Improving Magnetic Immunity of STT-MRAM in Strong External Magnetic Field Environments Using Magnetic Shield

Magnetic random access memory (MRAM) is proven to be the most eligible candidate to replace the flash technology. Low power consumption along with higher cycling endurance, faster speed, stability over the entire automotive temperature range (-40°C to 150°C) are the key features of MRAM. However, magnetic immunity in the strong magnetic field environments is one of the concerns for the present spin-transfer-torque magnetic random access memory (STT-MRAM) technology where the magnetic energy barrier between the two bi-stable memory states decreases in the presence of an external magnetic field. While the exposure of the MRAM chip to the external magnetic field cannot be avoided completely, the magnitude of the field at the chip can be significantly reduced by using a package-level magnetic shield. In this article, we have considered different external magnetic field environments created by permanent magnets of different dimensions and distances from the packaged MRAM chip. We have emphasized the importance of the design of the shield together with the choice of shield materials based on different ranges of external magnetic fields to be shielded. The reduction in the magnitude of the external magnetic field at the chip due to the introduction of shield improves the bit-error-rate significantly. We have also demonstrated that the position and dimensions of the field source are also important in determining the uniformity of the shielding effect throughout the chip by identifying the worst corner of the packaged chip against the external magnetic field.