By Brian Fuller
Silicon CMOS is a tough act to follow. The workhorse building block for the world’s electronics has been delivering for system designers for a half century. Despite hand-wringing over its apparent scalability limits, it shows only vague signs of slowing down.

For nearly as many years, it seems, the next great material or alternative to silicon CMOS has popped into the industry’s consciousness promising to be the next big thing—next year. Gallium arsenide, for example, has been next year’s hit technology for four decades.

The latest “it” material, however, could actually deliver on its early hype, and in the process enable the industry not only to continue scaling but to drive deep into previously unexpected depths of low-power design. Graphene—the two-dimensional crystalline form of carbon—first emerged as a term in the late 1980s and gained traction in 2004 when researchers at the University of Manchester extracted graphene layers from graphite—basically using Scotch tape—and then placing on silicon dioxide on a silicon wafer.

This time it’s different (maybe)
The material exhibited fantastic characteristics, including high electron mobility compared to silicon, twice the storage capacity of ultracapacitors, and it was rugged to boot. What’s more, its characteristics apparently remain stable down to the molecular level, unlike other materials used in semiconductor design. The graphene promise is such that in just the past three years, research papers are being written on graphene at the rate of one a day.

“There are two features that make graphene exceptional,” Kirill Bolotin, assistant professor in the Vanderbilt Department of Physics and Astronomy, said in a recent interview. “First, its molecular structure is so resistant to defects that researchers have had to hand-make them to study what effects they have. Second, the electrons that carry electrical charge travel much faster and generally behave as if they have far less mass than they do in ordinary metals or superconductors.”

Where some see glowing walls made of graphene circuitry and other exotic applications, people like James Meindl see an answer to scaling. Keynoting at the recent ISSCC (International Solid State Circuits Conference) in San Francisco, Meindl, director of the Joseph M. Pettit Microelectronics Research Center at the Georgia Institute of Technology in Atlanta, said: ”We will continue to scale vigorously for the next 15 years. Beyond silicon microchip technology, revolutionary developments in nanoelectronics, perhaps centering on graphene, may evolve.”

That’s music to the ears of many who, despite CMOS’s dogged determination, seeing scaling hitting a wall in the next decade.

“Look at Intel’s roadmap. They’re looking at 4nm in 2022,” said Michael Keating, a Synopsys Fellow. “As long as they’re charging down that road, graphene’s going to be a second-class citizen. But my guess is 2022 is not realistic for 4nm. Silicon will be seriously in trouble in that decade.”

“The reason graphene’s interesting is so much progress has been made in such a short time frame,” he added.

What’s all the fuss?
Graphene—a one-atom-thick planar sheet of sp2-bonded carbon atoms that resembles chicken wire—has a lot going for it.

Meindl, speaking at ISSCC, gave a half-dozen reasons graphene is going to win in the marketplace, including:

• No other known material has a higher mechanical strength-to-weight ratio.
• Carrier mobility exceeds 200,000-cm2/Vs.
• The capacity to conduct current densities as large as one thousand times greater than copper without electromigration.
• Graphene can serve as a source, channel drain regions of a field effect transistor (FET) and as an interconnect.

In addition to all the big talk, there’s been action.
• Fujitsu Laboratories Ltd. has developed a method to form graphene transistors directly on the entire surface of large-scale insulating substrates at low temperatures while employing popular chemical-vapor deposition (CVD) techniques.
• IBM in 2007 fabbed graphene field-effect transistors (FETs) using a single layer of carbon atoms atop a silicon wafer at its T.J. Watson Research Center at Yorktown Heights, N.Y.
• In February, IBM built, on 2-inch wafers, RF graphene transistors running at 100-GHz and operating at room temperature.
• At around the same time, Penn State researchers announced they have developed a way to fabricate graphene sheets on 4-inch wafers.
• Last year, Bolotin, working with colleagues at Columbia University, managed to get graphene to exhibit the fractional quantum Hall effect, where the electrons create new particles with electrical charges that are a fraction that of individual electrons, according to work published in the journal Nature.
• A venture-backed Austin, Texas, company, Graphene Energy, is working to commercialize graphine for energy storage.
• Javad Rafiee, a doctoral student at Rensselaer Polytechnic Institute developed a method of ultra-efficient hydrogen storage based on graphene. His approach stores hydrogen with 14 percent efficiency, better than any other material attempted to date.

What’s the catch?
There’s always a catch. While graphene is easier to manufacture than its cousin, the carbon nanotube, it’s no slam dunk yet. To date, there hasn’t been a simple way to create the p- and n-type devices required for CMOS transistors. But Georgia Tech recently reported it has used an electron beam doping process that simplifies the transistor manufacture.

In addition, graphene has no band gap so there’s no way to turn them “off.” But even that hurdle is being brought down. Researchers at Lawrence Berkeley National Lab last year engineered a controllable band gap in bilayer graphene—at room temperature.

When will we know when graphene gets the “next-year’s technology” monkey off its back for good?

Maybe relatively soon, suggested Synopsys’ Keating.
“CMOS has had an incredible run. It’s foolish to bet against CMOS. (But) graphene every year makes significant progress. It’s absolutely the promising thing right now. We’re a decade away.”

You’ve probably heard of printed batteries—or at least charge-storing devices that can be printed with a commercial inkjet printer. But how about paper batteries?

A group out of Rensselaer Polytechnic Institute in New York has developed a battery on a flexible “PowerWrapper.” They’ve also started a company known as—surprise—The Paper Battery Co. Our guess is they didn’t have to look around much to see who else was using that name. Disbelievers can watch the video.

There also are some interesting developments on the battery charging side. Green Plug has developed a connector that can deliver multiple voltages to charge devices intelligently, as opposed to one unique charger per device. The strategy should get rid of a wall of chargers for most families, where you have to try to figure out which charger connects to your phone and which one connects to those of your family members. It even can shut off when the device is fully juiced.

Finally, there’s a little device called the YoGen, which has a pull cord (click on the arrow to the right of the photo) for charging a cell phone battery, or any other mobile device battery. It’s like a miniature version of the pull cord on a lawn mower, except you don’t have to cut the grass afterward. You can just talk about it. In fact, you can keep talking until your minutes run out and your money runs out and…well…this can get very ugly from here.

–Ed Sperling

By Brian Fuller

The world has changed dramatically in the 209 years since Alessandro Volta hunched over his table by candlelight and figured out how to capture energy in his voltaic pile, the first electric battery. What has changed little, however, is the battery itself.

Since Volta’s conception, the battery has remained a cell with negative and positive electrodes, an electrolyte, and an ion conductor, all of which turns a chemical reaction into electricity. The chemistry that makes it happen has changed little.

Today the importance of batteries (estimated to be a $15 billion market in North America alone) on scales both large and small is more crucial than ever. System designers struggle with making portable equipment that runs longer on lighter batteries; others are grappling with how to power electric vehicles and maintain storage farms that are envisioned for solar and other renewable energy sources.

But battery improvement, unlike Moore’s Law, is measured in single-digital increments per year, not a doubling of capacity every 18 months. Chemistry, to abuse a phrase, is what it is. “The laws of physics and chemistry dictate what ultimate energy you can get in the battery system,” said Subra Iyer, principal technologist at Quantum Sphere, a Southern California startup using nano-materials to improve battery life and performance.

“There are things that make lithium ion technology almost fundamentally the best [the industry] can do,” said Robin Tichy, technical marketing manager at Micro Power Electronics Inc., Beaverton, Ore. “Look at periodic table of elements. Lithium is the lightest element that gives you highest energy at the lightest weight. There’s not a lot you can do from there. Everything else is going to be incremental.”

A busy world

Battery research in the past two years has been nothing if not frenetic:

• Recently Valence Technology announced plans to build a $760 million battery-manufacturing plant in Central Texas to supplement capacity it has in China. Valence manufactures large-format Li-ion prismatic cell batteries for electric vehicles.
• At the 2009 Consumer Electronics Show, Energizer Holdings said it is developing zinc air batteries suitable for devices such as MP3 players.
• Researchers at Stanford have claimed a tenfold increase in battery life by using silicon nanowires in the anode, similar to Quantum Sphere.
• Rensselaer Polytechnic Institute researchers developed a paper-thin battery by immersing a carpet of vertical nanotubes in an ionic liquid electrolyte.

These represent hope, investment and incremental change. But incremental change, according to Tichy, “can enable an awful lot.” The industry today finds itself knee-deep not only in fundamental research, but more important in delivering improvements in and around the battery to squeeze the most out of existing chemistry. These range from nano-scale research in materials development to packaging and metering to power management at the system level, among other approaches.

Balancing act

At Micro-Power, which makes power supplies, battery packs and chargers, engineers are focusing on power-balancing techniques in the hopes that “something seemingly small can make a revolutionary change for a given application,” according to Tichy.

The commercialization of lithium-ion batteries in 1991 brought relatively light weight, cost-effective portability to important markets, including laptops, medical devices and power tools. But lithium ion batteries tend to have a spiky power profile compared with smoother charge-discharge rates of alkaline batteries, and that can be a problem for systems that require accurate battery-capacity measurements.

Micro-Power has implemented fuel gauging for lithium ion batteries that’s 99% correct if used right, Tichy said. The current state of the art, as we know from the IT department, is to drain your laptop battery occasionally to ensure an accurate fuel gauge. But new fuel-gauge technology for laptops self-calibrates opportunistically. This approach can deliver another 15 minutes of run time on a laptop. Assuming a two-hour battery life, that’s an improvement in operation of more than 10%.

The importance of an accurate gauge of battery life is crucial in medical applications. For example, life-support ventilators have had to use lead acid batteries to ensure smooth voltage decline for consistent operation. The design tradeoff is weight and bulk.

More surgical tools, especially in the field, are battery-powered. As Tichy says, anything that’s been mechanical and motorized in the past is entertaining the idea of power by Li-ion battery today, as opposed to heavier nickel-cadmium batteries.

Micro-power helps systems “monitor and understand exactly what the runtime to empty is,” Tichy said. “For life-support medical equipment for obvious reasons, the FDA regulations say you have to have an accurate countdown from 30 minutes.

Quantum leap

Quantum Sphere is developing new nano catalysts, electrodes and process chemistries to try to double volumetric capacity over state of the art, according to its CEO, Kevin Maloney. The Santa Ana, Calif.-based company is focusing on two major components of battery performance: energy density and power density.

Quantum is attacking energy density issues as they impact system runtime by using different metals to improve the battery anode. Current Li-ion batteries use graphite for the anode, which limits the battery to 350mAh/gram. Quantum is using different amorphous metal alloys, including tin, magnesium and silicon, to pack more lithium into the anode to improve performance. Nanoscale materials have 2000% greater surface area with just 10% loading in the battery solution. This translates to commensurately higher reactivity, catalysis, energy density and power density.

“Anything that increases more lithium in the anode increases energy density,” Iyer said.

Power density is a way to measure the charge/discharge rate of lithium through the anode, cathode and electrolyte. The faster it gives up the lithium, the more high-power applications the battery can accommodate and the faster it can be recharged.

This is crucial to the development of electric vehicles, especially enabling a quick recharge in a world in which consumers are used to three-minute fill-ups at the gas station.

For example, utilizing QuantumSphere’s nano-integrated gas diffusion electrode, a 320% increase in power density is achieved in metal-air battery systems. This enables enhanced functionality in both consumer and military applications, where higher power and longer lifetime is required.

Power play

At NEC, the focus is on making sure the energy stored in those batteries is not being wasted as it powers the system.

“Power management technology is a key enabler,” said Steve Kawamoto, director of marketing for custom SOC solutions at NEC Electronics America in Santa Clara, Calif. For example, work is being done on radio technology to manage the burst-like nature of Internet data activity on a handset. “You’re powering up and down those [power] rails and that’s a very power-hungry aspect of the handset. So you want to power up and down as quickly as possible.”

Power-management techniques have gotten so sophisticated that they can manage power in between texting keystrokes, Kawamoto noted. If the power rails are on in between keystrokes, power is wasted.

“It’s about understanding the system context and what needs to be on in the rest of the system,” he said. “When the user is typing, I can power down other parts of the system, for example the graphics subsystems or other radios.”

Kawamoto notes that applications processor designers are doing “a lot of amazing things” to optimize their end of the battery bargain. “But all this innovation has to be fed back into the power management chip so that there is a device that enables that form factor. It’s important to enable that form factor. “

In a way, the world today is staring at the battery world, saying, in effect, “if only we could find the miracle chemistry” to power cars for 500 miles and enable days of constant use in a range of consumer devices. For now, that’s illusory. And consumers, in the end, are OK with it, whether they realize it consciously or not.

“There’s a threshold that people have,” said Kawamoto. “If they can find value in the device itself, they’ll put up with” battery limitations.