Studies of adhesives and metal contacts on silicon strip sensors for the ATLAS Inner Tracker

This thesis presents studies investigating the use of adhesives on the active area of silicon strip sensors for the construction of silicon strip detector modules for the ATLAS Phase-II Upgrade. 60 ATLAS07 miniature sensors were tested using three UV cure glues in comparison with the current baseline glue (a non-conductive epoxy). The impact of irradiation on the chemical composition of all adhesives under investigation was studied using three standard methods for chemical analysis: quadrupole time-of-flight mass spectroscopy, gel permeability chromatography and gas chromatography combined with mass spectrometry (GC-MS). GC-MS analyses of glue sample extracts before and after irradiation showed molecule cross-linking and broken chemical bonds to different extents and allowed to quantify the radiation hardness of the adhesives under investigation. Probe station measurements were used to investigate electrical characteristics of sensors partially covered with adhesives in comparison with sensors without adhesives. Leakage current, bulk capacitance, inter-strip capacitance and surface resistance were measured before and after gluing, after irradiation and after temperature cycling. The presence of glue on the active sensor area was found to increase the sensor leakage current and inter-strip capacitance and frequently led to early sensor breakdowns. Temperature cycling and irradiations reduced adverse effects due to glue to a small noise difference between sensors with and without glue. Charge collection efficiency measurements in a $\beta$-source setup were used to study the influence of adhesives on the silicon bulk. All sensors under investigation showed equivalent charge collection efficiencies for sensors with and without glue, as well as signal-to-noise ratios above the required minimum of ten for the foreseen bias voltage. Before irradiation, sensors with glue showed increased cluster sizes, which could be attributed to fluorescence effects inside the glue using testbeam measurements. During testbeam studies, sensor strips were found to respond inhomogeneously in bond pad regions. Follow-up measurements confirmed that the presence of bond pads affects the electric field within a sensor and leads to additional charge being collected around bond pads. As a result of these findings, the sensor bond pad layout was modified in order to minimise reduced tracking resolution caused by shifted strip responses.