SDD technology

Lienar SDD working principle

The working principle of the SDD is shown below: the cloud of electrons generated by the interaction of an X-ray photon is drifted towards the read-out anodes, driven by a constant electric field sustained by a progressively decreasing negative voltage applied to a series of cathodes, down to the anodes at ~0 V. The diffusion in Si causes the electron cloud to expand by a factor depending on the square root of the drift time. The charge distribution over the collecting anodes then depends on the absorption point in the detector.

Working principle of a linear SDD

The largest linear SDD ever built

The largest Silicon Drift Detector ever built

A new large area, 120 × 72 mm2, linear multi-anode SDD, REDSOX1, has been developed for modern space-borne X-ray astronomy applications. It features a sensitive area of 76 cm2, and an energy range of 2-50 keV with a spectral resolution below 260 eV at 6 keV. Taking into account the stringent constrains on the front-end power consumption of a real application (LOFT), the anode pitch has been optimized allowing a large leeway in the system level design, where parameters such as the orbit of the satellite and its operative temperature are tuned. This detector provides for spectroscopy timing on a ten microseconds scale, enabling the exploration of the X-ray sky with an unprecedented sensitivity due to the very large effective area that now can be instrumented.

Verified via a number of prototypes, the design guarantees the detector stability against the variation of external conditions while, at the same time, reducing at its minimum the surface component of the leakage current. The integrated voltage divider has been designed to satisfy the stringent limits of space-born applications, where the power consumption has to be lower than 0.5 mW/cm2 of sensitive area at room temperature. Lastly, the optimized drift cathode geometry has allowed enhancing the detector quantum efficiency at the low end of the energy range.
The REDSOX1 SDD has been adopted as the baseline detector for the LOFT mission design concept.

Multi-cell SDD for Low Energy X-Ray Fluorescence (LEXRF) spectroscopy

TwinMic is worldwide unique in combining transmission imaging, absorption spectroscopy and low-energy X-ray Fluorescence (LEXRF), which allows for analyzing simultaneously the morphology and elemental or chemical distribution of specimens with sub-micron resolution in the 400-2200 eV energy range.
A novel, multi-cell, trapezoidal Silicon Drift detector, optimized for LEXRF thas been designed, produced and tested.

The italian beamline XAFS at ELETTRA is dedicated to X-ray absorption spectroscopy. It combines the capability of X-ray absorption spectroscopy (XAS) to provide short range chemically specific structural information around the photoabsorber atom together with x-ray diffraction (XRD) sensitive to a longer range. Both techniques allow to fully characterize material structure.
XAFS is installed on a bending magnet source and cover the wide energy range from 2.4 keV to 27 keV.
A new configuration of th XAFS Si detector is under development to allow a more efficient employment of the facility by reducing the dead time (segmented detector) and the time of integration for a measurement (larger area) by means of a customized large-area Si drift detector which design is driven by specific simulations of the beamline set-up.