US-based NVE Corporation has announced that the US Patent and Trademark Office has issued the company a patent for a Magnetic RAM (MRAM) variant. The patent covers “thermally-assisted spin-momentum writing” and concerns spin-momentum of magnetic memory cells.
A recent paper by researchers from both the US Center for Nanoscale Systems (CNS) at Cornell University and NVE, reported that spin momentum produces spin orientation using less current than present methods. Consequently the invention has the potential to significantly reduce MRAM write currents with lithographic feature sizes of less than 100 nm. According to the company, this could enable MRAM cell densities comparable to those of DRAM or Flash. The findings were based on tests of “nanopillar” MRAM structures fabricated by CNS using material from NVE.
MRAM uses electron spins to encode data. Some pundits claim it is the “Holy Grail” of memory because it has the potential to combine the speed of SRAM, the density of DRAM, and the non-volatility of Flash.
• Chalcogenides and MRAMs have been suggested as the next step in a debate over what technology will come after floating gate.
Memories based on chalcogenides are variously called PCRAM (phase change RAM), PRAM (phase transition RAM) and ovonics unified memory. (Also see this issue page 34.)
Samsung has called its chalcogenide memory PRAM. It has a density of 64 Mbit, the highest yet recorded.
Widely seen as the leading contender to replace floating gate, MRAM has also received a boost with reports of a 4-Mbit device from Motorola - the highest density yet recorded for the technology.
It uses the same polarity and sequence of write current pulses to toggle the state of the bit cell, regardless of the initial state of the cell.
However, floating gate can still see off its challengers. Samsung has also reported a 4-Gbit NAND Flash memory made on a 90-nm process that has a chip size of 127.3 mm2.