报告题目：Ferroelectric Tunnel Junction and Spin Orbital Torque for Non-volatile Memory
Department of Materials Science and Engineering, National University of Singapore
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
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)
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).
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.