the ATLAS Pixel Detector: Overview and Status Sven Vahsen, LBNL for the ATLAS Pixel collaboration DPF 2006 Meeting, Honolulu, Hawaii October 30, 2006

Honolulu, October Sven Vahsen, LBNL2 Large Hadron Collider (LHC) under construction near Geneva, Switzerland Eventually 7-TeV proton-on-proton Beam crossings every 25 ns L = cm -2 s -1 (ATLAS / CMS) Near Geneva, Switzerland, underground… Full physics run (14TeV) First beams and collisions (0.9TeV)

Honolulu, October Sven Vahsen, LBNL3 Length = 55 m Width= 32 m Height= 35 m Weight = 7000 T ATLAS: multi-purpose particle detector Optimized for study of Electroweak symmetry breaking and search for physics beyond SM at the LHC Under construction around one of the LHC interaction points To be completed in time for first beam in 2007 * ATLAS = A Toroidal LHC Apparatus ATLAS!

Honolulu, October Sven Vahsen, LBNL4 Detection of charged particles takes place in 1744 identical ATLAS Pixel Modules 6 cm Pixel 50 x 400 μm x46080 ATLAS ATLAS Pixel Detector –Innermost tracking detector, surrounding beam pipe 1.3 m 1744 modules x pixels = 80 million channels! From ATLAS to Pixels: Mechanical Overview physicist

Honolulu, October Sven Vahsen, LBNL5 Pixel Project Overview Pixel Detector is last sub- detector to be installed in ATLAS April 2007 as the 7m “Pixel Package”, which includes —Service panels (connections for electrical, optical, cooling) —Be beam pipe Remaining work at CERN —Final stages of integration —Connection of service panels —Testing Remaining slides —Overview of the pixel detector and how it works —Status of the project Trial insertion of pixel frame into support tube

Honolulu, October Sven Vahsen, LBNL6 The LHC Tracking Challenge Only tracks with P T >1Gev, 0 0 shown Pixel Detector design constraints from LHC timing / event-environment physics, ATLAS design Tracking in high multiplicity environment  high granularity Good impact parameter resolution  high granularity + low mass Distinguishing hits 25ns apart  fast preamp rise time 3.2 μs trigger latency (LVL2)  on detector buffering of hits High radiation dose  low temp., high radiation tolerance ATLAS tracking : three sub-detectors from r = 5 cm m, inside 2T magnetic field. Pixel Detector innermost  highest granularity and radiation tolerance (3 sp) (4 sp) (36 sp) H ’ bb interaction With pile-up at design luminosity

Honolulu, October Sven Vahsen, LBNL7 –Modules overlap on the support structure to provide hermetic coverage: 3 space points for |η|<2.5 for collisions up to 11 cm from nominal IP –3 barrel layers at r = 5, 9, 12 cm –2 endcaps with 3 layers –Will be first large-scale active pixel device in operation –i.e. ~ each pixel read out by dedicated preamp: 80 million channels –Approx. 10 kW operating power in active volume, at 2V –Detector will operate at -7°C –Cooling integrated into local support structure via thinned aluminum tubes, C 3 F 8 evaporation –Total mass is 10% X 0 normal to beam The Pixel Detector Solution 1.3 m

Honolulu, October Sven Vahsen, LBNL8 The ATLAS Pixel Module Kapton flex circuit: routes signals between FE and MCC. Routes LV (2V, 1.6V) to chips and HV ( V) to sensor Sensor: where charged particles traversing detector liberate charge: 2 cm x 6 cm x 250 μm n bulk silicon rectangle, with 47,268 n+ pixels 16 Front End (FE) chips: preamp channels, each connected to sensor pixels via bump bonding Hits buffered for up to 3.2 μs (LVL2 latency) in “End Of Column” buffers on FE-chip Upon LVL2 trigger, Module Control Chip (MCC) combines hits from FE chips into event Data is read out electrically from module via 1m “Type 0” up to 160 Mb/s ~ 2 x 6 cm Data is converted between electrical and optical at far end of Type 0 cable 50 μm Solder bumps

Honolulu, October Sven Vahsen, LBNL9 The Pixel Detector Module –Sensor wafer –16 FE chips Bump-bonded onto sensor 50 μm pitch Solder bumps –Electronics Design Work started ~ 10 years ago –Final version (Dec 2003) of FE chip is “FE-I3”: – 0.25 μm CMOS process, IBM, 3M transistors!

Honolulu, October Sven Vahsen, LBNL10 Single Pixel: Detection of a Charged Particle apply ( V) reverse bias voltage Free charge carriers (electrons & holes) are removed: silicon “depleted” no incoming particles  only leakage current < 1 nA / pixel A passing charged particle at normal incidence liberated on average 22,000 electron-hole pairs per 300μm (~4fC) charge swept towards bumps and into FE preamp by electric field, where it is converted to voltage pulse charge typically shared by a few (1-3 pixels)

Honolulu, October Sven Vahsen, LBNL11 The Pixel Preamp (single pixel) In FE chip, charge-integrating amplifier converts charge pulse from sensor into voltage pulse Ouput voltage above threshold  digital hit  stored in EOC buffer Time over threshold (TOT) proportional to charge Information from hit ultimately preserved —Bunch crossing ID (BCID) —Time over threshold  charge —Pixel Geographical address Q=CV Sensor / bump threshold Digital controls for each pixel’s preamp threshold and more Time over threshold (TOT) can improve position resolution in case of charge sharing: charge-weight each pixel

Honolulu, October Sven Vahsen, LBNL12 Module Performance Many test beam measurements: efficiency, timing properties, charge collection, spatial resolution Results incorporated into ATLAS simulation/digitization High efficiency and good timing characteristics even after irradiation Single pion test beam efficiency vs. trigger timing (10ns/DIV) Unirradiated60MRad, ~10 15 n/cm 2

Honolulu, October Sven Vahsen, LBNL13 Pixel Performance  Tracking Performance Pixel single-point resolution in r/phi —TDR: want < 13 μm —Test beam: 7.5 μm before irradiation (at incidence angle 10 o ) 9.7 μm after irradiation (at incidence angle 15 o ) Determines resolution of transverse impact parameter, d0 (for b-tagging) —three tracking algorithms —“newTracking” takes full advantage TOT measurement to improve resolution in case of charge-sharing σ(d0) in μm —Simulation of single-muons, p T =200 GeV/c (low multiple scattering) —plot σ(d0 generated – d0 reconstructed )

Honolulu, October Sven Vahsen, LBNL14 Module Production & Testing: Done! Two commercial bump bonding vendors, six academic laboratories all running in parallel. ~ 12 FTE technicians and 15 FTE physicists & students for 2 years. Each individual pixel tested and characterized at intended operating temperature, -7°C Preamp properties with internal injection circuit Bump connectivity with 60- keV X-ray source Built more modules than needed, ranked them by quality, discarded the worst 1744

Honolulu, October Sven Vahsen, LBNL15 Local supports: Staves and Sectors “pigtail” Al cooling tube Highest-quality modules glued onto carbon support structures, which incorporate cooling tubes “Disk Sectors” in endcap (double sided) “Staves” in barrel “Type0” cable

Honolulu, October Sven Vahsen, LBNL16 Integration: Endcaps  Done! Sector  Disk  Endcap Both endcaps completed in U.S. and shipped to CERN Three completed Pixel disks (one end-cap) with 6.6 M channels x8 x3

Honolulu, October Sven Vahsen, LBNL17 Pixel Endcap C: Traveling in style! Geneva  CERN: Volvo, back seat, lots of padding SFO  Newark  Geneva, Business class!

Honolulu, October Sven Vahsen, LBNL18 Endcap quality Strict QC at all levels of integration —Bumps disconnecting when gluing modules on sector? —Increase in noise? —Placement precision? —Thermal performance? Everything within spec! —Dead channels Endcap C < ~0.2% Endcap A slightly worse  3 modules need work —No noise increase —Placement precision of modules on sectors: 2.6 μm w.r.t. to target position in sector place # MODULES PIXEL NOISE (e-) DEAD PIXELS # MODULES 10 -3

Honolulu, October Sven Vahsen, LBNL19 Integration: Barrels 13 modules “loaded” onto each stave and tested at European institutes Loaded staves then shipped to CERN for further integration, as shown here Dedicated tooling developed to do carry out each integration stage safely Layer 2 Layer 1 B Layer Two staves  bi-stave with cooling U-Link… …inserted into half-shells… Loaded half-shells clamped together

Honolulu, October Sven Vahsen, LBNL20 Pixel Layer2 – Half shell Pixel Layer2, after clamping Pixel Layer2, in Global SupportPixel Layer2, after clamping Layer 2 completed on Sept 10 Layer2 used lowest-quality accepted barrel modules. Still only < 0.3% bad channels

Honolulu, October Sven Vahsen, LBNL21 Layer1: finished last week (after pictures) Expect to finish b-layer in ~ 3 weeks Integrate all barrels and end-caps by the end of 2006 Pixel Layer1, 1 st half-shell completed Pixel Layer1, 2 nd half-shell. One bi-stave under test Integration of Remaining Barrel Layers

System Test and Cosmics Final integration takes place in December, but endcaps already complete  One endcap has been high- jacked for an 8% (6.6M of 80M channels) system test Will exercise many production parts of system not mentioned in this talk —Services —DAQ —Control and interlock system Use scintillators to trigger on vertical cosmics

Honolulu, October Sven Vahsen, LBNL23 The End Game Jan-Feb 2007 devoted to Service Panel integration If time left before installation (currently we have one month contingency) it could be used for cold test of whole pixel package Insertion of pixel package into ATLAS in April 2007, followed by months of connecting, cabling, and testing And then, hopefully, first LHC beam!

Conclusion Following nearly a decade of R&D, and years of production, Atlas Pixel Detector now in the final stages of integration —Both Endcaps complete and at CERN —Barrel L2, L1 complete, b-layer in a few weeks → 3 Layer Pixel Detector on schedule for installation in ATLAS in April 07!

BACKUP SLIDES

Problems Overcome cooling pipe corrosion breaking cables

Honolulu, October Sven Vahsen, LBNL27 In lab tests to date, typically tune to threshold of 4000 electrons Well above typical noise of ~170 electrons Modules work great, no stability issues! Tuning A Module A module has channels in 2 x 6 cm area, typically > 99.8% fully functional Process variation across FE chips, preamps differ  need “tuning” to make response of all pixels uniform Each preamp has digitial “knobs” for tuning the preamp behavior,.e.g. Tuning = find the settings for each pixel that give uniform response across module untuned moduletuned module Adjust threshold of each pixel

Honolulu, October Sven Vahsen, LBNL28 Actual ATLAS Pixel Sensor A diode junction forms wherever p-doped and n-doped regions touch. Depletion always begins at the diode junction as reverse external voltage is applied. Hadron irradiation introduced p-type defects. Eventually this will cause the bulk to “type invert” and become p-type. At this point the diode junction shifts to the top. This was chosen on purpose because it allows to operate without fully depleting the bulk. Leakage current increases drastically with irradiation! Lightly n-doped bulk Heavily n-doped pixel implants (doping too heavy to deplete) Heavily p-doped back side contact Guard rings P-spray doping to isolate individual pixels Diode junction Bumps connect to implants

Honolulu, October Sven Vahsen, LBNL29 Pixel Chip Front End comparator Input from Pixel sensor (bump goes here) preamp

Honolulu, October Sven Vahsen, LBNL30 The MOS transistor schematic of the FE-I3 charge amplifier Above is just one pixel! 2880 pixels / readout chip  ~3M (MOS) transistors / chip FE-I3).

Honolulu, October Sven Vahsen, LBNL31 Front End Features Programmable threshold = Global Threshold + Pixel Threshold Calibration charge injection Ability to measure leakage current Time over Threshold (TOT) charge measurement –How long the red curve says above threshold depends on the size of the input charge Can easily change threshold for whole chip Can fine tune each pixel to compensate for response differences (Tuning) V1 V2 switch Input from detector Good old charge amplifier Injection capacitor (must be small)