Noise measurements on Si sensors

Developing silicon strip sensors for the CMS Preshower detector we have noticed that some strips have a noise higher than the average and not correlated to a high leakage current. In order to investigate this effect we have developed a set-up for noise measurement on wafers and diced sensors that does not require bonding. The set-up is based on the DeltaStream chip coupled to a probe card. We have tested 45 sensors and found that the strips with an above average noise have a higher relative current increase as a function of voltage, DeltaI /(IDeltaV). We also observed that, on these strips, the breakdown occurs within about 60 V from the voltage at which the noise is observed. We describe our measurement method and present the results.