Anode capacitance measurement of silicon drift detectors in operating conditions

We describe a technique for measuring with high accuracy and precision the capacitance of the anode of a semiconductor drift detector (SDD) fully biased in operating conditions and connected to the front-end electronics. The proposed method does not require the use of a probe station, making it suitable for low-cost and easy-to-setup application environments. We have performed measurements on four SDDs with different geometries and production processes, observing a total capacitance ranging from 20 fF to 75 fF, depending on the bias conditions. Different components of the anode capacitance with respect to the front cathode and the adjacent drift cathodes have been measured and commented as well. Precision in the capacitance measurements better than 0.1 fF has been obtained. These results can be effectively used for the optimization of the front-end electronics for SDDs to achieve minimum electronic noise.