报 告 人：Jingsheng Chen, Department of Materials Science and Engineering, National University of Singapore
报告题目：Perovskite oxide thin films for the application of non-volatile memory
内容简介：The quest for a solid state non-volatile memory device on silicon with high storage density, high speed, and low power consumption has attracted intense research on new materials and novel device architectures. Perovskite oxide films show lots of unique properties due to strong coupling among charge, spin, orbital. In this presentation, I will report our recent works on ferroelectric tunnel junction, multiferroic induced in the ferroelectric/ferromagnetic heterostructures, ferroelectric polarization effects on spin orbital torque and low damping constant. 1)The ability to change states using voltage in ferroelectric tunnel junctions (FTJs) offers a route for lowering the switching energy of memories. A high TER (∼400%) can be achieved at BaTiO3 tunnel layer down to two unit cells (∼0.8 nm). Furthermore, we demonstrate ferroelectric tunnel junctions (Pt/BaTiO3/La0.67Sr0.33MnO3) epitaxially grown on silicon substrates. The write speed, data retention and fatigue properties of the device compare favorably with flash memories. We also demonstrated that the ferroelectricity can be persisted when BiFeO3 thickness is down to 1 unit cell and showed good FTJ function. 2)The artificial composite multiferroics, which combines the ferroelectric and magnetic constituents, utilizes the interface coupling, including charge modulation, the orbital reconstruction due to the ions displacement and magnetic order reconstruction.The magnetic properties of 5 unit cell La0.7Sr0.3MnO3 (LSMO) layer grown on BTO films with different polarization direction showed that saturation magnetization of LSMO films grown on BTO with polarization up is much larger than that of LSMO grown on BTO with polarization down. XAS and XMCD investigation showed that magnetism of Ti atoms in BTO was induced. Furthermore, the Ti atoms are ferromagnetically and antiferromagnetically coupled to Mn atoms for different ferroelectric polarization. 3) Spin orbital torque is considered to be originated from Rashba effect and spin Hall Effect. We have demonstrated that the ferroelectric built-in electric field has significant effect on spin orbital torque. The magnetic free-field switching is achieved. 4) In order for development of full oxide spintronic device, low damping ferroelectric oxide conductive materials is desired. We have successfully fabricated LaSrMnO3 films with the damping constant in the order of magnitude of 10-4 . The measurement is based on our home angle resolved FMR technique.
报告人介绍：Dr. Chen is Associate Professor in Department of Materials Science and Engineering, National University of Singapore. Prof. Chen got his Ph.D degree from Lanzhou University in 1999. During 1999-2001, he was postdoctoral fellow in Nanyang Technology University. From 2001-2007, as research Scientist in Data Storage Institute, he led a team to develop the ultrahigh density magnetic recording media toward 1 Tbits/in2. Until now, Seagate Technology, the largest hard disk drive company in the world, has sponsored him more than 1 million US dollars and a few invented technologies have been used in the product. Since he joined National University of Singapore, he has secured more than 14 million Singapore dollars research grant from Singapore government. Currently, Prof. Chen is leading a 9 million Singapore dollars research Programme to develop low power non-volatile memory and a 2 million Singapore dollar industry programme (Global foundries) to develop spin transfer torque MRAM with new perpendicular material. He is the editor board member of many Journals such as Scientific Report (Nature publisher), Spin (World Scientific publisher) etc. He is a managing committee member of SG-SPIN consortium in Singapore. He has published more than 200 SCI Journal papers, 3 book chapters and more than 30 invited presentation in the international conferences. His research work has obtained more than 3000 non-self-citations with H index of 26.