02-05-2018 | | By Rob Coppinger
Optical computing where circuits are replaced by light beams is a step closer with nanoantennaes that can be tuned to emit and receive particular wavelengths and manufactured without complex methods.
Optical computing could be faster than today’s computers, but the microchips that can send and receive the light transmissions must be able to process data just as fast as conventional chips and be as compact. Producing electronic components that can generate a viable light beam to transmit directly sufficient data and act as a receiver to achieve the clock speeds necessary requires a careful mix of materials.
For optical devices in microelectronics the light sources are at the nanoscale, 100 nanometres or smaller, so they can be integrated into the microchips. These nanoscale light sources and the nanoantennae that can receive the beam have been in use, but they have drawbacks. They are, limited in their efficiency in producing light, have an inability to properly focus the light in one direction and aim correctly at a receiver, are fixed to one wavelength, and have complicated fabrication processes. Fabrication could involve vacuum chambers and the chemical vapour deposition process, for example.
To overcome these problems, scientists from ITMO University in Saint Petersburg, Russia, have used the material halide perovskite, which is also a semiconductor. “Clean rooms are not needed with perovskite and we can manufacture optical resonance particles,” explained ITMO University nanophotonics and metamaterials researcher, Sergey Makarov. “[They] emit light, in red, green and yellow…so this is a simple technique and then you can put this nanoantenna within an optical chip very easily by laser ablation or nanomanipulator.”
The simulation results of nonlinear light scattering by a nanoantenna of two silicon particles. Credit: MIPT
Makarov’s team synthesize perovskite film and then transfer perovskite particles to another substrate using a pulsed laser ablation technique. The researchers describe this as, “relatively simple and cost-effective," compared to other manufacturing techniques.
Makarov points out that other materials used for light sources and nanoantennaes have been Germanium and Gallium Arsenide. He states that both have drawbacks, they are not as efficient in generating light, their manufacture requires clean rooms and special manufacturing technology, including what Makarov describes as, “complicated lithography.” Lithogaphy being the method of manufacturing microchips. There have also been efforts to grow Gallium nanostructures onto an optical chip, but there is a need to have a difficult crystalline lattice structure to avoid the stress and defects that can occur at the interface between the nanoantennae and the chip, undermining the performance.
In comparison, halide perovskite can be used for a nanoantennae that also emits light, removing one obstacle to transmissions and it does not have an interface problem. A perovskite nanoantennae can be fixed to a silicon microchip, “we can deposit simply which does not require such precise matching of anything,” Makarov explained. He added that his team of researchers are now working on how to tune the nanoantennae to produce different wavelengths, different colours of light. The halide perovskite can have its wavelength altered with laser ablation and still function, albeit differently; where other materials, if they are ablated, are so damaged they do not work.