Study of frequency-dependent strip admittance in silicon microstrip detectors

摘要

We report on detailed interstrip admittance measurements performed on double-sided, AC-coupled and punch-through biased silicon microstrip detectors. The sensors chosen have been fabricated on very high resistivity substrates, which translates in very low depletion voltages, in the range 10-20 V. This, together with the absence of bias resistors, allows a careful study of the strip admittance components over a wide range of bias voltages and frequencies. In some instances, beyond total depletion the measured interstrip capacitance and dissipation factor exhibit a marked voltage and frequency dependence, linked to the presence of some resistive component. A simple lumped electrical model has been developed to explain the observed features and 3-D numerical simulations have been performed, supporting the interpretation of the phenomena. These features of the admittance have been found to be closely correlated with a non-standard noise term, exhibiting a peculiar frequency/ time dependence, which adds in quadrature to the well known parallel and series noise sources.