Emerging and future 2D electronic materials such as graphene have the potential to exceed the capabilities of modern components in terms of carrier capacity, strength, and versatility. This article will discuss some of the potential advantages of two-dimensional electronics and the materials from which they will be constructed.
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Silicon has been the primary material used in the construction of transistors, semiconductors, and other electronic components since the 1950s, selected over competitors owing to favorable material and electronic properties and low cost. Since this time, Moore’s law, the observation that the number of transistors on an integrated circuit doubles every two (roughly) years, has vaguely held true, and silicon-based electronics have become increasingly powerful. However, since around 2010, the rate of progress has observably slowed, mainly owing to transistors reaching an almost atomic density that suffers from quantum effects such as electron transfer (tunneling) to neighboring components.
Why are 2D Electronic Materials Needed?
Silicon-based transistors have reached a scale in the order of nanometers, with numerous innovations having allowed them to reach this scale thus far; copper interconnects, the incorporation of dielectric materials, complementary metal oxide semiconductor field effect transistors (CMOS), and so on. Nanometer-thick silicon sheets provide individual charge carrier channels, though making them thinner significantly limits carrier mobility within the channel when approaching around 3 nm.
2D semiconductors of atomic thickness below 1 nm thick are innately thinner than possible for silicon sheets with superior carrier mobility; they are self-passivated in the third dimension and thus do not require any additional shielding in this direction and can be fine-tuned using layering strategies. Layered 2D materials with differing properties can be combined and connected via various gating methods to produce novel electronic heterostructures with precise electronic functions.
What are the Applications of 2D Electronics?
2D electronic materials are highly touted in sensing applications, mainly owing to their large and highly customizable surface chemistry. Any particle or molecule capable of adsorbing or chemically absorbing to the surface of a 2D electronic material may induce a change in electronic properties, namely impedance and, thus, current. The surface can be functionalized with complimentary molecules to one of interest, such as an antibody specific to a pathogenic antigen, and thus act as a highly sensitive and selective detector in a variety of mediums, both gas and liquid phase.
Two-dimensional electronic materials may be the solution to neuromorphic computing in the future; circuitry inspired by the architecture of brains. Within these devices, synapses and neurons are mimicked using computing-in-memory and memristive devices, the latter of which relates electric charge to magnetic flux linkage. These devices are rarely used in modern electronics and remain under intense development, but they have powerful potential applications as memory devices in quantum computing, physical neural networks, and reconfigurable computing.
Reconfigurable computing is a computer architecture that allows substantial changes to the datapath and control of flow through the circuit, allowing them to be configured for a specific task and then reconfigured for another, unlike ordinary microprocessors. Layered 2D heterostructures are ideally suited to reconfigurable computing, as they have the potential to be broken down layer-by-layer and the gating between layers adjusted. Complex overlapping circuitry is possible using 2D electronic materials owing to the aforementioned shielding in the third dimension, allowing the space to be utilized optimally.
What 2D Materials Will Be Used in Future Electronics?
Graphene may be amongst the most popular two-dimensional materials with potentially exciting applications in future electronics; it is constructed only from carbon atoms arranged in a hexagonal lattice that shares an extensive conjugated electron system. This is a common feature of 2D electronic materials, such as hexagonal boron nitride, which is structured similarly to graphene but contains alternating boron and nitrogen atoms.
This material is typically used in lubrication and coating applications where high temperature and chemical resistivity is desired, and unlike graphene, it acts as an insulator, though it can be used in short sections within 2D electronic circuits to act as a tunneling barrier.
Another 2D material with potential applications in future electronics is tungsten diselenide, which, rather than forming a one-atom thick planar structure, has a repeating monomeric unit containing two selenium atoms connected above and below one tungsten atom. This material is employed in solar cell applications, as it has a high bandgap and relatively low-efficiency loss with increasing temperature, and is used in particular gating components of 2D electronics, such as in reconfigurable computing.
Another inorganic 2D electronic material is black phosphorous, which exhibits a unique electronic structure, allowing for high charge carrier mobility. Of all the forms of phosphorous, black phosphorous is most thermodynamically stable at room temperature and again possesses a hexagonal lattice structure that allows overlapping p-type orbitals between atoms and contributes to high electrical conductivity.
Black phosphorous is of particular interest owing to its tunable bandgap by adjusting layer thickness, which fills the range between the aforementioned large bandgap of tungsten diselenide and other transition metal dichalcogenide monolayers and the zero band gap graphene.
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References and Further Reading
Lemme, M. C., Akinwande, D., Huyghebaert, C., & Stampfer, C. (2022). 2D materials for future heterogeneous electronics. Nature Communications, 13(1). https://doi.org/10.1038/s41467-022-29001-4
Fei, W., Trommer, J., Lemme, M. C., Mikolajick, T., & Heinzig, A. (2022). Emerging reconfigurable electronic devices based on two‐dimensional materials: A review. Infomat, 4(10). https://doi.org/10.1002/inf2.12355
Cheng, J., Gao, L., Li, T., Mei, S., Wang, C., Wen, B., Huang, W., Li, C., Zheng, G., Wang, H., & Zhang, H. (2020). Two-Dimensional Black Phosphorus Nanomaterials: Emerging Advances in Electrochemical Energy Storage Science. Nano-micro Letters, 12(1). https://doi.org/10.1007/s40820-020-00510-
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