72: First investigations of Ultra-Thin 3D silicon detectors as microdosimeters

Abstract

IMB-CNM (CSIC) has developed a new type of threedimensional diode on ultrathin SOI silicon wafers with 3D columnar structures with P-N junctions fabricated with micromachining techniques for plasma diagnostic applications or neutron detection in demanding environments [1, 2]. The three-dimensional electrodes are columns etched through the silicon instead of being deposited on the surface like in the standard planar diodes. The sensitive volume is a silicon membrane only 10 microns thick (fig.1). The ultra-thin sensors have shown to be insensitive to the gamma radiation background, their membrane structure avoids the backscattering contributions from the supporting silicon wafer and the confinement of the electric field given by the columnar electrodes reduces charge sharing. All these characteristics make the ultra-thin 3D devices the perfect candidates for microdosimetry. Recently, IMB-CNM have carried out the first tests of these devices with beams of 62MeV protons and 95MeV/u C ions. The results of these first experiments show that, although they were not specifically designed for microdosimetric applications, the detectors with ultra-thin 3D structure are able to characterize the therapeutic hadron beams. Results from these proof-of-concept tests will be presented and compared with Monte Carlo simulations using MCNPX and Geant4 codes.