Athanasios Dimoulas

Ferroelectric Tunnel Junction memristors for neuromorphic technologies

Abstract: Ferroelectric Tunnel Junction (FTJ) memristors show promise as electronic synapses for low power neuromorphic circuits. First, the progress will be reviewed in the field of perovskite and recently discovered Hafnia based ferroelectrics such as Hf0.5Zr0.5O2 (HZO), considering both double and single- layer gate stack designs. Then, the focus will shift on Metal-Ferroelectric-Semiconductor (MFS)-FTJs where the bottom electrode is a semiconductor (Ge or Nb:STO) and the top is W or TiN metal. The metastability of ferroelectricity due to depolarization fields will be discussed and the lower limits of HZO thickness to obtain stable ferroelectricity will be determined. It will be shown that HZO based MFS-FTJ behave as analog memristive non-volatile memories with very good endurance and retention and with a number of intermediate states showing synaptic plasticity, that is long term potentiation and depression as a function of the number of sequential pulses of varying amplitude or width. The role in the FTJ switching behavior of the Schottky barrier near the semiconductor/HZO interface will be elucidated. The programming and reading voltage of the synaptic devices are below 1V which makes them suitable for ultra-low power in-memory neuromorphic computing. Performance characteristics determining speed and low power operation of neuromorphic circuits will be addressed. Integration with CMOS either in the FEOL or the BEOL will also be discussed.

Dr. Athanasios Dimoulas is Research Director at NCSR-DEMOKRITOS in Athens. He is founder and head of Epitaxy and Surface Science Laboratory (ESSL) of the Institute of Nanoscience and Nanotechnology since 1999 and currently member of the advisor committee for physical sciences of the Greek government. He has been EC Human Capital and Mobility fellow at the university of Groningen, post-doctoral fellow at CALTECH and Research Associate at the University of Maryland. He has been visiting research scientist at IBM-Zurich and he has been appointed as Chair of Excellence at CEA-INAC(IRIG), and U. Grenoble Alpes, France. He has coordinated several collaborative EU projects and has been awarded the ERC advanced and proof of concept grants. He has served as chair of INFOS and chair of TPC committees of ESSDERC and IEDM. His current interests include 2D materials, topological materials and Hafnia based ferroelectric memristors for neuromorphic computing technologies.

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