Oxide Semiconductor TFT Crystal Orientation for Higher Mobility
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Solution Overview
Problem
The field-effect mobility of thin film transistors using conventional oxide semiconductor films is not high, despite the use of crystalline oxide semiconductor films, indicating a need to improve the crystal structure of these films to enhance mobility.
Innovation Solution
A thin film transistor is developed with an oxide semiconductor film having a novel crystal structure, comprising indium and other metal elements, with a bixbyite crystal structure and specific crystal grain orientations, achieved through a sputtering and annealing process, which includes controlling substrate temperature and oxygen partial pressure to optimize crystallinity and reduce oxygen deficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional oxide semiconductor films are used in thin film transistors, then the device can be manufactured with simple structure and low-temperature process, but the field-effect mobility remains low
Solution Approach 1:
The patent changes the crystal structure parameters of the oxide semiconductor film from conventional structures to a novel structure with specific crystal orientations (<110>, <200>, <220>) and lattice constants (a=b=3.9-4.1Å, c=5.2-5.4Å). This parameter change in the crystal structure achieves higher field-effect mobility while maintaining compatibility with low-temperature manufacturing processes
Solution Approach 2:
The patent creates a composite material system by combining the novel crystal structure of the oxide semiconductor film with specific crystal orientations and lattice arrangements. This composite structure, featuring multiple crystal grains with specific orientations, achieves enhanced mobility while preserving manufacturing simplicity
2Manufacturing precision
If crystalline oxide semiconductor films are used to improve mobility, then the crystal structure can be optimized, but the field-effect mobility is still not sufficiently high
Solution Approach 1:
The patent applies local quality by creating specific crystal orientations in different regions of the oxide semiconductor film. The film contains multiple crystal grains with predominant orientations of <110>, <200>, and <220>, where each grain's specific orientation contributes to overall high mobility. This local crystalline quality control achieves superior field-effect mobility beyond conventional crystalline films
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 novel crystal structure of the oxide semiconductor film results in larger crystal grains and improved field-effect mobility, leading to better electrical properties and higher mobility in thin film transistors compared to conventional designs.
Implementation Method 1
achieved through a sputtering and annealing process
Implementation Method 2
achieved through a sputtering and annealing process
Data Source
AI summary
A thin film transistor includes a metal oxide layer over the substrate, an oxide semiconductor layer having crystallinity in contact with the metal oxide layer, a gate electrode overlapping the oxide semiconductor layer, and an insulating layer between the oxide semiconductor layer and the gate electrode. The oxide semiconductor layer includes a plurality of crystal grains. Each of the plurality of crystal grains includes at least one of a crystal orientation <001>, a crystal orientation <101>, and a crystal orientation <111> obtained by an EBSD method. In occupancy rates of crystal orientations calculated based on measurement points having crystal orientations with a crystal orientation difference greater than or equal to 0 degrees and less than or equal to 15 degrees with respect to a normal direction of a surface of the substrate, an occupancy rate of the crystal orientation <001> is less than or equal to 5%.