STAR Vertex Detector Upgrade – HFT PIXEL Development

1. STAR Vertex Detector Upgrade –HFT PIXEL Development Outline: Heavy Flavor Tracker at STAR PIXEL detector as part of HFT PIXEL detector requirements Low mass detector design Sensor development for PIXEL Readout system development Prototyping results and outlook Michal Szelezniak on behalf of LBNL RNC group

2. PHOBOS BRAHMS PHENIX RHIC STAR Heavy Flavor Tracker @ STAR • Extend the physics reach of the STAR experiment for precision measurement of the yields and spectra of particles containing heavy quarks: • Study charm and beauty energy losses to test pQCD in a hot and dense medium at RHIC • Charm flow to test thermalization at RHIC • Direct reconstruction of charm decays with small cτ, including D0 and Λc+ • Method: Resolve displaced vertices (>60 µm) ~100 µm RHIC – Relativistic Heavy Ion Collider STAR – Solenoidal Tracker at RHIC

3. HFT and PIXEL detector • TPC points at the SSD ~ 1 mm • SSD points at the IST ~ 300 µm • IST points at the PIXEL ~ 250 µm • PIXEL points at the vertex <30 µm Heavy Flavor Tracker (HFT)‏ PIXEL at 2.5 and 8 cm IST at 14 cm SSD at 23 cm SSD – Silicon Strip Detector IST – Inner Silicon Tracker

4. PIXEL detector characteristics • Two layers at 2.5 & 8 cm radii • Sensor spatial resolution < 10 μm • Coverage 2πin φand |η|<1 • Over 400 M pixels • 0.3 % radiation length/layer • Thinned silicon sensors (50 μm thickness)‏ • Air cooled • Power dissipation ~100 mW/cm2 • Integration time <200 μs • Radiation environment at the level of up to 300 krad/year and 10×1012/cm2 Neq /year • Quick extraction and detector replacement • Stability and insertion reproducibility within a 30 μm window Very challenging mechanical and sensor design

5. Low mass detector design

6. PIXEL detector design Cabling and cooling infrastructure New beryllium beam pipe (0.5 mm thickness, 2 cm radius)‏ Mechanical support with kinematic mounts 2 layers Detector extraction at one end of the cone Ladder with 10 Monolithic Active Pixel Sensors (MAPS) (~ 2×2 cm each)

7. Low mass structure Cable • 4 layer - 150 micron thickness • Aluminum Conductor • Radiation Length ~ 0.1 % • 40 LVDS pair signal traces One of the preliminary designs LVDS – Low-Voltage Differential Signaling

8. Air cooling • MAPS 100 mW/cm2 (160 W total) + drivers 80 W • The temperature of operation is still under consideration. • An optimum temperature for the detectors is around 0 deg C, but they can be operated at 34 deg C without too much noise degradation. • The cooling system design is simplified if we can operate at 24 deg C, • if the cooler temperature is required the cooling system will be equipped with thermal isolation and condensation control when the system is shut down. • Cooling studies show that air velocities of 8 m/s are required over the detector surfaces and a total flow rate of 200 cfpm is sufficient to maintain silicon temperatures of less than 10 deg C above the air temperature.

9. Sensor design

10. Monolithic Active Pixel Sensors MAPS pixel cross-section (not to scale)‏ Properties: • Standard commercial CMOS technology • 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 → cluster size is about ~9 pixels (20-30 μm pitch)‏ • 100% fill-factor • Only NMOS transistors inside the pixels MAPS technology is an attractive choice for the PIXEL detector

11. MAPS @ Institut Pluridisciplinaire Hubert Curien • We are working in collaboration with IPHC to produce sensors that meet the requirements of the STAR PIXEL detector • IPHC-DRS (former IRES/LEPSI) proposed using MAPS for high energy physics in 1999 CNRS - IPHC, Strasbourg-Cronenbourg • More than 20 prototypes developed • several pixel sizes and architectures (simple 3-transistor cells, pixels with in-pixel amplifiers and CDS processing) • different readout strategies (sensors operated in current and voltage mode, analog and digital output) • Large variety of prototype sizes (from several hundreds of pixels up to 1M pixel prototype with full-reticule size)

12. ADC CDS Data sparsification readout to DAQ Pixel Sensors CDS Disc. Development plan Coupled nature of readout and sensor development 2010 (planned) Install 3-module engineering prototype (based on Phase1)‏ 2011 (planned) Install final detector Today First prototypes in hand and tested Complementary detector readout digital signals analog signals digital analog MimoSTAR sensors 4 ms integration time Phase-1 sensors 640 μs integration time Ultimate sensors < 200 μs integration time CDS – Correlated Double Sampling

13. Prototypes with analog readout Analog readout – simpler architecture but ultimately slower readout Prototypes in AMS 0.35 • MimoSTAR 2 • 128 × 128 pixel (30 µm pitch)‏ • MimoSTAR 3 • 320 × 640 pixel (30 µm pitch) • Half-reticle size‏ Based on tests of several different prototypes S/N>12 allows detection efficiency >99.6% MAPS show promising performance for the PIXEL detector MimoSTAR2 test results

14. Prototypes with binary readout IEEE TNS, vol 53, no 6, 2006, pp 3949 - 3955 IEEE TNS, vol 52, no 6, 2005, pp 3186 - 3193 Mimosa16 test results Significantly reduces pixel-to-pixel dispersions Prototypes Mimosa 8 and Mimosa 16 developed by IPHC and DAPNIA feature binary readout a major step towards on-chip data sparsificaiton Meets PIXEL requirements

15. ~ 3 mm Phase-1 prototype for PIXEL • Full reticule sensor • Architecture based on Mimosa8/16 • Binary readout of all pixels (4 outputs) • Integration time ~640 µs • The chip is ready for production Final sensor for the PIXEL detector • Phase-1 combined with on-chip zero suppression • 2 outputs per sensor • On-chip zero suppression has been successfully implemented and tested at IPHC as a small size prototype • The prototype zero-suppression circuitry works up to 115 MHz • Pixel reduced from 30×30 µm down to 18.4×18.4 µm to improve radiation tolerance against non-ionizing radiation damage

16. Readout system design

17. HFT PIXEL Readout Functional Goals • Triggered detector system fitting into existing STAR infrastructure (Trigger, DAQ, etc.) • Deliver full frame events to STAR DAQ for event building at approximately the same rate as the TPC (1 KHz for DAQ1000). • Reduce the total data rate of the detector to a manageable level (< TPC rate). • Reliable, robust, cost effective, etc. Example for a full detector:

18. Readout path 10 parallel independent readout modules (4 ladders per module)

19. Readout system - physical layout

20. Readout system implementation choices Xilinx Virtex-5 Development Board Motherboard Optical link • FF1760 Package • 800 I/O pins • 4.6 – 10.4 Mb block RAM • Up to 550 MHz internal clock • Individual IODELAY • Digital I/O LVDS Drivers • Cypress USB chipset • Fast SRAM • Serial interface • Trigger / Control input • Half duplex connection • Up to 1.2 Gbps • Part of DAQ1000 upgrade Commercial product Our design CERN ALICE RORC-SIU

21. Prototyping results and outlook • Prototyping of mechanical support structures is planned to begin in the next few months • Full reticle 2 × 2 cm Phase-1 should be available at the end of this year • detector engineering prototype (3/10 of the complete detector) will be constructed and should allow to perform physics measurements in 2010 • New prototypes with on-chip discriminators are capable of the required S/N ratio for >99% detection efficiency but with a limited safety margin • Resistance to radiation damage level that can be expected in the STAR environment with the final luminosity (8×1027 /cm2/s ) is being studied • The readout concept has been validated with LVDS readout test (BER <10-14 @ 160 MHz and 2 m fine twisted pair cable) and the full readout system production prototypes are being developed

22. Thank you for your attention

23. Backup slides

24. Fast, column-parallel architecture Developed in IPHC - DAPNIAcollaboration A1 Voff1 A2, Voff2 Vin1,2 VC VS_READ VREAD,CALIB CDS at column level (reduces Fixed Pattern Noise below temporal noise)

25. LVDS data transfer • The final detector system is expected to have LVDS data transfers at the maximum rate of 160 MHz Ladder mock-up with 1-to-4 LVDS fanout buffers 42 AWG wires Mass termination board + LU monitoring 24 AWG wires Buffered path 160 MHz 2.3 m cables Bit Error Rate < 10-14 Virtex-5 based RDO system with RORC link to PC Virtex-5 individual IODELAY was adjusted for each channel

26. RDO system for prototype with binary full-frame readout RDO system for the final sensor with on-chip zero suppresion