Readout Optimisation of Phase-Change Integrated Photonic Memory

Phase-change materials can be used for the realisation of non-volatile optical memory in integrated photonic systems [1]. These devices consist of patches of Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>Sb<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>Te<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> (GST) phase-change material deposited onto Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>N<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> or Si waveguides (Fig. 1a). Light propagating in the waveguide couples evanescently to the GST, triggering heating which can cause a switch between amorphous and crystalline phases, altering the device's optical transmission, so providing a memory and in-memory computing functionality [2]. Here, the geometry of the GST patch is investigated to optimise the readout contrast when the device undergoes the write process, where an amorphous mark is written into a fully crystalline starting state. Optimisations are carried out using finite-element thermo-optic simulations coupled to a bespoke phase-change model based on a Gillespie-type cellular automata and classical nucleation and growth theory [3], [4].