Microheater hotspot engineering for spatially resolved and repeatable multi-level switching in foundry-processed phase change silicon photonics

Nonvolatile photonic integrated circuits employing phase change materials have relied either on optical switching with precise multi-level control but poor scalability or electrical switching with seamless integration and scalability but mostly limited to a binary response. The main limitation of the latter is relying on stochastic nucleation, since its random nature hinders the repeatability of multi-level states. Here, we show engineered waveguide-integrated microheaters to achieve precise spatial control of the temperature profile (i.e., hotspot) and, thus, switch deterministic areas of an embedded phase change material. We experimentally demonstrate this concept using a variety of foundry-processed doped-silicon microheaters on a silicon-on-insulator platform featuring Sb₂Se₃ or Ge₂Sb₂Se₄Te and achieve 27 cycles with 7 repeatable levels each. We further characterize the microheaters' response using Transient Thermoreflectance Imaging. Our microstructure engineering concept demonstrates the evasive repeatable multi-levels employing a single microheater device, which is necessary for robust and energy-efficient reprogrammable phase change photonics in analog processing and computing.