Oxide TFT Active Layer Gradient for High On-Current, Low Leakage
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Solution Overview
Problem
Current transistor technologies face challenges in achieving optimal charge carrier concentration and reducing leakage current, particularly in oxide semiconductor-based transistors used for back-end-of-line integration, where existing fabrication methods can damage previous devices and fail to provide efficient on-current and off-state performance.
Innovation Solution
The use of an atomic layer deposition process to form an active layer with a compositionally non-homogeneous vertical atomic concentration profile, specifically a front channel layer with a higher post-transition metal element percentage and a lower acceptor-type element percentage than the back channel layer, to enhance charge carrier concentration and reduce leakage current, while integrating with CMOS-based semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication methods are used for oxide semiconductor transistors, then processing can be performed at low temperatures suitable for back-end-of-line integration, but the transistors exhibit high leakage current and insufficient on-current performance
Solution Approach 1:
The patent applies local quality by creating distinct regions within the active layer with different compositions: the first region contains a higher concentration of post-transition metal elements (In, Ga, Zn) while the second region contains a higher concentration of acceptor-type elements (Al, Ga). This spatial differentiation of material properties enables simultaneous optimization of charge carrier concentration and leakage current control within different parts of the same layer, resolving the contradiction between performance and manufacturability.
Solution Approach 2:
The patent employs composite materials by combining multiple oxide semiconductor materials with different functional properties within a single active layer structure. The first region uses post-transition metal-rich oxide semiconductors for high on-current, while the second region uses acceptor-type element-rich oxide semiconductors for low leakage current. This composite approach allows the transistor to achieve both low leakage and high drive current without requiring separate devices or high-temperature processing.
2Reliability
If the active layer uses uniform composition throughout, then fabrication is simplified, but charge carrier concentration cannot be optimized for both high on-current and low leakage current
Solution Approach 1:
The patent segments the active layer into two distinct regions with different material compositions and functions. The first region (higher post-transition metal content) is optimized for charge carrier generation and high on-current, while the second region (higher acceptor-type element content) is optimized for suppressing leakage current. This segmentation allows independent optimization of conflicting electrical properties without requiring complex multi-layer structures or additional processing steps.
Solution Approach 2:
The patent changes material composition parameters within the active layer by varying the concentrations of post-transition metal elements (In, Ga, Zn) and acceptor-type elements (Al, Ga) across different regions. By adjusting these compositional parameters, the patent achieves different electrical properties (charge carrier concentration, mobility, leakage current) in different regions, enabling simultaneous optimization of on-current and leakage current without increasing structural 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 approach increases on-current and reduces leakage current, providing improved performance and integration capabilities for oxide semiconductor transistors without damaging previous devices, thus addressing the limitations of existing technologies.
Implementation Method 1
The active layer includes a compound semiconductor material comprising a vertical compositional gradient formed by a atomic layer deposition process
Data Source
AI summary
A thin film transistor includes a stack of an active layer, a gate dielectric, and a gate electrode in a forward or in a reverse order. The active layer includes a compound semiconductor material containing oxygen, at least one acceptor-type element selected from Ga and W, and at least one heavy post-transition metal element selected from In and Sn. An atomic percentage of the at least one heavy post-transition metal element at a first surface portion of the active layer that contacts the gate dielectric is higher than an atomic percentage of the at least one heavy post-transition metal element at a second surface portion of the active layer located on an opposite side of the gate dielectric. The front channel current may be increased, and the back channel leakage current may be decreased.