Oxide Semiconductor TFT Buried Channel for Stable Mobility
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Solution Overview
Problem
Thin film transistors using oxide semiconductors face challenges in maintaining stable electric characteristics due to variations in composition and defects caused by manufacturing conditions, particularly in liquid crystal and organic electroluminescence display devices, where the back channel potential is easily influenced by external potentials and copper atoms can contaminate the channel region.
Innovation Solution
A transistor structure with an oxide semiconductor layer having a first region and a second region, where the second region has a lower carrier concentration and higher crystallization ratio, is used, with a first gate electrode overlapping the oxide semiconductor layer and insulating layers to form a buried channel, reducing charge trapping and threshold voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an oxide semiconductor film is used to manufacture a thin film transistor, then field effect mobility is improved and formation on large area substrates is easier, but composition variation and manufacturing condition sensitivity cause electric characteristics to fluctuate
Solution Approach 1:
The oxide semiconductor film is divided into a first region (channel formation region) and a second region (protective region). The second region has lower carrier concentration and acts as a protective layer that prevents composition variation and manufacturing condition sensitivity from affecting the channel region, thereby maintaining stable electric characteristics while allowing high mobility in the channel region
Solution Approach 2:
Different regions of the oxide semiconductor film are given different properties: the first region is optimized for high field effect mobility with appropriate carrier concentration, while the second region is designed with lower carrier concentration to provide protection and stability. This local differentiation resolves the contradiction by allowing each region to serve its specific function
2Speed
If a polycrystalline silicon semiconductor is used, then field effect mobility is high, but crystallization steps are required making uniform film formation on large area substrates difficult
Solution Approach 1:
The patent replaces the mechanical/thermal crystallization process (laser annealing) with an oxide semiconductor-based system that achieves high mobility through material selection and structural design rather than phase transformation. The oxide semiconductor provides high mobility intrinsically without requiring crystallization steps, enabling easy formation on large area substrates
3Ease of manufacture
If an amorphous silicon semiconductor film is used, then formation on large area substrates is easy, but field effect mobility is low
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the mobility characteristic while maintaining the ease of film formation. The oxide semiconductor can be deposited as an amorphous or microcrystalline film on large area substrates without complex crystallization processes, yet achieves high field effect mobility through its inherent material properties and the protective region structure
Data Source
AI summary
A transistor in an embodiment includes an oxide semiconductor layer on a substrate, the oxide semiconductor layer including a first region and a second region, a first gate electrode including a region overlapping the oxide semiconductor layer, the first gate electrode being arranged on a surface of the oxide semiconductor layer opposite to the substrate, a first insulating layer between the first gate electrode and the oxide semiconductor layer, and a first oxide conductive layer and a second oxide conductive layer between the oxide semiconductor layer and the substrate, the first oxide conductive layer and the second oxide conductive layer each including a region in contact with the oxide semiconductor layer.