New multi-bit non-volatile memory cells with higher data storage density
New multi-bit non-volatile memory cells with higher data storage density lead image
Spin transfer torque magnetoresistance random access memory (STT-MRAM) is a promising technology with potential application as non-volatile memory devices. It possesses numerous advantages including high-speed read/write and theoretically unlimited endurance. However, STT-MRAM technologies currently still lack capacity, primarily due to space limitations in existing one-transistor-per bit designs, and challenges in fabricating proposed multi-bit architectures.
Rzeszut et. al. report the proof-of-concept design and test results of single wafer stack, multi-bit MRAM storage cells driven by a single transistor. In the novel design, perpendicular magnetic tunnel junctions (pMTJs) are serially connected in a head-to-tail configuration, with the top contact of the first element connected to the bottom contact of the next element.
“Our design is easy to manufacture and is a significant improvement in MRAM technology enabling the storage of more data using the same area of memory,” said author Piotr Rzeszut.
The researchers fabricated thermally stable, state-of-the-art multilayer pMTJs with a measured magnetoresistance ratio above 135%. By electrically connecting the pMTJs in series, the team was able to create two- and three-bit storage cells, each with four and eight stable and switchable states respectively.
“Our multi-bit storage cell uses a single transistor rated for the same current as a single storage element and the critical current remains the same for any number of serially connected elements,” said Rzeszut.
According to the authors, the approach can be extended to create higher multi-bit systems and design artificial synapses for neuromorphic computing.
Source: “Multi-bit MRAM storage cells utilizing serially connected perpendicular magnetic tunnel junctions,” by Piotr Rzeszut, Witold Skowroński, Sławomir Ziętek, Jerzy Wrona and Tomasz Stobiecki, Journal of Applied Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5097748 .
