Reliable resistive switching of epitaxial single crystalline cubic Y-HfO₂ RRAMs with Si as bottom electrodes

Previous studies have mainly focused on the resistive switching (RS) of amorphous or polycrystalline HfO₂-RRAM. The RS of single crystalline HfO₂ films has been rarely reported. Yttrium doped HfO₂ (YDH) thin films were fabricated and successful Y incorporation into HfO₂ was confirmed by x-ray photoemission spectroscopy. A pure cubic phase of YDH and an abrupt YDH/Si interface were obtained and verified by x-ray diffraction, Raman spectroscopy and transmission electron microscopy. A Pt/YDH/n⁺⁺-Si heterostructure using Si as the bottom electrode was fabricated, which shows stable RS with an ON/OFF ratio of 100 and a reliable data retention (10⁴ s). The electron transport mechanism was investigated in detail. It indicates that hopping conduction is dominating when the device is at a high resistance state, while space charge limited conduction acts as the dominant factor at a low resistance state. Such behavior, which is different from devices using TiN or Ti as electrodes, was attributed to the Y doping and specific YDH/Si interface. Our results demonstrate a proof of concept study to use highly doped Si as bottom electrodes along with single crystalline YDH as insulator layer for such RRAM applications as wireless sensors and synaptic simulation.