Area and pulsewidth dependence of bipolar TDDB in MgO magnetic tunnel junction

Abstract

The time-dependent dielectric breakdown (TDDB) phenomenon has been investigated in a series of nominally identical dual-MgO CoFeB magnetic tunnel junctions (MTJs) by bipolar pulsed voltage endurance tests using 28 nm embedded MRAM (eMRAM) test chip. From the bipolar pulsed endurance tests on different size MTJ devices, we show that the dielectric breakdown for MgO deviates significantly from the Poisson area scaling law due to self-heating in larger area devices. The lifetime of the devices was found to be longer for stressing with shorter pulse widths for the same overall cumulative stress duration, which could be attributed to the self-heating effects that typically take about a few microseconds to reach the saturation temperature. We prove that self-heating effects play a more dominant role than extrinsic etch damage effects in determining the lifetime of STTRAM devices.