Wake-up free Hf_0.5Zr_0.5O₂ capacitors with MoO_x seed for ferroelectric memory applications

Abstract

This study examines the impact of inserting an ultrathin MoOx seed (<2nm) into HZO-based capacitors with TiN electrodes, while reducing the physical thickness of HZO, grown by atomic layer deposition, from 9 to 5 nm. The crystallinity of the stack was assessed using X-ray diffraction and transmission electron microscopy, while the grain size and phase analysis was analyzed in some cases by precession electron diffraction. X-ray photoelectron spectroscopy provided insights into the oxidation state of MoOx. Ferroelectric HZO with suppressed wake-up can be fabricated using MoOx seed, achieving remanent polarization between 25 μC/cm2 and 40μC/cm2 and an endurance of at least 108 cycles for HZO layers with a thickness of 5 to 9 nm. The study elucidates how the MoOx seed influences the phase equilibrium among tetragonal, orthorhombic, and monoclinic phases within HZO by regulating oxygen vacancies. This seed alters the size, distribution, and orientation of ferroelectric orthorhombic grains, which are essential for ferroelectric properties.