Impact of charge collection efficiency and electronic noise on the performance of solid-state 3D microdetectors

Abstract

Microdosimetry has been traditionally performed through gaseous proportional counters, although in recent years different solid-state microdosimeters have been proposed and constructed for this task. In this paper, we analyze the response of solid-state devices of micrometric size with no intrinsic gain developed by CNM-CSIC (Spain). There are two major aspects of the operation of these devices that affect the reconstruction of the probability distributions and momenta of stochastic quantities related to microdosimetry. For micrometric volumes, the drift and diffusion of the charge carriers gives rise to a partial charge collection efficiency in the peripheral region of the depleted volume. This effect produces a perturbation of the reconstructed pulse height (i.e. imparted energy) distributions with respect to the actual microdosimetric distributions. The relevance of this deviation depends on the size, geometry and operating conditions of the device. On the other hand, the electronic noise from the single-event readout set-up poses a limit on the minimum detectable lineal energy when the microdosimeter size is reduced. This article addresses these issues to provide a framework on the physical constraints for the design and operation of solid-state microdosimeters.

Microdosimetric measurements of a monoenergetic and modulated Bragg Peaks of 62 MeV therapeutic proton beam with a synthetic single crystal diamond microdosimeter

“…This decreasing of the noise is mainly due to: (a) the optimization of the encapsulation kit and (b) the increasing of the thickness of the diamond SV. 47 Such value is much lower than that reported for ΔE-E monolithic 2 µm thick silicon microdosimeter (corresponding to a water equivalent thickness of approximately 4.5 µm) tested in the same condition measurement. 20 Indeed, this low noise value is comparable with that of a silicon-on-insulator diode array-based microdosimeter 21,48 characterized by a water equivalent SV thickness very similar to that of our device (i.e., about 22 µm).…”

“…One first notes the significantly improved noise performance of the diamond microdosimeter in comparison to that one tested at CNAO facility, 29 about a factor of ten less, in terms of the minimum measurable lineal energy. This decreasing of the noise is mainly due to: (a) the optimization of the encapsulation kit and (b) the increasing of the thickness of the diamond SV 47 . Such value is much lower than that reported for ΔE‐E monolithic 2 µm thick silicon microdosimeter (corresponding to a water equivalent thickness of approximately 4.5 µm) tested in the same condition measurement 20 .…”

Silicon 3D Microdetectors for Microdosimetry in Hadron Therapy

“…The first one belongs to the U3DTHIN architecture [35,37,50,[57][58][59]. On the basis of the preliminary results with U3DTHIN detectors, a novel architecture based on 3D-cylindrical microstructures was proposed and specifically developed for microdosimetry in hadron therapy [32][33][34]36,[38][39][40][41].…”

“…For this purpose, we designed and fabricated novel radiation detectors with both 3D and 3D-cylindrical architectures, which were etched inside the silicon bulk in the National Center of Microelectronics (IMB-CNM, CSIC, Spain). These 3D microstructures were specifically customized for microdosimetry in PT and they overcame some of the technological challenges in this domain, namely the low noise capability, well-defined sensitive volume, high spatial resolution, and pile-up robustness [32][33][34][35][36][37][38][39][40][41]. Both architectures reduce the loss of charge carriers due to trapping effects, the charge collection time, and the voltage required for full depletion compared to planar silicon detectors.…”

“…Likewise, Agosteo et al created a ∆E_E silicon telescope that is useful for beam characterization [30]. On the other hand, the reliable measurement of lineal energy distributions above 1 keV/µm sets a lower limit on the mean chord length of the site used for silicon devices without an intrinsic gain of around 5 µm [40]. As a consequence, solid-state devices with the necessary low measurement threshold cannot be produced at the sub-micrometric scale.…”