Insulation Issues in Punch-Through Biased Silicon Microstrip Sensors

During the qualification tests of the punch-through biased, AC-coupled microstrip sensors for the Inner Tracking System of the ALICE experiment at CERN, sensors fabricated by one of the suppliers showed erratic loss of strip insulation on p-side. This has been attributed to local surface inversion, facilitated by the very low oxide charge density-order of 10
¹⁰
q/cm
²
-that can be obtained with (100) substrates. Numerical simulations providing quantitative insight into the phenomena, and electrical measurements that confirm the origin of the insulation problems are reported. A non-standard measurement technique suitable for investigating strip insulation issues is described.