When will we see CPUs without Heat sink

No device works at 100% efficiency .  Energy lost within electronic circuit come in the form of heat. this  heat is the difference between the input and the output power .Actually heat is the enemy of any electronic device .  A rise in temperature leads to a subsequent drop in performance. High-performance electronic components generate excessive heat that can damage the whole device if not extracted correctly. As a result, there is a need to remove heat from electronic devices.

Cooling Mechanisms

There are three mechanisms for transferring heat :

Conduction , convection and radiation

Conduction is the transfer of thermal energy through molecular vibration within solids.

Convection is the transfer of thermal energy through molecular motion and fluid flow in liquids and gases.

Radiation is the transfer of thermal energy through molecular vibration that converts to infrared energy

Choices for Cooling

There are four basic choices for transferring heat in electronic circuits:

◗ Heatsinks
◗ Fans
◗ Liquid cooling
◗ Refrigeration

Heatsinks use conduction to transfer heat from the electronics to a surface where the energy convects or radiates away.

Fans generate forced convection to cool surfaces with air

Liquid cooling uses water or an inert liquid in forced convection to cool subsystems.

Refrigeration relies on the phase change when a liquid boils into gas to absorb energy and cool the equipment.

But the Increase in the computational working speed and the decrease in  the size and shape of electronic devices generate more heat per unit area.

The more faster and denser the the integrated circuit is , the more it is expected to exceed it’s allowable temperature

In order to solve this problem, microchannel heat sinks were introduced in 1981 by Tuckerman and Pease

Multiple microchannels are machined on the back of the substrates of electronic components in integrated circuits. The heat generated by the electronic component is transferred to the coolant which is very close to it by forced convection.

this work rise up the researchers and engineer’s interests in the field of microchannel based heat extraction devices for cooling in electronics circuits

on 9 September 2020  a Research published in Nature shows that electronic devices can be more efficiently cooled by co-designing microfluidics and electronics into the same semiconductor substrate

Elison Matioli and colleagues at the Swiss Federal Institute of Technology in Lausanne (EPFL) have now developed a gallium-nitride-on-silicon chip that monolithically integrates a microfluidic cooling system.

The researchers create multiple microchannels (to act as heat sinks) in the silicon layer and create electronic devices (an a.c. to d.c. power converter) in the gallium nitride layer.

GaN epilayer provides the power electronics, and the silicon functions as a microchannel cooling and fluid-distribution network in a three-dimensional arrangement

a staggered pattern of narrow high-aspect-ratio slits is first etched through the AlGaN/GaN epilayer into the silicon. Next, an isotropic gas etch widens the channels in the silicon, coalescing under the epilayer

The openings in the epilayer are then sealed using electroplating, Through micrometre-sized openings in the epilayer, 125-µm-deep and 20-µm-wide channels were created in the silicon substrate

manifold channels are created with its inlet and outlet

So by integrating microfluidics and electronics the passive silicon substrate can be transferred into a high-performance heat sink which is 50 times more efficient than any other cooling technology that isn’t integrated within the semiconductor.

This is very great potential that can be used in electric cars or solar panels or even datacenters in which 30% of  energy consumption goes into cooling

References

R. K. Watts, W. Fichtner, E. N.Fuls, L. R . Thibault. and R . L.Johnston, “Electron Beam Lithography for Small MOSFETs,” IEDM Technical Digest, pp. 772-775, 1980.“Logic Packaging in the IBM 308 1,” ElectronicNews, P. 47, vol.17 Nov. 1980.

R . W. Keyes, “Physical Limits in Digital Electronics,” Proc.IEEE, vol. 63, pp. 740-767, May 1975; “Fundamental Limits in Digital Information Processing,” Proc. IEEE, vol. 69, pp. 267-278, Feb. 1981.

S. T. Poh and E. Y. K. Ng, Heat Transfer and Flow Issues in Manifold Microchannel HeatSinks: A CFD Approach, Proc. Electronic Packaging Technology Conference, EPTC, pp. 246–250, 1998.

van Erp, R., Soleimanzadeh, R., Nela, L. et al. Co-designing electronics with microfluidics for more sustainable cooling. Nature 585, 211–216 (2020). https://doi.org/10.1038/s41586-020-2666-1