Oxide Semiconductor Transistor Metal Oxide Buffer Layer
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 unstable electric characteristics.
Innovation Solution
A stacked structure is implemented with an oxide semiconductor film, a metal oxide film containing similar constituents, and a gate insulating film with different constituents, where the metal oxide film acts as an intermediary to suppress charge trapping, and the gate insulating film traps charges at its interface with the metal oxide film, thereby reducing charge accumulation at the oxide semiconductor interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an interfacial stability layer with the same characteristics as the gate insulating layer is provided, then the interface state with the active layer can be stabilized, but charge trapping occurs at the interface between the active layer and the interfacial stability layer
Solution Approach 1:
A metal oxide film with intermediate characteristics is introduced between the gate insulating layer and the oxide semiconductor active layer. This intermediary layer has a band gap that is wider than the active layer but narrower than the gate insulating layer, creating a gradual transition that prevents charge trapping while maintaining interface stability. The metal oxide film acts as a buffer that reconciles the conflicting requirements of interface stability and charge trapping suppression.
Solution Approach 2:
The band gap parameter is gradually changed across the three-layer structure: the metal oxide film has an intermediate band gap value between the gate insulating layer and the active layer. This parameter gradient prevents abrupt transitions that cause charge trapping, while the metal oxide film's specific band gap characteristics maintain favorable interface states with the active layer.
2Reliability
If a metal oxide film containing similar constituents to the oxide semiconductor film is provided, then charge trapping at the interface is suppressed, but the device structure becomes more complex
Solution Approach 1:
The gate insulating structure is formed as a composite of two distinct films: a gate insulating layer and a metal oxide film with specific compositional characteristics. The metal oxide film contains metal elements similar to those in the oxide semiconductor active layer, creating a composite structure that suppresses charge trapping through material compatibility while maintaining a relatively simple overall device architecture.
Data Source
AI summary
An object is to provide a semiconductor device including an oxide semiconductor, which has stable electric characteristics and high reliability. A semiconductor device includes an oxide semiconductor film, a source electrode and a drain electrode which are electrically connected to the oxide semiconductor film, a metal oxide film which is partly in contact with the oxide semiconductor film, a gate insulating film which is over and in contact with the metal oxide film, and a gate electrode over the gate insulating film. With such a structure, effect of charge on the oxide semiconductor film can be relaxed; thus, shift of the threshold voltage in the transistor, due to charge trapping at an interface of the oxide semiconductor film, can be suppressed.