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 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 operational malfunctions and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an interfacial stability layer with equivalent band gap to the oxide semiconductor active layer is used, then the manufacturing process is simplified, but charge trapping occurs at the interface leading to threshold voltage fluctuation and reduced reliability
Solution Approach 1:
A metal oxide film is introduced as an intermediary layer between the oxide semiconductor active layer and the gate insulating layer. This metal oxide film has a band gap larger than the active layer, creating an energy barrier that prevents charge trapping at the interface while maintaining manufacturing simplicity through sputtering deposition
Solution Approach 2:
The band gap parameter of the interfacial layer is changed from being equivalent to the active layer (causing charge trapping) to being larger than the active layer (preventing charge trapping). This parameter change fundamentally resolves the charge trapping issue while maintaining ease of manufacture
2Device complexity
If a conventional gate insulating layer is used directly in contact with the oxide semiconductor film, then the device structure is simplified, but charge trapping at the interface causes threshold voltage shift and operational instability
Solution Approach 1:
The metal oxide film serves as a mediator between the gate insulating layer and the oxide semiconductor active layer. It has larger band gap than both adjacent layers, creating energy barriers that prevent charge transfer and trapping, thus improving reliability without significantly increasing device complexity
Solution Approach 2:
The gate stack is designed as a composite structure with three distinct material layers: gate insulating layer, metal oxide film, and oxide semiconductor active layer. Each layer has specifically selected band gap properties that work together to prevent charge trapping while maintaining manageable device complexity
Data Source
AI summary
A transistor is provided in which the top 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 the impurities.