Single-Crystal Al2O3 Dielectric for Low-Leakage 2D Transistors
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Solution Overview
Problem
Current dielectric materials for two-dimensional transistors face challenges in achieving atomically thin thicknesses (EOT<1 nm), high gate leakage current, interface state density (Dit>1010 cm−2 eV−1), and low breakdown field strength (Ebd<10 MV/cm), hindering the development of high-performance low power consumption devices.
Innovation Solution
A single-crystalline Al2O3 dielectric is prepared using van der Waals epitaxy and intercalative oxidation techniques, involving epitaxial growth of a single-crystalline Al thin film on a single-crystalline graphene/germanium substrate, followed by peeling and oxidation to form a compatible dielectric layer on the lower surface, suitable for two-dimensional materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous oxide dielectrics (SiO2, Al2O3, HfO2) are used, then they are widely used in silicon-based transistors, but they cannot form uniform interfaces with two-dimensional materials due to surface dangling bonds and long-range disorder, resulting in large gate leakage current (J>1.5×10−2 A cm−2), high interface state density (Dit>1010 cm−2 eV−1), and low breakdown field strength (Ebd<10 MV/cm)
Solution Approach 1:
The patent changes the structural parameter of the dielectric material from amorphous to crystalline phase. By controlling the crystallization process and selecting appropriate substrates, the Al2O3 dielectric achieves a crystalline structure with well-defined atomic arrangement, eliminating the surface dangling bonds and long-range disorder present in amorphous oxides. This structural transformation resolves the interface quality issue while maintaining manufacturability through established crystallization techniques.
Solution Approach 2:
The patent employs a composite approach by combining crystalline Al2O3 dielectric with two-dimensional semiconductor materials on a carefully selected substrate system. The crystalline Al2O3 layer is integrated with the two-dimensional material through controlled growth conditions, creating a composite structure that leverages the advantages of both materials: the crystalline dielectric provides excellent interface quality and the two-dimensional material provides high carrier mobility, while the substrate ensures proper crystal orientation and stress management.
2Reliability
If crystalline dielectric materials (h-BN, CaF2, SrTiO3) are used, then they can form atomically sharp interfaces, but they face problems such as extremely high gate leakage current for h-BN, difficulty in preparation requiring complicated growth processes, and limitation to back-gate transistors
Solution Approach 1:
The patent changes the material composition parameter from alternative crystalline dielectrics (h-BN, CaF2, SrTiO3) to crystalline Al2O3. This material selection is driven by Al2O3's superior electrical properties including higher breakdown field strength and lower gate leakage current, while maintaining the benefit of crystalline interface sharpness. The crystallization process uses controlled thermal and chemical parameters to achieve high-quality interfaces without requiring complex growth processes.
Solution Approach 2:
The patent achieves universality by developing a crystalline Al2O3 dielectric that can be integrated with various two-dimensional semiconductor materials (such as MoS2, WS2, WSe2) on different substrate systems. The crystallization method and interface engineering approach are broadly applicable across different material systems, enabling top-gate transistor configurations and wafer-level preparation while maintaining high interface quality and electrical performance.
3Reliability
If two-dimensional h-BN is used, then it has atomically flat surface, but it exhibits extremely high gate leakage current (>103 A/cm) due to relatively narrow bandgap and low dielectric constant, making it impossible to scale the equivalent oxide thickness (EOT) to 1 nm or below
Solution Approach 1:
The patent changes the dielectric material parameters by selecting crystalline Al2O3 instead of h-BN. Al2O3 possesses a wider bandgap and higher dielectric constant compared to h-BN, which fundamentally reduces the gate leakage current. The crystalline structure of Al2O3 maintains the atomically flat surface quality needed for sharp interfaces, while the superior electrical properties eliminate the harmful high leakage current issue that plagues h-BN-based devices.
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 single-crystalline Al2O3 dielectric achieves low gate leakage current (J<1×10−5 A cm−2), interface state density (Dit=8.4×109 cm−2 eV−1), and dielectric strength (Ebd=17.4 MV/cm), meeting the requirements for low power consumption devices and enabling high-quality two-dimensional field effect transistors with steep subthreshold swing (SS) and ultra-high current on/off ratio (Ion/Ioff) of 108.
Implementation Method 1
intercalative oxidation is performed to produce the single-crystalline Al2O3 dielectric compatible with two-dimensional materials on the lower surface of the single-crystalline Al thin film
Implementation Method 2
Van der Waals (vdW) epitaxy of a single-crystalline Al thin film is performed on a single-crystalline graphene/germanium (110) substrate
Data Source
AI summary
The present invention relates to a single-crystalline Al2O3 dielectric compatible with two-dimensional materials and an integrated device thereof. A single-crystalline Al thin film is produced on a single-crystalline graphene/germanium (110) substrate via the van der Waals (vdW) epitaxy approach, the single-crystalline Al thin film is peeled off from the graphene/germanium substrate, and intercalative oxidation is performed to produce the single-crystalline Al2O3 dielectric compatible with two-dimensional materials on the lower surface of the single-crystalline Al thin film. The gate leakage current (J<1×10−5 A cm−2), interface state density (Dit=8.4×109 cm−2 eV−1), and dielectric strength (Ebd=17.4 MV/cm) of the single-crystalline Al2O3 dielectric obtained in the present invention can meet the requirements of the international roadmap for devices and systems (IRDS) for low power consumption devices.