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Standard and Slim Edge Pixel Sensors

Standard and Slim Edge Pixel Sensors. Gian-Franco Dalla Betta DII, Universit à di Trento INFN – Padova, Gruppo Collegato di Trento Tel.: +39-0461283904, e-mail: gianfranco.dallabetta@unitn.it. Outline. Status : Last Vipix batch from 2012 FBK restarting with 6 ’’ wafers

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Standard and Slim Edge Pixel Sensors

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  1. Standard and Slim Edge Pixel Sensors Gian-Franco Dalla Betta DII, Università di Trento INFN – Padova, Gruppo Collegato di Trento Tel.: +39-0461283904, e-mail: gianfranco.dallabetta@unitn.it

  2. Outline • Status : • Last Vipix batch from 2012 • FBK restarting with 6’’ wafers • Pixel sensors with active edge • First batch (PAE) • Further experience at FBK • Plan for a new batch …

  3. The 2012 batch (p-on-n) • 13 wafers • <111>, 200 mm • Poly-Si gettering • No processsplits • Alignmentmarks • compatible with both • bumpbonding (IZM) • and verticalintegration • (T-Micro) • 32x128 (54+54FP) • 128x128 (9+9FP) • 96Px128 (7) • Test structures

  4. Preliminary Results Test diode, 4mm2 • Very good leakage current (~0.2 nA/cm2) • Very low depletion voltage (~2 V)

  5. Active edge sensors: first batch (PAE) 14.3 um 4.2 um 9.4 um 1.2 um n- substrate Initial process • Wafer bonding (@SINTEF) • Trench etching with DRIE and thick oxide mask: • Aspect ratio ~1/20, deep etching (>200 um) • Trench doping by thermal diffusion • Trench filling with poly-Si (width ~10 um) • Lithography on severe topography: • Even after filling, trenches still represent a major obstacle for photoresist spin-coating. 2000x Improved process G.F. Dalla Betta et al., NSS 2011, N25-04

  6. Main Design Issues • Wafer layout with strips, pixels, and diodes • Back-side not accessible: • bulk contacts and pads on the front side • Gap between n and p regions: • trade-off between edge sensitivity and breakdown voltage (possibly increased with field plates and/or floating rings) Bulk contacts Bulk contacts Bulk pad Field plate Bulk pad Trench Trench Bias line DC pads AC pads Gap

  7. Electrical Characterization 5 mm Field plate no FP gap p+ n+ n/p gap Trench edge n- substrate FP=5um gap

  8. Edge Sensitivity (1) Position resolved laser setup at UniTN Layout Charge signal map @40V • Preliminary setup (laser spot size and alignment to be optimized) • Good charge collection efficiency edge up to few microns from the edge

  9. Edge Sensitivity (2) M. Povoli et al., Pisa Meeting 2012 Synchrotron X-rays (15 keV) at Diamond, UK Spot size ~3mm, scan step 5mm, different bias 2 diodes with common edge It confirms the good sensitivity up to a few mm from the physical edge

  10. Further experience at FBK (1) Edgeless pixels (p-on-n) for ALICE on epitaxial wafers (collaboration with CERN and INFN Bari and Trieste) I. Rachevskaya et al., Trento Workshop 2013

  11. Further experience at FBK (2) Edgeless pixels (n-on-p) for ATLAS upgrade (collaboration with LPNHE, Geneve and INFN Trieste) G. Giacomini et al., Trento Workshop 2013

  12. Plans for a new batch • Vipix has a credit with FBK for one batch, that could now be oriented to the new PixFEL project • FBK technology is sufficiently mature to make active edge pixels, although there has been no direct experience on 6’’ so far • For X-rays, sensor thickness should be not too small • Epi wafers are not an option • Need for wafer bonding (external service) • Trench etching and poly-Si filling to be optimized • Support wafer removal to be engineered

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