‘Truly remarkable’, the Greek philosopher Thales of Miletus must have thought when observing the strange attraction between loadstone and iron. Who could have ever imagined more than 2500 years ago that magnetic interactions would be indispensable in many of our modern day technologies?
Indeed, I’m talking about levitating trains, the use of magnetic nanoparticles for cancer treatment, speed and angular sensors in the automotive industry and last but not least: the development of MRAM devices for data storage.
Magnetoresistive Random Access Memory (or in short: MRAM) cells are booming business in the ever innovating world of the semiconductor industry. Companies such as Samsung and Intel are already incorporating this piece of new technology into their chips. The basis of MRAM devices are spin valves (figure) which essentially exist of 2 thin magnetic layers, separated by a nonmagnetic material. As for special magnetic alloys e.g. CoFe, the magnetization of these layers (represented by the arrows in the bottom figure) can only be aligned parallel or antiparallel, one can associate a ‘0 state’ or a ‘1 state’ with these configurations respectively. A spin valve can thus be considered as digital bit and so be used as a way to store digital information. By applying a magnetic field or a current on the spin valve, one can change its digital state (0 to 1 state or vice versa) and by probing the electrical resistance of the spin valve, one can read the digital state of the bit. So in short: we can read, write and store a bit in a spin valve, i.e. a memory cell is born!
By combining a huge number of spin valves, one can create an MRAM device, which has many advantages compared to present day methods for data storage. MRAM cells are nonvolatile (retention without power up to 10 years), are faster, have less power consumption and a good scalability. Since 2008, the company Everspin has already sold more than 60 million MRAM chips and in 2016 IBM reported to have made an 11 nanometer-sized MRAM chip with a switching rate of 10 nanoseconds. On top of that, Everspin has recently announced the world’s first pre-production of 1 Gb MRAM customer samples. The commercialization of MRAM chips is expected to explode in the next few years. Who knows MRAM chips might just be able to save Moore’s law?
Top figure: Typical MRAM architecture. An MRAM device is composed of many spin valves (green/white stacks), each representing a digital bit.
Bottom figure: Schematic representation of a spin valve. The 2 ferromagnetic layers (blue) are separated by a nonmagnetic material (green). The magnetization (arrows) of the 2 layers can be parallel (0 state) or antiparallel (1 state).
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