Characterisation of gamma-irradiated MCz-silicon detectors with a high-K negative oxide as field insulator

The high-luminosity operation of the Tracker in the Compact Muon Solenid (CMS) detector at the Large Hadron Collider (LHC) experiment calls for the development of silicon-based sensors. This involves implementation of AC-coupling to micro-scale pixel sensor areas to provide enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of AC-pixel sensors with negative oxides (such as aluminium oxide — Al₂O₃ and hafnium oxide — HfO₂) as field insulators that possess good dielectric strength and provide radiation hardness. Thin films of Al₂O₃ and HfO₂ grown by atomic layer deposition (ALD) method were used as dielectrics for capacitive coupling. A comparison study based on dielectric material used in MOS capacitors indicate HfO₂ as a better candidate since it provides higher sensitivity (where, the term sensitivity is defined as the ratio of the change in flat-band voltage to dose) to negative charge accumulation with gamma irradiation. Further, space charge sign inversion was observed for sensors processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates that were irradiated with gamma rays up to a dose of 1 MGy. The inter-pixel resistance values of heavily gamma irradiated AC-coupled pixel sensors suggest that high-K negative oxides as field insulators provide a good electrical isolation between the pixels.