Evaluation of Controlled-Drift Detectors in X-Ray Spectroscopic Imaging Applications

The Controlled-Drift Detector (CDD) is a fully-depleted silicon imager that allows 2D position sensing of X-rays in the 1-20keV range with excellent time resolution (few tens of µs) and with energy resolving capability of spectroscopic quality (200 eV FWHM @ 6 keV). Its working principle is based on a 2D matrix of potential wells which stores the generated charge during the integration phase, followed by a fast readout phase obtained by drifting the charges along the columns by means of a uniform electrostatic field. Owing to the fast readout mechanism (full-frame readout of about 2 μs for a 1cm-long detector) the integrate-readout cycle of a CDD is inherently shorter than the one of a Charge-Coupled Device (i.e. the reference X-ray imager). A further relevant benefit of the short integration time is the small leakage charge that allows operation at or near room temperature while still preserving a good energy resolution. Frontend JFET transistors integrated near the collecting anodes allow minimization of stray capacitances thus optimizing the energy resolution of each detected photon. The pixel size, typically of the order of 100 µm, can also be reduced down to 50µm. This poster presentation will focus on the working principle of CDDs and on the achievable performances in terms of frame frequency, energy resolution, operating temperature. Preliminary evaluation studies show how the acquisition of energy-resolved images of X-rays is a powerful tool in imaging experiments. In particular the poster will focus on the following application fields: Diffraction Enhanced Imaging, X-ray fluorescence Imaging, Absorption Contrast Imaging