Thin-Film Transistor Bixbyite Crystal Structure for Higher Mobility
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Solution Overview
Problem
The field-effect mobility of thin film transistors using conventional oxide semiconductor films with crystallinity is not high, necessitating an improvement in the crystal structure of the oxide semiconductor film to enhance mobility.
Innovation Solution
A thin film transistor is developed with an oxide semiconductor film having a novel crystal structure, specifically a bixbyite structure, where the occupancy rate of certain crystal orientations is optimized, and the film is manufactured using a sputtering and annealing process with controlled substrate temperature and oxygen partial pressure to achieve larger crystal grains and reduced oxygen deficiencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional oxide semiconductor films with crystallinity are used, then the thin film transistor can be manufactured with a simple structure and low-temperature process, but the field-effect mobility is not high
Solution Approach 1:
The patent changes the crystal structure parameters of the oxide semiconductor film from conventional structures (such as beta-sheet structure) to a novel crystal structure with specific space group (R-3c) and lattice constants. This parameter change in crystal structure leads to significantly improved field-effect mobility while maintaining the ease of low-temperature manufacturing process
Solution Approach 2:
The patent optimizes the local crystal orientation distribution by controlling the occupancy rates of different crystal orientations. Specifically, it sets the occupancy rate of <100> orientation to 40-70% and <110> orientation to 20-40%, creating a specific local quality distribution that enhances carrier mobility while keeping the manufacturing process simple
2Reliability
If the crystal structure of oxide semiconductor film is optimized for higher mobility, then field-effect mobility improves, but the manufacturing process becomes more complex
Solution Approach 1:
The patent identifies specific parameter ranges for the novel crystal structure (space group R-3c, lattice constants a=5.2-5.4Å, c=18.5-19.5Å, and specific occupancy rates of crystal orientations) that can be achieved through standard sputtering and annealing processes, thus improving mobility without significantly increasing manufacturing complexity
Solution Approach 2:
The patent performs preliminary optimization of the sputtering conditions and annealing parameters to pre-establish the novel crystal structure with desired orientation distribution before device fabrication. This preliminary action simplifies subsequent manufacturing steps while ensuring high mobility
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 results in a thin film transistor with higher field-effect mobility and improved electrical properties, maintaining excellent insulating properties without deteriorating the semiconductor properties.
Implementation Method 1
the film is manufactured using a sputtering and annealing process
Implementation Method 2
the film is manufactured using a sputtering and annealing process
Implementation Method 3
an oxide semiconductor layer having crystallinity over the substrate... The oxide semiconductor layer includes a plurality of crystal grains
Data Source
AI summary
A thin film transistor includes an oxide semiconductor layer having crystallinity over a substrate, 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 <111> is greater than an occupancy rate of the crystal orientation <001> and an occupancy rate of the crystal orientation <101>.