1 Abstract– A study of charge collection in SINTEF 3D active edge silicon detectors was carried out at ANSTO using Ion Beam Induced Charge (IBIC) technique. An IBIC study has shown that several different geometries of 3D detectors have full depletion under low applied bias. The effect of fast neutron and gamma radiation on their charge collection efficiency was also investigated. A 3D active edge silicon detector technology has demonstrated extremely promising performance for application of the 3D Sensitive Volumes (SVs) fabrication methods to SOI microdosimetry. Index Terms—Microdosimetry, 3D detector, radiation damage, charge collection, IBIC. I. INTRODUCTION HE microdosimetric approach involves measuring the stochastic lineal energy deposition, on an event-by-event basis. The energy depositions are, on a micron scale sensitive target volume (SV), comparable to human cell dimensions. These events arise from charged particles traversing the SV from either the primary radiation field or from secondary particles originating via nuclear interactions within the surrounding material. Using microdosimetry it is possible to be able to deduce the dose equivalent in any arbitrary mixed radiation field [1]. This is a major advantage over the other dosimetry methods that can only measure the absorbed dose or require prior knowledge of the field composition. Conventional microdosimeter uses a tissue equivalent proportional counter (TEPC) that incorporates a spherical SV filled with tissue equivalent gas and is able to model a micron sized biological cell by using low pressures. The TEPC has several limitations including high voltage operation, large size (i.e. poor spatial resolution), and is only able to mimic a single, isolated cell [2]. The solid state microdosimeter was L. T. Tran, M. Petasecca, M. L. F. Lerch and A. B. Rosenfeld are with the Centre for Medical Radiation Physics, University of Wollongong, NSW 2522, Australia (e-mail: tlt822@uowmail.edu.au; marcop@uow.edu.au, mlerch@uow.edu.au; anatoly@uow.edu.au). D. A. Prokopovich and M. I. Reinhard are with the Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW2234, Australia (e-mail: dpr@ansto.gov.au; mrz@ansto.gov.au). A.Kok and A.Summanwar are with the SINTEF MiNaLab, SINTEF, Oslo, Norway (email: angela.kok@sintef.no; Anand.Summanwar@sintef.no). C. Da Via is with the University of Manchester, UK (email: Cinzia.Da.Via@cern.ch). proposed as a new method of measuring the energy deposition in an array of micron sized SVs [2, 3]. The Centre for Medical Radiation Physics (CMRP) has developed three generations of microdosimeters based on silicon-on-insulator (SOI) substrates [4-8]. These SOI microdosimeters were based on planar and pseudo 3D mesa rectangular parallelepiped (RPP) and cylindrical SVs produced on p-SOI and n-SOI using diffusion or implantation techniques for forming laterally depleted p-i-n diodes. However, the previous generations have had lateral charge diffusion from outside the SVs in the device. The diffusion charge collection compromises the definition of the SV increasing the uncertainty in the microdosimetric parameters, such as an average chord and chords variance. In order to address these challenges, CMRP has proposed design of optimal SOI microdosimeter with free standing true 3D “mushroom” SVs. Three dimensional (3D) SVs embedded in polymethyl methacrylate (PMMA) can be fabricated using 3D detector technology via state-of-the-art silicon processing facilities which are well established at SINTEF MiNalab, Oslo, Norway. Fabrication of new SOI microdosimeters is a significant step forward in radiation dosimetry for radiation protection in space, avionics, and radiation therapy applications. The 3D detector concept was first proposed by S. Parker in 1995 and the active edge detector technology was proposed by C. Kenney in 1997. The developments of micro-machining and standard VLSI (Very Large Scale Integration) technologies, together with advanced technology - Deep Reactive Ion Etching (DRIE) make 3D detector fabrication possible [9]. 3D electrodes are achieved by precisely drilling cylindrical micro-holes in a silicon wafer using DRIE technology, which includes an inductively-coupled plasma etching and a sidewall passivation [10]. These holes are then filled with conductive boron or phosphorus doped polycrystalline silicon. Another important feature of the 3D detector is an active edge technology, which can be used in fabrication of the 3D SV for microdosimeters [11]. A principle of etching 3D technology is shown in Fig.1. In 2008 SINTEF MiNaLab was the second laboratory in the world that has successfully explored and fabricated the 3D detectors with the active edges on a small production scale [12, 14]. 3D Radiation Detectors: Charge Collection Characterisation and Applicability of Technology for Microdosimetry. Linh T. Tran, Student Member, IEEE, Dale A. Prokopovich, Marco Petasecca, Member, IEEE, Michael L. F. Lerch, Member, IEEE, Angela Kok, Anand Summanwar, Thor-Erik Hansen, Cinzia Da Via, Mark I. Reinhard, Member, IEEE and Anatoly B. Rosenfeld, SeniorMember, IEEE T Final version available at IEEEXplore : http://dx.doi.org/10.1109/TNS.2014.2301729