Breakdown Voltage of the AC coupling oxide for a VELO sensor

The LHCb VELO sensors were systematically tested for their current-voltage (IV) characteristics, depletion voltage and problem channels [1]. Below we describe additional tests which measured the voltage at which the AC coupling oxide breaks down. As these tests are, by necessity, destructive only one sensor was fully characterized this way. For production purposes all sensors had each strip measured and the breakdown voltage is known to be > 40V /strip. The measurement of the breakdown voltage is especially important as it enables some estimates to be made of to be made of the tolerance of the VELO modules to intense beam spills.