Oxide Layered Field-Effect Transistor for High Mobility and Low Off-Current
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Solution Overview
Problem
Existing field-effect transistors with IGZO oxide semiconductors face limitations in mobility and are prone to high off-current and bias stress, which restrict their application to only pixel circuits in displays, and improving mobility leads to deterioration in TFT properties.
Innovation Solution
A field-effect transistor with an active layer comprising multiple oxide layers, specifically a stacked structure of layers A and B, where layer A has a higher carrier concentration and lower bandgap, and layer B is semiconductive or insulative with a higher bandgap, functioning as a blocking layer to confine electrons or holes, thereby enhancing mobility and reducing off-current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If IGZO oxide semiconductor is used to improve mobility, then mobility increases, but off-current increases and bias stress occurs
Solution Approach 1:
The active layer is segmented into multiple oxide layers with different compositions and properties. Specifically, it includes an In-Ga-Zn-O layer and a In-Al-O layer stacked in a specific configuration, where each layer serves distinct functions: the In-Ga-Zn-O layer provides high mobility while the In-Al-O layer acts as a blocking layer to suppress off-current and reduce bias stress
Solution Approach 2:
Different regions of the active layer are assigned different local qualities through varying oxide compositions. The In-Ga-Zn-O layer has higher carrier concentration and lower bandgap for high mobility, while the In-Al-O layer has lower carrier concentration and higher bandgap for blocking harmful effects, creating localized functional zones within the active layer
2Speed
If mobility is improved by changing oxide layer composition, then mobility increases, but TFT properties deteriorate
Solution Approach 1:
The active layer uses a composite structure of multiple oxide materials (In-Ga-Zn-O and In-Al-O layers) rather than a single oxide material. This composite approach allows combining the high mobility advantage of IGZO with the stabilizing properties of In-Al-O, achieving both improved mobility and maintained TFT properties through material composition optimization
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 proposed structure achieves high mobility and low off-current, improving the overall performance of the field-effect transistor and enabling its use beyond pixel circuits in displays.
Implementation Method 1
layer B which is semiconductive or insulative and has a higher energy level of a conduction band lower edge than layer A
Data Source
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AI summary
A field-effect transistor including: a gate electrode, which is configured to apply gate voltage; a source electrode and a drain electrode, which are configured to transfer an electrical signal; an active layer, which is formed between the source electrode and the drain electrode; and a gate insulating layer, which is formed between the gate electrode and the active layer, the active layer including at least two kinds of oxide layers including layer A and layer B, and the active layer satisfying at least one of condition (1) and condition (2) below: condition (1): the active layer includes 3 or more oxide layers including 2 or more of the layer A; and condition (2): a band-gap of the layer A is lower than a band-gap of the layer B and an oxygen affinity of the layer A is equal to or higher than an oxygen affinity of the layer B.