Analysis and comparison of the breakdown performance of semi- insulator and dielectric passivated Si strip detectors

The harsh radiation environment in future high-energy physics (HEP) experiments like LHC provides a challenging task to the performance of Si microstrip detectors. Normal operating condition for silicon detectors in HEP experiments are in most cases not as favourable as for experiments in nuclear physics. In HEP experiments the detector may be exposed to moisture and other adverse atmospheric environment. It is therefore utmost important to protect the sensitive surfaces against such poisonous effects. These instabilities can be nearly eliminated and the performance of Si detectors can be improved by implementing suitably passivated metal-overhang structures. This paper presents the influence of the relative permittivity of the passivant on the breakdown performance of the Si detectors using computer simulations. The semi-insulator and the dielectric passivated metal-overhang structures are compared under optimal conditions. The influence of various parameters such as passivation layer thickness, junction depth, metal-overhang width, device depth, substrate resistivity and fixed oxide charge on the junction breakdown voltage of these structures is extensively studied. The results presented in this work clearly demonstrate the superiority of the metal-overhang structure design employing semi-insulator passivated structures over dielectric passivated ones in realising a given breakdown voltage. The effect of bulk damage caused by hadron environment in the passivated Si detectors is simulated, to a first order approximation, by varying effective carrier concentration (calculated using Hamburg Model) and minority carrier lifetime. This approach allows getting an insight of the device behaviour after radiation damage by evaluating the electric field distribution, and thus proves helpful in predicting some interesting results