Breakdown evaluation of ultrathin barrier magnetic tunnel junctions with V-Ramp testing

Ultrathin alumina barrier magnetic tunnel junctions (MTJs) were tested by ramping the voltage across the barrier at different rates ranging from 0.2 mV/s to 20 mV/s at room temperature. Two distributions of breakdown voltage - intrinsic and extrinsic, are found in the stress test of MTJs. The threshold voltage is 0.6-0.7 V and 0.3-0.5 V for the intrinsic and extrinsic breakdown respectively. Intrinsic breakdown is described by E-model, where lifetime decreases exponentially with increasing junction voltage. A logarithmic relationship between breakdown voltage and ramp rate is observed. Both intrinsic and extrinsic MTJ data fits well to Simmons´ model, and reasonable estimates for barrier height and barrier thickness are derived.