Recent advances in the development of high-resolution 3D cadmium–zinc–telluride drift strip detectors

Abstract

In the last two decades, great efforts have been made in the development of 3D cadmium–zinc–telluride (CZT) detectors operating at room temperature for gamma-ray spectroscopic imaging. This work presents the spectroscopic performance of new high-resolution CZT drift strip detectors, recently developed at IMEM-CNR of Parma (Italy) in collaboration with due2lab (Italy). The detectors (19.4 mm × 19.4 mm × 6 mm) are organized into collecting anode strips (pitch of 1.6 mm) and drift strips (pitch of 0.4 mm) which are negatively biased to optimize electron charge collection. The cathode is divided into strips orthogonal to the anode strips with a pitch of 2 mm. Dedicated pulse processing analysis was performed on a wide range of collected and induced charge pulse shapes using custom 32-channel digital readout electronics. Excellent room-temperature energy resolution (1.3% FWHM at 662 keV) was achieved using the detectors without any spectral corrections. Further improvements (0.8% FWHM at 662 keV) were also obtained through a novel correction technique based on the analysis of collected-induced charge pulses from anode and drift strips. These activities are in the framework of two Italian research projects on the development of spectroscopic gamma-ray imagers (10–1000 keV) for astrophysical and medical applications.

Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors

“…Cross-talk events can be given by the collected-charge pulses ; i.e., they are created by the charge carriers really collected by the pixels (e.g., fluorescent X rays) or by induced-charge pulses generated on neighboring non-collecting pixels [ 9 , 16 , 18 ]. These pulses, also called transient pulses , are due to the weighting potential cross-talk [ 9 , 10 , 11 , 18 , 20 ]; they are characterized by both positive and negative polarities and different shapes [ 9 ]. In our investigated energy range (up to 140 keV), a very low number of these transient pulses was detected.…”

“…This is due to the low investigated photon energies that produce very small transient pulses, which are often below our detection energy threshold (4 keV). Transient pulses are clearly visible at higher energies (e.g., at 662 keV) [ 9 , 10 ]; these pulses measured in temporal coincidence with the collected pulses are strongly used for both spatial and energy resolution improvements in gamma-ray detectors [ 9 , 10 ].…”

“…Moreover, fluorescent X rays, escaping from the pixels, can also produce cross-talk events between pixels. Cross-talk events can be given by the collected-charge pulses; i.e., they are created by the charge carriers really collected by the pixels (e.g., fluorescent X rays) or by induced-charge pulses generated on neighboring non-collecting pixels [9,16,18]. These pulses, also called transient pulses, are due to the weighting potential cross-talk [9][10][11]18,20]; they are characterized by both positive and negative polarities and different shapes [9].…”

“…Generally, RTSDs are represented by X-ray and gamma ray detectors based on high-Z and wide-bandgap compound semiconductors, with the goal to measure high-resolution energy spectra near room-temperature conditions. Currently, thin cadmium telluride (CdTe) and cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors, with thickness up to 3 mm are considered the best choice up to 150 keV [ 7 , 8 ], while thicker detectors (up to 15 mm), based on CZT [ 9 , 10 , 11 , 12 ] and thallium bromide (TlBr) [ 13 ], are very appealing up to 1 MeV. RTSDs with small pixels represent a key choice for energy resolution improvements, which is in agreement with the small pixel effect [ 7 ] and potentially to obtain high spatial resolution.…”

Quaternary Semiconductor Cd1−xZnxTe1−ySey for High-Resolution, Room-Temperature Gamma-Ray Detection

“…The working of Frisch grid has been demonstrated in Figure 3. Frisch grid effects can be enabled in large volume CZT detectors by adopting virtual Frisch grid electrode geometries such as small pixel [29,30], Frisch collar [31][32][33], coplanar grids [30,34], and drift strip electrode [35]. However, the fabrication of virtual Frisch grid geometries adds to the cost of manufacturing and often involves complicated peripheral electronics to process the signal.…”