Development of laser micromachined MicroWell detectors

MicroWell (MWD) detectors have been produced by laser micromachining of 125 μm thick Kapton^TM polyimide foil. Wells produced with this technique have near-vertical sidewalls with less than 10° of slope. It is an ideal tool to produce MWD prototype arrays with different well diameters for an experimental determination of the optimum ratio of well diameter to substrate thickness. Arrays with four different well diameters (60, 100, 150, and 180 μm) were machined into 125 μm thick Kapton^TM polyimide foil. Detectors with well diameters commensurate with the substrate thickness had better performance, with the best design being an array of 150 μm diameter wells on a 200 μm Cartesian grid. This design achieved a gas gain of 17,000 in a counting gas of 70% argon and 30% carbon dioxide. Other significant advantages of this design included good charge collection from the drift region and increased gas gain with higher drift fields