Characterisation of Gamma-irradiated MCz-Silicon Detectors with a High-$K$ Negative Oxide as Field Insulator

TL;DR

This study investigates gamma-irradiated MCz-silicon detectors with high-$K$ negative oxides as field insulators, demonstrating their potential for improved radiation hardness and electrical isolation in high-luminosity collider environments.

Contribution

It introduces the use of high-$K$ negative oxides like HfO$_2$ as field insulators in AC-coupled silicon sensors, showing enhanced radiation hardness and electrical isolation.

Findings

HfO$_2$ provides higher sensitivity to gamma radiation than Al$_2$O$_3$.

Space charge sign inversion occurs at high gamma doses in MCz-Si sensors.

High-$K$ negative oxides improve inter-pixel electrical isolation after irradiation.

Abstract

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 - Al$_2$O$_3$ and hafnium oxide - HfO$_2$) as field insulators that possess good dielectric strength and provide radiation hardness. Thin films of Al$_2$O$_3$ and HfO$_2$ 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 HfO$_2$ 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.