AUTHOR=Bharthuar S. , Golovleva M. , Bezak M. , Brücken E. , Gädda A. , Härkönen J. , Karadzhinova-Ferrer A. , Kramarenko N. , Kirschenmann S. , Koponen P. , Luukka P. , Mizohata K. , Ott J. , Tuominen E. TITLE=Characterization of Heavily Irradiated Dielectrics for Pixel Sensors Coupling Insulator Applications JOURNAL=Frontiers in Materials VOLUME=8 YEAR=2022 URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.769947 DOI=10.3389/fmats.2021.769947 ISSN=2296-8016 ABSTRACT=

An increase in the radiation levels during the high-luminosity operation of the Large Hadron Collider calls for the development of silicon-based pixel detectors that are used for particle tracking and vertex reconstruction. Unlike the conventionally used conductively coupled (DC-coupled) detectors that are prone to an increment in leakage currents due to radiation, capacitively coupled (AC-coupled) detectors are anticipated to be in operation in future collider experiments suitable for tracking purposes. The implementation of AC-coupling to micro-scale pixel sensor areas enables one to provide an enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of new generation capacitively coupled (AC-coupled) pixel sensors with coupling insulators having good dielectric strength and radiation hardness simultaneously. The AC-coupling insulator thin films were aluminum oxide (Al2O3) and hafnium oxide (HfO2) grown by the atomic layer deposition (ALD) method. A comparison study was performed based on the dielectric material used in MOS, MOSFET, and AC-coupled pixel prototypes processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates. Post-irradiation studies with 10 MeV protons up to a fluence of 1015 protons/cm2 suggest HfO2 to be a better candidate as it provides higher sensitivity with negative charge accumulation on irradiation. Furthermore, even though the nature of the dielectric does not affect the electric field within the AC-coupled pixel sensor, samples with HfO2 are comparatively less susceptible to undergo an early breakdown due to irradiation. Edge-transient current technique (e-TCT) measurements show a prominent double-junction effect as expected in heavily irradiated p-type detectors, in accordance with the simulation studies.