Polycrystalline Oxide Semiconductor Film for Higher TFT Mobility
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Solution Overview
Problem
Conventional oxide semiconductor films used in thin film transistors have low field-effect mobility despite using crystalline structures, necessitating an improvement in crystal structure to enhance performance.
Innovation Solution
Development of an oxide semiconductor film with a polycrystalline structure containing indium and specific metal elements, such as gallium, forming large crystal grains with significant crystal orientation changes, reducing grain boundary influence through a novel crystal structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oxide semiconductor films with crystalline structures are used, then the field-effect mobility remains low, but using amorphous silicon would simplify the manufacturing process
Solution Approach 1:
The patent changes the crystal structure parameters of the oxide semiconductor film by controlling the formation of large crystal grains with specific orientations (c-axis perpendicular to substrate). This structural parameter change enables high field-effect mobility while maintaining compatibility with low-temperature manufacturing processes, thus resolving the contradiction between performance and ease of manufacture
Solution Approach 2:
The patent creates a composite structure by forming a polycrystalline oxide semiconductor film with specific crystal grain characteristics (large grain size, specific orientation) on top of an amorphous silicon-based substrate. This composite approach allows the benefits of crystalline structure (high mobility) while maintaining the manufacturing simplicity of amorphous silicon processes
2Reliability
If oxide semiconductor films with small crystal grains are used, then the manufacturing process is simpler, but grain boundary scattering increases and reduces field-effect mobility
Solution Approach 1:
The patent applies local quality control by ensuring that crystal grains larger than a specific threshold size (5 μm) have their c-axis oriented perpendicular to the substrate surface. This localized structural optimization in critical regions reduces grain boundary scattering and enhances field-effect mobility without requiring complete structural control throughout the entire film
Solution Approach 2:
The patent addresses the grain boundary issue by transitioning from controlling grain size in two dimensions to controlling crystal orientation in the third dimension (perpendicular to substrate). This dimensional approach allows large crystal grains to span across the film, reducing the number of grain boundaries in the charge transport path and thereby improving mobility
Data Source
AI summary
An oxide semiconductor film includes a plurality of crystal grains over a substrate. The oxide semiconductor film includes indium and a first metal element selected from the group consisting of aluminum (Al), gallium (Ga), yttrium (Y), scandium (Sc), and lanthanoid elements. When a crystal orientation at each of a plurality of measurement points of the oxide semiconductor film is obtained based on an electron diffraction pattern obtained by transmitting an electron beam irradiated from a direction intersecting a thickness direction of the oxide semiconductor film, an average value of KAM values calculated at the plurality of measurement points is greater than or equal to 0.3 degrees.