A year ago Amigo Tsutsui, a senior researcher with Sony Semiconductor Solutions Corp. provided some details of a cross-point resistive RAM (ReRAM) that he indicated could appear in 2020 as a second-source or alternative component source to the phase-change memory (PCM) based Optane memory used for solid-state disks (SSDs) by Intel.
Tsutsui spoke at the Persistent Memory Summit organized by Storage Network Industry Association on January 24, 2019, and indicated that the ReRAM technology was a continuation of work disclosed at VLSI Technology Symposium in 2017, which itself could be traced back to an IEDM presentation in 2007.
Tsutsui said Sony Semiconductor is developing a cross-point ReRAM capable of high speed reads and writes and based on the electrically stimulated formation and destruction of copper filament between electrodes. He also said that components could appear in 2020 at 64Gbit or 128Gbit memory capacity while adding that an appropriate memory controller would be important to achieve the performance possibility of the native memory.
These would seem likely to be multi-chip modules composed of 16Gbit ICs.
The component would be aimed at storage-class memories, non-volatile memories that are higher speed than NAND flash memory and have the advantage of non-volatility over DRAM.
Next: Entering the business
However, Sony Semiconductor is not in the memory business and so would likely have to create a new division and it remains unclear as to whether Sony would wish to manufacture the memory in its own fabs, which are mainly given over to the production of CMOS image sensors, in which it is the world leader.
The copper ion migration and filamentary mode of operation gives Sony’s ReRAM some similarities to the conductive-bridging RAM of Adesto Technologies Inc. (Santa Clara, Calif.) and to the filamentary resistive RAM of Crossbar Inc. (Santa Clara, Calif.). However, very early in their research Crossbar replaced copper with silver as the conductive element.
However, one thing that makes Sony’s filamentary ReRAM unique is that it apparently includes chalcogenide and rare-earth materials. According to a slide shown by Tsutsui the filament is formed by migration of ions from a layer of conducting copper telluride into a layer of gadolinium.
I-V characteristic for set and reset of Sony filamentary reset. Source: SNIA and Sony Semiconductor Solutions Corp.
For the selector switch to enable array addressing Sony selected the phase-change chalcogenide switch known as the Ovonic Threshold Switch (OTS), named after US researcher Stanford Ovshinsky. Sony’s contribution is an OTS doped with boron and carbon that Sony states meets requirements for large cross point arrays with low leakage current, low threshold voltage variability, and high endurance.
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