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Samsung chief discusses what's limiting PRAM adoption

Posted: 25 Feb 2011 ?? ?Print Version ?Bookmark and Share

Keywords:PRAM? memory? LPDDR2-N?

Samsung Electronics Co. Ltd is scheduled to explain in detail its 1Gb 58nm phase-change memory (PRAM) technology at the 2011 International Solid-State Circuits Conference (ISSCC).

The South Korean electronics giant is seeking to beat rival Numonyx, now part of Micron Technologies Inc., to the punch in the 1Gb PRAM race. UBM TechInsights, part of the same group that publishes EE Times, also recently found a NOR flash memory-compatible, 512Mb PRAM from Samsung in a mobile handset.

But despite the hype for PRAM technology, shipments have been disappointing at best. Numonyx is late with their 1Gb PRAM device. And Samsung has shipped only limited quantities of PRAMs, reportedly the 512Mb device.

"We are shipping a little bit of PRAM in the market," said Oh-Hyun Kwon, president of Samsung's semiconductor business.

"Phase-change has some very nice features," Kwon told EE Times after a keynote at ISSCC. However, "systems guys" have been "very reluctant" to adopt the technology in mass quantities, he added.

During a keynote, the Samsung executive indicated that there has been an overall reluctance by the systems houses to adopt the various next-generation memory technologies, such as PRAM, MRAM and ReRAM.

The problem is that the next-generation memory types "are not compatible with today's technology," he said during the keynote. Kwon urged OEMs to collaborate more with the memory houses in order to get wider adoption for the next-generation memory types.

Phase-change memory itself is based on changing the material phase and the electrical resistance of a chalcogenide layer in each memory cell through the use of electrical heating. It is an attractive technology because of its non-volatility, theoretical high density and bit-alterability, and has been touted as a possible replacement for both flash memory and DRAM.

But the technology has proved difficult to commercialize and even as devices have made it to the market using 90nm and 65nm process technologies, questions have been asked about the ability to scale the technology beyond flash memory, which is already being made at close to 22nm.

Phase-change memory has been on the radar for decades, but vendors are unable to bring it into full production. Numonyx has delayed its 1Gb phase-change memory line, which is based on a 45nm process. It was supposed to ship by the end of 2010. Now, it's unclear when the device will ship.

Amid the delays, Samsung is jumping into the 1Gb PRAM race, although it's unclear when the chip giant will ship that device. In a paper, Samsung said its PRAM technology is implemented in a 58nm process, equipped with a low-power DDR nonvolatile memory (LPDDR2-N) interface.

The device consists of a 1Gb diode-switch cell array with 16 partitions. It also includes several blocks: an embedded controller, command-address input, data channel, row address buffer, decoders, PRAM core, program buffer with 1KB of SRAM, a row data buffer (256b sized row or 32B) and a data comparison write with an inversion flag scheme.

"The PRAM that has significantly low programming bandwidth compared to the DRAM-write (which) has a SRAM-based 1KB program buffer with 800Mbit/s write throughput," as stated in the paper.

"If the proposed DCWI enables, the program and overwrite bandwidth are measured by 6.4MBit/s and 2.3MBit/s, respectively," according to the paper.

"The output data valid window (for the device) is measured to be 3.4ns at VDD1 (at) 1.8V, 400Mbit/s," the paper states. "The tRCD value is measured to be 76ns at 85? C (and) VDD1 is 1.6V."

- Mark LaPedus
??EE Times

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