Electrons' injection in Multi-Linear Silicon Drift Detectors

Abstract

Multi-Linear Silicon Drift Detectors (ML-SDDs) are a recent evolution of silicon drift detectors for position sensing and low-noise spectroscopy. The multi-linear transport mechanism based on electrons drift accounts for a relevant reduction in the number of channels required for true 2D position sensing and on chip JFETs allows the full exploitation of the small anode capacitance (<100 fF) in the spectroscopic measurement of the collected charge. However, since the second coordinate is measured from the electron drift time, an accurate real-time calibration of the relationship drift time-drift coordinate is needed and the on-line continuous monitoring of electron drift variations can be only performed relying on electron injectors directly integrated on-chip. The MLSDD prototype called BUTTERFLY presented in this work features two main points of novelty: i) an array of electron injectors based on a MOS structure to exploit the electron accumulation in the potential pocket at the silicon-oxide interface created by the fixed positive oxide charge and ii) an array of independently biased field-plate contacts between the p+ field strips that allow a better control of the properties of the silicon-dioxide interface thus optimizing the electron drift velocity. This paper reviews the relevant aspect of the detector design and presents the detailed qualification of the detector prototype together with the study of the dependence of the amount of injected charge on the injector geometrical parameters and biasing conditions that are relevant issues for the design of calibrated injectors.