

Frustrated with how long it takes for your computer to boot up? That could change, say researchers who have made a breakthrough that could take the PC industry closer to truly instant-on capability for computer systems.

Scientists have found a way to add ferroelectric capability to silicon, which pushes the idea of building a completely ferroelectric transistor closer to reality.

"If ferroelectric transistors are ever realized, they can be turned off and back on instantly – no reboot, no 30-second wait, no nothing," says Darrell Schlom, lead researcher on the project and professor of material sciences at Cornell University. "For the user the computer would be ready to be used again immediately when power is applied."

Ferroelectric materials provide low-power, high-efficiency electronic memory and are already used in smart cards for subways and ATMs, among other things. Integrating ferroelectrics with silicon-based circuits like those in modern electronics would enable instant-on capability, and it could also provide higher speed and lower power consumption overall, making the ferroelectric circuits an attractive alternative to flash and other memory technologies. But integrating the two materials in a transistor has eluded researchers for more than half a century.

For the project researchers from three universities – Cornell, Penn State and Northwestern University – took strontium titanate, a normally non-ferroelectric variant of the ferroelectric material used in smart cards. They deposited it on silicon in such a way that the silicon squeezed it into a ferroelectric state.

So far approaches to instant-on computing have been software-driven, with companies such as Microsoft promising to create better operating systems that would cut down boot up time from a few minutes to 30-45 seconds. Phoenix Technologies has also attacked the problem with a super-lightweight operating system called Hyperspace designed for quick and easy access to e-mail, calendar, and other basic functions without having to boot into a fullblown OS like Windows; Hyperspace has recently shown up in some netbooks.

But materials science researchers have been pursuing an alternative track for decades.

In 1995, Bell Lab researchers first realized the benefits of a ferroelectric transistor. They used glue to attach various ferroelectric materials to semiconductors, says Schlom, but the result was not what they had expected because of the intervening layer of glue.

Since then attempts to get truly nonvolatile ferroelectric transitor technology haven't succeeded. Most have resulted in ferroelectric transistors that have data retention time, also known as operational lifetime for a memory card, of few hours to a few days. That means they could hold data in memory for a few days (or less) without being powered. It's an improvement over volatile RAM, but significantly short of the storage industry's ten-year retention requirement for a non-volatile memory device like a flash memory card.

But that's changed, says Schlom. "In subsequent work, the glue has been replaced by thinner intermediate layers, but ours is the first with no intermediate layer between a ferroelectric and silicon," says Schlom. "Our ferroelectric is made directly on silicon."

Schlom says the research team is still a ways off from its goal of creating a complete ferroelectric transistor. And he won't take a shot at speculating just when these transistors could become a reality. "We have just gotten rid of all of the intermediate layers," he says. "There could still be trouble with electronic traps at the interface, electrical leakage through the ferroelectric since it is quite thin and manufacturability."

But the latest breakthrough is an important step on the road to a new kind of silicon transistor, says Schlom.

*Photo: Structure of the Strontium Titanate-Silicion Interface (Jeremy Levy/ University of Pittsburgh)

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