Formation of a Ti → TiO 2 -graded layer and its effect on the memristive properties of TiO x (/Ti/TiO x ) structures

In this study DC reactive HiPIMS-sputtered TiO x /Ti/TiO x and TiO x -based memristors were fabricated. Metallic Ti layer was created on TiO 2 next to the bottom electrode, expected to create a soft transition from metallic state to TiO 2 as oxygen purged into the chamber. Each structure roughness remained well below nm. The band gap of thin-pure TiO 2 was found as 3.52 eV and 3.80 eV for TiO 2 with intermetallic layer from absorption measurements. Raman analysis indicates rutile and anatase phases. Ti 6 O 11 , TiO 2 , TiO 2 (rutile), TiO 2 (anatase), and Ti 3 O 5 phases from each sample are identified from XRD measurements. The memristive characteristics of both the devices were determined by time-dependent current–voltage ( I – V – t ) measurements and current transport mechanisms were investigated in terms of pinched hysteresis of I – V – t loops. The devices with Ti → TiO 2 transition layer exhibited much larger hysteresis area in comparison pure TiO 2 -based devices. All of the devices exhibited Fowler–Nordheim tunneling, Schottky emission, Space-Charge-Limited Conduction, and Poole–Frenkel emission, which depended on the voltage scanning direction and order of loops.