Spintronic RAM Gets a Little Closer to SRAM

Sometimes it seems as though everything old is new again. The earliest computers used magnetic memory such as magnetic core. As practical as that was compared to making for example each bit of memory be a vacuum tube or relay flip flop, newer technology such as SRAM and DRAM displaced core and similar technologies. However, some of the newest technologies once again use magnetic fields. FRAM or ferroelectric RAM and magnetoresistive or MRAM both use magnetic fields to store data. Now Japanese researchers think they are on track to make MRAM more competitive with traditional RAM chips.

The Tokyo Institute of Technology researchers use new material combinations to make chips that store data based on the spin of electrons — the underlying reason for the way magnets behave. Their recent paper discusses USMR or Unidirectional spin Hall magnetoresistance and using this effect could greatly simplify the construction of MRAM cells.

How much simpler? Conventional MRAM requires up to 30 fabrication layers. The new technology requires only two.

There are two different exotic materials and the magic happens at their interface, at which electrons with the same spin accumulate. By injecting them into the ferromagnetic layer, that layer flips its magnetic field. This works as a write operation and also changes the resistance of the structure due to USMR. An external circuit can measure this resistance change, but it is very small, especially in conventional MRAM cells — less than a 1% change.

The new materials break the 1% barrier. This makes them much simpler to read and combined with the easier fabrication should result in cheaper and denser MRAM devices.

There have been many memory technologies used over the years to store data. Among them were the really odd devices like the Radechon.

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