Planar Edgeless Silicon Detectors for the TOTEM Experiment 1.E-09 1.E-06 1.E /T, 1e3/K Current, A (294K) (256K)(227K)(204K) Gennaro Ruggiero, CERN, PH Department, CH-1211 Geneva 23, Switzerland On behalf of the TOTEM TOTEM Collaboration Gennaro Ruggiero, CERN, PH Department, CH-1211 Geneva 23, Switzerland On behalf of the TOTEM TOTEM Collaboration …the proof!!! The idea… To measure the total cross-section of the LHC the TOTEM experiment will detect leading protons coming from the Interaction Point 5 (IP5) The best choice for such detectors are silicon microstrips planes placed orthogonally to the beam axis. Nevertheless in standard fabrication these devices present an insensitive edge of 1mm where termination structures are placed to improve their breakdown performance. To reduce this dead region the TOTEM collaboration has developed a new approach for the realisation of devices with insensitive edges of only 50  m!!! The leading proton detectors will be installed in special beam insertion, the Roman Pots and will approach the 10  of the high intensity beam as close as possible. The conceptual idea of the new approach is to apply the full detector bias across the detector chip cut and collect the resulting leakage current on an outer ring, which surrounds the active area and which is biased at the same potential as the detecting strips. This ring is separated from the detector biasing electrode. Separating this ring from the bias ring strongly reduces the influence of the current generated at detector edge on the active detector area. In contrast with the other ring structures which provides voltage termination, this structure terminates the current, and therefore we have called it Current Terminating Structure. First silicon detectors with this CTS produced in August 2003 (joined effort between the TOTEM-CERN and Ioffe PTI- St.Petersburg/ RIMST Moscow). Bulk Leakage Current not influenced by the Edge Surface Current (I 2 << I 1 ) at 300K Bulk Leakage Current not influenced by the Edge Surface Current (I 2 << I 1 ) at 300K I 1 does not decrease exponentially with the Temperature I 1 does not decrease exponentially with the Temperature Terminating structure 40  m wide Self-referencing module made of a board in G10 laminated with kapton hosting a reference detector (RD) and two test detectors (TD). All the detectors readout with APV25 chips packed in the CMS TOB hybrid Self-referencing module with detectors and readout electronics Test Beam Results (at 300 K) (Sept. ‘03, muon beam in X5 at CERN) RD TD RD Data from Test Beam: (1229±8)  m TD TD Metrology: (1209±10)  m 40  m I2I2 I1I1 + - bias ring Al p+p+ n+n+ cut edge Al SiO 2 n-type bulk p+p+ current terminating ring Thermo-Electric Characterization Roman Pot Stations I1I1 I2I2 reverse bias of 100V The sensitivity at the edge of detectors with CTS has been measured with a muon beam by checking coincident hits in two Test Detectors with CTS with the cut edges, facing each other and being parallel, and in a Reference Detector placed on their back with the strip direction parallel to the sensitive edges of the two TD’s. Due to the high spatial resolution of the RD (strip pitch of 50 microns), the insensitive distance between the two TD’s can be measured precisely and can be compared with the mechanical distance enabling a precise determination of the efficiency drop at the edges of the test detectors Cross-section of a Silicon detector with Current Terminating Structure and its biasing scheme. Distribution of hits in the reference detector in coincidence with hits in the two test detectors. Their fit is compared to the beginning of the sensitive area of the two TD’s (dashed red line). Detail of the edge of a microstrip silicon detector with Current Terminating Structure. With this type of terminating structure the cut of the dice can be even just 40  m away from the end of the strips. New Development: Current Terminating Structure Excellent detector stability for biases higher than 200V at room temperature. Signal-to-noise distribution of the test detector at the edge as recorded by the reference detector at the end of the strip (position 74) and 50  m away (position 75 ) The signal-to-noise performance of the Test Detectors as a function of the x-position as recorded by the Reference Detector have shown a uniform value around 22 until 50  m away from the strips end. This suggests full efficiency up to this position. However, the S/N distributions at the edges show a slight decrease in the pulse height, indicating a loss in efficiency of %.