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Diamond Module Prototypes for the ATLAS SLHC Pixel Detector

This proposal outlines the upgrade plan for the ATLAS SLHC Pixel Detector using diamond sensor material prototypes. The goals include proving radiation tolerance, optimizing front-end electronics, and manufacturing 10 diamond sensor modules. The material includes polycrystalline and single crystal chemical vapor deposition diamond types. Radiation damage effects, parameterization, and test results are also discussed.

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Diamond Module Prototypes for the ATLAS SLHC Pixel Detector

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  1. Diamond Module Prototypesfor the ATLAS SLHC Pixel Detector PIXEL 2008 Workshop Fermilab, September 23-26 2008 Marko Mikuž University of Ljubljana & J. Stefan Institute

  2. Diamond tracker upgrade proposal Collaboration • Bonn • Carleton • CERN • Ljubljana • Ohio State • Toronto • Submitted May’07 • Updated Dec’07 • Approved by ATLAS EB Mar’08 • EDMS: ATU-RD-MN-0012

  3. R&D proposal goals • Prove radiation tolerance of CVD diamond pixel prototypes) • Industrialize bump bonding to diamond sensors (make 10 modules) • Optimisation of front-end electronics • Lightweight mechanical support – since minimal cooling required • Financial resources sought to make 10 parts: • Diamond sensors • Bump-bonding contracts • 200 FE-I3 + 25 MCC’s • Module support prototypes • Three year beam-test program (2008-2010)

  4. Diamond as sensor material

  5. Polycrystalline Chemical Vapour Deposition (pCVD) Grown in μ-wave reactors on non-diamond substrate Exist in Φ = 12 cm wafers, >2 mm thick Small grains merging with growth Grind off substrate side to improve quality → ~500-700 μm thick detectors Base-line diamond material for pixel sensor Diamond sensor types - pCVD Surface view of growth side Photo HK@OSU Side view Test dots on 1 cm grid Photograph courtesy of E6

  6. Single Crystal Chemical Vapour Deposition (scCVD) Grown on HTHP diamond substrate Exist in ~ 1 cm2 pieces, max 1.4 cm x 1.4 cm, thickness > 1 mm A true single crystal Fall-forward for B-layer upgrade (single chips, wafers ?) After heavy irradiations expect similar properties to pCVD Diamond sensor types - scCVD

  7. Signal from pCVD diamonds • No processing: put electrodes on, apply electric field • Trapping on grain boundaries and in bulk • much like in heavily irradiated silicon • Parameterized with Charge Collection Distance, defined by • CCD = average distance e-h pairs move apart • Coincides with mean free path in infinite (t ≫ CCD) detector  mean not most probable CCD measured on recent 1.4 mm thick pCVD wafer @ 2 V/ mm CCD of recent 0.5 mm thick pCVD detectors

  8. Radiation Damage - Basics • Charge trapping the only relevant radiation damage effect • NIEL scaling questionable a priori • Egap in diamond 5 times larger than in Si • Many processes freeze out • Typical emission times order of months • Like Si at 300/5 = 60 K – Boltzmann factor • Lazarus effect ? • Time dependent behaviour • A rich source of effects and (experimental) surprises !

  9. Radiation damage parameterization and NIEL • In Si most damage scales with NIEL • NIELin C at high E an order of magnitude smaller than in Si • NIELviolationobserved for n vs. p damage in diamonds W. de Boer et al. phys. stat. sol. (a) 204, No. 9 (2007)3009 • For mean free path in infinite detector expect • With CCD0 initial trapping on grain boundaries, k a damage constant • Larger CCD0performs better (larger collected charge) at any fluence • Can turn 1/ CCD0into effective “initial” fluence, expect CCD0~ ∞ for SC

  10. Diamond irradiations in 2007-08 • Fresh data on irradiations available – analysis mostly still preliminary • Done in context of RD-42 • 50 μm strip detectors (pixels !) read out by VA chip – S/N the measured parameter – calibrate noise to get charge • Procedure: test-beam → irradiation → test-beam … • scCVD (4) and pCVD (2) with PS 24 GeV protons up to 6x1015 p/cm2 (in 3 steps); k ~ 10-18μm-1cm-2, ~same as old pCVD proton data • pCVD (2) with reactor neutrons up to 1.3x1016 neq/cm2 (in 6 steps); k ~ 3-5x10-18μm-1cm-2, discrepancy between source and test-beam • pCVD with PSI 200 MeV pions up to 6x1014π/cm2; k consistent with ~1-3x10-18μm-1cm-2 • Re-measured pCVD at 1.8x1016p/cm2 result consistent with previous measurements KEK 70 MeV • Pion vs. proton looks roughly consistent with NIEL, neutron damage appears high • Radiation homogenizesdiamond – bulk damage starts to dominate, k appears universal • Analysis ongoing, khave large uncertainties, too early (and not easy) to draw hard sLHC implications • Need pion data to at least 1015 p/cm2, preferably on SC (more sensitive)

  11. Module after bump bonding Complete module under test Diamond Pixel Modules • modules built with ATLAS pixel chips @ OSU, IZM and Bonn • 1 full (16 chip) pCVD module • Test beam at DESY and CERN • Irradiated complete module to 1x1014 p/cm2 • SPS test beam 2007 • Irradiated to 7x1014 p/cm2 • SPS test beam 2008 • Analysis in progress • 1 single-chip scCVD module • CERN SPS test beam • Irradiated complete module to 1 and 7 x1014 p/cm2 • SPS test beam 2007, 2008 C-sensor in carrier Pattern with In bumps scCVD diamond scCVD module

  12. Diamond pCVD Pixel Module – Results • pCVD full module • Tests show no change of threshold and noise from bare chip to module – low sensor C & I • Noise 137 e, Threshold: mean 1450 e, spread 25 e, overdrive 800 e, reproduced in test beams • Many properties (e.g. resolution, time-walk) scale with S/N and S/T • Data from DESY test beam plagued by multiple scattering • Silicon telescope resolution 7 mm (CERN) → 37 mm (DESY) • Efficiency of 97.5 % a strict lower limit because of scattered tracks • Data from 2006 CERN SPS test beam not fully analyzed yet • Preliminary residual 18 mm, unfolding telescope contribution of 11 mm yields 14 mm, consistent with digital 50/√12 = 14.4 • Analysis code ported from Bonn • Push towards complete analysis of SPS data of un-irradiated and irradiated module Bare chip Noise = 137 e Thr = 1450 e Full module CERN DESY s = 18 mm Eff = 97.5 %

  13. Benefit of low C and I on pixel operation • Diamond pixel sensor has ~3 x smaller C than planar Si (ε, d) • Diamond has no Ileak • Both effects combine into superior noise performance even in a non-optimized FE • Lower noise • Lower threshold • Less overdrive (time-walk)

  14. Track distribution Diamond scCVD Pixel Module – Results scCVD single chip module • Analysis (M. Mathes PhD, Bonn) of SPS test beam data exhibits excellent module performance • Cluster signal nice Landau • Efficiency 99.98 %, excluding 6/800 problematic electronic channels • Unfolded track resolution using η-algorithm from TOT exhibits s≈ 8.9 mm • Charge sharing shows most of charge collected at high voltage on single pixel – optimal for performance after (heavy) irradiation • Data of irradiated (7x1014 p) module • Preliminary analysis A. La Rosa, H. Pernegger 100 V 400 V Cluster signal s = 8.9 mm Long side TOT - η Track resolution binary Very sensitive to calibration !

  15. Strawman 2008 of ATLAS ID inner part @ sLHC • Pixel layer 1: stave about 60 cm long at r ~ 3cm • Radiation for 3000 fb-1 • NIEL ~ 1.5 x 1016 cm-2 • > 90 % from (π, K, p) 5-10 % from n • About 0.12 (x2 ?) m2 of sensor in the innermost layer

  16. 2nd Pixel Layer 1rst Pixel Layer Any technology fit for layer 1 ? • Not really with current FE Signal required with present Pixel ASIC (= 2 x In-time threshold): H. Sadrozinski, SLAC 6/08 3D 4E 11800 3E 10600 2E 8600e Planar Si 7600e p/cm2 Diamond 4600e p/cm2

  17. Sensors - Diamond Detectors Ltd • All results shown obtained with their sensors (RD42 has research contract with DDL) • Outstanding purchase orders for three ATLAS pixel sensors • First part cut from fully characterised wafer • Suspect this had low as-grown collection distance ( 200μm) • DDL will thin to improve CCD • If resulting collection distance > 275μm we will accept (RD42 deal) • Element6/DDL growing new wafers to satisfy other orders • Delivery of pixel sensors expected by end of the year • ATLAS upgrade project has resources to place orders for three more • Waiting to see

  18. Sensors - Alternative Suppliers Large wafer growth and processing capability

  19. Thermo-mechanical considerations • Have brain-stormed a number of options to thin readout layers • Exploit thermal path through sensors to evacuate heat • Allow modules to run at 30° - 40° • Have started with “simple” analytical calculations • Exploring FEA capabilities with TRIUMF engineer • Plan to mock-up one or more solution(s) suggested by simulations • Less than 2% X0 for a double layer of sensors looks feasible

  20. Summary • Good progress on all fronts, despite late start with ATLAS approval in March’08 • Understanding of radiation hardness (RD42) • Building pixel modules • Test-beam data on strip and pixel modules • Securing sensor supply (RD42) • Start-up of thermo-mechanical studies • Goals for 2009 • Build & test 3-5 additional modules with FE-I3 • Build & test assemblies with I4 prototype • Diamonds are an option to be seriously considered for inner pixel layer at sLHC !

  21. Backup slides

  22. Backup – Charge collected in pCVD diamonds • Electrodes stripped off and reapplied at will • Test dot → strip → pixel on same diamond • 90Sr source data well separated from pedestal • <Qcol> = 11300 e • <QMP> ~ 9000 e • 99% of events above 4000 e • FWHM/MP ~ 1 (~ 0.5 for Si) • Consequence of large non-homogeneity of pCVD material Qcol measured @ 0.8 V/μm

  23. Charge collected in scCVD diamonds • CCD = thickness at E > 0.1 V/μm • Collect all created charge • “CCD” hardly makes sense • FWHM/MP ~ 1/3 • scCVD material homogenous • Can measure diamond bulk properties with TCT ~ same CCD as pCVD scCVD measured in Ljubljana e-injection with α-particles Current Transient time

  24. Single crystal irradiation results • Single Crystal CVD (scCVD) Diamond irradiated to 1.5x1015p/cm2 • PH distributions look narrow before and after irradiation • In-time thresholds are ∼ threshold (1500e) + overdrive (800e) • PH distributions after irradiation → η > 99%.

  25. Going edgeless • scCVD single-chip module is edgeless – patterning right up to the edge • Data exist on performance – needs to be analyzed scCVD module pattern

  26. Pixel BCM-stations Beam pipe Diamonds in ATLAS • BCM – 16 1x1 cm2 diamond pad detectors, TOT readout • Test beam performance at end of readout chain exhibits median/noise ~ 11:1 • Noise performance in ATLAS consistent with previous experience Noise rate vs. thr2 Eff vs. thr

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