Diamond Pixel Modules for the High Luminosity ATLAS Inner Detector Upgrade

1. Diamond Pixel Modules for the High Luminosity ATLAS Inner Detector Upgrade ATLAS Tracker Upgrade Workshop Valencia 12-14 December 2007 Marko Mikuž University of Ljubljana & J. Stefan Institute

2. Diamond as sensor material

3. 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 μm detectors Base-line diamond material for pixel sensor Diamond sensor types - pCVD Surface view of growth side All photographs courtesy of Element Six Side view Test dots on 1 cm grid

4. Single Crystal Chemical Vapour Deposition (scCVD) Grown on diamond substrate RD-42 has research contract with E6 to develop this material Exist in ~ 1 cm2 pieces, max 1.4 cm x 1.4 cm, thickness > 1 mm A true single crystal Not in time for B-layer replacement Fall-forward for B-layer upgrade (single chips, wafers ?) After heavy irradiations expect similar properties to pCVD Diamond sensor types - scCVD

5. 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

6. 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

7. 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

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 - Diamond Data • Done in context of RD-42 • 50 mm strip detectors (pixels !) read out by VA chip – S/N the measured parameter – calibrate noise to get charge • Two 500 mm thick detectors, CCD0 ~150 mm • Irradiated to 1.0 and 2.2x1015 p/cm2 at PS • Fully evaluated in test beam • S/N loss 57 → 49 → 47 (mean); 41 → 35 → 35 (MP) • Resolution improvement 11.5 → 9.1 → 7.4 mm • FWHM narrows:54 → 41 → 36 ( FWHM/m 0.95→0.84→0.77) • Two 500 mm thick detectors, CCD0 190 & 215 mm • Irradiated to 6 and 18x1015 p/cm2 • Source evaluation of S/N relative to before irradiation • Highest fluence point evaluated also at 2 V/ mm (1000 V) • 25 % of original signal retained → 33% at 2 V/ mm • Test beam data taken, not fully analyzed yet • Radiation homogenizes diamond – bulk damage starts to dominate 1 V/ mm 2 V/ mm

10. 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 • NIEL scaling not established for diamonds W. de Boer et al. arXiv:0705.0171v1 • For mean free path in infinite detector expect • With CCD0 initial trapping on grain boundaries, k a damage constant • Diamond with larger CCD0degrades faster • … but still performs better at any fluence • Fresh data of irradiations available – analysis still preliminary • scCVD with PS 24 GeV protons up to 2x1015 p/cm2 ; k~10-18μm-1cm-2, ~same as old pCVD proton data • pCVD with reactor neutrons up to 8x1015 neq/cm2; k~5x10-18μm-1cm-2 • pCVD with PSI 200 MeV pions up to 6x1014π/cm2 ; k consistent with ~2x10-18μm-1cm-2 • Looks roughly consistent with NIEL, neutron damage appears high – but no NIEL available for 1 MeV n on C ! • Analysis ongoing, khave large uncertainties, too early to draw hard sLHC implications

11. Module after bump bonding Complete module under test Diamond Pixel Modules • 3 modules built with ATLAS pixel chips @ OSU, IZM and Bonn • 1 full (16 chip) pCVD module • Test beam at DESY and CERN • Irradiated to 5x1014 p/cm2 • SPS test beam in August & October • 1 single-chip scCVD module • CERN SPS test beam • Irradiated to 5x1014 p/cm2 • SPS test beam in August & October • 1 single-chip pCVD module • Irradiated to 2x1015 p/cm2 • Electronics heavily damaged 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, 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 last year’s 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 • Efforts to port the analysis code 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 preliminary DESY s = 18 mm Eff = 97.5 %

13. Track distribution Diamond scCVD Pixel Module – Results • scCVD single chip module • Preliminary analysis (M. Mathes, Bonn) of SPS test beam data exhibits excellent performance of the module • Cluster signal nice Landau • Preliminary efficiency 99.98 %, excluding 6/800 problematic electronic channels • Residuals show pixel edge with s≈ 7 mm • Charge sharing shows most of charge collected on single pixel – optimal for performance after (heavy) irradiation • Looking forward to data of irradiated module ! Cluster signal Eff = 99.98 % sedge = 7 mm

14. 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 rate vs. thr2 Eff vs. thr

15. Diamond Sensors for Pixel sLHC Upgrade • Move forward on two fronts • Better understanding of sensor material – ongoing in RD-42 • Radiation hardness – statistics, pions, neutrons, NIEL, trapping characterization etc. • Material growth and processing optimization • Search for suppliers alternative to Diamond Detectors Limited • scCVD enlargement (larger samples ?, fusion ?) • Build up experience with (irradiated) modules – ATLAS upgrade proposal (Carleton, CERN, Bonn, JSI, OSU, Toronto) • Paramount to any upgrade proposal is to demonstrate experience with complete modules under realistic conditions, not bits and pieces • Solve production issues – bump bonding on wafer level • Get interest of material supplier(s) • Gain experience with modules after irradiations • Engineer a light(er) mass support structure of diamond detector layer(s) • ? x 1016 represents a quantum leap in challenge • Current electronics not suitable for tests much above 1015

16. Backup – 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