Impact of processing and stack optimization on the reliability of perpendicular STT-MRAM

The nanometer thin MgO barrier and the large write currents for STT-MRAM, result in an endurance bottle neck due to oxide breakdown. In this paper we present an in-depth analysis of the impact of processing on barrier breakdown, including etch techniques (ion beam etch and reactive ion etch), post etch treatments and variations of the spacer layers in the MRAM stack. We find that variability in breakdown characteristics can be significantly reduced using an optimized etch. Secondly we propose an oxygen scavenging model to explain the different reliability behavior for various stack configurations.