Characterization of HV-CMOS detectors in BCD8 technology and of a controlled hybridization technique

Radiation detectors built in high-voltage and high-resistivity CMOS technology are an interesting option for the large area pixel-trackers sought for the upgrade of the Large Hadron Collider experiments. A characterisation of the BCD8 technology by STMicroelectronics process has been performed to evaluate its suitability for the realisation of CMOS sensors with a depleted region of several tens of micrometer. Sensors featuring 50×250 μm2 pixels on a 125 Ωcm resistivity substrate have been characterized. The response to ionizing radiation is tested using radioactive sources and an X-ray tune, reading out the detector with an external spectroscopy chain. Irradiation tests were performed up to proton fluences exceeding 5⋅1015 p/cm2 and they show the depletion and breakdown voltages increases with irradiation. A hybridization process for capacitive coupling has been developed. Assemblies have been performed using the ATLAS FE-I4 readout ASIC and prototype CMOS sensors. Measurements show a planarity better than 1.5 μm peak-to-peak on the 5 mm length of the HV-CMOS chip. To evaluate more precisely the achievable uniformity dummy chips of FE-I4 sizes have been made on 6-inch wafers. The measurement of the 24 capacitors on each chip is expected to achieve a precise estimation of the real thickness uniformity. The goal is to achieve less then 10% variation on the glue thickness (∼0.5 μm).