I’m old enough that, in my early years as an engineer, we used devices you youngsters may have heard of, called vacuum tubes — transistors were there but had limited applications. Integrated circuits (ICs), what we now call chips, were in their infancy.
So, obviously, when we carry around our cell phones, computers that are orders of magnitude more powerful than the earliest behemoths, we have had a revolution in technology — right? My answer, as my answers so often are, is yes … and no.
Yes, this never could have happened if it weren’t for the invention of solid-state electronics. That is what made possible all of this incredible technology that is part of our everyday lives, and which “we can’t live without.”
We can even point to when and where the solid-state revolution started: at Bell Laboratories in New Jersey when three men were given the assignment to find a solid material to replace vacuum tubes. William Shockley, who was a brilliant theorist; Walter Brattain, who was a skilled experimenter; and John Bardeen, who had the ability to understand and communicate with both theorists and experimenters, built the first working model of a solid-state amplifying device — the transistor — in November of 1947.1
Yes, this was a unique development in terms of the physical structure of the amplifying device, but the way it was used was not that much different from the way vacuum tubes were used. The fundamental building block of a computer is a solid-state switch that has two states, which are named zero and one. But vacuum tube circuits that we called flip-flops were used in the early digital computers in the same way.
Vacuum tubes were also used in operational amplifiers (op amps), which were commercially available in the 1950s and became the fundamental building blocks of analog circuits. The same basic circuitry was built using solid-state electronics in integrated circuits in the 1960s and are still in wide use today.
The thing is that the ideas of what could be done with electronics and how to do it are not radically different now from what they were then. The huge difference is that using solid-state electronics instead of vacuum tubes as the way to implement the ideas is what has made the world of modern technology possible.
Speaking of ideas, the physicist Richard P. Feynman, gave a lecture in 1959, entitled “There’s Plenty of Room at the Bottom,” in which he suggested that atoms could be manipulated and controlled, thus providing “an enormous number of technical applications.” He outlined how it would be theoretically possible to write the entire 24 (printed) volumes of the Encyclopedia Britannica on the head of a pin. But the practical development of nanotechnology didn’t begin until the 1980s.
Berkeley Lab Breakthrough
I started thinking about these things, when I came across an article about the discovery of a new physical phenomenon that will likely have a significant impact on nanotechnology.
Like so many breakthrough advances in technology, this started with a problem that needed solving — how to practically make microchips smaller and faster without running into heating limitations. The problem was that silicon, which is the material for most ICs, while a good conductor of electricity, is a poor conductor of heat. And when you’re squishing a few billion silicon transistors into a microchip, heat becomes a limiting factor in how far you can expand.
The theoretical answer to improving the thermal conductivity of silicon has been around for decades — use pure silicon-28. The only trouble with that is silicon doesn’t naturally occur in pure form and processing isotopes to get there requires so much energy as to be completely impractical for everyday use.
In the early 2000s, Joel Ager, a Berkeley Lab material sciences research scientist and Eugene Haller, one of the world’s leading experts in growing and applying ultrapure semiconductor material, were able to produce pure silicon-28 crystals for a project on quantum computing.
Ager kept what remained of this material in a safe place at Berkeley Lab, just in case other scientists might need it, because few people have the resources to make or even purchase isotopically pure silicon.
Fast forward to 2019 when Junqiao Wu and Penghong Ci were looking for new ways to improve the heat transfer rate in silicon chips. They came up with the idea of using stacked silicon nanowires as a new form of transistor — a good idea, except for the question of how to quickly extract the generated heat. Their answer was to make the nanowires from our old friend, isotopically pure siicon-28.
In fact, Ager and Haller had earlier demonstrated a heat-efficiency gain of about 10 percent. But that was not a significant enough improvement to make it economically feasible for manufacturers.
But Ager was willing to let Wu and Ci use some of his precious pure silicon to see what it could do in the form of these new nanowire transistors.
They started by testing the thermal conductivity of the bulk crystals and sure enough they only saw a small improvement. Then, using a technique called electroless etching, they used the bulk silicon-28 to fabricate the nanowires. And much to everyone’s surprise, there was a 150 percent improvement in heat conductivity.
To solve the puzzle, they turned to a high-resolution transmission electron microscopy (TEM) team at Rice University. The resulting images showed a glass-like layer of silicon-dioxide on the surface of the nanowires.
Then they turned over the images to experts at the University of Massachusetts Amherst and discovered that two separate heat-transmitting mechanisms were present and worked synergistically to produce the surprising results.
Said Ager, “Junqiao and the team discovered a new physical phenomenon. This is a real triumph for curiosity-driven science. It’s quite exciting.”
So, How Do Technological Innovations Happen?
A few things jump out at me from the Berkeley Lab study. Just as with the birth of transistors and integrated circuits and nanotechnology, technology breakthroughs often happen when:
- There are theoretical insights that don’t yet have practical applications.
- Scientists are free to go where their curiosity sends them.
- There are problems looking for solutions.
- People who are excited about their work connect with each other and trade ideas.
- People with different sorts of expertise collaborate with each other.
- There is a back and forth between theory and practice. Theory provides ideas that can be implemented in practice. Practical results can expand theory, which can then lead to more innovations in a “virtuous circle.“
Do you agree? Share your questions and comments below.
- Walter Isaacson, The Innovators, Simon & Schuster Paperbacks, 2014.