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The DØ Silicon Microstrip Tracker

The DØ Silicon Microstrip Tracker. Frank Filthaut University of Nijmegen / NIKHEF NIKHEF, 4 August 2000. Tevatron Run II Upgrade. Modification of Tevatron parameters :. Start of Run II: 1 March 2001 Aim: collect 2 fb -1 in  two years (might be more…)

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The DØ Silicon Microstrip Tracker

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  1. The DØ Silicon Microstrip Tracker Frank Filthaut University of Nijmegen / NIKHEF NIKHEF, 4 August 2000

  2. Tevatron Run II Upgrade Modificationof Tevatron parameters: Start of Run II: 1 March 2001 Aim: collect 2 fb-1 in  two years(might be more…) Switch from 396 ns to 132 ns bunch spacing atluminosity  1032 cm-2 s-1 Keep zero crossing angle for 396 ns operation; aim for 136 rad angle for 132 ns operation Beam spot:  35 m transverse, 25 cm longitudinal (10 cm for nonzero crossing angle) NIKHEF

  3. DØ Run II Upgrade • Addition of central axial 2T magnetic field (SC solenoid in front of calorimeter cryostat) • Replacement of tracking system by combination of scintillating fibers (Central Fiber Tracker) and silicon sensors (Silicon Microstrip Tracker) • Central (CPS) and forward (FPS) preshower detectors • Extend muon chamber coverage to larger , smaller granularity • Upgraded calorimeter, trigger, DAQ electronics Physics aims: • B-tagging based on b lifetime • Improved electron and muon identification and triggering • Improved tau identification • Charge sign determination  High pt central physics (tt, EW, Higgs and other searches): high multiplicity Low pt physics (bb, QCD): requires good forward coverage (e.g. lepton ID for|| < 3)  NIKHEF

  4. DØ Run II Upgrade NIKHEF

  5. DØ Run II Upgrade - Tracking Fiber Tracker Silicon Microstrip Tracker Forward Preshower Solenoid Central Preshower All share the same SVX IIe front-end electronics NIKHEF

  6. SMT Design 12 11 10 9 6 5 4 4 3 2 3 1 2 1 8 7 6 5 Barrels F-Disks H-Disks Layers/planes 4 12 4 Readout 12.4 cm 7.5 cm 14.6 cm Length Inner Radius 2.7 cm 2.6 cm 9.5 cm Outer Radius 9.4 cm 10.5 cm 26 cm Basic SMT Design: • 6 barrels • 12 F disks • 4 H disks Totals: 793k channels 3.0 m2 (of which 1.6 m2 DS) Axial strips to be used in 2nd level Silicon Track Trigger (STT)  stringent requirements on alignment NIKHEF

  7. SMT Design SMT barrel cross-section: • Layers 1 (3): 12 (24) DS, DM 900 ladders produced from 6” wafers (barrels 1 & 6: SS axial ladders from 4” wafers) • Layers 2 (4): 12 (24) DS 20 ladders produced from 4” wafers Ladder count: 72 SS + 144 DS (900) + 216 DS (20) NIKHEF

  8. Anatomy of a Ladder • Ladders supported by “active” (cooled) and “passive” bulkheads • Ladders fixed by engaging precision notches in beryllium substrates on posts on bulkheads • Beryllium cools electronics • expect chips to operate at 25 0C using 80% H2O/20% ethyl glycol mixture at –10 0C • silicon should be at 5-10 0C • High Density Interconnect (HDI) tail routed out between outer layers • Carbon-fibre/Rohacell rails glued to sensors for structural stiffness NIKHEF

  9. Silicon Calculated radiation dose as a function of radius (z=0): • Significant fraction of silicon will undergo type inversion • Prefer high initial Vdepl for silicon at low radii • Specification of Vdepl, Vbreak • Selection of sensors at hand Quality control at vendors & DØ institutes: • Ileak < 10 A at Vbias = Vdepl + 10V • 20V < Vdepl < 60V • Polysilicon bias resistors: 1 M < Rbias < 10 M (DC bias pad) • Rinter-strip G • Coupling capacitors: 10-15 pF/cm • f(shorted cap’s) < 2% at min(Vdepl+15V, 90V) NIKHEF

  10. Sensors Single-sided • Need 144 sensors (2/detector) • Pitch: 50 m • Typical Vdepl: 30 V • All sensors delivered by Micron • Flatness problems ( 60 m) a concern NIKHEF

  11. Sensors p-side n-side Double-sided 20 • Need 432 sensors (2/detector) • Pitch: p-side 50 m, n-side 62.5 m • Typical Vdepl: 20-40 V • Slow sensor delivery by Micron  accepting sensors with higher Rbias NIKHEF

  12. Sensors Double-sided, double-metal • Need 144 sensors • Pitch: p-side 50m, 900n-side 153 m • Produced from single sensor (6” technology) • Using DM layer, gang 2 n-side strips together to form 1 readout channel • Typical Vdepl: 50 V NIKHEF

  13. Sensors Double-sided, double-metal • Sensor delivery from Micron has been slow (30% yield) mainly due to p-stop defects on mask (noise affecting  10-15 strips)   5 sensors / week  schedule problem, accepting few sensors with 1 p-stop defect NIKHEF

  14. Sensors F-wedge • Need 144 sensors (12 detectors/disk) • Pitch: n-side 62.5m, p-side 50 m (flexible pitch adaptor on n-side) • Stereo angles: 150 • Sensor delivery: • Micron: delivered 125 sensors with reasonable characteristics: Vdepl  60-70 V • Eurisys: delivered 65 sensors: • First two batches: Vdepl  15-20 V, Vbreak  70-80 V • Last batch ( 25 sensors) with better implants: Vdepl  30-40 V, Vbreak  80-100 V NIKHEF

  15. Sensors H-wedge • Need 384 sensors (2/detector, 48 detectors/disk) • Single-sided, glued back-to-back • Pitch: 80 m • Stereo angles: 7.50 • Typical Vdepl: 60 V • All sensors delivered by ELMA NIKHEF

  16. SVX IIe Chip • SVX chip originally designed by LBL - FNAL for readout of CDF vertex detector, optimised for capacitances of 10-35 pF, ENC = 350e- + 50e-/pF • 128-channel 8-bit digital chip, 1.2 m rad-hard technology • Both signal polarities • Rise time set to integrate 99% of signal in 100 ns (for 132 ns operation) • Double correlated sampling for dynamic “pedestal” subtraction • Front end capacitor discharged during “beam gaps” • Pipeline depth 32 max. • 106 MHz readout speed (both edges of 53 MHz clock) NIKHEF

  17. SVX IIe Chip • Daisy-chained readout of max. 9 chips • Online sparsification using common threshold. Modes: • All channels • Only above threshold • Include 1 or 2 neighbours on either side (even if on adjacent chips) • Adjustable ramp rate (dynamic range) • Power dissipation  5 mW/channel • Unlike SVX III now in use by CDF, not deadtime-less NIKHEF

  18. High Density Interconnect Need 912 HDI’s • Two-layer flex-circuit mounted directly on silicon, housing SVX chips as well as passive electronics • Kapton based, trace pitch 200 m • Connects to “low-mass” cable using Hirose connector • 9 different types for the 5 sensor types • 2 for each sensor type except H disks • 2 types for each ladder differ only in tail length • Laminated to beryllium substrate (total mass  0.041 X0, of which 0.014 X0 from Si) 9-chip HDI H-wedge HDI NIKHEF

  19. Production Sequence Silicon Sensors HDI Micron Eurisys ELMA Probe Test Silicon Sensor at Micron Test Bare HDI Dyconex Laminate HDI Mount components on HDI Promex Silitronics Probe Test Silicon Sensor in house Test stuffed HDI “fail” Burn-in HDI Build Ladder/Wedge Mount HDI on Silicon Wirebond Detector Burn-in Ladder “fail” Laser Test Build Full Wedge (H) Mount on Support structure Outside Co. University Read out Detector Fermilab NIKHEF

  20. Ladder Production in steps (9-chip) 1. Apply pattern of non-conductive epoxy on p-side beryllium 2. Align beryllium with respect to active sensor, apply pressure and cure for 24 hr 3. Align active & passive sensors w.r.t. each other, apply wirebonds. Then use separate fixture to position carbon-fibre rails. Use conductive epoxy to ground “passive” beryllium. Cure for 24 hr NIKHEF

  21. Ladder Production in steps (9-chip) 4. Use “flip fixture” to have n-side on top 5. Apply epoxy to n-side beryllium, fold over and secure HDI. Apply pressure and cure for 24 hr. Then apply n-side Si-Si and Si-SVX wirebonds 6. Encapsulate bonds at HDI edges. Connect “active” beryllium to cable ground NIKHEF

  22. Testing & Repairs Bonds need to be plucked Bad ground connection • Broken capacitors: cause SVX front-end to saturate, tends to affect neighbouring channels as well  pluck corresponding bonds • Bad grounding of beryllium substrates causes large pedestal structures as well as high noise  ensure RBe-gnd < 10 • Repair broken / wrong bonds • Replace chips / repair tails damaged during processing NIKHEF

  23. Burn-in & Laser Tests Laser Dead Channel Burn-in Test: Long-term (72 hr, 30’ between runs) test of whole ladder/wedge (conditions close to those in experiment) Laser Test: • Energy just < Si bandgap (atten. length  400 m  test whole sensor) • Find dead & noisy channels • Determine initial operating voltages (from pulse height plateau, Ileak-V curve) x-y movable laser head NIKHEF

  24. Overall Quality (first half-cylinder) Detector classification: • Dead channel: laser response < 40 ADC counts • Noisy channel: pedestal width > 6 ADC counts (normally < 2 counts excluding coherent noise) • Grade A: less than 2.6% dead/noisy channels • Grade B: less than 5.2% dead/noisy channels Use only detector grades A,B; mechanically OK Example for 9-chip detectors: Dead Noisy (better for other detector types) NIKHEF

  25. Production Status and Projection (as of July 7) Nov 1, 00 Aug 10, 00 50% line July 7 • Projected rates: assumed yield capacity • 9-chip: 9.0/week 80% 15/wk • 6-chip: 5.4/week 85% 10/wk • H-wedge: 6.2 week 85% 10/wk • F-wedge: 4.3/week 90% 15/wk Rates include production, but in general dominated by sensor delivery. However, HDI “stuffing” at Promex (9-chip) also a concern (wire bond pull strength, HDI bubbling during surface mount) NIKHEF

  26. Barrel Assembly in steps • Rule of thumb: • Align to 20 m (trigger) • Survey to 5 m (offline) • Precisely machined bulkheads • Barrel assembly done inside out (protect wire bonds) 1. Insert individual ladders into rotating fixture using 3D movable table 2. Manually push notches against posts (all under CMM) NIKHEF

  27. Barrel Assembly • Layer 4 glued to bulkheads (providing structural stiffness, holding passive BH) • Thermally conductive grease applied (active BH only) for other layers 3. Secure ladder using tapered pins First 3 barrels assembled( 4 weeks/barrel, excluding survey) NIKHEF

  28. Barrel Alignment    Results for first barrel (similar for other two): • Shift d across ladder (3 m) • Shift  in radius (from ladder flatness, better than 60 m) • Rotation  in ladder plane (10 m  3 m) • Rotation  about short ladder axis (70 m  4.6 m) • Rotation  about long ladder axis (80 m  3.2 m) Note: relevant quantities are distributions’ RMS values (trigger accounts for average offsets)  Example: distribution for : Should be OK for trigger purposes NIKHEF

  29. F-Disk Assembly z=0 H H L H L H L H H Vdepl M M L • F-disk assembly less critical (not included in trigger), nevertheless performed under CMM • Quick process • After assembly, “central” F-disk cooling rings screwed onto active barrel bulkheads Distribution of different quality devices over disks: H/M = Micron high/medium Vdepl, L = Eurisys low Vdepl NIKHEF

  30. Support Cylinder • Double-walled carbon fibre structure supporting all but H disks (supported by CFT layer 3) • Split support (cut at z=0) introduced very late: gain 6 months of “schedule time” (installation can be done with end-cap calorimeter cryostats on platform) • First half-cylinder ready NIKHEF

  31. Readout Electronics HDI 3M Low Mass IB Optical Link 1Gb/s SEQ SEQ SEQ NRZ/ CLK platform 1 5 5 3 VBD 68k VME V R B VRB Controller L3 HOST Secondary Datapath Examine • For 5% occupancy, 1 kHz trigger rate: 1010 bits/s  need error rate  10-15 • Exercise readout system as much as possible before installation in experiment  10% system test using full readout chain (readout full F disk, barrel, barrel-disk assembly, H disk) • Complete readout chain (including L3 analysis, data storage) tested on several detectors Monitoring Control NIKHEF

  32. Schedule Done Done Done In preparation Done Done Done Done Done Done Done Started Started Half done NIKHEF

  33. Cost NIKHEF

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