Chip makers look beyond DRAM

Chip makers look beyond DRAM

Intel and ST Microelectronics are collaborating on developing a new type of memory that could eventually replace both flash and dynamic random access memory.

The two chipmakers will present a jointly authored paper on phase change memory (PCM), also known as PRAM and Ovonic Unified Memory, at the VLSI Technology Symposium in Honolulu, Hawaii, later this month, according to a report in EE Times, an industry journal for electronics engineers.

The two companies are collaborating in some other areas, such as NOR flash memory, and have been researching PCM separately. ST has developed a 128 Mbit PCM prototype using a 90-nanometre (nm) process and is looking into production of multi-gigabit PCM using a 45nm or 32nm process, according to EE Times.

In the paper, the two will outline what they call promising results using a 90nm process, a chalcogenide material storage element and a vertical PNP bipolar junction transistor as a selection device, according to the report. The companies obtained small cell area, good electrical results and high reliability, according to the companies' paper.

PCM is a type of nonvolatile memory, meaning it retains data even when power is removed, unlike DRAM. It relies on the behavior of chalcogenide glass, which can be structurally altered by the heat generated by a controlled input of electricity.

This heat can leave the chalcogenide in either a crystalline or amorphous state, each of which has a distinct electrical resistance. The two states can thus represent binary digits, with the amorphous, high-resistance state representing 1 and the crystalline state 0.

Chalcogenide is also used in rewritable optical media, where its optical, rather than electrical properties, are manipulated.

Stanford Ovshinsky first began researching the properties of chalcogenide glass at Energy Conversion Devices in the 1960s, and the research of Intel, ST and others is still carried out under license from ECD subsidiary Ovonyx.

So far commercialisation has been held back by issues with material quality and power consumption. Companies are now showing more interest in PCM because it could be more suitable for shrinking chip lithography techniques than flash and DRAM memory.

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