Cylindrical silicon-on-insulator microdosimeter: Design, fabrication and TCAD modeling

This work presents a new generation silicon-on- insulator (SOI)microdosimeter device . This new device was designed and fabricated using planar processing techniques to produce a micrometer sized cylindrical shaped, well defined microdosimeter sensitive volume. Cylindrical structures were employed to allow for a better definition of the average chord length of the sensitive volume compared to the previous elongated parallelepiped solid state designs. The structures were manufactured on individual mesas situated on top of a buried oxide insulating layer. These mesa designs eliminated lateral charge diffusion. Two kinds of test structures were designed with sensitive region widths of 2 mum and 10 mum. ISE TCAD modeling of the electrostatic potential and electric field profile of the cylindrical microdosimeter were carried out to obtain 3D potential and electric field profiles. The modeling found that as expected a radial electric field was established across the cylindrical shaped sensitive volume. The modeling also found it was possible to increase the reverse bias voltage to a point where internal amplification of event signals was obtained. This is important finding for the measurements of low linear energy transfer (LET) events.