A SPICE model of the ohmic side of double-sided Si microstrip detectors

Abstract

We have developed a SPICE model for the ohmic side of AC-coupled Si microstrip detectors where interstrip isolation is obtained via field plates. The interstrip isolation has been measured in various conditions by varying the field plate voltage. Simulations have been compared with experimental data in order to determine the values of the SPICE parameters for different voltages applied to the field plates. The model is able to predict correctly the frequency dependence of the coupling between adjacent strips. Furthermore, we have used such model for the study of the signal propagation along the detector when a current signal is injected in a strip. Only electrical coupling is considered here, without any contribution due to charge sharing derived from carrier diffusion. For this purpose, the AC pads of the strips have been connected to a read-out electronics and the current signal has been injected into a DC pad. Good agreement between measurements and simulations has been reached for the central strip and the first neighbours. Experimental tests and computer simulations have been performed for four different strip and field plate layouts, in order to investigate how the detector geometry affects the parameters of the SPICE model and the signal propagation. Furthermore we have considered neutron irradiated devices to study the modifications induced by radiation on the detector performance and the impact on the SPICE model.