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Antonio Bulgheroni University of Milan – Italy on behalf of

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

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Antonio Bulgheroni University of Milan – Italy on behalf of

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  1. 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.

  2. Calorimeter Layout Total of 50 layers 27 X0 Absorber Silicon pad detectors 25 x 25 x 0.3 cm3 Scintillator 3 layers 725 Pads ~ 1 x 1 cm2 2, 6 and 12 X0 25 Cells 5 x 5 cm2

  3. Sensor details 6 cm • Main characteristics: • Sensor thickness: 300mm • Resistivity: 4-6k • AC coupling (2 ways) • Silicon dioxide thickness: 265 nm • SMD capacitors • Bias grid and guard ring • 3M poly-Si bias resistors • Symmetric structure ~0.9 cm 7 cm ~0.9 cm Bias pad Guard ring pad

  4. Hybridisation details • Hybridisation through conductive glue • Analogue Readout Chip: VA-HDR9c (IdeAs) • VA  Viking family • HDR  High dynamic range • 9c  Four selectable gains SMD caps *Measured value

  5. Motherboard design • 6 sensors per motherboard with serial readout. • Status of production: • 24 sensors available • 3 motherboards fully and 2 partiallyequipped • Signal routing through Erni connectors

  6. Soft Breakdown GOOD! “Leaky” pads How we get there… step by step 3 technological runs First batch of 11 sensors (spring ’02) Next batch will be ready next months Second batch of 9 sensors (summer ’02) Third batch of 9 sensors (summer ’03)

  7. Soft breakdown • Bias current reasonable (few mA) • Strange shape with a “soft” breakdown • n+ or metal shallow impurities on the backplane Depletion region 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! n n+ Impurities Metal

  8. p+ n “Leaky” pads: a surface effect • No pin holes in SiO2 • Surface leakage  residua of polysilicon after the etching of the polysilicon layer • Equivalent circuit with two opposite diodes. Al bridge Readout metal Polysilicon residua Resistor Bias grid Solution: remove the integrated capacitors

  9. Yield Quite uniform behaviour of the depletion voltage

  10. 1st batch: ~ 10 2nd batch: ~ 15 3rd batch: ~ 18 Test beam: Signal to Noise ratio Theory: + + = Theoretical* SNR ~ 20 *Value obtained for detector of the 3rd batch

  11. Test beam: shower reconstruction / 1 20 GeV e- @ 2X0 Forward tracker @ 6X0 @ 12X0

  12. Test beam: shower reconstruction / 2 20 GeV e- @ 2X0 Forward tracker @ 6X0 @ 12X0

  13. Test beam: energy linearity • Silicon wafers rearranged in 5 planes ant tested alone • Pb of 2.5 cm • Electrons beam • Error bars = sigma distribution

  14. Summary • 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 … Thanks

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