Dual-Mode Operation of Epitaxial Hf0.5Zr0.5O2: Ferroelectric and Filamentary-Type Resistive Switching

Abstract

Since the discovery of its ferroelectricity, hafnium oxide is widely used for applications in ferroelectric field-effect transistors and ferroelectric tunnel junctions. (Formula presented.) is especially favored for its robust ferroelectricity and high remanent polarization at low thicknesses. In addition, (Formula presented.) is well established as amorphous or crystalline oxide layer in resistive switching devices. Herein, ferroelectric switching is found coexisting with high on/off ratio resistive switching in sub-10 nm epitaxial (Formula presented.). The resistive switching shows typical characteristics of a filamentary-type valence change memory (VCM), clearly contradicting the polarization charges as the origin of different resistance states. In contrast to previous observations, no electroforming step is required to initiate VCM switching. The (Formula presented.) bottom electrode enables a RESET to the virgin state, allowing subsequent ferroelectric hysteresis measurements. It is possible to change between both switching schemes repeatedly without impacting the ferroelectric performance. This indicates that ferroelectric switching and oxygen vacancy movement do not interfere with each other, and both switching phenomena can exist independently. This finding opens up ways to unite the different strengths of both switching mechanisms in the same stack. It becomes possible to assign the two operating principles to artificial neural network training and inference according to their respective advantages.