Metal Oxide Field-Effect Transistor with Mosaic Band-Gap Control
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Solution Overview
Problem
Existing transistors using In-Ga-Zn-based metal oxides suffer from high subthreshold swing (S value) and threshold voltage (Vth), leading to normally-on characteristics and suboptimal electrical performance.
Innovation Solution
A field-effect transistor with a channel formation region comprising nano-size particles of two different energy band widths, dispersed in a mosaic pattern, where one material has a wider band gap and the other has a narrower band gap, enhancing carrier flow control and reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer metal oxide structure is used, then the device structure is simple, but the electrical characteristics are suboptimal with high S value and normally-on characteristics
Solution Approach 1:
The patent employs a two-layer composite metal oxide structure where the first layer contains In-Ga-Zn-O and the second layer contains In-Zn-O. This composite structure combines the advantages of both materials to achieve superior electrical characteristics including low S value (0.1-0.3 V/decade) and stable threshold voltage, eliminating the normally-on characteristic while maintaining high field-effect mobility.
Solution Approach 2:
The patent applies local quality by creating distinct functional zones within the metal oxide layer. The first layer (In-Ga-Zn-O) provides high mobility and conductive properties, while the second layer (In-Zn-O) provides insulating properties and threshold control. This spatial differentiation of material properties enables simultaneous optimization of both conductivity and switching characteristics.
2Speed
If high field-effect mobility is achieved, then carrier flow is improved, but off-state current increases due to normally-on characteristics
Solution Approach 1:
The patent changes the band gap parameter by combining two different metal oxide materials with different energy band structures. The In-Ga-Zn-O layer provides narrow band gap for high carrier mobility, while the In-Zn-O layer provides wide band gap for low off-state current. This parameter differentiation enables the transistor to achieve high on-state current with minimal off-state leakage.
3Adaptability or versatility
If metal oxide materials are used, then semiconductor characteristics are obtained, but threshold voltage control is difficult resulting in normally-on behavior
Solution Approach 1:
The patent introduces an intermediate In-Zn-O layer between the In-Ga-Zn-O layer and the gate insulator. This intermediate layer acts as a mediator that provides threshold voltage control by adjusting its thickness and composition. The intermediate layer enables precise tuning of the threshold voltage to achieve normally-off characteristics while maintaining the semiconductor properties of the metal oxide system.
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 transistor achieves high field-effect mobility, low off-state current, and stable electrical characteristics by complementing the insulating and conductive properties of the nano-particles, resulting in improved reliability and switching performance.
Implementation Method 1
In the case where a gate voltage is applied to the transistor in the forward direction, the material having at least two different energy band widths has a first function of allowing each carrier to flow from a source to a drain
Implementation Method 2
In the case where a gate voltage is applied to the transistor in the reverse direction, the material having at least two different energy band widths has a second function of preventing each carrier from flowing from the source to the drain
Data Source
AI summary
To provide a novel material. In a field-effect transistor including a metal oxide, a channel formation region of the transistor includes a material having at least two different energy band widths. The material includes nano-size particles each with a size of greater than or equal to 0.5 nm and less than or equal to 10 nm. The nano-size particles are dispersed or distributed in a mosaic pattern.