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

2. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 2 Diamond as sensor material PropertyDiamondSilicon Band gap [eV]5.51.12 Low leakage Breakdown field [V/cm]10 7 3x10 5 Intrinsic resistivity @ R.T. [Ω cm]> 10 11 2.3x10 5 Intrinsic carrier density [cm -3 ]< 10 3 1.5x10 10 Electron mobility [cm 2 /Vs]19001350 Hole mobility [cm 2 /Vs]2300480 Saturation velocity [cm/s]0.9(e)-1.4(h)x 10 7 0.82x 10 7 Density [g/cm 3 ]3.522.33 Atomic number - Z614 Dielectric constant - ε5.711.9 Low capacitance Displacement energy [eV/atom]4313-20 Radiation hard Thermal conductivity [W/m.K]2000150 Heat spreader Energy to create e-h pair [eV]133.61 Radiation length [cm]12.29.36 Spec. Ionization Loss [MeV/cm]4.693.21 Aver. Signal Created / 100 μm [e 0 ]36028892  Low signal Aver. Signal Created / 0.1 X 0 [e 0 ]44018323

3. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 3 Diamond sensor types - pCVD 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 Test dots on 1 cm grid Surface view of growth side Side view All photographs courtesy of Element Six

4. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 4 Diamond sensor types - scCVD Single Crystal Chemical Vapour Deposition (scCVD) –Grown on diamond substrate –RD-42 has research contract with E6 to develop this material –Exist in ~ 1 cm 2 pieces, max 1.4 cm x 1.4 cm, thickness > 1 mm –A true single crystal L Not in time for B-layer replacement J Fall-forward for B-layer upgrade (single chips, wafers ?)  After heavy irradiations expect similar properties to pCVD

5. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 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 CCD measured on recent 1.4 mm thick pCVD wafer  mean not most probable

6. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 6 Charge collected in pCVD diamonds Electrodes stripped off and reapplied at will –Test dot → strip → pixel on same diamond 90 Sr source data well separated from pedestal  = 11300 e  ~ 9000 e  99% of events above 4000 e  FWHM/MP ~ 1 (~ 0.5 for Si) –Consequence of large non-homogeneity of pCVD material Q col measured @ 0.8 V/μm

7. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 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 e-injection with α-particles scCVD measured in Ljubljana Transient time Current

8. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 8 Radiation Damage - Basics  Charge trapping the only relevant radiation damage effect  NIEL scaling questionable a priori G E gap 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 ! Radiation induced effect Diamond Operational consequence Silicon Operational consequence Leakage current small & decreases none I/V = αΦ α ~ 4x10 -17 A/cm Heating Thermal runaway Space charge~ nonenone ΔN eff ≈ -βΦ β ~ 0.15 cm -1 Increase of full depletion voltage Charge trappingYes Charge loss Polarization 1/τ eff = βΦ β ~ 5-7x10 -16 cm 2 /ns Charge loss Polarization

9. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 9 Radiation Damage - Diamond Data Done in context of RD-42 50  m strip detectors (pixels !) read out by VA chip – S/N the measured parameter – calibrate noise to get charge Two 500  m thick detectors, CCD 0 ~150  m Irradiated to 1.0 and 2.2x10 15 p/cm 2 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  m FWHM narrows: 54 → 41 → 36 ( FWHM/  0.95→0.84→0.77) Two 500  m thick detectors, CCD 0 190 & 215  m Irradiated to 6 and 18x10 15 p/cm 2 Source evaluation of S/N relative to before irradiation Highest fluence point evaluated also at 2 V/  m (1000 V) 25 % of original signal retained → 33% at 2 V/  m Test beam data taken, not fully analyzed yet Radiation homogenizes diamond – bulk damage starts to dominate 1 V/  m2 V/  m

10. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 10  For mean free path in infinite detector expect  With CCD 0 initial trapping on grain boundaries, k a damage constant @ Diamond with larger CCD 0 degrades faster J … but still performs better at any fluence @ Fresh data of irradiations available – analysis still preliminary  scCVD with PS 24 GeV protons up to 2x10 15 p/cm 2 ; k~10 -18 μm -1 cm -2, ~same as old pCVD proton data  pCVD with reactor neutrons up to 8x10 15 n eq /cm 2 ; k~5x10 -18 μm -1 cm -2  pCVD with PSI 200 MeV pions up to 6x10 14 π/cm 2 ; k consistent with ~2x10 -18 μm -1 cm -2 @ Looks roughly consistent with NIEL, neutron damage appears high – but no NIEL available for 1 MeV n on C !  Analysis ongoing, k have large uncertainties, too early to draw hard sLHC implications Radiation damage parameterization and NIEL  In Si most damage scales with NIEL J NIEL in C at high E an order of magnitude smaller than in Si G NIEL scaling not established for diamonds W. de Boer et al. arXiv:0705.0171v1

11. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 11 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 5x10 14 p/cm 2 SPS test beam in August & October 1 single-chip scCVD module CERN SPS test beam Irradiated to 5x10 14 p/cm 2 SPS test beam in August & October 1 single-chip pCVD module Irradiated to 2x10 15 p/cm 2 L Electronics heavily damaged C-sensor in carrier Pattern with In bumps Complete module under testModule after bump bonding scCVD diamondscCVD module

12. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 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  m (CERN) → 37  m (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  m, unfolding telescope contribution of 11  m yields 14  m, 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 Full module  = 18  m Eff = 97.5 % Thr = 1450 e Noise = 137 e CERN preliminaryDESY

13. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 13 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  ≈ 7  m 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  edge = 7  m Track distribution Eff = 99.98 %

14. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 14 Diamonds in ATLAS BCM – 16 1x1 cm 2 diamond pad detectors, TOT readout Test beam performance at end of readout chain exhibits median/noise ~ 11:1 BCM-stations Beam pipe Pixel Noise rate vs. thr 2 Eff vs. thr

15. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 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 10 16 represents a quantum leap in challenge Current electronics not suitable for tests much above 10 15

16. Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 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