[NanoIC topic] Investigation of magnetic material properties for enhanced SOT-MRAM performance

With the increasing demand for data storage, the present charge-based memory technologies are reaching their fundamental limits due to their poor reliability and volatile nature. Spintronic devices, leveraging spin's degree of freedom, offers a promising solution thanks to their non-volatility, fast processing, and higher integration capabilities.

Spintronics has already been instrumental in various storage technologies, from hard disk drive read heads to Magnetic Random-Access Memory (MRAM). The heart of MRAM technology lies in the Magnetic Tunnel Junction (MTJ), comprising an oxide tunnel barrier between two ferromagnetic layers.

While Spin-Transfer Torque (STT)-MRAM has matured, its write operation by injecting current through the junction to switch the free-layer magnetization, faces intrinsic trade-offs between switching speed and endurance due to shared read/write current paths.

To overcome these limitations, Spin-Orbit Torque (SOT)-MRAM employs separated write and read paths, enabling faster operation and improved endurance, making it a promising next-generation memory technology. SOT-MRAM operates by converting charge current into spin current in a heavy metal layer adjacent to the MTJ, allowing efficient switching of the storage magnetic layer.

SOT-MRAM devices with perpendicular magnetic anisotropy, crucial for scalability potential, require an external in-plane magnetic field for deterministic switching, limiting practical applications. Although field-free approaches using stray fields or structural symmetry breaking have been explored, achieving reliable and robust field-free switching remains a key challenge for SOT-MRAM technology.

Recently, field-free SOT switching has been demonstrated by adding an extra spin source by placing an in-plane magnetic layer beneath a non-magnetic metal. These bi-layers materials generate an unconventional spin current to enable the switching without an external magnetic field. In this concept, the in-plane magnet is critical for field-free switching of the MTJ. However, recent results from imec showed that weak magnetization can destabilize the in-plane magnet, thereby limiting the reliability of field-free switching. Therefore, improving magnetic properties of in-plane magnetic plays an important role in advancing this device concept.

The internship project aims to systematically investigate the magnetic properties of the in-plane ferromagnet, like saturation magnetization and canting by varying the material and substrate.The study will leverage advanced magnetic characterization techniques, including vibrating-sample magnetometry (VSM) and ferromagnetic resonance (FMR) technique to correlate processing conditions with magnetic performance.

Additionally, microscale hallbar structures can be fabricated in imec cleanroom for preliminary understanding of patterning effect, i.e. shape anisotropy, offering guidance for nanoscale structures. Furthermore, structural analysis like TEM and EDS can be applied to understand the interdiffusion of the in-plane magnet and the adjacent layers. The outcomes of this research will provide practical guidelines for materials engineering, paving the way for improved reliability and performance of next-generation SOT-MRAM technology.