Fluorite-Structured HfO2/ZrO2/HfO2 Superlattice Based Self-Rectifying Ferroelectric Tunnel Junction Synapse

Abstract

A self-rectifying ferroelectric tunnel junction that employs a HfO₂/ZrO₂/HfO₂ superlattice (HZH SL) combined with Al₂O₃ and TiO₂ layers is proposed. The 6 nm-thick HZH SL effectively suppresses the formation of non-ferroelectric phases while increasing remnant polarization (P_r). This enlarged P_r modulates the energy barrier configuration, consequently achieving a large on/off ratio of 1,273 by altering the conduction mechanism from off-state thermal injection to on-state Fowler-Nordheim tunneling. Moreover, the asymmetric Schottky barriers at the top TiN/TiO₂ and bottom HfO₂/Pt interfaces enable a self-rectifying property with a rectifying ratio of 1,550. Through calculations and simulations, the device demonstrates the potential for an integrated array size exceeding 7k while maintaining a 10% read margin and supporting neuromorphic applications for artificial synapses with an image recognition accuracy above 92%. Finally, the self-rectifying behavior and device-to-device variation reliability are confirmed in a 9 × 9 crossbar array structure.