Offset Field Control for VCMA-MRAM

One of the key challenges in the industrialisation of Voltage Controlled Magnetic Anisotropy-Magnetic Random Access Memory (VCMA-MRAM) is the reliability of the writing process. As VCMA is a non-deterministic write process, it is more sensitive to any offset of the Free Layer (FL) ( $\mu _{0}H_{off}$ ) due to stray fields generated by the Hard Layer (HL)/Reference Layer (RL), as compared to alternative MRAM technologies. In this work, a simple method for the control of $\mu _{0}H_{off}$ is demonstrated. The relative moments of the HL and RL can be tuned by varying the Co concentration, and number of repeats, in a typical Co/Pt HL. The effect of this is demonstrated at thin film and device level where a FL offset of $\mu _{0}H_{off}=0$  mT is obtained, with minimal change in any other device properties. Furthermore, the switching probability distribution, with respect to VCMA pulse width, is shown to be symmetric in the optimised device. This result shows that with simple tuning, one of the key challenges to VCMA-MRAM can be solved.