Silicon chip with nanoscale copper plasmonic components. Credit: Image courtesy of Moscow Institute of Physics and Technology
It was previously believed only gold and silver components have the required properties for this. Copper components are not only just as good as components based on noble metals, but, unlike them, they can easily be implemented in integrated circuits using industry-standard fabrication processes. “This is a kind of revolution – using copper will solve one of the main problems in nanophotonics,” say the authors of the paper. In the very near future copper nanophotonic components will form a basis for the development of energy-efficient light sources, ultra-sensitive sensors, as well as high-performance optoelectronic processors with several thousand cores.
Nanophotonics aims to replace existing components in data processing devices with more modern components by using photons instead of electrons. However, while the main component in modern electronics, the transistor, can be scaled down in size to a few nanometres, the diffraction of light limits the minimum dimensions of photonic components to the size of about the light wavelength (~1 micrometre). Despite the fundamental nature of this so-called diffraction limit, one can overcome it by using metal-dielectric structures to create truly nanoscale photonic components.
1. most metals show a negative permittivity at optical frequencies, and light cannot propagate through them, penetrating to a depth of only 25nm. 2. light may be converted into surface plasmon polaritons, surface waves propagating along the surface of a metal. This makes it possible to switch from conventional 3D photonics to 2D surface plasmon photonics, which is known as plasmonics. This gives a possibility to control light at the scale of the order of 100 nanometres, i.e. far beyond diffraction limit.
It was previously believed that only 2 metals – gold and silver – could be used to build efficient nanophotonic metal-dielectric nanostructures and it was also thought that all other metals could not be an alternative to these materials, since they exhibit strong absorption. However, in practice, creating components using gold and silver is not possible because both metals, as they are noble, do not enter into chemical reactions and therefore it is extremely difficult, expensive and in many cases simply impossible to use them to create nanostructures – the basis of modern photonics.
Based on a generalization of the theory for so-called plasmonic metals, in 2012 MIPT’s Laboratory of Nanooptics and Plasmonics found that copper, as an optical material, is not only able to compete with gold, but it can also be a better alternative. Unlike gold, copper can be easily structured using wet or dry etching. This gives a possibility to make nanoscale components that are easily integrated into silicon photonic or electronic integrated circuits.
The researchers note that the optical properties of thin polycrystalline copper films are determined by their internal structure, and the ability to control this structure, achieve and consistently reproduce the required parameters in technological cycles is the most difficult task. However, they have managed to solve this problem demonstrating that it is possible not only to achieve the required properties with copper, but also that this can be done in nanoscale components, which can be integrated both with silicon nanoelectronics and silicon nanophotonics. “We conducted ellipsometry of the copper films and then confirmed these results using near-field scanning optical microscopy of the nanostructures. This proves that the properties of copper are not impaired during the whole process of manufacturing nanoscale plasmonic components,” says Fedyanin.
These studies provide a foundation for the practical use of copper nanophotonic and plasmonic components, which in the very near future will be used to create LEDs, nanolasers, highly sensitive sensors and transducers for mobile devices, and high performance optoelectronic processors with several tens of thousand cores for graphics cards, personal computers, and supercomputers. http://www.eurekalert.org/pub_releases/2016-02/miop-ppa022516.php
Recent Comments