TopmetalSe: Development of a CMOS Imager for Selena

Abstract

The Selena experiment couples an amorphous selenium (aSe) ionization target to a custom complementary metal–oxide–semiconductor (CMOS) pixel array to create an imaging detector for next-generation neutrino physics. Hybrid aSe/CMOS devices combine the high-Z stopping power and room-temperature operation of aSe with the fine-pitch, low-noise readout of modern CMOS sensors, enabling precise reconstruction of ionization tracks for advanced background discrimination. This work presents the comprehensive simulated modeling and hardware development of Selena as a candidate search for neutrinoless double-beta decay in 82Se. A detailed simulation framework is developed to model double-beta events in a Selena detector, incorporating charge generation, drift, and collection processes, along with dedicated reconstruction techniques for event topology and energy response. In parallel, the Topmetal-Se prototype, fabricated in the open-source SkyWater 130 nm CMOS process, demonstrates direct charge sensing, low noise, and fine pixel pitch ionization track imaging when coupled to amorphous selenium. Together, these developments establish Selena as a viable platform for high-resolution ionization imaging and rare-event detection.