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

V.M. Blanco Carballo

    Research output: ThesisPhD Thesis - Research UT, graduation UT

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    In this thesis several wafer post-processing steps have been applied to CMOS chips. Amplification gas strucutures are built on top of the microchips. A complete radiation imaging detector is obtained this way. 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, three dimensional reconstruction of charged particles trajectory, a fine pixel pitch and it has 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 fairly compared as same materials and dimentions can be used. It was found that GEM-like structures having a big amount of insulator perform worse than similar Micromegas-like structures. The maximum achievable gain before sparks is lower for GEM-like that 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 postprocessing. Tge devices were fully operational and cosmic rays could be detected. The spark rate of multistage detectors compared to single detectors must be studied. Also the signal development in these detectors is expected to be faster that in single stage detectors. Spark damage is a commong 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 layer deposited on top of the CMOS chip can help to reduce the spark problems. Discharges energy is reduced and microchips can survive the discharges that before would destroy them. Future detectors are not required any more not to spark as they can now be made spark proof. Integrated detectors can suffer reliability problems because of degradation due to moisture exposure. Also mechanical attacks will make the devices not to work. We have evaluated these problems to give storage and transportations recommendations. The use of other materials less sensitive to humidity were also studied.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • University of Twente
    • Schmitz, Jurriaan, Supervisor
    • Salm, Cora, Advisor
    Thesis sponsors
    Award date17 Jun 2009
    Place of PublicationEnschede
    Print ISBNs978-90-365-2855-9
    Publication statusPublished - 17 Jun 2009


    • IR-61528
    • SC-RID: Radiation Imaging detectors
    • EWI-15476
    • METIS-263896


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