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A century has passed since the discovery of ferroelectricity in Rochelle salt. Since then, we have learned a great deal about the fascinating physics of ferroelectric materials. Based on the functionalities and switchable polarization that arise from them, we have developed a host of practical devices, such as ferroelectric random-access memory, actuators, transducers, infrared detectors, and electro-optic modulators.
Previous studies have focused mostly on ferroelectric materials with three-dimensional (3D) lattices. For integration with the semiconductor industry, thin films are often grown on lattice-matching substrates, and free-standing films can be prepared using sacrificial layers. However, the chemical and structural discontinuities at the surface/interface not only hinder investigations of the fundamental effects of reduced dimensionality, but also pose challenges for applications in electronics.
Chair Professor Junling Wang from the Department of Physics at the Southern University of Science and Technology (SUSTech) recently collaborated with researchers from Soochow University and the University of Washington to publish a perspective article on the key developments in the exploration of two-dimensional (2D)-vdW materials.
Their article, entitled “Towards two-dimensional van der Waals ferroelectrics”, was published in Nature Materials, a top research journal focusing on material science and technology.
The researchers’ work first discusses the various mechanisms of the origin of spontaneous polarization in 2D-vdW ferroelectric materials (such as sliding ferroelectricity), introduces the anomalous physical properties (such as negative piezoelectric coefficient and ferroelectric metal) brought by the reduction of lattice dimension, as well as the new prototype devices and unique properties (such as 2D-vdW ferroelectric memory and field effect transistor) based on 2D-vdW ferroelectric materials. The future challenges and possible research directions in the field of 2D-vdW ferroelectrics are also prospected (Figure 1).
The article points out that as new aspects of ferroelectric materials and physics continue to be uncovered and insights gained, we expect to see device concepts making use of the unique or enhanced properties of 2D-vdW ferroelectrics/multiferroics being developed and tested. For instance, the coupling between ferroelectric polarization and ionic activity may lead to permanent retention, a multi-well polarization state, and ferroionic devices with neuromorphic characteristics.
The coupling between electron spin, momentum, and switchable properties such as polarization, Rashba SOC field, Berry curvature dipole, and magnetization offers many new opportunities to design non-volatile in-memory computing architectures based on 2D-vdW ferroelectrics/multiferroics, breaking the “memory wall” in conventional von Neumann computing architectures. The flourishing of 2D ferroelectrics will expand the catalogue of long-range order and coupling phenomena in low-dimensional systems, and creates new possibilities for next-generation nanoelectronics and spintronics.
Figure 1. Opportunities and challenges in 2D-vdW ferroelectrics
Research Asst. Prof. Chuanshou Wang from the Department of Physics at SUSTech is the first author of this paper. Prof. Lu You from the Department of Physics at Soochow University and Chair Prof. Junling Wang from SUSTech are the corresponding authors. The Department of Physics at SUSTech is the first affiliated institution of the paper.
The above research was supported by a number of domestic and international projects, including the National Natural Science Foundation of China (NSFC), Guangdong Provincial Key Laboratory Program from the Department of Science and Technology of Guangdong Province, and the Start-Up Fund provided by SUSTech.