Modelling of time-dependent dielectric barrier breakdown mechanisms in MgO-based magnetic tunnel junctions

Abstract

An investigation of barrier endurance till electrical breakdown in MgO-based magnetic tunnel junctions (MTJs) is presented. Samples were tested under pulsed electrical stress. By studying the effect of delay between successive pulses, an optimum endurance of MTJs is observed for an intermediate value of delay between pulses corresponding to an optimum trade-off between the average density of charge trapped in the barrier and the amplitude of its time-modulation at each voltage pulse. A charge trapping–detrapping model was developed which shows good coherence with experimental results. The influence of the delay between pulses on the trapped charge density in the tunnel barrier and on its time-modulation is discussed. The average density of trapped charges and its time-modulation are, respectively, responsible for a static and dynamic stress within the tunnel barrier, both leading to breakdown. The probability of breakdown of the MTJ for different applied pulse conditions has been evaluated. The expected endurance of the MTJs was deduced depending on the characteristics of the electrical stress in terms of delay, and unipolarity versus bipolarity. The study emphasizes the role of electron trapping/detrapping mechanisms on the tunnel barrier reliability. It also shows that extremely long endurance could be obtained in MTJs by reducing the density of electron trapping sites in the tunnel barrier.

Modeling of Breakdown-Limited Endurance in Spin-Transfer Torque Magnetic Memory Under Pulsed Cycling Regime

“…In fact, as t D increases, defects efficiently diffuse toward the opposite interface, thus making the difference between unipolar and bipolar stress increasingly negligible. Note that the weak dependence of bipolar endurance on t D is consistent with previous results in [32]. On the other hand, our data for unipolar stress show no dramatic dependence on t D , in contrast to [32], which might be explained by a different structure or etch damage profile in our MgO layer.…”

Impact of Spin-Orbit Torque on Spin-Transfer Torque Switching in Magnetic Tunnel Junctions

“…The current density for switching of STT-MRAM is relatively large and hence large transistors are inevitable to drive it, which thus significantly limits their future use for memory applications 6,7 . The sustainability of higher switching current density of the tunnel barrier also raises reliability issues and leads to the degradation of related MTJ performance, such as, tunnel magneto resistance (TMR), write current margin, and write speed on the time span [8][9][10] . The situation will be even much worse when further scaling of STT-MRAM enters into a nanometer regime.…”

Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1−xFexO thin films

“…The ability to manipulate the spin of charge carriers has resulted in the giant magnetoresistance effect and magnetic tunnel junction (MTJ), and further realization of non-volatile magnetoresistive random access memories [1][2][3][4]. Among the oxide complexes with high dielectric constant, MgO based MTJs [2,3,[5][6][7] are generally preferred since it enhances spin polarization of charge tunneling via an additional spinfiltering mechanism [3,8]. Although many studies have been carried out on the functional properties of Fe/MgO/Fe MTJs, an understanding for the often observed barrier breakdown and how lattice defects radically modify the paradigm of wave function engineering in the Fe/MgO/Fe MTJs remains [9].…”

“…The ability to manipulate the spin of charge carriers has resulted in the giant magnetoresistance effect and magnetic tunnel junction (MTJ), and further realization of non-volatile magnetoresistive random access memories [1][2][3][4]. Among the oxide complexes with high dielectric constant, MgO based MTJs [2,3,[5][6][7] are generally preferred since it enhances spin polarization of charge tunneling via an additional spinfiltering mechanism [3,8].…”