Investigating the Statistical-Physical Nature of MgO Dielectric Breakdown in STT-MRAM at Different Operating Conditions

Abstract

Ultra-thin dielectric breakdown (BD) has been studied in-depth for SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in CMOS devices in the past. In general, the degradation physics and model governing BD in these materials are assumed to hold true for MgO. This study provides evidences that this assumption may not be true by investigating in detail the statistical nature of BD in MgO dielectrics for wide range of operating conditions, relevant to its application as spin transfer torque magnetic random access memory (STT-MRAM). Our analysis shows that - MgO BD is polarity dependent; lifetime is lower for bipolar (AC) stress; defect generation is clustered in space and time; self-heating dominates for low frequencies; temperature within the percolation path exhibits fast transients (thermal runaway); Weibull model does not apply to BD statistics and defect generation (F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) is charge fluence driven (and field assisted) with power law model being most suited for lifetime extrapolation.