Design of microlens arrays for thermal imaging with spintronic Poisson bolometers

Abstract Infrared (IR) detectors are widely used due to their ability to sense thermal radiation. Recently, a room-temperature IR detector known as the spintronic Poisson bolometer (SPB) was introduced. While offering fast digital readout, its sensitivity is currently limited by its small photosensitive area and array fill factor (FF). Beyond this specific detector, many emerging detector architectures also require substantial in-pixel electronics or engineering tradeoffs, which can reduce the FF and degrade optical coupling efficiency. In this work, we present design guidelines for spherical plano-convex microlens arrays (MLAs) that enhance light collection in SPB arrays in the mid-wave IR (MWIR). Guided by the simulations, we fabricate a MLA sample to demonstrate that the chosen geometrical parameters are experimentally attainable and compatible with the fabrication process. We then systematically explore the scaling laws between sensor active size, microlens geometries, and the resulting light collection metrics, yielding practical design rules that are broadly relevant to MWIR detector arrays with limited active area. A radiometric-stochastic model is used to quantify the resulting sensitivity improvements for the SPB. Our work is the first systematic simulation of a microlens design with SPB arrays, bridging microphotonics, spintronics, and thermal imaging.