Everything from cloud computing to video streaming can be achieved by using data centers. They use a lot of energy in the process. Data centers are under increased pressure to become more energy efficient.
There are physical connections that allow for the exchange of data in data centers. One way to reduce energy consumption in data centers is to use light to communicate with electrical switches that control the flow of light. The continued expansion of data centers requires multi-functional switches and energy efficient ones.
In a paper published online July 4 in Nature Nanotechnology, a team led by University of Washington scientists reported the design of an energy efficient, Silicon-based non-volatile switch that manipulates light through the use of a phase- change material and a Graphene heater.
The platform pushes the limits of energy efficiency, according to co-corresponding author Arka Majumdar, an associate professor of physics and electrical and computer engineering at the University of Washington. This technology would greatly reduce the energy needs of data centers and make them more sustainable.
Semiconductor fabrication techniques can be used to make Silicon photonic switches. In the past, thermal effect has been used to change the optical properties of a switch by applying heat to it. The changes it causes are not permanent. The material returns to its previous state when the current is taken out.
The "set and forget" switch created by the team is capable of maintaining the connection without any additional energy. They used a phase- change material that is non-volatile, meaning the material is transformed by briefly heating it, and it remains in that state until it receives another heat pulse. The need to input energy to maintain the desired state is eliminated.
Doped Silicon has been used to heat phase change. Silicon can both conduct electricity and light without any excess absorption when it is doped with different elements. The phase change material can be switched on by a current pumped through the doped Silicon. This is not a very energy efficient process. The amount of energy needed to switch the phase- change material is the same as the amount of energy used by traditional thermo-optic switches This is due to the fact that the entire 220 nanometer thick doped Silicon layer has to be heated to change its color. A lot of energy is wasted heating a large amount of material to make a small change.
The author said that they had to figure out how to reduce the volume that needed to be heated in order to boost the efficiency of the switches.
If you want to make a thinner film, you have to make it at a thinner wavelength. They used an un-doped 220 nm Silicon layer and a layer of Graphene between it and the phase change material to conduct electricity. Graphene is an excellent conductor of electricity, but unlike metal, it is atomically thin. The design eliminates wasted energy by using heat generated by the Graphene to change the phase- change material. The switching energy density of this setup, which is calculated by taking the switching energy divided by the volume of the material being switched, is only 8.7 attojoules. It's within one order of magnitude of the fundamental limit of energy density.
The phase change material can still interact with the light propagating in the Silicon layer despite the fact that it causes some optical losses. The team found that a Graphene-based heater can switch the state of the phase- change material more than 1,000 times. The doped Silicon heaters only have an endurance of around 500 cycles.
Majumdar said that even 1000 is not enough. We are currently working on a billion cycles endurance.
A key step towards establishing their use in data centers will be shown by the team when they demonstrate that light can be controlled using a phase- change material and Graphene Heater. They would like to use this technology to make quantum computing possible.
Majumdar said that the ability to tune the optical properties of a material is a game-changer. The exceptional performance of our system in terms of energy efficiency and reliability is very rare.
Some of the co-authors are electrical and computer engineering students from the University of Washington and other universities.
More information: Zhuoran Fang et al, Ultra-low-energy programmable non-volatile silicon photonics based on phase-change materials with graphene heaters, Nature Nanotechnology (2022). DOI: 10.1038/s41565-022-01153-w Journal information: Nature Nanotechnology
All Rights Reserved © 2024
