2D materials readiness for the transistor performance breakthrough

Layered Deep-UV Optical Crystal KZn₂BO₃Br₂ as a High-κ Dielectric for 2D Electronic Devices

The development of dielectrics with atomic planes and van der Waals (vdW) interfaces is essential for enhancing the performance of 2D devices. However, vdW dielectrics often have smaller bandgaps compared to traditional 3D dielectrics, limiting their options. This study introduces AZBX (AZn₂BO₃X₂, where A = K or Rb, X = Cl or Br), a nonlinear deep-ultraviolet optical crystal, as a quasi-vdW layered dielectric ideal for 2D electronic devices. Focusing on KZBB, it's excellent dielectric properties, including a wide bandgap, high dielectric constant (high-κ), and smooth interfaces are demonstrated. When used as the top gate dielectric in a KZBB/MoS₂ field-effect transistor (FET) with MoS₂ channels and graphene contacts, the device exhibits outstanding performance, with a steep subthreshold swing (≈ 73 mV dec-1), high on/off ratio (≈ 10⁷), negligible hysteresis (0-8 mV), and stable, low leakage current (≈10⁻⁷ A cm- 2) before breakdown. This work expands the 2D material and dielectric landscape and highlights the strong potential of AZBX as high-performance dielectrics.

Prospects of Band Structure Engineering in MXenes for Active Switching MXetronics: Computational Insights and Experimental Approaches

MXenes, two-dimensional (2D) transition metal carbides and nitrides, have shown promise in a variety of applications. The use of MXenes in active electronic devices is restricted to electrode materials due to their metallic nature. However, MXenes can be modified to be semiconducting and can be used for next-generation channel materials. The inherent metallic characteristics of pristine Mn+1Xn-structured MXene can be tuned to semiconducting by (i) functionalizing MXenes with different moieties, (ii) applying external strain, and (iii) varying the composition. These strategies effectively modify the metallic electronic structure of MXene into a semiconducting one. This review focuses on the potential of tuning the electronic band structure of MXenes by surface functionalization, strain engineering, and compositional variation. The computational and experimental approaches to tuning the electronic band structure using these strategies are discussed in detail. In addition, the experimental methods which can be used to prepare semiconducting MXenes are described.

Performance Limits and Advancements in Single 2D Transition Metal Dichalcogenide Transistor

Two-dimensional (2D) transition metal dichalcogenides (TMDs) allow for atomic-scale manipulation, challenging the conventional limitations of semiconductor materials. This capability may overcome the short-channel effect, sparking significant advancements in electronic devices that utilize 2D TMDs. Exploring the dimension and performance limits of transistors based on 2D TMDs has gained substantial importance. This review provides a comprehensive investigation into these limits of the single 2D-TMD transistor. It delves into the impacts of miniaturization, including the reduction of channel length, gate length, source/drain contact length, and dielectric thickness on transistor operation and performance. In addition, this review provides a detailed analysis of performance parameters such as source/drain contact resistance, subthreshold swing, hysteresis loop, carrier mobility, on/off ratio, and the development of p-type and single logic transistors. This review details the two logical expressions of the single 2D-TMD logic transistor, including current and voltage. It also emphasizes the role of 2D TMD-based transistors as memory devices, focusing on enhancing memory operation speed, endurance, data retention, and extinction ratio, as well as reducing energy consumption in memory devices functioning as artificial synapses. This review demonstrates the two calculating methods for dynamic energy consumption of 2D synaptic devices. This review not only summarizes the current state of the art in this field but also highlights potential future research directions and applications. It underscores the anticipated challenges, opportunities, and potential solutions in navigating the dimension and performance boundaries of 2D transistors.

Mixed-Dimensional Integration of 3D-on-2D Heterostructures for Advanced Electronics

Two-dimensional (2D) materials have garnered significant attention due to their exceptional properties requisite for next-generation electronics, including ultrahigh carrier mobility, superior mechanical flexibility, and unusual optical characteristics. Despite their great potential, one of the major technical difficulties toward lab-to-fab transition exists in the seamless integration of 2D materials with classic material systems, typically composed of three-dimensional (3D) materials. Owing to the self-passivated nature of 2D surfaces, it is particularly challenging to achieve well-defined interfaces when forming 3D materials on 2D materials (3D-on-2D) heterostructures. Here, we comprehensively review recent progress in 3D-on-2D incorporation strategies, ranging from direct-growth- to layer-transfer-based approaches and from non-epitaxial to epitaxial integration methods. Their technological advances and obstacles are rigorously discussed to explore optimal, yet viable, integration strategies of 3D-on-2D heterostructures. We conclude with an outlook on mixed-dimensional integration processes, identifying key challenges in state-of-the-art technology and suggesting potential opportunities for future innovation.

Layer-by-layer thinning of two-dimensional materials

Etching technology - one of the representative modern semiconductor device makers - serves as a broad descriptor for the process of removing material from the surfaces of various materials, whether partially or entirely. Meanwhile, thinning technology represents a novel and highly specialized approach within the realm of etching technology. It indicates the importance of achieving an exceptionally sophisticated and precise removal of material, layer-by-layer, at the nanoscale. Notably, thinning technology has gained substantial momentum, particularly in top-down strategies aimed at pushing the frontiers of nano-worlds. This rapid development in thinning technology has generated substantial interest among researchers from diverse backgrounds, including those in the fields of chemistry, physics, and engineering. Precisely and expertly controlling the layer numbers of 2D materials through the thinning procedure has been considered as a crucial step. This is because the thinning processes lead to variations in the electrical and optical characteristics. In this comprehensive review, the strategies for top-down thinning of representative 2D materials (e.g., graphene, black phosphorus, MoS2, h-BN, WS2, MoSe2, and WSe2) based on conventional plasma-assisted thinning, integrated cyclic plasma-assisted thinning, laser-assisted thinning, metal-assisted splitting, and layer-resolved splitting are covered in detail, along with their mechanisms and benefits. Additionally, this review further explores the latest advancements in terms of the potential advantages of semiconductor devices achieved by top-down 2D material thinning procedures.