolving the contradiction between substrate area and field-effect mobility.
2Speed
If polycrystalline silicon is used to achieve high field-effect mobility, then the mobility is high, but they are not suitable for larger glass substrates
Solution Approach 1:
The patent employs parameter changes by transitioning from polycrystalline silicon to oxide semiconductor materials, and specifically by controlling the crystalline orientation to form c-axis-aligned structures. This material substitution and structural control enable the formation of high-mobility transistors over large glass substrates, resolving the contradiction between achieving high mobility and maintaining substrate compatibility.
3Reliability
If oxide semiconductor transistors are used in large-sized display devices, then sufficient performance can be obtained for switching elements, but there is a limit to their use as driver devices due to limited crystallinity
Solution Approach 1:
The patent applies phase transition principles by controlling the crystallization process of oxide semiconductors to form c-axis-aligned crystal structures. This controlled phase transition from amorphous or poorly crystalline states to highly ordered c-axis-aligned crystalline structures significantly improves field-effect mobility, enabling oxide semiconductor transistors to function effectively as driver devices in large-sized displays, thereby resolving the contradiction between switching element performance and crystallinity requirements for driver applications.
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 approach significantly enhances field-effect mobility, improving display characteristics by shortening switching times and enabling the manufacture of high-performance semiconductor devices suitable for large-sized displays and diverse electronic appliances.
Implementation Method 1
an oxide semiconductor layer is crystallized. Annealing is performed after a first oxide semiconductor layer is formed, and a second oxide semiconductor layer is formed thereover. And then, crystal growth is caused from the film surface toward a surface of the second oxide semiconductor layer formed above.
Implementation Method 2
Annealing is performed after a first oxide semiconductor layer is formed, and a second oxide semiconductor layer is formed thereover.
Implementation Method 3
after oxygen is supplied to the oxide semiconductor layer
Data Source
AI summary
One embodiment of the present invention is to achieve high mobility in a device using an oxide semiconductor and provide a highly reliable display device. An oxide semiconductor layer including a crystal region in which c-axis is aligned in a direction substantially perpendicular to a surface is formed and an oxide insulating layer is formed over and in contact with the oxide semiconductor layer. Oxygen is supplied to the oxide semiconductor layer by third heat treatment. A nitride insulating layer containing hydrogen is formed over the oxide insulating layer and fourth heat treatment is performed, so that hydrogen is supplied at least to an interface between the oxide semiconductor layer and the oxide insulating layer.