The ATLAS Pixel Detector Claudia Gemme INFN and University of Genova

1. The ATLAS Pixel Detector Claudia Gemme INFN and University of Genova on behalf of the ATLAS Pixel Collaboration

2. ~380 mm ~1850 mm The ATLAS Pixel Detector • It is the innermost part of the silicon vertex tracker . • It consists of two parts: • 3 barrel layers (12 cm ext and 5cm int radii); • 3+3 forward-backward disks. • ~1.7 m2 of sensitive area with 67M (barrel) + 13M (disks) channels. • n+ on n oxygenated sensors, 400mm x 50mm pixels. • Total dose 50 Mrad on the middle layer in 10 years of LHC.

3. Flex Hybrid MCC sensor FE chip FE chip Pixel Modules • Modules are the basic building elements of the detector (1456 in the barrel, 288 in the end-caps). • The sensitive area is read out by 16 FE chips which are controlled by a Module Controller Chip (MCC). • A Flex-Hybrid circuit glued on the sensor backside provides the signal/power routing. • A pigtail (barrel) + Al/Cu wire bundle connect flex hybrid to patch panels at either end of pixel detector. Pigtail is the only difference between barrel and disks modules. Wirebondings Schematic cross section (through here) bumps

4. Bare module • Hybridization will be done by AMS and IZM. • It consists of bump deposition on surfaces and flip-chip of 16 FEs. • Quality of bumps is checked by x-rays. Electrical tests contacting each chip individually are done before further assembling. AMS - In IZM – PbSn X-rays inspection of bumps to control quality 16 thinned FEs, ~50k bumps 16.4mm Sensor 60.8mm

5. Chip B reworked AMS module noise map Milano Bare Module reworking • Reworking at the bare module level may be necessary to keep the yield up (even if we operate on KGDs) as yieldmodule = (yieldchip)16 • Techniques for reworking in hand both for In and SnPb bumps and results are satisfying.

6. Sensor • Baseline design: • n+ pixel in n-bulk material: • Moderated p-spray isolation. • Bias grid to allow testing before module assembly. • Oxygenated silicon to improve radiation resistance and increase allowable time to room temperature (for repair/upgrades). • Two vendors: Cis and Tesla 3 tiles wafer, n side Charge collection efficiency (meas) n+ implants and bias grid

7. Optical driver FE chip MCC 100m sensor FE chip 1m Optical receiver ….. power optical LVDS control HV bias bump bonds LVDS data out Electronics Overview • On-detector chips fabricated in 0.25mm DSM. Used circuit library with special layout rules for radiation tolerance. • MCC: decode data/cmd signals, generate control signal for 16 FEs, collect data from FEs and accumulate in FIFOs, check event consistency, build module event and sends to DAQ, handle errors. • FE chip: control 18x160 pixels. Amplify sensor signal, on-chip data buffering in EOC FIFOs until trigger signal arrives, send data on serial link to MCC. • VDC: drive data off detector. DORIC: regenerate clock and data/cmd signals.

8. Rad-hard electronics • After one year of experience with modules of first generation DSM, we have received back in May the second generation of chips (FEI2 and MCCI2). • many improvements correcting limitations, • yield about 90%, • rad-hard for reliable operation at LHC dose (verified at PS) but… • one fault in each design does not allow using them for the production, • anyway problems have been easily fixed and respin of wafers not completely processed has produced chips good for production (MCCI2.1) or as a backup in case they need (FEI2.1). • A new submission of the FE is on-going in these days (FEI3: the last one!)

9. FEI2: threshold dispersion • Initial dispersion (untuned) is about 600e (compared to 900e for FEI1) which is roughly the expected improvement. • Using the threshold 7-bit high-quality TDAC which is present in each pixel, it is possible to achieve 26e dispersion on threshold (50e using simpler and faster algorithms). Linearity of this TDAC is very good (shown for one pixel). Col 0 row 0

10. Mean Threshold Threshold dispersion GDAC GDAC FEI2: threshold vs Global DAC • A Global Threshold 5-bit DAC (GDAC) is also present. Mean threshold is well linear respect to this DAC. • A tuned distribution can now be shifted without significant dispersion increase. In the plots below, thresholds have been tuned at GDAC=7.

11. A performance problem on FE-I1 was the large timewalk, giving a significant threshold overdrive for ganged pixels (~7000e for in-time acceptance ). The situation is much improved in FE-I2. Test Beam 2003: Time Walk FE-I1 FE-I2

12. Better timewalk performances immediately translate in better efficiency and in a plateau of full efficiency in the 25ns window of the BCO. There is still a small delay between ganged and the other pixels, but the efficiency plateau is significantly overlapping. Test Beam 2003: Efficiency FE-I2 FE-I1

13. System tests • System tests (with regulators and final cables) have been done both on: • realistic set-up (i.e. 6 modules on a sector support) in lab • under irradiation (7 modules on C-C support irradiated to >30 Mrad) at PS.

14. System tests • System tests have demonstrated that operation of modules is not affected by multiplicity and realistic services (i.e. patch panel, cables lengths and x-sections ). • threshold (~3000e) and noise (~180e) are the same as single modules; • plots indicate difference between the two cases: Dthr=17e, Dnoise=6e

15. Detector building blocks: staves • Barrel staves and disk sectors are the local supports that hold and cool pixel modules(T sensors <0oC). • They are carbon-carbon structures to minimize material. • The cooling fluid (C3F8) flow in thin Al tubes (0.2mm) both for staves and disks. Bi-stave assembly is replicated to form Barrel layers. 2x13 modules. Same unit repeated many times for production line assembly, uniformity of work at different sites

16. Detector building blocks: disks Exploded view of sector Sector is replicated to form disks. 3+3 modules (back side looks the same)

17. Global structure • The global pixel support has been delivered. • It is carbon composites made as itneeds a very stiff low mass structures with near zero CTE (build at room temperature- operate down to –25C). Disks Barrel Disks

18. Pixel and Beam Pipe Assembly Beam Pipe Support Structure Pixel Detector Not Shown PP0 Patch Panel Beam Pipe Beam Pipe Support Structure A “package” that can be inserted in place into the inner detector (and removed also). Fits into the support tube PST. Service Panels PP1 Patch Panel(pipes and cables not shown!)

19. Conclusions • The sensor production is well in schedule – a half of the production is ready, end of the production in summer 2004. • Flex Hybrid production is started. • Mechanics production of local supports is ongoing as well as other global supports. • Problems in electronics are not very serious and can certainly be corrected in the needed timescale. • Many modules have been built using prototype chips: they have been very useful to characterize the detector but also to qualify test and assembly setups. • Achieved technical progress is excellent, it has been demonstrated that pixels can really meet all LHC requirements.