Oxide Semiconductor Transistor Composition for Stable Normally-Off Switching
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Solution Overview
Problem
Current semiconductor devices with oxide semiconductor transistors face challenges in achieving a positive threshold voltage, high-speed operation, and long-term reliability, particularly in maintaining stable threshold voltage over time.
Innovation Solution
A semiconductor device structure incorporating an oxide semiconductor layer with a composition ratio of indium, gallium, and zinc, where indium's atomic percentage is twice that of gallium and zinc, is used, along with a gate insulating film and electrode layers, to create a channel formation region with low-resistance regions and controlled oxygen content for improved electrical characteristics and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxide semiconductor transistor is fabricated with conventional materials and methods, then the device can be manufactured, but the threshold voltage cannot be maintained as positive, preventing normally-off switching operation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the atomic ratios of elements in the oxide semiconductor layer. Specifically, it uses an In-Ga-Zn-O system where the atomic ratio satisfies In:(Ga+Zn) = 3:1, and the Ga:Zn ratio is controlled within 1:4 to 1:1. These compositional parameter changes enable the threshold voltage to be maintained as positive, achieving normally-off switching operation that was not possible with conventional oxide semiconductor compositions.
Solution Approach 2:
The patent employs composite materials by creating a multi-element oxide semiconductor system combining indium, gallium, zinc, and oxygen. This In-Ga-Zn-O composite material provides synergistic effects where indium contributes to high carrier mobility, while gallium and zinc work together to stabilize the threshold voltage as positive. The composite material approach resolves the contradiction by enabling both manufacturability and normally-off switching capability.
2Speed
If the oxide semiconductor composition is optimized for high-speed operation, then field-effect mobility improves, but threshold voltage stability over long periods deteriorates
Solution Approach 1:
The patent resolves this contradiction through precise parameter changes in the oxide semiconductor composition. By controlling the atomic ratios to satisfy In:(Ga+Zn) = 3:1 and Ga:Zn = 1:4 to 1:1, the material achieves optimal balance between high field-effect mobility (enabling high-speed operation) and stable positive threshold voltage (ensuring long-term reliability). This specific compositional parameter optimization allows both high-speed performance and threshold voltage stability to coexist.
Solution Approach 2:
The patent applies local quality by creating distinct functional regions within the oxide semiconductor layer through controlled composition gradients and oxygen concentration variations. The core region maintains the stoichiometric In-Ga-Zn-O ratio for high mobility, while peripheral regions and interface zones are optimized for threshold voltage stability. This spatial differentiation of material properties enables simultaneous achievement of high-speed operation and long-term threshold voltage stability.
3Reliability
If the oxide semiconductor layer is highly purified to reduce oxygen defects, then reliability improves, but manufacturing complexity increases
Solution Approach 1:
The patent reduces manufacturing complexity while maintaining high reliability by changing the compositional parameters of the oxide semiconductor material itself. By selecting the In-Ga-Zn-O system with specific atomic ratios (In:(Ga+Zn) = 3:1, Ga:Zn = 1:4 to 1:1), the material becomes inherently more tolerant to manufacturing variations and less prone to oxygen defects. This material parameter optimization achieves high reliability without requiring excessively complex purification and fabrication processes.
Data Source
AI summary
Provided is a structure of a transistor, which enables a so-called normally-off switching element, and a manufacturing method thereof. Provided is a structure of a semiconductor device which achieves high-speed response and high-speed operation by improving on characteristics of a transistor, and a manufacturing method thereof. Provided is a highly reliable semiconductor device. In the transistor in which a semiconductor layer, source and drain electrode layers, a gate insulating layer, and a gate electrode layer are stacked in that order. As the semiconductor layer, an oxide semiconductor layer which contains at least four kinds of elements of indium, gallium, zinc, and oxygen, and has a composition ratio (atomic percentage) of indium as twice or more as a composition ratio of gallium and a composition ratio of zinc, is used.