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Next-gen memory race heats up as bets roll

Posted: 08 Feb 2008 ?? ?Print Version ?Bookmark and Share

Keywords:flash memory? phase-change memory? DRAM? FRAM?

As the next-generation memory race intensifies with more vendors jumping out of the starting blocks, the question remains if these devices will ever become mainstream parts.

At the International Solid-State Circuits Conference (ISSCC), Intel Corp. and STMicroelectronics Inc. announced that they have begun shipping prototype samples of their previously-announced phase-change memory (PCM) line. The 90nm, 128Mbit product is slightly late to the market; the companies were supposed to ship the device late last year.

Meanwhile, Freescale Semiconductor Inc., NEC Electronics Corp. and others have recently rolled out rival MRAM devices. Texas Instruments Inc. and others also claim to be shipping another competitive technology called FRAM.

Others are pushing the limits of current technology. SanDisk Corp. announced that it expects to start mass production of the world's first commercial three-bit-per-cell NAND flash memory in March or April. The technology was co-developed by its memory partner, Toshiba Corp.

SanDisk also announced the introduction of a standard multilevel cell (MLC) NAND flash memory, using 43nm process technology. The technology was also co-developed with Toshiba. Separately, Toshiba rolled out what it claimed to be the fastest embedded DRAM.

DRAM, flash replacements
Next-generation memories!such as FRAM, MRAM, PCM and others!are supposed to replace today's DRAMs and flash memory technologies. Current memory devices are expected to hit the wall, as the floating-gate reaches its physical limits.

Today's flash memories are expected to scale at least to the 22nm node, said Giulio Casagrande, director of advanced R&D in the memory products group at ST. DRAM scaling could end "even sooner," he told EE Times.

But after years of R&D, next-generation memories are still struggling to get off the starting blocks, due to manufacturing problems, cost and a lack of applications.

Some have been working on the technology for years!if not decades. Intel has been doing R&D on ovonic unified memory (OUM)!or PCM !with Ovonyx since 2000. At that time, Intel took a stake in that company. ST entered development with Ovonyx in 2001.

Intel and ST have finally shipped the product, after introducing the device last year. That device, codenamed "Alverstone," is the first PCM product from the companies.

Unofficially, the 90nm, 128Mbit part is being billed as a NOR flash-compatible replacement. Cliff Smith, technical industry manager at Intel, said that the part provides fast read and write speeds at lower power than conventional flash, and allows for bit alterability normally seen in RAM.

The non-volatile memory technology is based on the electrically induced phase change of chalcogenide materials, which have been difficult to manufacture reliably in volumes. Phase-change materials have both crystalline and noncrystalline states that can represent "0" or "1," and it's possible to toggle between them by applying a small reset current.

"Alverstone" and future products will become a key part of Numonyx, a new independent semiconductor company created through an agreement among ST, Intel and Francisco Partners. Signed in May 2007, the venture is expected to close in Q1.

Rival technologies
Others are pushing competitive technologies. For example, Japan's NEC recently claimed that it has developed the world's fastest MRAM. NEC's new "SRAM-compatible, MRAM" can operate at 250MHz. The MRAM has a memory capacity of 1Mbit. Incorporating a memory cell with two transistors, one magnetic tunnel junction and a newly developed circuit scheme, the design achieves an operation speed of 250MHz.

The MRAM is still in the development stages, and eventually, it will be targeted for select markets, said Masao Fukuma, senior VP of NEC. "Embedded memory is our first target."

Others are extending current technology, which is expected to remain in the mainstream for several years. At ISSCC, SanDisk rolled out its three-bit-per-cell NAND flash memory technology, which was co-developed with Toshiba.

The first so-called x3 product, a 16Gbit device, is based on 56nm technology. x3 enables higher manufacturing efficiency and lower die cost for the same capital investment, according to SanDisk.

SanDisk and Toshiba also presented a joint paper on 43nm 16Gbit NAND flash memory. The 43nm technology provides twice the density per chip, as compared to 56nm process technology, thus lowering the die-cost. During Q2 2008, SanDisk intends to begin shipping products. Shipments will start with 16Gbit devices, followed by 32Gbit parts in the 2H 08.

Embedded DRAM
Not to be outdone at the ISSCC, Toshiba claimed that it has "realized" the world's fastest circuit technology for embedded DRAM for system LSIs.

Achieving a speed of 833MHz at 32Mbit, the technology will be applied to graphic processing LSIs.

Toshiba applied a "pseudo two port system," a technology that divides the overall memory into two and then reads and writes data in parallel and alternately. By replacing conventional serial read and write system with the new parallel technology, and optimizing such circuits as the command structure, Toshiba said it achieved the world's highest level of embedded DRAM performance at 32Mbit densities.

Toshiba plans to apply this technology to its leading edge 65nm system LSI process.

- Mark LaPedus
EE Times

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