Silicon drift detectors with spiralling electron transport and reduced lateral broadening

A new cylindrical drift detector has been designed, fabricated and tested in which the external applied field has radial symmetry but the electron cloud, generated by an ionizing radiation, follows a spiral-shaped path towards one central collecting electrode. Regions of deep p- and n- implants are used to generate the spiralling drift channel for the electrons close to the implanted side of the detector wafer and to suppress broadening in the direction transverse to the drift. A detailed study of the new detector (design, simulation and experimental measurements) is presented which shows the combined effect of the deep implants and of the external applied field on the electron transport. Applications of this technique are discussed, e.g. 2D position-sensing drift detectors with single output channel, compact delay lines in the microsecond range and study of long term electron drift.