Correlation between Barrier Width, Barrier Height, and DC Bias Voltage Dependences on the Magnetoresistance Ratio in Ir–Mn Exchange Biased Single and Double Tunnel Junctions

Dual spin-valve-type double tunnel junctions (DTJs) of Ir–Mn/CoFe/AlO x /Co 90 Fe 10 /AlO x /CoFe/Ir–Mn and spin-valve-type single tunnel junctions (STJs) of Ir–Mn/CoFe/AlO x /CoFe/Ni–Fe were fabricated using an ultrahigh vacuum sputtering system, conventional photolithography and ion-beam milling. The STJs could be fabricated with various barrier heights by changing the oxidization conditions during deposition and changing the annealing temperature after deposition, while the AlO x layer thickness remained unchanged. There was a correlation between barrier width, height estimated using Simmons' expressions, and dc bias voltage dependence on the MR ratio. The V B dependence on the tunneling magnetoresistance ( TMR ) ratio was mainly related to the barrier width, and the decrease in the TMR ratio with increasing bias voltage is well explained, taking into account the spin-independent two-step tunneling via defect states in the barrier, as a main mechanism, at room temperature. Under optimized oxidization and annealing conditions, the maximum TMR ratio at a low bias voltage, and the dc bias voltage value at which the TMR ratio decreases in value by half ( V 1/2 ) were 42.4% and 952 mV in DTJs, and 49.0% and 425 mV in STJs, respectively.