ARM is paying attention to this because of the potential to be highly disruptive in the logic space and therefore at the platform (hardware-software) level, Yeric said. "There's resistive RAMs of various types and magnetic RAM and TSMC has recently made an embedded ReRAM so there's a lot going on. ARM has its own DARPA-funded research into correlated electron RAM (CeRAM, see Applied, ARM to develop CeRAM for neuromorphic applications)."
Yeric explained that at 28nm flash memory cannot really scale any more – hence the move to 3D stacking for stand-alone flash memories. "Flash is power hungry and very slow."
To try and exploit this opportunity several memory technologies have been research and developed over decades, many trying to be the "universal" memory that could replace everything including basic SRAM cells inside logic, but without success so far, said Yeric. There have been numerous partial successes in terms of one performance metric or another. The result has been multiple technologies each targeting different niches and a certain fragmentation and lack of commercial traction, but plenty of grist for the semiconductor research mill, Yeric explained.
So many memories
"Generally ReRAMs don't have the endurance. MRAM does have the endurance but the on/off ratio is very low," said Yeric. This means that engineers have had to choose their application targets with care, whether these are solid-state drives – in competition with 3D-NAND flash – or as embedded memory next to microcontrollers, where phase-change memory, ReRAM and MRAM are all contenders.
"There's a lot of hope that a follow-on version of MRAM could replace SRAM for cache requirements. The IMEC research institute has a project to replace six-transistor SRAM with one-transistor MRAM," said Yeric. "For microcontroller on-chip memory applications MRAM is the leader," he agreed.
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