Structural properties and electroforming-free resistive switching characteristics of GdO_x, TbO_x, and HoO_x memory devices

Resistive random access memory (RRAM) using the Ru/REO_x/TaN (rare-earth, RE, RE = Gd, Tb and Ho) structures is fabricated with full room temperature process and is not required the electroforming process. X-ray diffraction and X-ray photoelectron spectroscopy were used to study the structural and chemical features of REO_x films. The conduction mechanism of REO_x-based RRAM memory devices in the low-resistance state is Ohmic emission, whereas the high-resistance state is space-charge-limited conduction. The GdO_x-based RRAM devices show high-resistance ratio of about 10⁴, reliable data retention of 10⁵ s, and stable cycling behaviors for up to 190 cycles. This result suggests the high concentration of the metallic Gd⁰ and oxygen vacancies in GdO_x film. The Ru/GdO_x/TaN structure memory is a possible candidate for next-generation nonvolatile memory applications.