Flash in the Can? More Powerful Next-Gen Memory Chips Wait in the Wings

Processor chips are the brains of today’s consumer digital devices, but memory is actually at their heart, with flash memory being the favored approach for cards that plug into mobile phones, cameras and PCs. Whereas hard drives store large amounts of long-term data, RAM—also called “solid state” memory—retains information outside the hard drive, where it can be accessed quickly and repeatedly. Flash memory, the cheapest RAM variety at only about $1.50 per gigabyte (after that is dynamic RAM, or DRAM, more than a dozen times more expensive), does not require much power and can retain data after a device is powered down, key to gadget-makers ability to turn out smaller, more powerful devices.

But flash has its limitations and will someday reach a scaling barrier that would leave subsequent generations of digital cameras and cell phones unable to store significantly more information or operate orders of magnitude faster than their predecessors—at least not without costing a lot more. “What it comes down to is that we’ve gotten spoiled with our gadgets,” says Stan Williams, Hewlett–Packard senior fellow and founding director of HP’s Information and Quantum Systems Lab. “We’ve come to expect exponentially faster devices, but technologies like flash are getting toward the end of their ability to scale.”

Flash is also less durable than static RAM (SRAM) or DRAM, wearing out and becoming less reliable over time. SRAM, which costs about $450 per gigabyte, is often used for cache memory in microprocessors and can rapidly read and write data.

For these reasons HP, IBM and others are grooming new technologies to be the replacement for flash as soon as these limitations catch up to the demands of manufacturers and consumers.

A smarter type of memory
A recently announced alliance between HP and Hynix Semiconductor aims to fill the imminent gap with a denser and more energy-efficient technology called resistive random access memory (RRAM) that could roll off the assembly line in the next few years.

RRAM technology (sometimes called ReRAM) is in a relatively early stage of development but has managed to garner attention from HP, Sharp, Samsung and several other companies that have received RRAM-related patents in the past decade.

The key component of HP’s RRAM, so named because data flows with the help of changes in electrical resistance, is a switch called a memristor (or memory resistor). In addition to holding nonvolatile memory (it can retain information even when off), HP says a memristor can also perform computations, a feature that other types of RAM do not have. This versatility gives the company hope that it will someday be able to replace memory and central processing units (CPUs) with a single chip that performs both functions.

Although scientists have known about memristor dynamics for about 40 years, only recently have they been able to design the technology into integrated circuits, Williams says. RRAM involves a subtle motion of atoms, changing the film of a resistor by a matter of nanometers. “People have been talking about this for 40 years but weren’t able to fully understand or control the process,” Williams says.

Whereas a one-bit flash memory can be switched on and off hundreds of thousands of times (a switch might involve taking or deleting a picture on a digital camera), a memristor has a much longer lifespan than flash, Williams says. On the memory sticks and digital cameras where flash has flourished, switching is not done in the same volume as in other types of memory, so flash can get away with its lower level of endurance, he says.

In April, HP Labs announced its discovery that a memristor could also perform logic, enabling computation to one day be performed in chips where data is stored, rather than on a specialized CPU. HP researchers also say they have designed an architecture where multiple layers of memristor memory can be stacked on top of one another in a single chip to increase storage capacity without taking up much more space.

Although much of RRAM and memristor’s future is speculative, HP has no shortage of plans for the technology. The company’s goal is to develop and commercialize a RRAM chip in roughly three years that is faster and more durable than flash yet uses less power and features twice the number of bits for storage, Williams says. “We would redesign products around memristor technology,” he adds. HP’s long-term play is for RRAM to compete with flash, DRAM and even hard disks.

Competing with DRAM, however, requires much greater endurance. A DRAM used by a supercomputer doing climate modeling might read or erase data one quintillion (one million trillion) times over the course of three or four years, Williams says. “That’s daunting, but that’s what we’re going to have to do to compete head-to-head with DRAM,” he adds.

For all of their excitement over memristors HP still faces a number of challenges in bringing its RRAM to market. For one, “HP’s memristor is made using a titanium oxide, which is not common to put on semiconductors and appears to be difficult to manage today,” says Jim Handy, an analyst with the semiconductor market research firm Objective Analysis in Los Gatos, Calif. HP disputes this characterization of titanium oxide, saying there are established protocols for applying it to semiconductor material and that titanium oxide is compatible with current complementary metal-oxide-semiconductor (CMOS) technology used to build integrated circuits.

Source: Scientific American Magazine

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