Barrier Breakdown Mechanisms in MgO-Based Magnetic Tunnel Junctions under Pulsed Conditions

A thorough investigation of barrier breakdown in MgO based Magnetic Tunnel Junctions is presented. Our samples were tested under pulsed electrical stress. By studying the effect of delay between two pulses, we observe that an optimum endurance of MTJs is obtained for an intermediate value of delay between pulses which allows a partial discharge of the trapping sites between two pulses. The charge trapping-detrapping model that we have developed shows a good coherence with experimental results. We discuss how delay between two pulses affects the charge state of the sample. The average value in time and the time-modulation of this charge give rise to distinct breakdown mechanisms. We evaluate the MTJ probability of breakdown for different applied pulse conditions. We then deduce an expected endurance of the MTJs depending on the characteristics of the electrical stress in terms of delay, amplitude, unipolarity versus bipolarity. A charge trapping-detrapping model was proposed to explain our experimental observations.