Two dimensional materials are considered to be promising solutions to the current limitations in computing technology. Utilizing 2D materials for the enhancement of silicon based semiconductors, lead to considerable improvements in operation speed, memory and data storage solutions, transistor and interconnection performance.
The rapid development of computer technology has been fascinating from day one. In a short period of time, computers have made their way into almost every aspect of human life and drastically changed the way we handle information. The technology still shows no signs of slowing down. On the contrary, it has picked up the pace in the era of “Big Data”. The growing data-driven demand has pushed scientists to develop new solutions and technologies. In-memory computing and transistor-based computing are the leaders of today’s computing solutions, while brain inspired computing and quantum computing are starting to emerge as novel solutions. These technologies mostly depend on electronics utilizing silicon semiconductors. The advances in computing technology in the past five decades have mostly been achieved through dimensional scaling of silicon based semiconductors. The scaling process involves scaling down field effect transistors (FETs) on all physical dimensions simultaneously while scaling up the doping concentration of the transistor channel. However, as the performance requirements increased, this field scaling has reached its limits due to the challenging doping processes and the excessive leakage current through the thin silicon dioxide gate insulator. Thus, new materials are required for both the improvement of in-memory and transistor-based computing and the development of brain inspired computing and quantum computing. At this point, two dimensional materials have come to the rescue. The compact nature and enhanced electrical properties of 2D materials have made them ideal candidates for future improvements in computing technology.
Important Two Dimensional Materials in Computing Technology
The first two dimensional material to attract the attention of material scientists was graphene. This material that has dazzled scientists from the moment of its discovery has proved to be a promising material to improve transistor technology. The high electrical conductivity, atom thick structure, and desirable chemical properties of graphene are desirable in computing technology. Graphene is not only utilized in the form of graphene sheets but also in the form of graphene ribbon, graphene nanotubes, and graphene oxide.
Following the graphene trend, different two dimensional materials have also made their way into computing technology. Two dimensional transition metal dichalcogenides (TMDCs) are amongst these newly introduced materials. TMDCs are semiconductors of the type MX2 where M represents transition metal atoms such as molybdenum (Mo) and tungsten (W) and X represents chalcogen atoms such as sulfur (S), selenium (Se), and tellurium (Te). The atomic-scale thickness, direct bandgap, and favorable electronic and mechanical properties of TMDCs make them desirable materials for computing technologies. Amongst various combinations of transitional metals and chalcogens, MoS2 and WS2 are the most well-known two dimensional materials. The electronic structure of a TMDC is greatly affected by its crystal phase and able to show a range of electronic characteristics, including metallic, semimetallic, semiconducting, and superconducting (SC), for different TMDCs. Thus, these materials are utilized in different applications.
Two dimensional transition metal oxides (TMOs) are another group of 2D materials attracting the attention of computing technology. Various transitional metal oxides are showing a range of different properties. Amongst these options, TMOs with wide band gaps, minimal current leakage, low loss, and high permittivity are suitable for computing technology applications. Such materials include ferroelectric oxides and perovskites.
These two dimensional materials are under excessive investigation for the improvement of computing technology.
How do Two Dimensional Materials Affect Computing Technology?
2D materials play an exceptionally important role in the improvement of semiconductors which are the key components of any device utilized in computing technology. Semiconductors are used in transistors, interconnects, memory, and data storage devices. 2D materials are candidates for FETs since they offer solutions to leakage current problems and similar problems that exist in Si-based semiconductors. These materials show good carrier transport even for atomically thin layers below 1 nm. Graphene was first used to improve logic gates which are the key element of microprocessors used in computer technology and built by putting together a number of transistors. Research shows that graphene based transistors provide processing speed in the terahertz range which is dramatically high compared to the speed of today’s silicon based transistors commonly operating in the gigahertz range. Furthermore, graphene based transistors provide two orders of magnitude decrease in power consumption. Considering that operation speed and power consumption are among the key elements for computing technology, graphene based transistors show great potential for further development. The knowledge established by the research on graphene based computing technologies has then been started to utilize for the development of TMDC FETs. Transitional metal dichalcogenide based transistors can provide unique ultrathin-body device structures with diverse electrical characteristics. Different TMDC FETs can offer n-type, p-type, or ambipolar properties. For example, MoS2 and MoSe2 are typically n-type devices, while black phosphorus and intrinsic TMDCs offer ambipolar characteristics that can be selectively engineered for p- or n-type transport. The enhanced gate coupling offered by 2D ferroelectric insulators such as HfOx offers power efficient device structures. Utilizing TMDCs with bandgaps in the range of 1–2 eV overcome the drawbacks of graphene and allow further scaling down. Furthermore, coating hexagonal boron nitride (hBN) -a 2D dielectric- on 2D FETs improves the performance of 2D electronics by providing a clean and smooth interface.
Another important area of computing technology is data storage. Solid state memories or data storage devices have enabled the rapid development of smartphones, tablets, and other similar electronic devices. Still, the further improvement in data storage, calls for higher-density, higher-capacity, power efficient devices. Different innovative technologies such as RRAM (resistive random-access memory), PCM (phase-change memory), and FeRAM (ferroelectric random-access memory) have been offered to meet these requirements. Two dimensional materials are found to be the ideal candidates for the development and implementation of these memory technologies. The ultra-thin nature of 2D materials enables stacking more layers in a confined space and provides high density along with a low cost. Utilizing 2D materials in place of the thick metal/nitride floating gate eliminates capacitive coupling between memory cells and improves the performance of flash memories. 2D material based transistors that avoid leakage currents can also improve the performance of memory arrays. The large bandgap of TMDCs provides a reduction in ‘off’ current and improvement in retention time.
Two dimensional materials can also aid the circuit delay due to wires. Conventionally copper wires are utilized in computing devices due to its desirable conductivity. However, at smaller scales, the resistance of Cu interconnects rises rapidly due to surface and grain-boundary scattering. This limitation causes increased power consumption and the use of larger areas. Two dimensional materials can be utilized to solve this problem in two different ways. Good conductive 2D material such as single layered graphene, hBN, and MoS2 can be used as an effective copper diffusion material improving processor speed mainly due to reduced effective resistivity. Alternatively, engineered 2D wires with higher conductivity such as FeCl3-doped multilayer graphene ribbons can be used to replace Cu wires and improve device performance.
These mentioned uses of two dimensional materials in computing technology and related devices represent a summary of a broad research area and demonstrate the great potential of 2D materials. Next-generation computing technologies such as quantum computing, brain inspired computing, and in-memory computing takes advantage of the promising characteristics of 2D materials for further development.
Computing technology has been one of the most dynamic fields of research and development. Computers, smartphones, tablets, and similar electronic devices have become an essential part of human life in a short period of time and are under constant development. Unfortunately, silicon based semiconductors – an important element of electronic devices- have reached their limits and fail to meet the requirements for future developments in computing technology. Scientists consider 2D materials as promising candidates to improve the performance of semiconductors by eliminating common problems such as undesired leakage currents. 2D materials including graphene, transition metal dichalcogenides (TMDCs), transition metal oxides (TMOs) are utilized in semiconductors. The enhancement of semiconductors directly affects the performance of transistors, memory, and data storage devices, and interconnects in electronic circuits. Such improvements help scientists to lay the groundwork for the development of in-memory computing, brain inspired computing and quantum computing.
1.Liu, C., Chen, H., Wang, S., Liu, Q., Jiang, Y. G., Zhang, D. W., ... & Zhou, P. (2020). Two-dimensional materials for next-generation computing technologies. Nature Nanotechnology, 15(7), 545-557.
2.Seo, S., Lee, J. J., Lee, H. J., Lee, H. W., Oh, S., Lee, J. J., ... & Park, J. H. (2020). Recent Progress in Artificial Synapses Based on Two-Dimensional van der Waals Materials for Brain-Inspired Computing. ACS Applied Electronic Materials, 2(2), 371-388.
3.John Wenz, K. (2019, December 02). Move over Graphene: Next-Gen 2D Materials Could Revolutionize Technology. Retrieved October 26, 2020, from https://www.discovermagazine.com/the-sciences/mov...
4.Akinwande, D., Huyghebaert, C., Wang, C. H., Serna, M. I., Goossens, S., Li, L. J., ... & Koppens, F. H. (2019). Graphene and two-dimensional materials for silicon technology. Nature, 573(7775), 507-518.