STMicro Develops Memory Beyond Flash

Online staff -- Electronic News, 6/16/2004

Alas, flash memory is not to be forever. STMicroelectronics said it has made significant progress toward the development of Phase-Change Memory (PCM), a new type of memory aimed at eventually supplanting flash memory technology, the company said today.

Flash, along with other types of non-volatile memory, are integral parts of many electronic devices from mobile phones, digital cameras, and set-top boxes to automotive engine controllers because of the ability to store data even when the power is turned off.

PCM is believed to provide better performance than flash and is better suited to continued cost and speed shrinks, ST said.

Although the flash memory market is very large today and is one of the fastest growing sectors in semiconductors, it is widely accepted that it will become increasingly difficult to continue basic flash memory cell size reduction, ST said. These shrinks are essential to electronics equipment manufacturers because it enables electronic memories, and the equipment that relies on them, cheaper, thereby stimulating market growth.

For example, from 1990 to 2000, the size of an individual flash cell was reduced by a factor of 30, but chip manufacturers said they would be able to continue developing new flash products only for another ten years before facing difficult challenges to overcome physical limits.

Therefore, three years ago, ST said it realized PCM technology, developed by California-based Ovonyx Inc., already used in re-writable CDs, could be adapted as a semiconductor memory technology. For that reason, ST licensed the technology, also known as Ovonic Unified Memory, and the two companies set up a joint-development team, largely based in Agrate Brianza, near Milan, Italy, where ST’s worldwide non-volatile memory development is located.

PCM benefits hinge the ability of certain "chalcogenide" materials can be switched between two stable states -- one amorphous with a high electrical resistance, the other crystalline with a low resistance -- by appropriately heating the material, ST said. A chalcogen is any material that contains sulphur, selenium or tellurium, all of which have closely related chemical properties. A memory cell in PCM technology consists of a variable resistance formed by the tellurium material and its tiny electrical heater, along with a selection transistor used for the read/write operations.

ST detailed its progress toward commercializing PCM technology in two papers presented during the VLSI Technology and Circuits Symposia in Honolulu, Hawaii, this week. In one paper, ST showed a cell structure that can be integrated into the mainstream chip manufacturing process, which gives good indications of its manufacturability and cost. In another paper, ST described practical implementation of PCM technology in the form of an 8Mbit demonstrator chip, designed to determine feasibility of cost-effective large non-volatile memories.

ST predicts PCM technology would be used in medium-density, stand-alone memories and embedded applications based on the results it has obtained. Further the company believes PCM will become a mainstream non-volatile memory technology because of its ability to be scaled.