An example method includes: forming a bottom electrode on a substrate and forming a patterned mask layer on the bottom electrode; thermal oxidizing the bottom electrode layer via the patterned mask layer by applying a thermal process and a first plasma; removing a gaseous status of the bottom electrode oxide using a first vacuum purge; removing a solid status of the bottom electrode oxide by applying a second plasma; removing the gaseous status and the solid status of the bottom electrode oxide using a second vacuum purge to form a patterned bottom electrode; removing the patterned mask layer; forming a filament forming layer on the patterned bottom electrode; and a top electrode on the filament forming layer. The filament forming layer is configured to form a filament within the filament forming layer responsive to a switching voltage being applied to the filament forming layer.