Perpendicular magnetic materials with lower damping constant in magnetic tunnel junction devices (ref. P1312-08) Topic description 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. This non-volatile memory is considered as next generation of consumer mass-scale application of spintronics, following the widespread read head technology that hard drives use nowadays. It could open the way to a new era in which nano-spintronics complements or even replaces nano-electronics. Spintronics is a rapidly growing field of solid-state electronics that aims to take advantage of the spin of electrons, in addition to their electric charge, as a way of implementing new electronic functions. STT-MRAM includes a magnetic tunnel junctions (MTJ) stack; the stack 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 magnetoresistance, i.e., the strong dependence of the electrical resistance on the relative magnetization orientation of the ferromagnetic layers. Switching of the state of one of the layers can be done by transferring the spin torque when applying a current through a magnetized layer. However, each magnetic layer has a Gilbert damping constant (α) which forces the magnetization to be stable at one direction. A high α will increase the current that is needed to switch the magnetization, and consequently the energy that is needed to perform a write operation. Therefore, controlling α is a crucial importance for future power-efficient STT-MRAM devices. To develop STT-MRAM devices imec uses a dedicated 300-mm wafer platform which allows exploring the full technological potential of MRAM towards 10 nm technology nodes. In this context, advanced magnetic materials and devices must be developed and the complex interplay between spin transport, magnetization dynamics, material properties, and the necessarily complex geometry associated with advanced spintronic devices needs to be studied. This will be tackled in this PhD by following activities: • Build up a ferromagnetic resonance set up (FMR) in order to measure the α for each magnetic layer, down to 1 nm magnetic layer thickness. • Develop a novel perpendicular MTJ stack with high thermal stability (∆ = 70, MTR = 150 %, RA=1 Ohm.um2). • Investigate the physical, magnetic and electrical properties of these novel materials and MTJ stacks, doing different characterization methods, such as x-ray diffraction (XRD) for stack crystallinity, vibrating sample magnetometer (VSM) and Magneto-optic kerr effect (MOKE) for magnetic measurements, and CIPT for magnetoresistance signal measurements. • Advanced characterization of STT-RAM cells, including high-frequency magneto-electrical methods, such as high-frequency switching, analysis of spin-wave related noise in confined geometries and ferromagnetic resonance. Required background: physics, electrical engineering, material engineering or equivalent. Solid understanding of magnetic materials and magnetism. Type of work: 10% literature, 70% design and experiments, 20% data analysis Daily advisors: Taiebeh Tahmasebi and Johan Swerts
Posted on: Sun, 27 Oct 2013 12:17:46 +0000
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