Radiation imaging detectors made by wafer post-processing of CMOS chips

Gas amplification structures are built on top of the microchips by means of wafer post-processing. A complete radiation imaging gaseous detector is obtained this way. The purpose of the research presented in this thesis is to develop the technology needed to fabricate the previously mentioned radiation imaging detectors and determine its performance. Integrated Micromegas-like and GEM-like structures were fabricated on top of Timepix CMOS chips. Single electron efficiency, measured by counting the number of detected electrons from an 55Fe conversion in Ar/iC4H10 (95/5) was found to be well above 90%. The detector provides high single electron efficiency and three dimensional reconstruction of the trajectory of electrically charged particles. It has a fine pixel pitch and a low mass. All these features make it a suitable candidate for tracking of charged particles in future detectors like ATLAS or CMS after the LHC upgrade or the International Linear Collider. Micromegas-like and GEM-like structures can be compared fairly as same materials and dimensions can be used. It was found that GEM-like structures having a large amount of insulator perform worse than similar Micromegas-like structures. The maximum achievable gain before sparks appear is lower for GEM-like than for Micromegas-like. When the amount of insulator is reduced in the GEM-like structures, having recessed insulator walls with respect to the metal electrodes, the performance is similar to Micromegas-like structures. Multistage detectors on top of Timepix chips were also built using wafer post-processing. The devices were fully operational and cosmic rays could be detected. The spark rate of multistage detectors compared to single detectors must be studied further. Spark damage is a common problem in gaseous detectors. Sparks can destroy the readout electronics. We have deposited a-Si:H and SiRN on Timepix chips. We have shown that these high resistive layers deposited on top of the CMOS chip can help to reduce the spark problems. Discharge energy is reduced and microchips can survive discharges that otherwise would destroy them. Future detectors no longer need to be spark-less as they can now be made spark proof.