Oxide Semiconductor Thin Film Transistor Mobility Stabilization
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Solution Overview
Problem
Thin film transistors using oxide semiconductors face challenges with low field effect mobility and unstable electrical characteristics, particularly when in contact with insulating films, which affects the performance of liquid crystal display devices.
Innovation Solution
A semiconductor device structure is implemented where an oxide semiconductor layer with indium, gallium, and zinc is used, and a semiconductor or conductive layer with higher electrical conductivity is formed over it, ensuring electrical connection and partial contact with the gate insulating layer and source/drain electrode layers, stabilizing the oxide semiconductor layer's composition and quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a thin film transistor uses an oxide semiconductor layer, then the manufacturing process becomes easier and can be formed at lower temperatures, but the field effect mobility is lower compared to polycrystalline silicon
Solution Approach 1:
The patent uses a composite structure combining oxide semiconductor layer with other semiconductor layers (such as In-Ga-Zn-O-based semiconductor layer) to achieve both ease of manufacture and high field effect mobility. The composite material approach allows leveraging the low-temperature processing advantage of oxide semiconductors while incorporating materials with higher carrier mobility to overcome the mobility limitation.
2Device complexity
If an oxide semiconductor layer is in contact with insulating films, then the structure is simplified, but the composition changes and film quality deteriorates causing unstable electrical characteristics
Solution Approach 1:
The patent introduces an intermediary layer between the oxide semiconductor layer and insulating films to prevent direct contact that causes composition changes and quality deterioration. This intermediary layer acts as a protective barrier that maintains the electrical characteristics stability while allowing the overall structure to remain relatively simple.
Solution Approach 2:
The patent extracts or removes the problematic direct contact interface between oxide semiconductor and insulating films by introducing separate functional layers, thereby eliminating the source of composition changes and quality deterioration while maintaining structural simplicity.
3Reliability
If a thin film transistor uses polycrystalline silicon, then the field effect mobility is high, but the manufacturing process requires crystallization processes and takes enormous time over large substrates
Solution Approach 1:
The patent replaces the thermal crystallization process (mechanical/thermal system) required for polycrystalline silicon with a low-temperature deposition process using oxide semiconductors. This substitution eliminates the need for high-temperature crystallization steps and laser annealing, dramatically reducing manufacturing time while achieving comparable or sufficient mobility through the oxide semiconductor's inherent properties and composite structure.
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
This configuration enhances the field effect mobility of the thin film transistor and stabilizes its electrical characteristics, enabling the use of oxide semiconductor-based transistors in high-definition liquid crystal display devices with improved reliability.
Implementation Method 1
The oxide semiconductor film can be formed by a sputtering method or the like at a temperature of 300° C. or lower
Data Source
AI summary
An object is to increase field effect mobility of a thin film transistor including an oxide semiconductor. Another object is to stabilize electrical characteristics of the thin film transistor. In a thin film transistor including an oxide semiconductor layer, a semiconductor layer or a conductive layer having higher electrical conductivity than the oxide semiconductor is formed over the oxide semiconductor layer, whereby field effect mobility of the thin film transistor can be increased. Further, by forming a semiconductor layer or a conductive layer having higher electrical conductivity than the oxide semiconductor between the oxide semiconductor layer and a protective insulating layer of the thin film transistor, change in composition or deterioration in film quality of the oxide semiconductor layer is prevented, so that electrical characteristics of the thin film transistor can be stabilized.