Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
Silicon Drift Detectors (SDDs) are used as X-ray sensors in a wide spectrum of applications in science and industry. The Semiconductor Laboratory of the Max-Planck-Institutes of Physics and Extraterrestrial Physics (MPI/HLL) and the company PNSensor are designing and fabricating these devices since many years.In honour of the benefits which have been achieved within the last 40 years in Energy Dispersive Spectroscopy (EDS) in Scanning Electron Microscopes (SEM) it is demonstrated and high-lightened by various examples that the SDDs represent an optimum measurement tool for that specific application allowing results at the physical limits.The most dominant aspect is that SDDs provide an energy resolution at the theoretical Fano Limit (FWHM 123 eV @ MnKα). This is true for a comfortable operation temperature of about -20 o C which is easily achieved by a peltier cooler. The reasons are to be searched in an ultrapure semiconductor detector fabrication process and a detector design which features a minimum signal anode and a first amplification step directly integrated into the sensor chip.It is even more interesting that the energy resolution is kept excellent also for very high count rates (up to 10 6 cps for a single cell SDD). This is one of the main differences to e.g. a Si(Li) detector. And again the reason is to be found in the detector design featuring a minimum signal capacitance. This aspect becomes most challenging when multi-cell structures are used.Third, leading the radiation entrance window to a technology which provides a minimum dead layer thickness allows together with the good energy resolution an excellent light element performance providing gaussian shaped spectra for Boron and Carbon and even Beryllium with perfect resolution (FWHM 38eV @ B_K). The peak-to background and the peak-to-valley ratios are maximized (P/B > 20.000 @ MnKα).A high quantum efficiency (> 60 %) is achieved by the same means for light elments and by expanding the sensor thickness for hard X-rays. Combining the SDD with a scintillator provides detection capability for gammas. The detection efficiency can be even enhanced by a dedicated sensor design which allows an optimum adjustment of the sensor close to the probe in its direct field of view.A large sensor area improves throughput and the capability of detecting trace elements. Various examples for applications with either large single cell areas (up to 1 sqcm) or multielement devices (up to 100 cells or 5 sqcm active area) are provided.
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