1. L. Greiner 1ATLAS Workshop LBL - September, 2013 STAR HFT LBNL Leo Greiner, Eric Anderssen, Giacomo Contin, Thorsten Stezelberger, Joe Silber, Xiangming Sun, Michal Szelezniak, Chinh Vu, Howard Wieman, Sam Woodmansee UT at Austin Jerry Hoffman, Jo Schambach IPHC Strasburg Marc Winter CMOS PICSEL group Assembly and testing of a MAPS based vertex detector for the STAR experiment at RHIC

2. 2ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Talk Outline Short overview of detector design. Design of ladders, sectors, insertion mechanism. Detector assembly, yields, integration and installation for engineering run. In progress production, assembly and QA for the primary detector. The primary focus of this talk is technical and on instrumentation.

3. 3ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL in STAR Inner Detector Upgrades TPC – Time Projection Chamber (main tracking detector in STAR) HFT – Heavy Flavor Tracker SSD – Silicon Strip Detector r = 22 cm IST – Inner Silicon Tracker r = 14 cm PXL – Pixel Detector r = 2.7, 8 cm We track inward from the TPC with graded resolution: TPCSSDISTPXL ~1mm~300µm~250µm<30µm Direct topological reconstruction of Charm vertex

4. 4ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL Detector Requirements and Design Choices -1 ≤ Eta ≤ 1, full Phi coverage (TPC coverage) ≤ 30 µm DCA pointing resolution required for 750 MeV/c kaon –Two or more layers with a separation of > 5 cm. –Pixel size of ≤ 30 µm –Radiation length as low as possible but should be ≤ 0.5% / layer (including support structure). The goal is 0.37% / layer (limits MCS) Integration time of < 200 μs (limit pile-up, occupancy of ~250 hits/inner sensor) Sensor efficiency ≥ 99% with accidental rate ≤ 10 -4. Survive radiation environment. Air cooling Thinned silicon sensors (50 μm thickness) MAPS (Monolithic Active Pixel Sensor) pixel technology –Sensor power dissipation ~170 mW/cm 2 –Sensor integration time <200 μs (L=8×10 27 ) Quick detector installation or replacement (1 day) Requirements Design Choices

5. 5ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL Detector Design Mechanical support with kinematic mounts (insertion side) Insertion from one side 2 layers (tiled) 5 sectors / half (10 sectors total) 4 ladders/sector Aluminum conductor Ladder Flex Cable Ladder with 10 MAPS sensors (~ 2×2 cm each) carbon fiber sector tubes (~ 200 µm thick) 20 cm

6. 6ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT 2 m (42 AWG TP) 11 m (24 AWG TP) 100 m (fiber optic) Highly parallel system 4 ladders per sector 1 Mass Termination Board (MTB) per sector 1 RDO board per sector 10 Sector chains in the PXL system RDO motherboard w/ Xilinx Virtex-6 FPGA DAQ PC with fiber link to RDO board Mass Termination Board (signal buffering) + latch-up protected power PXL Detector Basic Unit (RDO) Clk, config, data, powerClk, config, data PXL built events Trigger, Slow control, Configuration, etc. Existing STAR infrastructure

7. 7ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Detector Characteristics Pointing resolution (12  19 GeV/p  c)  m LayersLayer 1 at 2.7 cm radius Layer 2 at 8 cm radius Pixel size 20.7  m X 20.7  m Hit resolution 6  m Position stability 6  m rms (20  m envelope) Radiation length per layerX/X 0 = 0.37% Number of pixels356 M Integration time (affects pileup) 185.6  s Radiation environment20 to 90 kRad / year 2*10 11 to 10 12 1MeV n eq/cm 2 Rapid detector replacement~ 1 day 356 M pixels on ~0.16 m 2 of Silicon

8. 8ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL Detector Highlights The HFT upgrade to STAR received DOE CD-2/3 approval in September 2011 and became a construction project. We installed a 3 sector engineering run detector into the STAR experiment on May 8, 2013 and ran the detector until June 10, 2013. The production detector is scheduled to be installed in December of 2013. We will build 2 complete detectors and enough good ladders to build a third. These serve as spares for rework if necessary. I will give a brief overview of the PXL detector design details, components and assembly in the following areas: Sensors Ladder assembly and QA Sector assembly and QA Detector Half Insertion mechanics RDO System Engineering run

9. 9ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Sensors

10. 10ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Standard commercial CMOS technology Room temperature operation Sensor and signal processing are integrated in the same silicon wafer Signal is created in the low-doped epitaxial layer (typically ~10-15 μm) → MIP signal is limited to <1000 electrons Charge collection is mainly through thermal diffusion (~100 ns), reflective boundaries at p-well and substrate. High resistivity epi for larger depleted region → more efficient charge collection, radiation tolerance. 100% fill-factor Fast readout Proven thinning to 50 micron MAPS pixel cross-section (not to scale)‏ Monolithic Active Pixel Sensors

11. 11ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL detector Ult -1/2 Sensor Reticle size (~ 4 cm²) Pixel pitch 20.7 μm 928 x 960 array ~890 k pixels Power dissipation ~170 mW/cm² @ 3.3V Short integration time 185.6 μs In pixel CDS Discriminators at the end of each column (each row processed in parallel) 2 LVDS data outputs @ 160 MHz Zero suppression and run length encoding on rows with up to 9 hits/row. Ping-pong memory for frame readout (~1500 hits deep) 4 sub-arrays to help with process variation JTAG configuration of many internal parameters. Individual discriminator disable, etc. Built in automated testing routines for sensor probe testing and characterization. High Res Si option – significantly increases S/N and radiation tolerance. Developed by IPHC, Strasbourg France

12. 12ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ultimate 1 efficiency vs. fake hit rate Tested for STAR Operating conditions Developed and tested by IPHC Marc Winter CMOS Group IPHC, Strasbourg, France

13. 13ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladder assembly Sector assembly Half detector assembly

14. 14ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladder Design Ladder assembly is the primary task for the detector fabrication. We assemble ladders by edge bumping sensors on a vacuum chuck (the soft acrylic adhesive provides mechanical decoupling for CTE mismatches) DRIE needed for precise sensor size. (most engineering run sensors were saw cut and this gave significant variations in the assembled length of the 10 sensor array, after DRIE, length variation in butted edge sensor array is ~50um) Wire bonding is very sensitive to small sensor position variations (small displacements cause the bonding pads on the ladder to displace wrt bonding pads on the sensors and wire bonds then require steep angles).

15. 15ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladder Design Ladder cable concept

16. 16ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladder assembly work flow chart Probe tested sensors Electrically tested low mass cables Electrically tested driver boards Dimensionally checked composite backer Ladder assembly Ladder wire bonding Wire bond encapsulation Quick test Full functionality test Complete ladder Ladder characterization Reworking and troubleshooting Quality assessment Initial validation 1 day without problems Full functionality test  bias optimization  Threshold scan  Normal readout mode test  Accidental hit rate scan Quick test  Threshold scan @ nominal bias settings

17. 17ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Sector/half-detector work flow chart Tested Ladders Sized Sector Tubes machined Dovetail/D-tube Elect tested MTB/cables/insertion Sector assembly Full functionality test Quick test Half detector head assembly Sector metrology ½ HFT PXL Quick test Half detector head metrology Full Half detector assembly Quick test

18. 18ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Overall detector design factors (metrology) We intend to insert a fully mapped detector with all pixel positions known and stable. We have gone to great lengths to ensure that the ladder/sector/half detector mechanics are stable to 30um for all forces (gravity, vibration and deflection due to air cooling (~10 m/s), thermal distortion, mechanical stress from cable loading, etc.) anticipated during running. We map each sector using fiducials on the sensors and relate pixel positions to tooling balls on the sectors. We then assemble half detectors and map the sector tooling balls to give the pixel positions for each half detector.

19. 19ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Sensor Thinning We use sensors thinned to 50 µm thickness. We use DRIE processing on the wafers to give accurate sensor dimensions and edge quality. Wafers are delivered with DRIE trenches 70 µm deep. The wafers are back- thinned and polished at Aptek to release the dies from the wafer (yield started quite low, but is now significantly improved). First 25 production wafers, 5 were lost completely during thinning as process was refined. Last 17 wafers thinned had >99% yield. Die position on the wafer and wafer # are preserved through the thinning process and this identifies the die in our database. We select dies based on probe testing of thinned sensors. 50 um thick sensors are curved, up to 2 mm out of plane, this has implications.

20. 20ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Probe card with readout electronics – derived from individual sensor test card Analog and digital sensor readout Full speed readout at 160 MHz Full sensor characterization at full speed –Test results used for initial settings in ladder testing and PXL detector configuration 2 nd generation probe card for production testing – only digital readout pins loaded Yield modeling makes probe testing critical to the goal of assembling functional 10 sensor ladders. We test thinned and diced 50 µm thick sensors (curved). This is not easy. Assembling sensors into ladders – Probe Testing

21. 21ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Assembling sensors into ladders – Probe Testing Vacuum chuck for testing 20 thin sensors (50 µm) –Thin sensors are sensitive to chuck surface imperfections –Need a special probe pin design and to work in clean environment Testing up to 18 sensors per batch –Optimized for sensor handling in 9- sensor carrier boxes Manual alignment (18 sensors ~ 1 hr) – Testing time is ~ 15 minutes per sensor (3 supply voltages) (4.5 hr testing time) Threshold DAC counts (x5) Column number LabWindows GUI Discriminator Threshold

22. 22ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Examples of failures D07_w_12 E01_w_8 (@3.0V) E05_w_12 E06_w_12 E05_w_08 C04_w_12 OK Faulty columns Sub-arrays Faulty rows 3.3 or 3.0 V

23. 23ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL Sensor selection Automated interface to a database (18 config + 68 result parameters) Sensors are binned according to performance Example of wafer maps for Ultimate-2 wafers with DRIE processing (ion etching) ~65% - 70% yield (Tier 1-3) 40% Tier 1-2

24. 24ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Building sensors into ladders

25. 25ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Assembling sensors into ladders – Hybrid Cable The cable is needed to deliver power and ground and provide signal routing to and from the sensors on the ladder with minimal radiation length. Production aluminum conductor flex cables are being fabricated in the CERN PCB shop. (difficult to produce, only one real vendor) Hybrid Copper / Aluminum conductor flex cable design concept Low mass region calculated X/X 0 for Al conductor = 0.079 % Low mass region calculated X/X 0 for Cu conductor = 0.232 % 20 differential signal output pairs JTAG, 2 temp diodes, CLK, START VDD, VDA, GND - ~1.8 A / ladder Layout (in copper)

26. 26ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Assembling sensors into ladders – Assembly We use precision vacuum chuck fixtures to position sensors and assemble ladders. Sensors are positioned with butted edges. Acrylic adhesive mechanically decouples sensors from the cable and prevents CTE difference based damage. Weights taken at all assembly steps to track material and as QA. Reference pins for cable/sensor alignment

27. 27ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Assembling sensors into ladders – Assembly Hybrid cable with carbon fiber stiffener plate on back in position to glue on sensors. The cable reference holes are used for all aspects of assembly of ladders and sectors.

28. 28ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT QA/QC for Sector Production Completed ladder in anti-static carrying box with follower and check off list. Assembled ladder with driver board, wire bonded and encapsulated

29. 29ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Engineering Run Ladder Yield The assembly of ladders and sectors for the PXL Engineering Run has been crucial for process optimization and we have dealt with a number of unexpected issues. Thanks to this experience, we were able to refine the assembly procedure and to develop effective tools for troubleshooting ladders. The final ladder assembly statistics for the engineering run detector are: Quality assessment (03/20/2013)#% Fully operating ladders1555.6 Lower quality operating ladders (>8 operating chips)414.8 Recoverable not operating ladders (need fix or workaround) 414.8 Dead ladders (not recoverable)414.8 Total27100.0 The primary lessons learned had to do with the need for coverlay on the cable, modification of tooling that was damaging sensors, adjustment of adhesive sizes and backing plates, proper adjustment of sensor array on the cable.

30. 30ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladders to sectors

31. 31ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladders to sectors

32. 32ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Ladders to sectors Sector in optical metrology machine Sensor fiducial positions on sector are measured optically and related to tooling balls. Surface profiles of sensors (sensors are not flat) are measured using feather touch probe CMM and pixel positions are related to sensor fiducials using thin plate spline fit. Now we have pixel positions related to the tooling balls. After touch probe measurements, sectors are tested electrically for damage from metrology.

33. 33ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT sectors to detector half (ER) Sectors are mounted in dovetail slots on detector half. Metrology is done to relate sector balls to each other and to kinematic mounts. We now have pixel positions for the half detector object.

34. 34ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL detector mechanics

35. 35ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Mechanical Development Silicon power: tested at 170 mW/cm 2 (~ power of sunlight) 350 W total in the ladder region (Si + drivers) computational fluid dynamics Air-flow based cooling system for PXL to minimize material budget. Detector mockup to study cooling efficiency ladder region

36. 36ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Power ~340 W Airflow 10.1 m/s Thermal camera image of sector 1 (composite image): Mechanical Development unsuported end mid-section fixed end Solid – inner layer Open – outer layer 340 W with ambient air = 26.8 C NTC thermistors (averaged at same “Z” position) Measurement results agree with simulations and meets calculated stability envelope tolerance. Air flow-induced vibrations (10 m/s) are within required stability window.

37. 37ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL detector – insertion mechanics Unusual mechanical approach. Cantilevered and insertable (1 day) Pre-surveyed and mechanically stable to a level that preserves the survey. Detector inserts and initiates a clamshell closing around beam pipe, and is locked into position on kinematic mounts.

38. 38ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL insertion mechanics Interaction point view of the PXL insertion rails and kinematic mount points Carbon fiber rails Kinematic mounts

39. 39ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL insertion mechanics PXL detector half with complete insertion mechanism

40. 40ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Engineering Run Left detector half being inserted Right detector half being inserted

41. 41ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Engineering Run PXL eng detector inserted, cabled and working in 1 day access

42. 42ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Engineering Run PXL system working with 3 sectors Integrated with STAR trigger, DAQ, slow controls, online event pool. Software and firmware for performing data quality checks were modified and optimized. Hit display for PXL engineering run detector.

43. 43ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Preliminary results from Engineering Run First tracking results show good matching of TPC tracks to hits on PXL sensors Residuals compatible with TPC track resolutions on the sensors (~1-2 mm) 3mm beam shift reflects the PXL&TPC relative position

44. 44ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Lessons learned “Full dress rehearsals” are critical to success. We discovered a mechanical conflict in the ladder driver board section that necessitated a sector tube redesign. Tooling that would fracture sensors during assembly was modified. Our ladder temperature monitoring system didn’t work properly and was re-designed. Other electronics / sensor issues are still under investigation and will require further updating of the existing systems.

45. 45ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Production detector We are currently building ladders for the production detector. Mechanical thinning yields are now close to 100%. Current ladder yields are much better. 36 ladders produced, 26 tested, 1 ladder has 1 damaged sensor, all others tested are fully functional. Production sector assembly will start in mid- September.

46. 46ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT end

47. 47ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Extra slides

48. 48ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT

49. 49ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Read-out Electronics 1.The detector is 10 parallel sector chains. 2.Each sector is configured and delivers data to the RDO boards continuously into a data pipeline. 3.The receipt of a trigger opens an event buffer for 1 frame of data. (2 actual frames with address selection performed to give one compete frame based on the time the trigger is received) 4.The data is formed into an event and shipped to the DAQ receiver PCs. Full PXL RDO fits into 1 crate

50. 50ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT First 25 production wafers.

51. Radiation Length of active area NOTE: Does not include sector tube side walls

52. 52ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT HFT PXL status – fabrication and tooling

53. L. Greiner 53ATLAS Workshop LBL - September, 2013 STAR HFT 22 GEANT: Realistic detector geometry + Standard STAR tracking including the pixel pileup hits at RHIC-II luminosity Hand Calculation: Multiple Coulomb Scattering + Detector hit resolution PXL telescope limit: Two PIXEL layers only, hit resolution only Mean p T 30  m Expected DCA resolution performance

54. 54ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT PXL Detector Production Path (post CD – 2/3) Sensor development Readout development Mechanical development Cable development Pre- production prototype Ult Probe tests Infrastructure development Ult sensor prototype 10 sensor Cu+kapton pre-prod Eng run Sector prototype Final Ladder readout Final individual readout Update mech for size Prod readout production sensors Prod Probe tests 10 sensor Al+kapton prod prod Sector Eng run detector prod detector May 2013 Dec 2013 Culmination of >9 years of development

55. 55ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Pixel signal extraction and operation Capacitor Storage for Correlated Double Sampling (CDS)  ~ 100s ms Discriminator Zero suppression and memory LVDS outputs 160 MHz 1 23 (Sample 1 – Sample 2) > threshold => hit (Sample 2 – Sample 3) no hit CDS Simplified description O Self-biased configuration

56. 56ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Driver section ~ 6 cm Sensor section ~20 cm Kapton cables with copper traces forming heaters allow us to dissipate the expected amount of power in the detector 6 NTC thermistors on each ladder Sector 1 was equipped with 10 thinned dummy silicon chips per ladder with Pt heaters vapor deposited on top of the silicon and wire bonded to heater power. Power ~340 W Airflow 10.1 m/s Thermal camera image of sector 1 (composite image): Mechanical Development

57. 57ATLAS Workshop LBL - September, 2013 L. Greiner STAR HFT Alternate Technologies Considered Hybrid –X 0 large (1.2%) –Pixel Size large (50  m x 450  m) –Specialized manufacturing - not readily available CCDs –Limited radiation tolerance –Slow frame rate, pileup issues –Specialized manufacturing DEPFET –Specialized manufacturing –very aggressive unproven technology MAPS sensors are the technology selected