Exploration and development of novel rutile oxide materials for next generation spin torque transfer heterostructures

As the scaling of traditional CMOS goes beyond the 32 nm node, spin torque transfer random access memory (STT-RAM) has the potential to replace all other memory technologies. However, the switching current density needed to program a bit is still an order of magnitude too high to be drive by a conventional CMOS transistor and needs to be lowered to 105 A/cm 2. In this thesis a materials tool-kit was developed for an all oxide heterostructure that could deliver superior performance to the current state-of-art STT-RAM device. Utilizing the reactive bias target ion beam deposition (RBTIBD) growth technique, the growth and characterization of three transition metal oxides was investigated. These include vanadium dioxide (VO2), substitutionally alloyed chromium vanadium dioxide (Cr:VO2) and substitutionally alloyed ruthenium chromium dioxide (Ru:CrO2). In VO2 thin films on sapphire, a current induced metal-insulator transition (MIT) was observed at room temperature that occurred at a current density of 3.4 x 104 A/cm2 The MIT temperature (TMI) was found to be dependent on the strain of the (001) spacing of VO2 and TMI ranged between 293 K and 340 K for thin films deposited on TiO2 of various orientations. Conductivity anisotropy was observed in the in-plane directions of VO2 thin films prepared on TiO2 (100) and (011) substrates. Room temperature ferromagnetism was reported for Ru:CrO2 thin films where the Ru concentration ranged from 6--9 at%. A spin polarization as high as 70% was reported for Ru:CrO2/TiO2 (001) where Ru concentration was 9 at%. Ru:CrO2/TiO2 (001) shows metallic like transport with a room temperature resistivity of 377 muO·cm for films with 25 at% Ru. The ferromagnetic state of Ru:CrO2 is stable and does not suffer from phase competition as compared to Cr:VO 2. In addition an intrinsic positive exchange bias was reported inherent to this material. Furthermore the exchange biased loop can be modulated with an external magnetic field to the opposite side of the magnetic field axis. When the field cycle is swept from high positive field to high negative field and back, an inverted magnetic hysteresis is reported with nearly zero loss.