Silicon-on-insulator microdosimetry for space application

This thesis describes the electrical and charge collection characteristics of the updated second generation and third generation silicon-on-insulator (SOI) microdosimeter and its application to space and other areas. A microdosimeter is an important device used to measure the linear energy transfer (LET) distribution of radiation interacting with a biological system or electronics. It is important to have a good measure of the dose equivalent for medical and occupational safety purposes. The accurate measurement of the relative biological effect (RBE) of radiation field in these situations requires this portable microdosimeter device with a sensitive volume of the micron scale, equivalent to the size to a biological cell. The Centre for Medical Radiation Physics (CMRP) at the University of Wollongong (UOW) has previously developed a SOI device capable of measuring the pattern of energy deposited in small sensitive volumes (SV) of biological cell size. Despite good results being achieved with this device in clinical and radiation protection studies, further improved performance could be achieved via revision of the design. Together with its collaborative partners CMRP has developed the updated secondgeneration SOI microdosimeter on p-type high resistivity SOI with a 3D cylindrical pn junction sensitive volume (SV), which reduces the chord length variance and supports a radial electric field. The surface above the region outside the SV is topped with an N+ guard electrode to reduce any collection of laterally diffused charge. Two designs were tested: one where a defined guard ring electrode surrounds each individual SV and another where the guard ring electrode is covering contiguously the regions between all SVs. Fabrication and preliminary testing of different versions of the device is being performed at the semiconductor nanofabrication facility at the University of New South Wales (UNSW) and testing with ionising radiation is underway at the Australian Nuclear Science and Technology Organisation (ANSTO). Standard electrical characterisation techniques along with ion beam induced charge collection (IBIC) studies were used to assess the charge collection properties of the new devices. The I-V tests showed the properly functioning SVs of microdosimeters; additionally these devices were tested using alpha spectroscopy from Am-241 source and on a heavy ion microbeam utilizing Ion Beam Induced Current (IBIC) studies. Results show that with both types of guard ring devices the SV maintains a well defined cylindrical geometry