Heat flow control for future nanoelectronics

August 29, 2012, Aalto University

Electronic devices and their components are getting smaller and smaller. Through his doctoral research at the Department of Applied Physics in Aalto University, Tomi Ruokola has examined how the heat generated by electronic components could be controlled and utilised.

There is little research in the area of heat flows and their control. Ruokola's study tackles the basic questions of the field: how heat transfer occurs from one point to another and how this flow can be controlled in approaching nano-scale?

"Heat flows are considerably more difficult to control than electrical currents. Heat is pure energy, electricity on the other hand is charges that can be accurately measured. Heat flows are not directly accessible in the same way, which makes experimental research hard," explains Ruokola.

Ruokola has designed two mesoscopic—a size between macroscopic and microscopic—devices for . They are based on single-electron phenomena: the movement of single electrons through the constructed system. Electrons carry, in addition to their , an arbitrary amount of heat.

"The smaller the scale of devices and components becomes, the more phenomena come to the fore. This requires new ideas and methods for heat transfer as well."

Together with researcher Teemu Ojanen of O.V. Lounasmaa Laboratory in Aalto University, Ruokola developed a single-electron diode, a rectifier, which allows heat to flow only in one direction and blocks the flow to the other. The idea comes from the well-known electronic component of a similar function.

"The flow between different temperatures is normally symmetric: the flow goes from a hotter point to a cooler one, as the temperatures seek to balance each other out. If we want to control the flows, we need to manipulate them to flow in the direction desired. The we present are ideas for how to come up with a strongly asymmetrical ."

"The diode we developed performed remarkably well compared to existing literature," says Ruokola.

Groundbreaking applications require experimental research

Ruokola tells that basic nano-level research of heat flows is severely held back by a lack of experimental setups.

"The motivation behind my research was above all the desire and need to understand the basic phenomena and control of and flows."

If the problems in basic research and experimentation were to be solved, future applications in nanoelectronics would be outstanding.

Computers could work on heat currents instead of electricity, and the vast amount of waste heat in server farms could be captured and converted already on microchip level. Microchips smaller than a nanometre would also work in room temperature; making use of quantum level phenomena would not anymore require temperatures approaching absolute zero.

"These are of course out of reach, at least a decade, or decades, away."

Nonetheless Ruokola is intrigued by the utilisation of waste heat. As outlined in his dissertation, he built a thermoelectric heat engine, which puts waste heat energy back into work. In the engine the charge flows of doing the work and the heat-transferring flows of photons can be separated from each other.

"In heat engines and waste energy, the main issue usually is the efficiency of energy use. However, when there is an abundance of waste heat, the most crucial thing is not efficiency, but rather the maximum power that can be extracted from the heat," Ruokola points out.

"As long as there is cold and a hot spot in microchip, the heat flow between them can be put back into the chip as useful work."

In the diodes the main problem is transferring large currents. In the single-electron systems built by Ruokola, the currents and power levels are of course low. Similar systems of high interaction—and with large currents—would be of great demand.

"These are the basic issues yet to be solved in heat flow control in nanoelectronics. There is still a lot do get our heads around in basic theory," believes Ruokola.

Explore further: Controlling heat flow with atomic-level precision

More information: Tomi Ruokola's doctoral dissertation Thermal Transport in Mesoscopic Devices: lib.tkk.fi/Diss/2012/isbn97895 … sbn9789526047157.pdf

Related Stories

Controlling heat flow with atomic-level precision

April 22, 2012

Through a combination of atomic-scale materials design and ultrafast measurements, researchers at the University of Illinois have revealed new insights about how heat flows across an interface between two materials.

NIST helps heat pumps 'go with the flow' to boost output

January 23, 2008

Air-source heat pumps typically deliver 1 1/2 to three times more heating energy to a home than the electric energy they consume. This is possible because heat pumps move heat rather than convert it from a fuel (as combustion ...

Temperature fluctuations cause excess noise

May 14, 2010

The thermal noise of the electric current has been well known for almost a century. In an article published this week in Physical Review Letters, a group of researchers from the Low Temperature Laboratory of Aalto University ...

Energy harvesters transform waste into electricity

May 16, 2011

Billions of dollars lost each year as waste heat from industrial processes can be converted into electricity with a technology being developed at the Department of Energy's Oak Ridge National Laboratory.

Jumping droplets take a lot of heat

December 12, 2011

Microscopic water droplets jumping from one surface to another may hold the key to a wide array of more energy efficient products, ranging from large solar panels to compact laptop computers.

Recommended for you

Reinventing the inductor

February 21, 2018

A basic building block of modern technology, inductors are everywhere: cellphones, laptops, radios, televisions, cars. And surprisingly, they are essentially the same today as in 1831, when they were first created by English ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.