Microchip Nanofridge for Super-fast Computing
Researchers from the UAB and CSIC have worked together to create a material which could act as a nanorefrigerator in computers and make it easier to build smaller
chips. The material, which is based on germanium (Ge) nanostructures, presents a significant reduction in thermal conductivity and therefore could be a potential option in the development of thermoelectric systems compatible with silicon. This would make it possible to use the material in common semiconductor devices.
In the past few years, the design and manufacturing of circuits at nanoscopic scale for integrated devices has become one of the frontier fields in new material science and technology. The significant reduction achieved in these devices often is accompanied by new discoveries in how they behave when the systems are of extremely small dimensions. Understanding this new physics at the nanoscopic scale has enabled researchers to study the possibility of designing new materials with innovative characteristics.
One of the crucial properties when designing chips is the thermal conductivity of the devices integrated in the chip, i.e. their capacity to remove or accumulate energy. This property is essential to control the heating of micro-sized circuits, which represents one of the current physical limitations to computing potential. Combining heat and electricity creates thermoelectric effects which would allow circuits to cool down and would increase the power of computing.
Until now, no material has contained the properties needed to be efficient enough in terms of thermoelectric behavior. This is why obtaining materials at nanometric scale can be useful for the improvement of thermoelectric properties, since these materials can achieve a significant reduction in thermal conductivity and, at the same time, maintain a high level of electrical conductivity, which is needed to obtain a high thermoelectric efficiency.
In this project, researchers of the UAB Department of Physics and the Barcelona Institute of Materials Science (ICMAB-CSIC) have worked together to develop a new material based on supernets formed with two alternative layers, one made up of silicon (Si) and the other of germanium (Ge) nanocrystals (quantum dots). In comparison to previous improvements, this project proposes to place the quantum dots in an uncorrelated fashion on consecutive layers. In other words, the dots on one layer would not be vertically aligned with those of the lower layer. This is achieved by introducing a small sub-layer of carbon between each silicon-Ge nanodots layer, which hides the information of the quantum dots found on the lower levels.
The main result of the uncorrelation between consecutive layers is the reduction in thermal conductivity since it becomes more difficult to transport heat perpendicularly from the multilayers. Researchers were able to prove that this reduction reached a factor in excess of two when compared to structures with a vertical correlation of dots. This could greatly influence the design of new materials with improved thermoelectric characteristics and pave the way for the creation of nanofridges for common semiconductor devices, given that it is compatible to silicon technology.
Ge-based structures also could be used in high-temperature applications, such as in recovering heat generated in combustion processes and converting it to electrical energy.
A second and important aspect of this project is the theoretic study of the thermal properties this new material contains through a simple model based on the modification of the Fourier heat equation, which can predict its behavior according to the dimensions of its characteristics. Thus, with the help of results from previous studies, researchers were able to understand the theoretical foundations of thermal conductivity of this nanostructured material. Research members are now working to develop a material with a good level of electric conductivity through controlled doping of the structure.
The research was coordinated by Javier Rodríguez, professor at the UAB Department of Physics, with the participation of Jaime Alvarez, Xavier Alvarez and David Jou, also from the UAB Department of Physics, as well as CSIC researchers Paul Lacharmoise, Alessandro Bernardi, Isabel Alonso, and ICREA researcher Alejandro Goñi. Part of the research was carried out at the Nanotechnology Lab of the MATGAS research centre located at the UAB Research Park. The research recently was published in Applied Physics Letters.