Fabrication and Characterisations of New Ultra-thin Silicon Detectors as Pre-Cell Hit Detectors for a Cell Irradiation Facility at LIBAF

University dissertation from Lund University

Abstract: For the development of single–ion irradiation system for living cells at the Lund Ion Beam Analysis facility (LIBAF) newly developed pre-cell (PC) detectors have been investigated. Central to the thesis is the fabrication and initial characterization of more than 100 ultra-thin silicon detectors having different thicknesses down to 5 μm with active areas ranging from 0.71 to 0.172 mm2, to be used as PC detectors. The fabrication and packaging processes of these devices were carried out on the double-polished silicon substrate n-type wafer using Silicon Microfabrication Technology. The main design considerations of our thin detectors were a very low leakage current below 12 nA and a low full depletion voltage at a reverse bias less than 1.5 V. The performance of the thin detectors as particle trackers was investigated with 5.487 MeV alpha particles, obtaining a good energy resolution (FWHM) and high efficiency. During the detector tests as a pre-detection stage of 2.55 MeV protons in ΔE-E configuration, the results showed that best performing detector 9.7 μm thick, had a detection efficiency of 96%. This efficiency is good enough to be utilized as good single-proton identifier. In conclusion, the fabricated devices are well suited for living cell irradiation experiments.

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