By Josh Perry, Editor
University of California – Irvine (UCI) scientists have developed holey silicon, a computer chip wafer that has tiny, vertically-etched orifices that channel heat to the desired location and that they believe could be a breakthrough in electronics cooling.
Jaeho Lee, UCI assistant professor of mechanical and aerospace engineering, believes that holey silicon might be a breakthrough in the quest to keep modern electronics cool.
Researchers found that heat prefers traveling vertically rather than laterally across holey silicon, according to a report from the university, which allows the etched channels to transfer heat from local hot spots to on-chip cooling systems without requiring a lateral temperature gradient for thermoelectric junctions.
Tests demonstrated that holey silicon performed 400 times better than chalcongenides, which are materials commonly used in thermoelectric devices.
A study that was published in January 2017 showed the team that “small, neck-shaped structures created by the etched holes in holey silicon cause phonon backscattering, a particle effect leading to low in-plane thermal conductivity. High cross-plane thermal conductivity was caused by long-wavelength phonons that help to move heat away.”
The goal of this research is to find cooling solutions to match the increasing component density in modern electronics systems, particularly coupled with increasing miniaturization.
The most recent research was published in Nanotechnology. The abstract read:
“Artificial nanostructures have improved prospects of thermoelectric systems by enabling selective scattering of phonons and demonstrating significant thermal conductivity reductions. While the low thermal conductivity provides necessary temperature gradients for thermoelectric conversion, the heat generation is detrimental to electronic systems where high thermal conductivity are preferred. The contrasting needs of thermal conductivity are evident in thermoelectric cooling systems, which call for a fundamental breakthrough.
“Here we show a silicon nanostructure with vertically etched holes, or holey silicon, uniquely combines the low thermal conductivity in the in-plane direction and the high thermal conductivity in the cross-plane direction, and that the anisotropy is ideal for lateral thermoelectric cooling. The low in-plane thermal conductivity due to substantial phonon boundary scattering in small necks sustains large temperature gradients for lateral Peltier junctions.
“The high cross-plane thermal conductivity due to persistent long-wavelength phonons effectively dissipates heat from a hot spot to the on-chip cooling system. Our scaling analysis based on spectral phonon properties captures the anisotropic size effects in holey silicon and predicts the thermal conductivity anisotropy ratio up to 20.
“Our numerical simulations demonstrate the thermoelectric cooling effectiveness of holey silicon is at least 30% greater than that of high-thermal-conductivity bulk silicon and 400% greater than that of low-thermal-conductivity chalcogenides; these results contrast with the conventional perception preferring either high or low thermal conductivity materials.
“The thermal conductivity anisotropy is even more favorable in laterally confined systems and will provide effective thermal management solutions for advanced electronics.”