Novel high‐resolution silicon drift detectors

Silicon drift detectors (SDDs) are used as energy‐dispersive detectors for x‐ray fluorescence analysis in commercial systems. Because of the low capacitance of the readout anode, achieved by the device topology and by the integration of the first FET on the chip, noise contributions are very small, allowing good energy resolution at low shaping times and high count rates. Typical energy resolution is better than 147 eV FWHM at 5.9 keV (Mn Kα), at ?10°C. This allows the chips to be cooled with a thermoelectric element, avoiding the use of liquid nitrogen. SDD chips are produced at MPI‐Halbleiterlabor in Munich with different geometries and areas. Recently, a new SDD has been developed which places the anode and the integrated JFET at the margin of the chip where it can easily be shielded from direct irradiation with the use of a collimator. The new layout allows the design of a readout anode with smaller area and therefore reduces the capacitance to values of about 120 fF compared with 200–250 fF with standard SDDs. The result is an improvement in energy resolution down to 128 eV at ?15°C. A second effect is the enhancement of the peak‐to‐background values to 6000 homogeneously across the active area of the detector. Copyright © 2004 John Wiley & Sons, Ltd.