报告题目：Ferroelectric Tunnel Junction and Spin Orbital Torque for Non-volatile Memory
报告人：Jingsheng CHEN教授
Department of Materials Science and Engineering, National University of Singapore
报告时间：2019年10月29日星期二，15:30
报告地点：物理科技楼101
报告邀请人：汤如俊
报告摘要：The advances in information technology stimulate researchers to search for a universal memory: high speed, high density, low power, non-volatile memory.Current non-volatile memories in product and under development include flash, phase change RAM (PCRAM), spin transfer torque magnetic RAM (STT-MRAM), resistance RAM (RRAM) and ferroelectric tunnel junction based RAM (FTJ-RAM). In this talk, I will briefly introduce the works we have done recently on ferroelectric tunnel junction and spin orbital torque (one variant for STT-MARM). (1) The ability to change states using voltage in ferroelectric tunnel junctions (FTJs) offers a route for lowering the switching energy of memories. We conducted systematic investigation on the effects of the various asymmetries of ferroelectric/electrode interfaces on the tunnelling electroresistances. Enhanced tunnelling electroresistance (on/off ratio as large as 107) in FTJ can be achieved by asymmetric electrodes or introducing metal−insulator transition interlayers or engineering the termination of interfaces.1-2Surprisingly, we found that even though the thickness of ferroelectric barrier (BiFeO3) decreases to one unit cell, ferroelectric remains and the on/off ratio is as large as 370%.3(2) Spin orbital torque MRAM as a variant of STT-MRAM is believed to have higher speed and lower power consumption than STT-MRAM. The current induced spin-orbit torque (SOT) in heavy metal/ferromagnet (HM/FM) bilayers is attributed to the spin Hall effect in the HM and/or the Rashba effect at the interfaces. We found that L10IrMnantiferromagnets and 2D MoS2, has a large spin orbit torque efficiency (0.6), which is 6-8 times than currently used Ta and Pt.4-5In addition, we have discovered one kind of materials (L10FePt, CoPt) with crystal centrosymmetry which can be electric switched in the form of single layer. By introducing spin-current gradient and controlling the easy axis, free-field electric current switching of perpendicularly magnetized oxide and metallic films are achieved.6-8
References
1.R. Guo, J.S. Chen et.al.,ACS Applied Materials & Interfaces,10, 12862−12869 (2018),
2.H.Y. Young, J.S. Chen, et.al,Advanced Functional Materials, 1806037 (2018)
3.H. Wang, J.S. Chen et.al.,Nature Communication, 9 (1), 3319 (2018).
4.J. Zhou, J.S .Chen, et.al.Science Advance, 5 (5), eaau6696 (2019).
5.Q.D. Xie, J.S. Chen, et.al.Advanced Materials, 31 (21), 1900776 (2019)
6.L. Liu, J.S. Chen, et.al.Nature Nanotechnology(2019)
doi: 10.1038/s41565-019-0534-7
7.S.H. Chen, J.S. Chen,et.al. ACS Appl. Mater. Interfaces, 11, 30446 (2019).
8.Q. Qin, J.S.Chen, et.al.Advanced Materials, 1807008 (2019).
报告人简介：
Dr Jingsheng Chenisa tenure-trackAssociate Professor in Department of Materials Science and Engineering, NUS. He obtained his Ph.D degree in 1999 in Lanzhou University, China and joined NUS in December 2007. During 2001-2007 he worked at the Data Storage Institute as a research scientist. He has authored/co-authored more than 240 refereed journal papers including Nature Nanotechnology, Nature Comm. Science Advance, Advanced Materials, Physical Review X, etc., 3 book chapters, holds over ten patents and has made more than 50 invited presentation in the international conferences. His research work has obtained more than 5600 citations with H index of 36. His research interest includes magnetic and oxide based non-volatile memories, spintronics, ferroelectric tunnel junction, strongly correlated oxide materials. He secured more than S$17 million research grants from government and around US$ 1 million from Seagate Technology and more than S$ 1 million from Globalfoundries. The magnetic recording media in the newest generation of HDD (HAMR) utilized a few of his inventions.
