LONDON – Samsung Electronics Co. Ltd. is set to re-ignite debate about whether phase-change memory is commercially viable with the presentation of an 8-Gbit, 20-nm device at the 2012 International Solid-State Circuits Conference.
The development was not unexpected as Samsung engineers are due to present a 20-nm phase-change random access memory cell at the International Electron Devices Meeting coming up in Washington DC on Dec. 5 to 7, 2011.
Nonetheless a 20-nm, 8-Gbit phase-change random access memory is a large jump forward from the previous state of the art. In February at ISSCC 2011 Samsung engineers presented a 1-Gbit phase-change memory implemented in a 58-nm manufacturing process technology equipped with a low-power double-data-rate nonvolatile memory (LPDDR2-N) interface.
Samsung – and Micron Technologies Inc. through its acquisition of Numonyx NV – are the only two companies that have got close to offering non-volatile phase change memory for commercial use, despite years of research and development. And even so there are almost no reports of phase-change memories in the field.
Samsung is now set to present a large device in a 20-nm process technology operating at 1.8-V and with a 40-Mbyte/s programming bandwidth. This puts phase-change memory at close to the same geometry and memory cell density as NAND flash.
The ability within NAND flash to store and detect multiple bits per cell still gives flash a memory capacity advantage over PCM. Flash memory is also expected to go to a form that could stack multiple memory cells vertically, providing further memory capacity scaling.
Phase-change memory works by detecting the change in resistance of a chalcogenide alloy as it moves between amorphous and crystalline states under the action of resistive heating. It has long been hoped that the technology could combine the scaling advantages of a cross-point memory with the non-volatility of flash memory while offering superior endurance and bit addressability.
However, PCM has hit a number of barriers to deployment, not least the ability to get ahead of the fast scaling of NAND flash memory. Technical challenges to PCM continue to exist over the ability of the heating effect to scale both within the memory cell and due to thermal cross-talk effects on neighboring cells. There are also concerns on whether this sensitivity to temperature could prevent pre-programmed phase-change memories being taken through printed circuit board production processes such as solder baths.
The rules of ISSCC always were that papers could only be accepted if researchers had made real devices and taken physical measurements – in other words no simulation papers or ones based on design data. However, it was not necessary that devices worked fully or as intended.
Related links and articles:
ISSCC 2012 advanced program
IEDM: PCM research moves to 20-nm
IEDM: Hynix takes NAND flash to 15-nm
IBM reports drift-tolerant multilevel cell PCM
China develops phase-change RAM
Samsung CEO: Headwinds hinder PRAM
NAND, PCM vie for attention at ISSCC 2011