Oxide Semiconductor Transistor Metal Oxide Interlayer
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Solution Overview
Problem
Transistors using oxide semiconductors face reliability issues due to charge trapping at the interface between the active layer and the interfacial stability layer, leading to fluctuations in electric characteristics, particularly in threshold voltage, especially when the interfacial stability layer and active layer have equivalent band gaps.
Innovation Solution
A stacked-layer structure is introduced, comprising an oxide semiconductor film, a metal oxide film with similar constituents, and an insulating film with different constituents, where the metal oxide film is thicker than the oxide semiconductor film to suppress charge trapping by trapping charges at the interface between the metal oxide film and the insulating film, thereby reducing charge trapping at the oxide semiconductor interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an interfacial stability layer with the same characteristics as gate insulating layer and protective layer is used, then the transistor can operate at higher speed and be manufactured more easily, but charge trapping occurs at the interface between the active layer and interfacial stability layer causing threshold voltage fluctuation
Solution Approach 1:
A metal oxide film is introduced as an intermediary layer between the oxide semiconductor active layer and the insulating layer. This metal oxide film contains constituents similar to the oxide semiconductor film, creating a gradual transition that reduces interface discontinuity and suppresses charge trapping while maintaining the electrical characteristics needed for high-speed operation.
Solution Approach 2:
The structure employs a composite layered configuration combining oxide semiconductor film, metal oxide film, and insulating film. Each layer has distinct but compatible characteristics, with the metal oxide film serving as a bridge that combines the benefits of both the oxide semiconductor (high-speed operation) and the insulating layer (stability), thereby resolving the contradiction between speed and reliability.
2Device complexity
If the interfacial stability layer has equivalent band gap to the active layer, then the structure is simpler, but charge is more likely to be stored at the interface causing reliability degradation
Solution Approach 1:
The metal oxide film introduces local variation in band gap characteristics at the critical interface region. By having the metal oxide film contain constituents similar to the oxide semiconductor but with different band gap properties, the structure creates a localized transition zone that prevents charge accumulation while maintaining overall structural simplicity.
3Reliability
If a metal oxide film containing constituents similar to oxide semiconductor film is provided, then charge trapping at the oxide semiconductor interface is suppressed, but the device structure becomes more complex
Solution Approach 1:
The metal oxide film merges characteristics of both the oxide semiconductor film and the insulating layer into a single intermediate layer. By containing constituents similar to the oxide semiconductor while providing interface stability, it combines multiple functions into one layer, reducing the need for additional separate layers and mitigating the increase in device complexity.
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 reliability of semiconductor devices by stabilizing electric characteristics, reducing operation malfunctions, and minimizing changes in threshold voltage and off-state current, even under temperature and light exposure.
Implementation Method 1
sufficiently suppress trapping of charge or the like, which can be generated due to the operation of a semiconductor device, at the interface of the insulating film and the oxide semiconductor film
Data Source
AI summary
A transistor is provided in which the bottom surface portion of an oxide semiconductor film is provided with a metal oxide film containing a constituent similar to that of the oxide semiconductor film, and an insulating film containing a different constituent from the metal oxide film and the oxide semiconductor film is formed in contact with a surface of the metal oxide film, which is opposite to the surface in contact with the oxide semiconductor film. In addition, the oxide semiconductor film used for the active layer of the transistor is an oxide semiconductor film highly purified to be electrically i-type (intrinsic) through heat treatment in which impurities such as hydrogen, moisture, hydroxyl, and hydride are removed from the oxide semiconductor and oxygen which is one of main component materials of the oxide semiconductor is supplied and is also reduced in a step of removing impurities.