Plasma-based etching approach for GEM detector microfabrication at FBK for X-ray polarimetry in space

Gas Electron Multiplier (GEM) detectors are crucial for enabling high -resolution X-ray polarization of astrophysical sources when coupled to custom pixel readout ASIC in Gas Pixel Detectors (GPD), as in the Imaging X-ray Polarimetry Explorer (IXPE), the Polarlight cubesat pathfinder and the PFA telescope onboard the future large enhanced X-ray Timing and Polarimetry (eXTP) Chinese mission. The R&D efforts of the IXPE collaboration have resulted in mature GPD technology. However, limitations in the classical wet -etch or laser -drilled fabrication process of GEMs motivated our exploration of alternative methods. This work focuses on investigating a plasma -based etching approach for fabricating GEM patterns at Fondazione Bruno Kessler (FBK). The objective is improve the aspect ratio of the GEM holes, to mitigate the charging of the GEM dielectric which generates rate -dependent gain changes. Unlike the traditional wet -etch process, Reactive Ion Etching (RIE) enables more vertical etching profiles and thus better aspect ratios. Moreover, the RIE process promises to overcome non -uniformities in the GEM hole patterns which are believed to cause systemic effects in the azimuthal response of GPDs equipped with either laser -drilled or wet -etch GEMs. We present a GEM geometry with 20 mu m in diameter and 50 mu m pitch, accompanied characterization (SEM and PFIB) of the structural features and aspect ratios. The with INFN Pisa and Turin enabled us to compare the electrical properties of these detectors their performance in their use as electron multipliers in GPDs. Although this R&D initial stages, it holds promise for enhancing the sensitivity of the IXPE mission in X-ray measurements through GEM pattern with more vertical hole profiles. The outcomes have the potential to advance the current technological platforms and improve the future space-based X-ray polarimetry missions.