Memory effect in two dimensional atomically-thin sheets




Ge, Ruijing

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Two-dimensional (2D) materials have attracted much attention over the last decade in nanoelectronics due to their remarkable electronic, optical, mechanical, and thermal properties. In this dissertation, we report intriguing observation of stable non-volatile resistive switching (NVRS) in single layer 2D atomic sheets sandwiched between metal electrodes. These devices can be collectively labeled atomristor, in essence, memristor effect in atomically-thin nanomaterials or atomic sheets. The systematic investigation for 2D-based-NVRS is conducted in terms of performance, materials, mechanisms, and applications and presented in separate chapters. Chapter 1 is an introduction to 2D materials and non-volatile memories. In Chapter 2, molybdenum disulfide (MoS₂) based atomristor is demonstrated showing large on/off ratio, forming-free characteristic and small switching voltages. In chapter 3, we further expand the collection of 2D materials showing NVRS, including transition metal dichalcogenides (MX₂, M=transition metal atom, e.g. Mo, W, Re, Sn or Pt; X=chalcogen atom, e.g. S, Se or Te), a heterostructure (WS₂/MoS₂) and an insulator (h-BN), indicating the universality of the phenomenon in various 2D atomic sheets. Then a possible mechanism dissociation-diffusion-adsorption (DDA) model is presented in Chapter 4, supported by both first-principle calculation results and scanning tunneling microscope (STM) atomistic imaging. In chapter 5, emerging device concepts in non-volatile flexible memory and zero-static power radio frequency (RF) switches are demonstrated, which could benefit substantially from the wide 2D materials design space. Our findings overturn the contemporary thinking that non-volatile switching is not scalable to sub nanometer and thus motivate further research in defect engineering, interface modification and ionic diffusion, which is discussed in the last Chapter 6


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