Multi-bit MRAM storage cells utilizing serially connected perpendicular magnetic tunnel junctions

Abstract

Serial connection of multiple memory cells using perpendicular magnetic tunnel junctions (pMTJs) is proposed as a way to increase magnetic random access memory (MRAM) storage density. A multibit storage element is designed using pMTJs fabricated on a single wafer stack, with serial connections realized using top-to-bottom vias. The tunneling magnetoresistance effect above 130%, current induced magnetization switching in zero external magnetic field, and stability diagram analysis of single, two-bit, and three-bit cells are presented together with thermal stability. The proposed design is easy to manufacture and can lead to an increased capacity of future MRAM devices.