Silicon pad detector for an electromagnetic calorimeter at
- Slides: 14
Silicon pad detector for an electromagnetic calorimeter at future linear collider experiments: characterisation and test beam results Antonio Bulgheroni University of Milan – Italy on behalf of LCCAL: Official INFN R&D project, official DESY R&D project PRC R&D 00/02 Contributors (Como, LNF, Padova, Trieste): M. Alemi, M. Bettini, S. Bertolucci, E. Borsato, M. Caccia, P. Checchia, C. Fanin, G. Fedel, J. Marczewski, S. Miscetti , M. Nicoletto, M. Prest, R. Peghin, L. Ramina, E. Vallazza.
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Calorimeter Layout Absorber 25 x 0. 3 cm 3 Scintillator 25 Cells 5 x 5 cm 2 Silicon pad detectors Total of 50 layers 27 X 0 3 layers 725 Pads ~ 1 x 1 cm 2 2, 6 and 12 X 0
Main characteristics: n n Sensor thickness: 300 mm Resistivity: 4 -6 k AC coupling (2 ways) n Silicon dioxide thickness: 265 nm n SMD capacitors Bias grid and guard ring n 3 M poly-Si bias resistors n Symmetric structure ~0. 9 cm n 6 cm 7 cm 8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Sensor details ~0. 9 cm Bias pad Guard ring pad
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Hybridisation details n n Hybridisation through conductive glue Analogue Readout Chip: VA-HDR 9 c (Ide. As) SMD caps n n n VA Viking family HDR High dynamic range 9 c Four selectable gains Gain* [mv/f. C] DR [mip] 3. 3 2. 5 1. 7 1. 2 ± 100 ± 140 ± 200 ± 300 *Measured value
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Motherboard design n n 6 sensors per motherboard with serial readout. Status of production: n n n 24 sensors available 3 motherboards fully and 2 partially equipped Signal routing through Erni connectors
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 How we get there… step by step 3 technological runs First batch of 11 sensors (spring ’ 02) Next batch will be ready next months GOOD! Third batch of 9 sensors (summer ’ 03) Soft Breakdown Second batch of 9 sensors (summer ’ 02) “Leaky” pads
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Soft breakdown Bias current reasonable (few m. A) Strange shape with a “soft” breakdown n+ or metal shallow impurities on the backplane n n n Depletion region n n+ Metal Solution 1: replace the implanted backside contact with a diffused one, but it does not work! Solution 2: replace the mash backplane contact with a uniform one, it works! Impurities
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 “Leaky” pads: a surface effect n n n No pin holes in Si. O 2 Surface leakage residua of polysilicon after the etching of the polysilicon layer Equivalent circuit with two opposite diodes. Al bridge Readout Polysilicon metal residua Resistor p+ Solution: remove the integrated capacitors n Bias grid
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Yield Quite uniform behaviour of the depletion voltage YIELD 1 st Batch 2 nd Batch 3 rd Batch Coupling AC AC DC Wafer Rejected 1/11 2/9 0/9 Depletion Voltage 32 V 27 V 28 V Current @ depletion 2. 1 m. A 0. 8 m. A 0. 6 m. A Not depleted pads 0/420 8/249 0/378
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Test beam: Signal to Noise ratio Theory: + + = Theoretical* SNR ~ 20 *Value obtained for detector of the 3 rd batch 1 st batch: ~ 10 2 nd batch: ~ 15 3 rd batch: ~ 18
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Test beam: shower reconstruction / 1 20 Ge. V e@ 2 X 0 Forward tracker @ 6 X 0 @ 12 X 0
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Test beam: shower reconstruction / 2 20 Ge. V e@ 2 X 0 Forward tracker @ 6 X 0 @ 12 X 0
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Test beam: energy linearity n n Silicon wafers rearranged in 5 planes ant tested alone Pb of 2. 5 cm Electrons beam Error bars = sigma distribution
8 th ICATPP – Villa Erba (Como), 6 th October ‘ 03 Summary n n Some technological problems fixed with the last batch Detector performances very close to the design rules and hopefully will improve with the next and last batch Shower reconstruction capability and energy linearity are shown in the first test beam … we keep going …