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Chip-level advances that may change computing

Imagine a world with electronic devices that can power themselves, music players that hold a lifetime of songs, self-healing batteries, and chips that can change abilities on the fly. Based on what's going on in America's research laboratories, these things are not only possible, but likely.

"The next five years will be a very exciting time for electronics," says David Seiler, chief of the semiconductor electronics division at the Department of Commerce's National Institute of Standards and Technology (NIST) in Gaithersburg, Md. "There will be lots of things that today seem like far-out fantasy but will start to be commonplace."

In this two-part series, we'll take you on a tour of what could be the future of electronics. Some of these ideas may sound fantastic, others simply a long-overdue dose of common sense, but the common thread is that they have all been demonstrated in the lab and have the potential to become commercially available products in the next five years or so.

Today's story focuses on chip-level advances, from processors that transmit data via lasers instead of wires to circuits made with new materials that leave conventional silicon ones in the dust. These technologies could be the building blocks for a plethora of new and innovative products, some of which we can't even conceive of today.

Chips without wires: The laser connection

An up-close look at any microprocessor reveals millions of tiny wires going every which way to connect its active elements. Go below the surface, and there can be more than five times as many wires. Jurgen Michel, a researcher at MIT's Microphotonics Center in Cambridge, Mass., wants to replace all those wires with flashing germanium (Ge) lasers that transmit data via infrared light.

"As processors get more cores and components," explains Michel, "the interconnecting wires become clogged with data and are the weak link. We're using photons, rather than electrons, to do it better."

[ Related reading: Shining a light on the chip interconnect bottleneck ]

Capable of moving data at, well, the speed of light, a Ge laser can transmit bits and bytes 100 times faster than electricity moving through wires can, which means the critical connections between the chip's processing cores and its memory, for example, won't hold the rest of the device back. Just as fiber-optic communications made phone calls more efficient a generation ago, using lasers inside chips could put computing into overdrive.

The best part is that MIT's system doesn't require tiny fiber cables buried inside each processor. Instead, the chip is crisscrossed with a series of subterranean tunnels and caverns to transmit the pulses of light; tiny mirrors and sensors relay and interpret the data.

This mixing of traditional silicon electronics with optical components -- a practice known as silicon photonics -- can make computers greener as well. That's because lasers use less power than the wires they replace and give off less heat that needs to be cooled.

"Optoelectronics is a holy grail," says Seiler. "It can broaden electronics and is a great way to cut power use because you don't have all those wires acting like space heaters."

In February 2010, Michel and his collaborators, Lionel Kimerling and Jifeng Liu, successfully created and tested a functioning circuit that incorporates Ge laser data transfers. The chip hit speeds of over a terabit per second, or two orders of magnitude faster than today's best chips with wired connectors can do.

The chip is manufactured using current semiconductor processing techniques with some small additions, so Michel thinks that the transition to laser-based connections can happen over the next five years. If further tests are successful, MIT says it will license the process; this type of chip could become available around 2015.

The need has never been greater. By 2015, it's likely that there will be computer chips with up to 64 independent processing cores, each working simultaneously. "Connecting them with wires is a dead end," Michel says. "Using a germanium laser to connect them has huge potential and a big payoff."

Novel circuits: Memristors

If your MP3 player is filling up with tunes but you feel like a cultural murderer every time you delete a song, memristor technology might be arriving just in time.

The first fundamentally new electronic component to appear since silicon transistors came on the scene in the 1950s, the memristor presents a faster, more durable and potentially much cheaper alternative to flash memory. And with about twice the capacity of flash chips, there's plenty of room for everything from Leonard Bernstein to Lady Gaga.

"If we were redesigning computer technology today, we'd use memristor memory," says R. Stanley Williams, senior researcher and head of the Quantum Science Research (QSR) group at HP Labs in Palo Alto, Calif. "It's the fundamental structure for the future of electronics."

The memristor -- basically a resistor with memory -- was first posited in 1971 by University of California, Berkeley, professor Leon Chua, but HP Labs' memristor prototypes weren't publicly demonstrated until 2008.

To build its memristors, HP uses alternating layers of titanium dioxide and platinum; under an electron microscope they look like a series of long parallel ridges. Below the surface is a similar setup at a right angle, producing a grid-like array.

"Think of it as a series of cubes that are 2 to 3 nanometers (nm) on a side," says Williams. (A nanometer is one-billionth of a meter, roughly one ten-thousandth the thickness of a human hair.)

The key is that any two adjacent wires can be connected with an electrical switch beneath the surface, creating a memory cell. By adjusting the voltage applied to the cubes, scientists can open and close tiny electronic switches, storing data like traditional flash memory chips. (See IEEE Spectrum's excellent 6-Minute Memristor Guide for more details from Williams about how memristors work.)

Called ReRAM, for resistive random access memory, these chips can store roughly twice the data as flash chips but are more than 1,000 times faster than flash memory and could last for millions of rewrite cycles, compared with the 100,000 that flash memory is certified for. The bonus is that ReRAM's read and write speeds are comparable, while flash takes a lot longer to write data than to read it.

HP and South Korea's Hynix have teamed up to mass-produce ReRAM chips that could be used in a variety of small devices, such as media players that can hold terabytes of songs, videos and e-books. They expect to see the first products on the market sometime in 2013.

ReRAM can also replace dynamic RAM in computers. Because it's nonvolatile, ReRAM won't lose its contents when the system is turned off or loses power, as DRAM does. In fact, Williams thinks it could lead to an era of instant-on computing. Even when today's devices are merely put to sleep instead of being fully shut down, it takes anywhere from a few seconds to a minute for them to access stored data upon awakening. But with ReRAM devices, you'd be able to pick up where you left off instantaneously.

What's more, Williams says, it's possible to stack memristor arrays on top of each other within a single chip. This could create 3-D memory elements that better use the space within a chip. Rather than just using the surface of the chip, these memory elements can be built deep down into the chip, creating much more memory in the same physical volume.

"There's no fundamental limit to the number of layers we can produce," adds Williams. "We can get to petabit chips within about 10 years." That's a million gigabits of storage space, or enough to hold more than a year's worth of high-definition video on a chip the size of a fingernail.

"The first application for memristors will likely be memory," says NIST's Seiler, "but there's much more to it than that. There's a lot of potential beyond memory."

Further out on the digital horizon, perhaps 20 years or so, the technology could rewrite basic computer design. In 2010, the HP researchers discovered that memristors can be used for logic computations in addition to storage. That means that both functions could theoretically occur in the same chip.

Says Williams, "A single memristor can replace a handful of other circuits, simplifying how computers are designed, made and operated." For instance, he says, one memristor could do the job of the six transistors that are currently used to create a single static RAM memory cell in a processor's cache.

Williams thinks it might even be possible to create an artificial neural synapse with memristor technology that could mimic the way the brain works. That's decades off in the future, however, if possible at all.

The memristor certainly has the power to rewrite the rules of electronics, says Supratik Guha, director of the physical sciences department at IBM. But, Guha notes, the technology still needs to prove itself. "There may be potential as a memory element," he says. "But like any other technology, you need to crawl before you walk and walk before you run."

In other words, memristor technology won't happen overnight. It will take a lot of evolution and time before memristors are as prevalent as DRAM or flash memory.

Changeable chips: Programmable layers

From the fastest processor to the smallest memory module, just about every chip used in electronics today has one thing in common: Its active elements reside in the top 1% to 2% of the silicon material it's made of.

That will change over the next few years as chip makers go vertical to squeeze in more and more components. Some vendors, such as Intel, have resorted to gluing completed chips together, while University of Rochester researchers have designed and built 3-D circuits layer by layer internally. Both approaches are enormously complicated and expensive, observes IBM's Guha.

But what if you could trick the circuit into rearranging itself on demand so that it only appeared to other components to have several layers of active elements? That's the idea behind Tabula's Spacetime technology and its ABAX chip design.

Rather than having several layers of hardwired components that are permanently etched into silicon and never change, ABAX uses reprogrammable circuits that can change their abilities on demand. Its current products deliver the equivalent of up to eight different chip layers that can be changed faster than the blink of an eye.

"Think of it as like a department store with eight floors," says Steve Tieg, Tabula's president and chief technology officer. "You'd take an elevator to go between floors to shop for different items." But rather than having eight different physical floors, each with its own internal arrangement and assortment of goods, Tabula has figured out a way to have a single layer (or floor) that reconfigures itself as needed.

"It's as if while you're on the elevator, they're inside rearranging the floor to create a different layout with different products," adds Tieg. "It looks to the outside world as if there are eight floors, but there's only one."

Glossary

Epitaxy: The process of growing a thin crystalline layer on the surface of another crystal so that the layer mimics the structure of the substrate.

Germanium: In between gallium and arsenic and one row below silicon on the periodic table of the elements, germanium (Ge) is used in fiber-optic cables.

Graphene: A single layer of carbon arranged in a honeycomb lattice, graphene has a variety of novel electronic properties, such as the electrons' ability to move much faster than in silicon.

Memristor: A novel electronic structure that combines memory with a resistor, this device can simplify and speed up how electronics perform.

Moore's Law: Postulated by Intel co-founder Gordon Moore in the late 1960s, it states that every two years the density of transistors on a chip will roughly double, making for ever more powerful chips.

ReRAM: Resistive random access memory is built from memristor technology and can replace flash memory.

To work, the chip's reprogrammable circuits are fed with its next series of assignments and duties in just 80 picoseconds -- 1,000 times faster than the chip's computational cycle. That way, the layers can be changed on the fly while the chip is waiting for its next commands.

In a real sense, ABAX does more with less. Made with conventional semiconductor processing technology, Tabula's ABAX chips cost roughly the same to manufacture as traditional ones. The design still uses only the top surface of the chip, but that single layer does the work of eight different chips. According to Tieg, the technology can increase the density of circuits twofold, and memory and video throughput can be boosted by as much as 3.5 times.

This idea could potentially usher in a new era in semiconductors where a single chip replaces several or adds abilities without the cost and power use of extra parts. "Virtualizing the operations of a chip can have a big payoff in terms of efficiency and flexibility," says NIST's Seiler. "The key is how it gets programmed."

So far, instead of a direct assault on the big guns of the semiconductor business, such as processors, graphics and memory, Tabula has concentrated on the market for special-purpose chips. These circuits are the workhorses of our time, making things like wireless routers and cell-phone tower equipment possible.

Next, Tabula plans to target the chips found in everyday mainstream electronics, such as digital cameras, video games and maybe even full computers. The company's current eight-level design is in production, and Tabula is well on the way to creating a 12-layer version, with a 20-level chip on the drawing board. "There's no limit to the number of levels we can integrate," Tieg says.

From soot to circuits: Graphene

For the past 45 years, almost like clockwork, the number of transistors on a state-of-the-art silicon computer chip has roughly doubled every two years, making Moore's Law as reliable as the law of gravity. As the active elements on a chip have gotten smaller and cheaper to make, more of them could be shoehorned into devices of increasing complexity, ability and power -- all at roughly the same cost as the previous generation of products.

This embarrassment of digital riches may at last be heading toward a dead end. Scientists trying to stuff ever more transistors onto a silicon chip are having trouble reliably making active elements smaller than the current best of 14 nm -- roughly double the size of a hemoglobin molecule in blood or about one-thousandth the size of a grain of talcum powder.

A substance called graphene could breathe new life into Moore's Law by augmenting silicon technology. Made from nothing more glamorous than soot, graphene is an atom-thick layer of carbon atoms arranged in a hexagonal pattern. Under an electron microscope, graphene looks like a cross between chicken wire and a honeycomb.

"It not only looks strange but has incredible properties," says Walt de Heer at his nanoscience lab at the Georgia Institute of Technology. "Graphene is a wonderful material to make electronics out of," he says. "It's fast, doesn't use a lot of power and can be made with very small features. It outperforms silicon and does things silicon can't. It could be the future of electronics."

Semiconductor researchers have been experimenting with graphene since the 1970s but have had problems making ultrathin layers of the honeycomb. University of Manchester researchers Andre Geim and Konstantin Novoselov successfully produced graphene layers in 2004 (this and other advances in graphene research earned them the 2010 Nobel Prize in physics), and the field has advanced rapidly since then.

Earlier this year, de Heer's group fabricated graphene wires -- an essential first step in making microchips -- that were about 10 nm wide by using epitaxy to deposit a sheet of pure graphene onto a silicon chip. (Epitaxy is the process of growing a thin crystalline layer on the surface of another crystal so that the layer mimics the structure of the substrate.)

Eventually, electronic structures as small as 1 nm and much faster than silicon are possible, de Heer says. "If it pans out, graphene could yield a terahertz processor," he predicts -- roughly 20 times faster than today's best silicon chip.

Next year, the Georgia Tech group hopes to finish work on a prototype graphene integrated circuit to use as a test bed for exploring the material's unique properties and refining the technology for creating circuits.

Meanwhile, researchers at IBM have produced experimental graphene-based transistors and integrated circuits using standard semiconductor manufacturing techniques. IBM's Guha points to these as the first steps toward graphene being used on an industrial scale.

"This area has great potential," he says. "It has applications in military and wireless technology and the possibilities for integration with silicon. What is needed now is a lot of hard work to demonstrate the ability to build amplifier circuits and to create large areas of high-quality graphene active circuits integrated in them."

While the first graphene products could appear in the 2013 time frame, don't expect to see super-fast laptops powered by graphene chips anytime soon. Because of their expense, they are likely to show up initially for specialty uses where cost doesn't matter as much as top speed and low power use.

Similarly, integrated circuits that seem rudimentary today were once expensive specialty items used in military and space applications where cost wasn't the main consideration. "The history of this area," says NIST's Seiler, "is that these things start out expensive and rare and become inexpensive and everywhere."

HP Labs' Williams adds, "It's like creating a new way of making chips that could be a lot faster. Graphene has a lot of potential and could be in everyday items in 10 years."

Standard semiconductor processing involves a series of intricate steps that need to be carried out in an expensive clean room that's free of electronics-destroying dust and contaminants. But Xerox is working on a cheaper and easier way to make electronics by printing circuits on a plastic sheet. The process uses equipment that might cost hundreds of thousands of dollars, not the billions needed for traditional chip-making plants like the one Intel recently broke ground for in Chandler, Ariz.

"Conventional electronics are fast, small and expensive," observes Jennifer Ernst, formerly director of business development at Xerox's PARC research lab in Palo Alto, Calif. By printing them directly on plastic, however, PARC is making electronics that are "slow, big and cheap," says Ernst, now a vice president at Thin Film Electronics.

PARC's design prints circuits directly on the base material in a process that's often only slightly more involved than printing a mailing label. It requires some special materials, like silver ink, but these devices can be printed on flexible polyethylene sheets rather than on brittle silicon. In fact, the results probably shouldn't even be called chips anymore.

By adapting a variety of printing techniques, including ink-jetting, stamping and silk screening, PARC has made amplifiers, batteries and switches for a fraction of what it costs to manufacture them the traditional way. The company recently succeeded in making a 20-bit memory and controller circuit this way, and will start selling it next year. It's a drop in the digital bucket compared with megabit flash and DRAM chips, but it's a start.

Another interesting printed-circuit project is the blast detection sensor tape that PARC is developing for the U.S. Defense Advanced Research Projects Agency (DARPA). It's made by printing circuits on a flexible tape that can be pressed onto a soldier's helmet. With a flexible film battery on the back, the sensors measure the pressure (up to 100 psi), acceleration (up to 1,000 Gs), sound levels (up to 175 decibels) and light (up to 400 lux) experienced in battlefield conditions.

After a week on the front line, the soldier tears the tape off the helmet and sends it to a lab, where the data is downloaded and analyzed so that doctors can see if the soldier is in danger of a debilitating brain injury. "It replaces a $7 sensor, costs less than $1 and performs just as well," says Ernst.

On the downside, printed circuits will likely never catch up to silicon in terms of speed or the ability to put billions of transistors on something the size of a fingernail. But there are lots of places where cost counts for more than speed. As early as 2012, printed devices should start showing up in toys and games that incorporate rudimentary computing, like synthetic voices, as well as in car seat sensors for controlling the deployment of air bags in an accident. (Printed circuits are slow compared to traditional silicon electronics, but still fast enough to for air bag deployment.)

Further out -- around 2015, Ernst estimates -- printed circuits could end up in some very interesting places, such as flexible e-book readers that can be rolled up when not in use or clothing made of a solar-cell fabric that can charge a music player or cell phone. Market analysis firm IDTechEx forecasts that sales of these flexible printed circuits will grow from $1 billion in 2010 to $45 billion in 2016 and show up in a variety of devices.

IBM's Guha also sees a bright future for printed circuits. "Anytime you remove a clean room from making electronics, it becomes much cheaper," he says. "Cheap and dirty is good enough for many uses, provided that the circuits can be made with acceptable quality."

For more breakthrough technologies, be sure to check back next week, when we'll look at innovations in access, power and computer control.


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