Oxide Semiconductor TFT Fabrication for Light Illumination Stability
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Solution Overview
Problem
Field effect transistors using IGZO semiconductors face challenges in maintaining TFT characteristics during light illumination due to surface defects caused by film formation techniques like sputtering or CVD, which lead to threshold shifts, and existing heat treatment methods do not effectively rectify these defects.
Innovation Solution
A field effect transistor fabrication method involving multiple heat treatments and specific adjustments in the thickness and composition of oxide semiconductor films, including a first, second, and third oxide semiconductor film structure, with heat treatments over 300°C in an oxidizing atmosphere to diffuse oxygen and stabilize the channel layer, reducing surface defects and improving threshold stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If film formation techniques like sputtering or CVD are used to form oxide semiconductor films, then productivity and barrier properties are improved, but surface defects are generated that cause threshold shifts during light illumination
Solution Approach 1:
The patent applies a first heat treatment step immediately after forming the first oxide semiconductor film by sputtering or CVD, before subsequent films are deposited. This preliminary heat treatment rectifies surface defects generated during film formation, preventing threshold shifts during later light illumination while maintaining the productivity benefits of plasma-based deposition methods.
Solution Approach 2:
The patent employs multiple heat treatment steps at different temperatures (first heat treatment at 250-450°C, second heat treatment at 300-500°C) to selectively address different types of defects at different stages of fabrication. This parameter-based approach allows optimization of both deposition efficiency and final device reliability.
2Device complexity
If a single oxide semiconductor film is used, then device complexity is reduced, but TFT characteristics deteriorate under light illumination due to insufficient defect rectification
Solution Approach 1:
The patent divides the oxide semiconductor layer into multiple films (first oxide semiconductor film, second oxide semiconductor film, and optionally third film) with different compositions and functions. The first film serves as the primary active layer, while subsequent films provide defect passivation and stability, collectively improving light illumination characteristics without excessive complexity.
Solution Approach 2:
The patent uses composite oxide semiconductor structures with different materials (IGZO, InO3, GaO3, ZnO) in different layers. Each material is selected for specific properties: IGZO for high mobility, InO3 for defect rectification, and ZnO for surface passivation, creating a composite structure that achieves superior stability under light illumination.
3Reliability
If heat treatment is applied after forming the complete oxide semiconductor layer, then surface defects are reduced, but oxygen diffusion is insufficient to reach deeper regions of the active layer
Solution Approach 1:
The patent performs the first heat treatment immediately after forming the first oxide semiconductor film, before subsequent films are deposited. This timing allows oxygen to diffuse deeply into the first film when it is most accessible, ensuring thorough defect rectification in the active region before the structure becomes more complex.
Solution Approach 2:
The patent uses multiple heat treatment steps at different temperatures to achieve oxygen diffusion at different depths and stages. The first heat treatment at lower temperature addresses surface defects, while the second heat treatment at higher temperature ensures deep oxygen diffusion, creating a multi-dimensional approach to defect remediation.
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 method effectively stabilizes TFT characteristics during light illumination by reducing surface defects and improving oxygen diffusion, leading to enhanced field effect mobility and threshold stability, suitable for applications in display devices and sensors.
Implementation Method 1
heat treatments over 300°C in an oxidizing atmosphere to diffuse oxygen and stabilize the channel layer
Implementation Method 2
applying a heat treatment at over 300° C. in an oxidizing atmosphere
Implementation Method 3
heat treatments over 300°C in an oxidizing atmosphere
Data Source
AI summary
There is provided a method of fabricating a field effect transistor including: forming a first oxide semiconductor film on a gate insulation layer disposed on a gate electrode; forming a second oxide semiconductor film on the first oxide semiconductor film, the second oxide semiconductor film differing in cation composition from the first oxide semiconductor film and being lower in electrical conductivity than the first oxide semiconductor film; applying a heat treatment at over 300° C. in an oxidizing atmosphere; forming a third oxide semiconductor film on the second oxide semiconductor film, the third oxide semiconductor film differing in cation composition from the first oxide semiconductor film and being lower in electrical conductivity than the first oxide semiconductor film; applying a heat treatment in an oxidizing atmosphere; and, forming a source electrode and a drain electrode on the third oxide semiconductor film.