Forming-Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices

A model device based on an epitaxial stack combination of titanium nitride (111) and monoclinic hafnia (11 (Formula presented.)) is grown onto a c-cut Al 2O 3-substrate to target the role of grain boundaries in resistive switching. The texture transfer results in 120° in-plane rotated m-HfO 2 grains, and thus, in a defined subset of allowed grain boundary orientations of high symmetry. These engineered grain boundaries thread the whole dielectric layer, thereby providing predefined breakdown paths for electroforming-free resistive random access memory devices. Combining X-ray diffraction and scanning transmission electron microscopy (STEM)–based localized automated crystal orientation mapping (ACOM), a nanoscale picture of crystal growth and grain boundary orientation is obtained. High-resolution STEM reveals low-energy grain boundaries with facing ((Formula presented.)) and ((Formula presented.) 21) surfaces. The uniform distribution of forming voltages below 2 V—within the operation regime—and the stable switching voltages indicates reduced intra- and device-to-device variation in grain boundary engineered hafnium-oxide-based random access memory devices.