Project Summary: The ability to engineer potential profiles of multilayered materials is critical for designing high-performance tunneling devices such as ferroelectric tunnel junctions (FTJs). FTJs promise electrically switchable memories, sensors, and logic devices. However, traditional FTJs comprising metal/oxide heterostructures only exhibit modest tunneling electroresistance (TER; usually <106), which is limited by defect states and interface trap states. In this work, the group led by Prof. Gong at University of Maryland demonstrated an emerging class of FTJs by employing 2D van der Waals (vdW) ferroelectrics and 2D electronic materials (e.g., graphene, MoS2, WSe2). A giant TER of >1010 is achieved due to the gigantic ferroelectric modulation of band alignments of vdW stacks. In the FTJ multilayered structures, inserting a monolayer MoS2 or WSe2 in between ferroelectrics/graphene effectively enhances TER by ten times. The discovery of the giant TER in vdW FTJs opens up a new solid-state paradigm in which electrons’ potential profiles can be tailored in an unprecedented layer-by-layer fashion, enhancing the ability to control electrons’ tunneling behaviors for emerging tunneling devices. The detailed findings are published in Matter. 5, 4425 (2022).
2DCC Role: The high-quality WSe2 single crystals used in this study were synthesized using the 2DCC chemical vapor transport instrumentation. The close collaboration between 2DCC researchers and the users, together with the 2DCC’s combined capacity of bulk crystal growth and characterization, enable this achievement.
What Has Been Achieved: This work demonstrated an emerging class of FTJs by employing 2D van der Waals (vdW) ferroelectrics and 2D electronic materials (e.g., graphene, MoS2 and WSe2). A giant TER of >1010 is achieved due to the gigantic ferroelectric modulation of band alignments of vdW stacks.
Importance of the Achievement: This work opens the door to the emerging class of vdW heterostructures for studying the fundamental tunneling physics and exploring tunneling devices such as nonvolatile memories, logics, and logic-in-memory devices
Unique Feature(s) of the MIP that Enabled this Achievement: The 2DCC researchers not only synthesized WSe2 single crystals using the chemical vapor transport method, but also carefully characterized the grown crystals using XRD and EDS. The combined capacity of bulk crystal growth and advanced characterization at 2DCC-MIP enables this achievement.
Publication: Qinqin Wang, Ti Xie, Nicholas A. Blumenschein, Zhihao Song, Jimmy C. Kotsakidis, Aubrey T. Hanbicki, Michael A. Susner, Benjamin S. Conner, Qishuo Tan, Seng Huat Lee, Zhiqiang Mao, Xi Ling, Tony Low, Jian-Ping Wang, Adam L. Friedman, and Cheng Gong, Matter. 5, 4425 (2022).
Acknowledgements: C.G. acknowledges the grant support from Air Force Office of Scientific Research under the award number FA9550-22-1-0349, Naval AirWarfare Center Aircraft Division under the award number N00421-22-1-0001, and Army Research Laboratory under the cooperative agreement number W911NF-19-2-0181. J.-P.W. acknowledges the support of the Robert F. Hartmann Endowed Chair Professorship. M.A.S. and B.S.C. acknowledge support through the United States Air Force Office of Scientific Research (AFOSR) LRIR 18RQCOR100 and AOARD-MOST grant number F4GGA21207H002. B.S.C. further acknowledges the National Research Council Senior Fellowship award. Financial support forWSe2 sample preparation was provided by the National Science Foundation through the Penn State 2D Crystal Consortium-Materials Innovation Platform (2DCC-MIP) under National Science Foundation cooperative agreement DMR-2039351. Q.W. acknowledges DFT support from Dr. Qirui Cui.