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Diamond Module Prototypes for the ATLAS SLHC Pixel Detector

Diamond Module Prototypes for the ATLAS SLHC Pixel Detector. PIXEL 2008 Workshop Fermilab, September 23-26 2008. Marko Mikuž University of Ljubljana & J. Stefan Institute. Diamond tracker upgrade proposal. Collaboration Bonn Carleton CERN Ljubljana Ohio State Toronto Submitted May’07

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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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