Four point probe ramped voltage stress as an efficient method to understand breakdown of STT-MRAM MgO tunnel junctions

The study of reliability and understanding of the MgO barrier breakdown mechanism is essential for the development of STT-MRAM, a promising non-volatile memory. However, for STT-MRAM it is unclear what the preferred method is for studying barrier breakdown. In this paper we compare four point probe Ramped Voltage Stress (4PP-RVS) with a conventional Constant Voltage Stress (CVS) technique and with pulsed breakdown (RF-BD). We show the equivalence of breakdown time distributions determined by 4PP-RVS and CVS. 4PP makes the investigation of area scaling possible and avoids potential lifetime misjudgments of more than one order of magnitude. In a short and predictable time RVS can measure large populations subject to strong lifetime variability, typical for STT-MRAM cells. We also compare 4PP-RVS with pulsed breakdown (RF-BD) and observe a more favorable reliability for RF-BD. 4PP-RVS allows an efficient in depth breakdown analysis for STT-MRAM.