Advances in reducing the resistance and enhancing the magnetoresistance (MR%) of the magnetic tunnel junction (MTJ) material has made it useful for magnetoresistive random access memory as well as magnetic field sensing applications. One of the most important aspects for producing the MTJ material is the method used for forming the tunnel barrier, and its impact on the properties of MTJ such as resistance and area product (RA), MR%, and RA uniformity across a large area. We have explored forming the aluminum oxide tunnel barrier with air; reactive sputtering; plasma oxidation with plasma source; plasma oxidation with power introduced from the target side; and plasma oxidation with power introduced from the substrate side. Our results show that all techniques can be made to work. Plasma oxidation is favored due to its simplicity and manufacturing compatibility. It was also discovered that different oxidation methods used in this study caused little difference in MTJ resistance uniformity. The latter is mainly determined by the Al metal-thickness uniformity. Modeling based on Simmons’ theory supports our experimental finding. This illustrates the importance in improving Al metal-film uniformity for producing MTJ with ultra-uniform resistance.
Synthetic antiferromagnet (SAF) structures are a key element of TMR and GMR read heads and MRAM devices. Control of the SAF coupling strength and thermal endurance are key issues for these technologies. We find that the coupling strength increases with stronger crystalline texture in polycrystalline NiFe SAFs, and, surprisingly, we observe a strong dependence on seed layer in amorphous CoFeB SAFs. We also have developed an analysis method for evaluating thermal endurance of SAFs and show that failure of the SAF can be modeled as a thermally activated diffusion process. The analysis is used to predict the time to failure at any temperature, thus allowing accelerated failure analysis for SAF-based devices. The stability improves dramatically with increasing Ru spacer thickness. The time to failure for typical NiFe SAFs was found to be 10 years at 120 C.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.