Fabrication and nuclear reactor tests of ultra-thin 3D silicon neutron detectors with a boron carbide converter

Abstract

We describe the design, fabrication process and characterization of a thermal neutron detector based on ultra-thin silicon PIN diodes with 3D electrodes and a 10B4C neutron converter layer. The sensors were fabricated on SOI silicon with an active thickness of 20 μm which allows for a low gamma sensitivity, while the 3D structure of the electrodes results in a lower capacitance that in the equivalent planar sensor. The 2.7 μm 10B4C converter layer was deposited through RF magnetron sputtering on a whole silicon wafer, opening the path for mass-production. The detectors were tested in a thermal neutron beam at the nuclear reactor at the Instituto Superior Técnico in Lisbon and their intrinsic detection efficiency for themal neutrons and the gamma sensitivity as a function of the energy threshold were obtained.