Laser Ablation of Polyimide Foil for Applications as Electrodes in the Micro-Pattern Gaseous Detectors

Abstract

New manufacturing routes and materials need to be constantly developed to improve the performance of a new type of gas detector–a high-gain and fast-timing micro-pattern gaseous detector (MPGD)–which works as a gas electron multiplier. The cylindrical symmetry of microholes in perforated electrodes is desired in such detectors to ensure denser electric field lines and higher sensitivity, as well as stability of the detector. On the other hand, the probability of discharge between the electrodes arises at high gains. The discharge issue can be solved using a resistive layer with controlled electrical conductivity. In this work, we developed an ultrashort pulse laser ablation route to produce electrodes based on microstructuring of polyimide (Kapton™) foil that allows avoiding the wet-etching process and opens another level of variability in hole diameters and distribution over the surface. Femtosecond laser ablation was used to micromachine multiple arrays of cone-shaped through holes with narrowing diameters in an area of $3\times 3$ mm² in polyimide foil. By employing an unbalanced direct current magnetron sputtering method obtained micropatterned polyimide surface was covered with a diamond-like carbon layer of 50 nm thickness and $4.36~\pm ~2.49$ M $\Omega $ /sq average sheet resistance ( $R_{\mathbf {S}}$ ) as a resistive layer, which would be reconcilable with the technologies used in the fast-timing MPGD detectors.[2025-0230]