GEM-type detectors using LIGA and etchable glass technologies

Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by ultraviolet (UV) processes using a UV etchable glass. The gain, stability, and rate capability for these detectors are described. The LIGA detectors described consist of PMMA sheets of various thicknesses, 125-350 μm, and have 150×150 μm² holes spaced with a pitch of 300 μm. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin-base layer. For various thicknesses of PMMA, measurements have been made of absolute gain versus voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO₂ (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability.