Appl. Phys. Lett., 101, 171101 (2012)

Credit: © 2012 APS

According to Wolfram Pernice and Harish Bhaskaran from the Karlsruhe Institute of Technology in Germany and the University of Exeter in the UK, the fabrication of non-volatile optical memories should be possible by depositing thin films of the chalcogenide Ge2Sb2Te5 (GST) onto silicon nitride waveguides. Their idea is to coat a short section of a ring waveguide resonator with GST, which switches between amorphous and crystalline phases when heated. Visible control light from a nearby waveguide would be evanescently coupled to the GST-coated section of the ring, which would trigger optically induced heating and thus a phase change of GST into its crystalline state. This would show up as a change in the ring resonator's transmission characteristics, as it would become significantly more lossy in its crystalline state. By sending a 1,550 nm probe beam into the ring resonator, its phase status (amorphous or crystalline) could be determined and used to represent a digital data bit. Numerical analysis suggests that a 600 fs optical pulse with a power of 5.4 pJ would be sufficient to raise the temperature of the GST to 400°C and thus induce crystallization. The phase state can then be reset by re-amorphization by heating the GST to an even higher temperature.