Back To The Future for Vacuum Tube Technology

You may call it a valve, electron valve, electron tube, vacuum tube or simply a tube but we all love them just the same.  We use them in our home audio and guitar amplifiers for making some seriously amazing tone, but their history goes way beyond that.  Back in the day tubes had a vast array of jobs.  They could be found in TV’s, radios, cameras, medical devices, computers, space equipment, radars, planes, trains, and automobiles.  At one time they were so common you could pick up a new tube at every general store.  Eventually technological advancements pushed the vacuum tube towards extinction and they were headed the way of the dinosaur thanks to the transistor.  The power of the musical world has held on tight though and kept the tube alive through these dark ages.

Things tend to go in cycles and it seems that tube technology could be making a comeback in the future.  As you will read in this article from The New York Times, tube technology is being developed on a microscopic level.  The day may come where we see vacuum tubes being used once again in all of the equipment they were previously retired from.  Our grandchildren’s tubes may not look like our grandparent’s tubes but they will follow the same basic principles.

Smaller Chips May Depend on Vacuum Tube Technology

PASADENA, Calif. — The future of computing may be in its past.

The silicon transistor, the tiny switch that is the building block of modern microelectronics, replaced the vacuum tube in many consumer products in the 1970s. Now as shrinking transistors to even more Lilliputian dimensions is becoming vastly more challenging, the vacuum tube may be on the verge of a comeback.

In a darkened laboratory here, two stories beneath the California Institute of Technology campus, two students stare through the walls of a thick plastic vacuum chamber at what they hope will be the next small thing — a computer chip made from circuits like vacuum tubes whose dimensions are each roughly one-thousandth the size of a red blood cell.

At stake is the future of what electronic engineers call scaling, the ability to continue to shrink the size of electronic circuits, which is becoming harder to do as they become as small as viruses.

It has been more than half a century since the physicist Richard Feynman predicted the rise of microelectronics, noting “there’s plenty of room at the bottom.” He used the phrase in 1959 when he speculated about engineering with individual atoms. Several years later, Gordon Moore, co-founder of Intel, wrote that the number of transistors that could be etched into silicon wafers would double at regular intervals for the foreseeable future.

Now, however, there is growing evidence that space, if still available, is increasingly at a premium. Progress is slowing down. The time between each new chip generation is stretching out, and the cost of individual transistors, although infinitesimal, is no longer falling. The tiny transistors also bedevil chip designers because as they get smaller, they generate unwanted heat.

For Axel Scherer, who heads the Nanofabrication Group at Caltech, that means going back to the future. With his students Max Jones and Daniil Lukin, he is pursuing what is in effect an ultrasmall vacuum tube as a candidate to replace the transistor. In their laboratory here, they have fabricated circuits that function like vacuum tubes but are a millionth the size of that 100-year-old technology.

“Computer technologies seem to work in cycles,” said Alan Huang, a former electrical engineer for Bell Laboratories. “Some of the same algorithms that were developed for the last generation can sometimes be used for the next generation.”
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The last time researchers explored vacuum tubes was in the 1990s, when they were a promising option for building flat-panel displays. The technology failed to take off, however, because of cheaper and more efficient liquid crystal displays.

“The vacuum tube comes back about every decade,” Dr. Scherer said with a laugh.

And for decades, that has been the story of vacuum tubes: There has always been a better option. Transistors replaced vacuum tubes because they were more compact, did not generate skin-burning heat and did not need a vacuum — the absence of atmosphere made it possible for electrons to jump between positively and negatively charged elements.

The vacuum tubes the Caltech researchers are looking at are nothing like the bulky objects that hummed in the old family radio and even early computers. Both transistors and vacuum tubes — the British called the devices valves — control the flow of electricity, but they do so differently.

The researchers have created a tiny tube formed from metal and capable of turning on and off the flow of electrons between four even smaller probes, which under an electron microscope appear like the tips of four ballpoint pens almost touching one another.

The Achilles’ heel of today’s transistors is the smaller they get, the more they leak electrons. In modern computer chips, as much as half of the power consumed is lost to electrons leaking from transistors that are only dozens of atoms wide. Those electrons waste energy and generate heat.

In contrast, Dr. Scherer’s miniature vacuum tube switches perform a jujitsu move by using the same mechanism that causes leakage in transistors — known by physicists as quantum tunneling — to switch on and off the flow of electrons without leakage. As a result, he believes that modern vacuum tube circuits have the potential to use less power and work faster than today’s transistor-based chips.

“Effects that are currently problems in scaling are precisely those that we would like to use for switching in these next-generation devices,” Dr. Scherer said, noting that while there are efforts to redesign semiconductor-based transistors around the tunneling effect, his approach is significantly simpler.

Vacuum tubes are one of a range of ideas that engineers are looking at as they work to create chips that can do more while using less power. Other promising approaches include exotic materials such as carbon nanotubes and even microscopic mechanical switches that can be opened and closed just like an electronic gate.

The Caltech researchers returned to the idea of vacuum tubes several years ago after they had begun experimenting with the idea of making ultrasmall incandescent light bulbs no larger than a modern transistor that would be bright enough to be seen by the naked eye from across a room.

The group previously worked in research areas like quantum dots, nanoscale structures now used in television displays to produce precise colors, and optoelectronics, a field that explores the use of lasers in electronic circuits. But they decided to look for new research areas that were less crowded with competitors.

Today, semiconductor companies like Intel are making silicon chips with minimum dimensions between 10 and 20 nanometers. (A strand of DNA is roughly 2.5 nanometers in diameter.) Once the industry shrinks below 10 nanometers, Dr. Scherer expects that researchers will be surprised by the behavior of silicon at such atomic dimensions.

For one thing, silicon emits light below 10 nanometers, he said. More significantly, it also becomes remarkably elastic as it becomes that small.

“It’s a different material, and it gives you this different behavior,” he said. He sees the future in other materials and in old ideas that would be made new again.

In contrast to silicon, a semiconductor, which can either conduct or insulate, depending on how it is chemically modified, Dr. Scherer’s tubes can be made from a range of conducting metals, such as tungsten, molybdenum, gold and platinum. This will be an advantage because it will significantly simplify the tiny switches at the atomic scale.

Dr. Scherer does not think the tiny tube will immediately replace the transistor, but the possibility of applications in space and aviation has caught the attention of Boeing, which is financing the research. Such specialty chips might be ready commercially before the end of the decade.

“Ten years ago, silicon transistors could meet all of our demands,” he said. “In the next decade, that will no longer be true.”


Image courtesy of Tau Zero

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