The Punch-Through Effect in Silicon Strip Detectors

In order to protect AC-coupled Silicon strip detectors (SSD) in beam accidents, punch-through protection (PTP) structures are implemented, which are designed to clamp the strip potential to ground when large charges in the bulk break down the electric field. We present a study where we cause the field in the bulk to collapse by illumination with 1064 nm IR pulses, and measure the voltages on the strips as a function of the bias voltage. These voltages are compared with the results of DC I-V measurements, which are commonly used to characterize the effectiveness of the PTP structures, and we find that the PTP structures are only effective at very large currents (several mA), and clamp the strips to much larger voltage than the one derived from DC scans. We also find that the finite resistance of the strip implant compromises the effectiveness of the PTP structures. Radiation damage effects are also presented.