Phase Change and Memory
Ningbo University, Ningbo, China
Prof. Shen Xiang received his PhD degree from the Shanghai Institute of Technical Physics (Chinese Academy of Sciences) in 2009. He was a Visiting Scientist at the Austrian National University. Currently, he is the executive vice dean of School of Information Science and Engineering, Ningbo University, and he also serves as the head of the Laboratory of Infrared Materials and Devices Laboratory, Ningbo University. Prof. Shen won the second prize of National Science and Technology Invention Award (4/6, 2014), the China Industry-University-Research Institute Cooperation Innovation Award (Individual, 2021), the second prize of Ningbo Science and Technology Award (1/8, 2019), etc. His current research interest mainly focuses on the develop and implementation of novel chalcogenide phase-change materials for neuromorphic computing, and infrared chalcogenide glass materials and their application in optical devices. His research works are supported by the Joint Funds of the National Natural Science Foundation of China, the National Natural Science Foundation of China, the Key R&D program of Zhejiang Province, etc. And part of the works have been published in journals as Acta Materialia, Optics Letters, Optics Express, Applied Physics Letters and Crystal Growth & Design, etc.
Abstract for Presentation
Thickness dependent crystallization kinetics of GeTe ultrathin films
Current phase-change random access memory (PCRAM) could not meet the requirements of ideal neuro-inspired in-memory computing due to the large resistance drift and high energy consumption of conventional phase-change films. Scaling down of phase-change films (reduce film thickness to nano-size) is an efficient way to alleviate resistance drift and reduce energy consumption for PCRAM. However, numbers of issue that can affect the phase-change kinetics features significantly, would arise in the nano-size or ultrathin films. In this work, the crystallization kinetics of ultrathin GeTe phase-change films with [GeTe(n)/W(6nm)]x multilayer structures (n = 350, 17, 3.5 nm; x= 1, 17, 30) have been investigated. Together with Flash DSC measurements and generalized Mauro-Yue-Ellison-Gupta-Allan viscosity model, we revealed the distinct fragile-to-strong crossover transition behavior, which is beneficial to solve the contradiction between good thermal stability nearby glass transition temperature and fast crystal growth rate around melting temperature, presents in ultrathin GeTe films as the thickness is less than ~20 nm. Moreover, it is found that the relation between maximum crystal growth rate (Umax) and film thickness (d) of GeTe can be expressed as, U_max=U_(max,bulk)-Ae^(-d/c), where Umax,bulk is the maximum crystal growth rate of 3.55 m s-1 for bulk material or thick film, A is the growth rate attenuation coefficient of 1.5 (m s-1), and c is the threshold thickness related constant of 2 (nm). Above knowledges of temperature dependent crystallization kinetics for GeTe ultrathin film, must be thought-provoking and a guidance in the field of low-dimensional PCRAM, which is the key cell for neuro-inspired in-memory computing.
 X.-B. Li, N.-K. Chen, X.-P. Wang, H.-B. Sun, Adv. Funct. Mater., 28 (2018) 1803380.
 P. Ma, H. Tong, M. Xu, X. Cheng, X. Miao, Appl. Phys. Lett., 117 (2020) 022109.
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