Samsung CEO: Headwinds hinder PRAM

SAN FRANCISCO - At the 2011 International Solid-State Circuits Conference (ISSCC) here, Samsung Electronics Co. Ltd. will describe more details about its 1-Gbit, 58-nm phase-change memory (PRAM) technology.

The South Korean electronics giant is seeking to beat rival Numonyx, now part of Micron Technologies Inc., to the punch in the 1-Gbit PRAM race. UBM TechInsights, part of the same group that publishes EE Times, also recently found a NOR flash memory compatible, 512-Mbit 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 1-Gbit PRAM device. And Samsung has shipped only limited quantities of PRAMs, reportedly the 512-Mbit 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,’’ he told EE Times after a keynote at ISSCC here, but the ''systems guys’’ have been ''very reluctant’’ to adopt the technology in mass quantities.

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.  He urged OEMs to collaborate more with the memory houses in order to get wider adoption for the next-generation memory types.

PCM 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 market using 90-nm and 65-nm process technologies, questions have been asked about the ability to scale the technology beyond flash memory, which is already being made at close to 22-nm.

Phase-change has been on the radar for decades, but vendors are unable to bring it into full production. Numonyx has delayed its 1-Gbit phase-change memory line, which is based on a 45-nm 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 1-Gbit 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 58-nm process, equipped with a low-power double-data-rate nonvolatile memory (LPDDR2-N) interface.

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

''The PRAM that has significantly low programming bandwidth compared to the DRAM-write (which) has a SRAM-based 1KB program buffer with 800Mb/s write throughput,’’ according to the paper.

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

''The output data valid window (for the device) is measured to be 3.4-ns at VDD1 (at) 1.8V, 400Mb/s,’’ according to the paper. ''The tRCD value is measured to be 76ns at 85 degrees C (and) VDD1 is 1.6V.’’