Ferroelectric tunnel junction based on ultrathin Zr0.75Hf0.25O2

Abstract

Ferroelectric tunnel junction (FTJ) based on hafnia/zirconia-based thin films has emerged as a promising class of nonvolatile memory, owing to their fast switching speeds, low power consumption, and full compatibility with complementary metal-oxide-semiconductor technology. Here, we report the fabrication of a high-performance FTJ based on 3.5 nm-thick Zr0.75Hf0.25O2 (ZHO) ferroelectrics with a remanent polarization of 12 μC/cm2. The fabricated TiN/WOx/ZHO/Pt FTJs exhibited large ON/OFF ratios (>1000) and good endurance of over 106 cycles, attributable to the robust ferroelectric properties and stability of electrodes. Micrometer-sized FTJ devices in crossbar structure delivered ultra-high read current densities of up to 520 A/cm2, and, importantly, the current density increases with shrinking FTJ, being attributed to a higher edge/corner effect from smaller electrodes. In addition, crossbar FTJ showed reliable synaptic phenomena including long-term potentiation/depression, paired-pulse facilitation/depression, and spike timing-dependent plasticity. This work demonstrates the excellent scalability of zirconia-based ferroelectric memory and their capability to emulate biological synapses.