Author:

Abstract:

As the demand for faster, smaller and more power-efficient devices is increasing, conventional memories such as DRAM and SRAM are reaching their scaling limits. New emerging memories are being developed and the spin-transfer torque magnetic random access memory (STT-MRAM) is considered as one of the most promising replacements. STT-MRAM includes a magnetic tunnel junction (MTJ) that junction is composed of two ferromagnetic electrodes separated by an insulator tunnel barrier. The information in these devices is stored in the relative orientation of the ferromagnetic layers. The underlying physical phenomenon is magneto-resistance, i.e., the strong dependence of tunnel magneto-resistance (TMR) on the relative magnetization orientation of the ferromagnetic layers. It is key to develop an MTJ which requires low switching current and maintain adequate data retention. Data retention over 10 years requires large perpendicular magnetic anisotropy (PMA) energy, especially when the volume shrinks. For the sub-15 nm technology nodes, it is believed that the interfacial anisotropy originating from typical MgO/CoFeB interface is insufficient to deliver the high PMA. Introduction of alternative high PMA free layer materials and advanced free layer stacks are envisaged. On the other hand, the high PMA free layers systems will likely also require high switching currents. Thus, materials with tunable PMA in order to optimize for thermal stability and the switching current are therefore a must. To enable high thermal stability in MRAM based devices for the sub 15 nm technology node, deeper fundamental understanding is sought for in the following areas: 1. growth of ultra-thin high PMA materials with tunable anisotropy 2. study of their magnetic and structural properties in the ultra-thin film regime (sub-10 nm) 3. integration of the high PMA material in the MgO-based perpendicular MTJ technology 4. micromagnetic simulation or macrospin model is also used for the study of switching behavior of the high PMA materials as free layer.