Signal formation on a serpentine delay-line electrode patterned on the CdZnTe detector

Delay-line electrodes can simplify the readout hardware and reduce the power requirements of a nuclear radiation detector by replacing dozens or hundreds of readout circuits with only one or two time-sensitive readouts per detector face. The simplified means of lateral position-sensing with micrometer-range resolution was previously validated upon high-resistivity silicon, with the ultimate goal of mapping the recoil electrons from gamma-ray events, thereby increasing the angular resolution of gamma-cameras. However, the effect of the induced current on non-collecting legs of the meander pattern was not evaluated, a deficiency addressed in this paper, in which a Cd0.9Zn0.1Te (CZT) bulk crystal was used as the substrate. We present simulations of: (1) the electric field distribution, as calculated with MAXWELL® 12.0, within the CZT detector with the delay-line electrode, (2) the charge carrier drift motion within the semiconductor, and (3) the propagation of the induced charge signal along the meandering electrode pattern. CZT detectors purchased from ORBOTECH were reprocessed for studying various metal-semiconductor contacts, and with optimized interfaces, the fabrication of the delay-line electrode was performed using photolithographic processes in the Lurie Nanofabrication Facility in the University of Michigan. Current–voltage (I–V) characteristic curves were obtained for performance evaluation and compared with pre-processing data. Readout circuits were connected to the fabricated CZT detector to test the lateral position-sensing, and the overlay design used to balance the transmission line electrode is discussed.