A Low Temperature Functioning CoFeB/MgO Based Perpendicular Magnetic Tunnel Junction for Cryogenic Nonvolatile Random Access Memory

TL;DR

This study demonstrates that CoFeB/MgO based perpendicular magnetic tunnel junctions maintain high performance at cryogenic temperatures, showing increased endurance and magnetic stability, making them promising for cryogenic nonvolatile memory applications.

Contribution

The paper provides the first detailed analysis of low temperature performance of CoFeB/MgO pMTJs, revealing enhanced endurance and magnetic properties at cryogenic temperatures.

Findings

Endurance exceeds 10^12 cycles at 9 K

Switching voltage increases by 33% at 9 K compared to 350 K

High magnetoresistance (>120%) and reliable switching with nanosecond pulses

Abstract

We investigated the low temperature performance of CoFeB/MgO based perpendicular magnetic tunnel junctions (pMTJs) by characterizing their quasi-static switching voltage, high speed pulse write error rate and endurance down to 9 K. pMTJ devices exhibited high magnetoresistance (>120%) and reliable (error rate<10-4) bi-directional switching with 2 to 200 ns voltage pulses. The endurance of the devices at 9 K surpassed that at 300 K by three orders of magnitude under the same write conditions, functioning for more than 10^12 cycles with 10 ns write pulses. The critical switching voltage at 9 K was observed to increase by 33% to 93%, depending on pulse duration, compared to that at 350 K. Ferromagnetic resonance and magnetization measurements on blanket pMTJ film stacks suggest that the increased switching voltage is associated with an increase in effective magnetic anisotropy and magnetization of free layer with decreasing temperature. Our work demonstrates that CoFeB/MgO based pMTJs have great potential to enable cryogenic MRAM and that their low temperature magnetization and effective magnetic anisotropy can be further optimized to lower operating power and improve endurance.