Heat dissipation is one of the biggest obstacles in semiconductor reduction. A team at the University of California has developed nanowires that can significantly improve heat dissipation characteristics and shape the future of silicon chip design.

Heat Dissipation

One characteristic of circuits that arguably causes some of the biggest design problems is heat dissipation. Most (if not all), electrical properties of materials are dependent on the temperature of that material. For example, the resistance of a material increases as the temperature increases, which is problematic for designs which deal with large amounts of current.

The conductive ability of a BJT increases with an increase in a temperature which can lead to thermal runaway if left unchecked. Heat dissipation also causes issues with semiconductors because, as the temperature rises in a semiconductor, the resistance decreases which in turn results in a larger leakage current. This larger leakage current then generates more heat which causes a thermal runaway effect.

 

Heatsinks are important when trying to keep ICs cool. Image via Wikipedia

 

Heat dissipation in electronics comes in a wide variety of forms. The most common techniques involve heat sinks and IC packages that are designed to handle heat dissipation (such as the TO-3 metal transistor case). Methods for combating against large amounts of heat dissipation (PCs, for example) include water cooling, mineral oil submersion, liquid nitrogen, and even liquid helium.

Companies that own data centers and mainframes, such as Microsoft, are also beginning to look at submerging computers in the sea as a method for cooling without needing to expend energy in the process.

 

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However, engineers may no longer need to agonize over how their design will dissipate heat thanks to a research team at the University of California who may have found an efficient method for heat dissipation.

 

Gallium Arsenide (GaAs) Nanowires

An international team lead by a researcher at the University of California has modified the energy spectrum of acoustic phonons by confining them to nanowire structures. Fundamentally, heat is the vibration of atoms whereby an increase in this vibration results in an increase of temperature.

Interestingly, James Prescott Joule developed an experiment which showed that mechanical work could be used to increase the temperature of a system, hence suggesting that motion was related to heat. A phonon, in relation to heat, is the collective vibration throughout a crystalline material which can be thought of as ripples in a pond or a sound wave in the air. The oscillations are all coherent and in phase which gives rise to a natural frequency for that structure.

What the research team has done is essentially confine these vibrations into nano-scale Gallium Arsenide and, through that confinement, can alter the energy spectrum or dispersion by changing the size and shape of the wires.

 

Nanostructures used to confine phonons in the crystalline structure. Image courtesy of Nature

 

In the past, nanostructures have been used to alter thermal conductivity by creating nanoscale boundaries and interfaces for scattered phonons. This new method instead uses nanowires to confine acoustic phonons. This affects how the phonons behave in several ways, including their velocity, their interactions with electrons, and—importantly for electronics work—how they carry heat.

The team's leader, Alexander Balandin, said in a statement that the research "creates new opportunities for tuning thermal and electronic properties of semiconductor materials."

 

Potential Application of GaAs Nanowires

The ability to manipulate the vibrations in crystalline structures, such as those found in semiconductors, would bring about revolutionary methods for heat dissipation and control. Processors utilizing such heat dissipation technology could be kept incredibly cold without the need for large expensive heat removal techniques. This would also reduce the energy needed to keep such systems cool which could be extremely advantageous in applications like server farms, data centers, and mainframe computers.

However, it is not just computers and mobile devices that could really benefit from such heat dissipation capabilities. Devices such as thermoelectric generators which rely on a temperature gradient could be made much more efficient with the use of the GaAs nanowires by keeping the gradient as large as possible. Solar panels, whose efficiency drops as temperature rises, could be designed to handle the heating gained from absorbing sunlight and thus keep them at their peak efficiency without the need for cooling.

 

Peltier Coolers are thermoelectric generators that could benefit from such heat control. Image courtesy of michbich (own creation) [CC BY 3.0]

 

Summary

Heat management in electronics is an issue that always has engineers hitting their heads against their desks. Heat dissipation usually necessitates large devices because it requires larger components or heat dissipation systems. These components or systems also often complicate the physical dimensions or power consumption of the devices they inhabit.

Even with high efficiency techniques—switch mode power supplies, CMOS-based integrated circuits, large copper pours, and even specialized component mounting—the demands of modern life have made devices run hotter than ever before. Hopefully, this new technology will help to keep devices cool and efficient in the future.

 

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