Oxide Semiconductor Transistor Stack for Stable Threshold Voltage
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Solution Overview
Problem
Oxygen vacancies and impurities in oxide semiconductor films lead to poor electrical characteristics, increased power consumption, and fluctuating threshold voltage in transistors, causing operational malfunctions and eyestrain in display devices.
Innovation Solution
A semiconductor device with a multilayer film structure comprising an oxide semiconductor film and an oxide film containing In or Ga, where the second oxide insulating film has a higher oxygen content than stoichiometric composition, and is permeable to oxygen, reducing oxygen vacancies and impurity concentration, thereby stabilizing threshold voltage and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If oxygen vacancies and impurities are present in oxide semiconductor films, then the film can be formed more easily, but electrical characteristics deteriorate and threshold voltage becomes unstable
Solution Approach 1:
The oxide semiconductor film is divided into multiple layers with different functions: a first oxide semiconductor layer that is easier to form, and a second oxide semiconductor layer that provides stable electrical characteristics. This segmentation allows each layer to be optimized independently for its specific purpose.
Solution Approach 2:
A gate insulating film serves as an intermediary layer between the oxide semiconductor film and the gate electrode. This intermediary structure helps stabilize the threshold voltage by providing a controlled interface that reduces the impact of oxygen vacancies and impurities on electrical characteristics.
2Reliability
If oxygen vacancies are reduced in oxide semiconductor films, then electrical characteristics improve, but manufacturing complexity increases
Solution Approach 1:
The first oxide semiconductor layer is formed with controlled oxygen vacancies to facilitate easy manufacturing, while the second oxide semiconductor layer is subsequently formed with reduced oxygen vacancies to provide stable electrical characteristics. The preliminary formation of the first layer simplifies the overall manufacturing process while still achieving the desired electrical performance.
Solution Approach 2:
Different regions of the oxide semiconductor film structure are given different oxygen vacancy concentrations suited to their specific functions. The first layer has higher oxygen vacancy tolerance for ease of formation, while the second layer has lower oxygen vacancy concentration for electrical stability, creating local quality variations that optimize both manufacturing and performance.
3Reliability
If impurity concentration is reduced in oxide semiconductor films, then threshold voltage stability improves, but manufacturing difficulty increases
Solution Approach 1:
The oxide semiconductor film is segmented into multiple layers where the first layer can tolerate higher impurity concentrations for easier manufacturing, while the second layer is formed with lower impurity concentrations to ensure threshold voltage stability. This segmentation allows impurity control to be applied selectively.
Solution Approach 2:
The impurity concentration parameter is changed across different layers of the oxide semiconductor film. The first layer uses higher impurity tolerance parameters for ease of manufacture, while the second layer uses lower impurity concentration parameters for threshold voltage stability, demonstrating parameter optimization at different locations.
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 solution effectively reduces oxygen vacancies and impurities, stabilizing threshold voltage, enhancing electrical characteristics, reducing off-state current, and minimizing power consumption, while providing a transparent and less eyestrain-inducing display device.
Implementation Method 1
the second oxide insulating film is an oxide insulating film containing more oxygen than that in the stoichiometric composition
Implementation Method 2
the first oxide insulating film is an oxide insulating film through which oxygen is permeated
Data Source
AI summary
To reduce defects in an oxide semiconductor film in a semiconductor device. To improve the electrical characteristics and the reliability of a semiconductor device including an oxide semiconductor film. In a semiconductor device including a transistor including agate electrode formed over a substrate, a gate insulating film covering the gate electrode, a multilayer film overlapping with the gate electrode with the gate insulating film provided therebetween, and a pair of electrodes in contact with the multilayer film, a first oxide insulating film covering the transistor, and a second oxide insulating film formed over the first oxide insulating film, the multilayer film includes an oxide semiconductor film and an oxide film containing In or Ga, the first oxide insulating film is an oxide insulating film through which oxygen is permeated, and the second oxide insulating film is an oxide insulating film containing more oxygen than that in the stoichiometric composition.