Switchable Nanolayers for Photonics on Silicon: towards novel High-efficiency Optoelectronics building blocks – SNAPSHOT

We live in a digital and connected world that relies on the fast transmission and treatment of numerical data. This is mainly due to the development of the microelectronics industry, which is the basis of most of the modern technological devices. This field currently faces scientific bottlenecks linked to the metal interconnects, preventing further progress in terms of speed and energy efficiency. The Electronics/Photonics convergence is currently considered as one of the most promising solution to rapidly solve this problem. However, Silicon, the backbone material of microelectronics’ industry is intrinsically limited in terms of electro-optical properties. In that context, a large interest is directed towards the heterogeneous integration of new (i.e. not silicon-based) functional materials on silicon substrates. The relevance of this strategy is twofold: first, it can enable the use of naturally functional materials with electro-optical properties far superior than those of silicon. And second, keeping silicon as a platform allows the integration of both electronics and photonics functionalities. Such an exciting challenge necessarily involves several fields of physics, from basic material research to electrical and optical engineering.

The SNAPSHOT project aims at developing novel active optoelectronic concepts and integrated devices that exploit the unique tunable properties of switchable materials. We define here switchable materials as those in which we can controllably modify the refractive index value by an external signal. In this project we focus on three of them that present complementary properties: VO2, GeSbTe and GeSe. The first one has unique properties of ultra-fast insulator-to-metal transition. This translates into an exceptionally large refractive index modulation (delta n > 1) at ultra-fast time-scale (~100 fs). The other two materials (GeSbTe and GeSe) belong to the so-called ‘chalcogenide’ class of materials and can be switched from an amorphous state to a crystalline state in a sub-nanosecond time-scale. These amorphous/crystalline states with different refractive indices (delta n = 0.4) are stable and therefore enable reconfigurable photonic environment and devices.

In this framework, our main goal is to implement a phase-change materials platform for photonics on silicon, not only to drastically boost silicon photonics’ existing building blocks in terms of speed, bandwidth and energy consumption, but also to open it up to new functionalities such as non-volatile reconfigurability that cannot be realized by silicon alone. A photonic design strategy will enable to fully exploit the unique properties of these materials while circumventing their drawbacks. We will design and fabricate original tunable low-footprint nanophotonic devices monolithically integrated on silicon whose usefulness will be demonstrated in two main class of devices: (1) Novel ultra-efficient approaches to integrated waveguide modulators. (2) Original tunable and reconfigurable metasurfaces and metamaterials.

The goal of this disruptive heterogeneous integration strategy is to make a significant step toward the full integration of actively tunable nanophotonic devices with silicon microelectronics technology. To reach this objective, we will conduct an ambitious project that both rely on the coordinator’s expertise in silicon photonics and phase-change materials, as well as the expertise from the team in nanophotonic devices and associated nanofabrication processes.