1. L. Greiner 1FEE 2014 – STAR PXL Vertex Detector 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 PICSEL group of IPHC-Strasbourg (Marc Winter et al.,) Experience from construction and operation of the first Vertex Detector based on MAPS

2. 2FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Talk Outline STAR vertex detector upgrades at RHIC. Pixel detector design and characteristics. Sensors and mechanics. Detector assembly and integration with lessons learned. Installation for 2014 run and first results. Lessons learned and outlook.

3. 3FEE 2014 – STAR PXL Vertex Detector 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 = 2.8, 8 cm We track inward from the TPC with graded resolution: TPCSSDISTPXL ~1mm~300µm~250µm<30µm Direct topological reconstruction of Charm vertex

4. 4FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL Detector Design Mechanical support with kinematic mounts (insertion side) Insertion from one side 2 layers 5 sectors / half (10 sectors total) 4 ladders/sector Aluminum conductor Ladder Flex Cable Ladder with 10 MAPS sensors (approx. 2×2 cm each) carbon fiber sector tubes (~ 200 µm thick) 20 cm

5. 5FEE 2014 – STAR PXL Vertex Detector 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 RDO boards in the PXL system RDO motherboard w/ Xilinx Virtex-6 FPGA RDO PC with fiber link to RDO board Mass Termination Board (signal buffering) + latch-up protected power PXL Detector Basic Unit (RDO) Clk, config, data, power Clk, config, data PXL built events Trigger, Slow control, Configuration, etc. Existing STAR infrastructure PXL Sector

6. 6FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Detector Design Characteristics DCA Pointing resolution (12*  24 GeV/p  c)  m LayersLayer 1 at 2.8 cm radius Layer 2 at 8 cm radius Pixel size 20.7  m X 20.7  m Hit resolution 3.7  m (6  m geometric) Position stability 6  m rms (20  m envelope) Radiation length first layerX/X 0 = 0.39% (Al conductor cable) 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 * Simple geometric component, cluster centriod fitting gives factor of ~1.7 better.

7. 7FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL detector Ultimate-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 (air cooling) 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. Sensors thinned to 50 µm. Developed by PICSEL group of IPHC-Strasbourg Optimized for the STAR environment

8. 8FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL Ladder Assembly Precision vacuum chuck fixtures to position sensors by hand. Sensors are positioned with butted edges. Acrylic adhesive prevents CTE difference based damage. Weights taken at all assembly steps to track material and as QA. Assembled ladder Cable reference holes for assembly Hybrid cable with carbon fiber stiffener plate on back in position to glue on sensors. Sensor positioning FR-4 Handler

9. 9FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Sector and detector half assembly Metrology picture Sectors  Ladders are glued on carbon fiber sector tubes in 4 steps  Pixel positions on sector are measured and related to tooling balls  After touch probe measurements, sectors are tested electrically for damage from metrology Detector half  Sectors are mounted in dovetail slots on detector half  Metrology is done to relate sector tooling balls to each other and to kinematic mounts  Detector half mapped Sector assembly fixture A detector half Sector in the metrology setup

10. 10FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Yields sensor yield sensorsafter thinningprobe tested after probe testing (tier 1&2)Probe testing yield batch 111521003 4640.46 batch 21152113910565460.52 batch 312481174357217(new probe card) 0.608 yield0.9340.508 ladder yield ladders assembled after assembly + bonding after encapsulation after sector mountingafter metrology Tot113103855348 Tested92595348 Good845448 yield0.910.920.911.00 Production is still ongoing.

11. 11FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL insertion Mechanics PXL has a unique mechanical design. The PXL detector is inserted along rails and locks into a kinematic mount on the insertion end of the detector. This allows for rapid (1 day) replacement with a characterized spare detector. Yes – we push it in by hand Kinematic mounts Insertion of PXL detector

12. 12FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Detector Installation Pxl installation pics 1.Clean room 2.Installed and cabled PXL assembled in the STAR clean room PXL inserted into the STAR TPC inner field cage, cabled and operational. Total installation time = 2 days.

13. 13FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Lessons learned during construction and installation Sensors –Build testing functionality into the sensor design from the start optimized for probe testing/module testing. We developed the parametric testing requirements first and implemented them in the design with IPHC. Readout –Co-develop the RDO with the sensor. It is then guaranteed to work and you have time to find and fix incompatibilities and quirks. Probe testing –Proper probe pin design for curved thinned sensors. –Spend time on whole probe system yield (ours varied between 46% - 60%). –Administrative control of sensor ID worked well for us. Engineering run –Do a proper full system test (if possible) in the correct environment with partial full detector and infrastructure. –We discovered mechanical problems even in a fully solid modeled system (interferences, kinematic mount insertion, etc.). Assembly –Spend time optimizing full yield through all production steps. Original ladder and sector yields were much lower until all the problems were worked out. –Acrylic adhesive works well as a CTE stress decoupling method. Things that worked well and things that didn’t

14. 14FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Cosmic Ray Running PXL was installed with all sensors (400) working. < 2k bad pixels out of 356M. All pixel positions on each detector half were mapped in CMM prior to installation. PXL RDO and integration with STAR DAQ, trigger, etc. complete and working well. Automated threshold setting scripts applied (1600 thresholds need to be set). Noise rate is ~1-2 x 10 -6 per sensor for most of the sensors. Last few sensors were tuned manually. All parameters are stable and preliminary alignment with cosmic ray tracks was made. Some misalignment in the kinematic mounts (~1mm). Sensor positions on detector halves appear to be as measured in the CMM before installation.

15. 15FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL preliminary half-to-half pointing residuals Consistent with expectations for alignment and momentum of muons. Preliminary Preliminary alignment by Alex Schmah Inner layer Outer layer

16. 16FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT 15 GeV/c and 200 GeV/c running - status 15 GeV start Jan 25 PXL install Feb 14 200 GeV start Mar 14 now May 21 Jul 7 The HFT (PXL + IST) was used only intermittently in the 15 GeV/c Au+Au run. The HFT (PXL + IST) has been operated in the 200 GeV/c Au+Au since the start. The SSD is still commissioning and is expected to join the data taking in some weeks. We have 700M events stored and are on track to take >1G events in this run. This should meet the physics requirements. End of run Projection of current data rate to end of run

17. 17FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Preliminary DCA Pointing resolution Preliminary 750 MeV Kaon * Alignment still not complete 200 GeV/c Au-Au data Simulation with Al Cable TPC + IST + PXL CD-4 requirement

18. 18FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Lessons learned from operation Perform full LU/rad environment testing of thinned production sensors/modules for all expected conditions. –Sensors were being damaged in radiation field. We have lost ~15/400 sensors. –Damage apparently halted by limiting the energy available to a latch-up event (set LU current thresholds to ~120mA over the ladder running current). –This is still under investigation. We will be performing additional LU testing in the near future with thinned production sensors. Have backup solutions – e.g. Cu rather than Al conductor cables –Our aluminum conductor flex PCBs had problems during fabrication and, due to late delivery, only 2 ladders with aluminum conductor were installed in the first run of the detector. Implement as much remote configuration of sensor/module and detector operating parameters as possible to allow for remediation of surprises. –We implemented remote setting of ladder LU thresholds, voltage supplied to the ladders, voltage read, current read after first engineering run tests. –This allowed us to diagnose and stop the damage described above.

19. 19FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT outlook The PXL detector at STAR was installed for the 2014 Au-Au run. The detector system appears to operate as designed, integration with STAR infrastructure is complete. The DCA pointing resolution performance of the installed HFT detectors appears to be as expected. Sensor damage related to the radiation field was observed. The damage appears to be able to be halted by using operational methods. Based on our observations, we should hopefully be able to prevent damage to the next installed detector. We expect to be able to deploy the spare detector (with Al conductor cable on the inner ladders) for the next run and repair the damage to the existing detector with the spare ladders being fabricated. At this point, it appears that the installed PXL detector will be able to complete the physics goals for this run. The spare detector should be ready in ~1 month. MAPS appear to be working well as a technology for vertex detectors.

20. 20FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Extra slides

21. 21FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Possible Mechanisms Non-ionizing (Neutron) damage? – Dislocation of atoms in the matrix generally results in permanent damage to silicon. This is consistent with what we observe. In discussions with Matt Durham who worked on the Phenix FVTX detector, he indicated that the beam tune into Phenix had some component of scraping against a magnet or beam pipe surface that caused spallation neutron based damage in their detector and that the neutron rate was nearly 3 orders of magnitude above what was calculated. In our case, we have no information about the neutron flux at low radii from the beamline. Ionizing radiation damage? – The primary source of ionizing radiation damage is expected to come from the transit of MIPs through the sensors. This is expected to show up in hits registered in sensor pixels. The occupancy of charged tracks is approximately what was projected in the simulations ( ~300 hits per frame on the inner ladders and ~100 hits per frame in the outer ladders). The likelihood of normal beam activities causing the damage observed is judged to be low. There have been, however, a significant number of non-standard events during this run. Particularly during the 15 GeV run period. LU related damage? – It is possible that LU events could cause damage in the silicon. This would need to be a phenomenon particular to thinned silicon and/or high resistivity epi. We did extensive testing of full thickness sensors at the BASE facility at the 88” cyclotron at LBNL where we exposed sensors to many thousands of LU events to measure the LU LET onset and cross-section.

22. 22FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Digital current on the inner ladders NOW Before operational optimizations Amps

23. 23FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL increased current consumption 23

24. 24FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Proposed Testing Plan Proton Irradiation The testing done for ionizing radiation dose was done with gamma rays. This is a generally accepted method of assessing the radiation tolerance of silicon designs. The proton irradiation more closely mimics the environment at the operating STAR experiment and adds displacement damage to the mix. We propose to expose an existing powered PXL ladder to proton beams at the 88” cyclotron at LBNL at various rates up to 300 kRad as well as testing the latch-up cross section due to proton irradiation (if possible, the primary proton LU mechanism of energy deposition from recoil only turns on at ~100 MeV). Latch-up Testing It is possible that the damage observed is related to latch-up. The fact that the sensors are now thinned to 50um could give opportunity for other failure mechanisms such as micro-fracturing due to higher LU point temperature excursions. We propose to expose an existing PXL ladder and thinned sensor on testing cards to heavy ion beams at the 88” Cyclotron BASE facility for up to 5k latch-up events on a sensor. We will also measure the voltage discharge profile on the ladder to understand the profile of energy deposition in the silicon LU area. The production sensors have high resistivity epi and the initial LU test sensors were standard epi. Neutron Irradiation It is possible that we are being exposed to a much higher neutron flux than has been anticipated. We propose to irradiate some sensors to doses of 10 13, 10 14 and 10 15 1MeV N eq / cm 2. These sensors have already been sent to Sandia for irradiation with a batch of ATLAS sensors.

25. 25FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Run 15090063 - Mon Mar 31 21:16:0 Sector 10 L1 = 1.57 A L2 = 0.78 A L3 = 0.78 A L4 = 0.78 A

26. 26FEE 2014 – STAR PXL Vertex Detector 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

27. 27FEE 2014 – STAR PXL Vertex Detector 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

28. 28FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Ladder Design Ladder cable concept

29. 29FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT Radiation length in low mass area Si 50um (0.0529%) acrylic 50um (0.0148%) Encapsulant + bond wires (0.070%) Capacitors + solder (0.0035%) Coverlay (0.0075%) Al 30um – both sides (0.0248%) kapton 50um (0.0148%) acrylic 50um (0.0148%) Carbon composite 125um (0.0293%) 0.0677% 0.128% 0.0441% from older estimate Carbon composite 250um (0.1017%) Si adhesive 100 um (0.0469%) 0.1486% Total = 0.388% NOTE: Does not include sector tube side walls

30. 30FEE 2014 – STAR PXL Vertex Detector L. Greiner STAR HFT PXL insertion mechanics Interaction point view of the PXL insertion rails and kinematic mount points Carbon fiber rails Kinematic mounts

31. 31FEE 2014 – STAR PXL Vertex Detector 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