Marko MikužUniversity of Ljubljana & J. Stefan Institute
Diamond Pixel Modules for the High Luminosity ATLAS Inner Detector Upgrade
ATLAS Tracker Upgrade WorkshopValencia 12-14 December 2007
Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 2
Diamond as sensor material
Property Diamond SiliconBand gap [eV] 5.5 1.12 Low leakage
Breakdown field [V/cm] 107 3x105
Intrinsic resistivity @ R.T. [Ω cm] > 1011 2.3x105
Intrinsic carrier density [cm-3] < 103 1.5x1010
Electron mobility [cm2/Vs] 1900 1350
Hole mobility [cm2/Vs] 2300 480
Saturation velocity [cm/s] 0.9(e)-1.4(h)x 107 0.82x 107
Density [g/cm3] 3.52 2.33
Atomic number - Z 6 14
Dielectric constant - ε 5.7 11.9 Low capacitance
Displacement energy [eV/atom] 43 13-20 Radiation hard
Thermal conductivity [W/m.K] 2000 150 Heat spreader
Energy to create e-h pair [eV] 13 3.61
Radiation length [cm] 12.2 9.36
Spec. Ionization Loss [MeV/cm] 4.69 3.21
Aver. Signal Created / 100 μm [e0] 3602 8892 Low signal
Aver. Signal Created / 0.1 X0 [e0] 4401 8323
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
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 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
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
hicknessdetector t -
apart moveh -e distance
t
dddt
dQQ
he
createdcol
μme
36 0
colQ
CCD
CCD measured on recent1.4 mm thick pCVD wafer
mean notmost probable
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
• 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
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
Cu
rren
t
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
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 !
Radiation induced effect
DiamondOperational consequence
SiliconOperational consequence
Leakage currentsmall &
decreasesnone
I/V = αΦ
α ~ 4x10-17 A/cm
Heating
Thermal runaway
Space charge ~ none noneΔNeff ≈ -βΦ
β ~ 0.15 cm-1
Increase of full depletion voltage
Charge trapping YesCharge loss
Polarization
1/τeff = βΦ
β ~ 5-7x10-16 cm2/ns
Charge loss
Polarization
t
thttteff
vPN
)1(1
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, CCD0 ~150 m
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 m FWHM narrows: 54 → 41 → 36 ( FWHM/
0.95→0.84→0.77) Two 500 m thick detectors, CCD0 190 & 215 m
Irradiated to 6 and 18x1015 p/cm2
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/ m 2 V/ m
Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 10
For mean free path in infinite detector expect
With CCD0 initial trapping on grain boundaries, k a damage constant Diamond with larger CCD0 degrades 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~10-18 μm-1cm-2, ~same as old pCVD proton data pCVD with reactor neutrons up to 8x1015 neq/cm2; k~5x10-18 μm-1cm-2
pCVD with PSI 200 MeV pions up to 6x1014 π/cm2 ; k consistent with ~2x10-18 μm-1cm-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
kCCDCCD 0
11
In Si most damage scales with NIEL
NIEL in C at high E an order of magnitude smaller than in Si
NIEL scaling not established for diamonds W
. de
Boe
r et
al.
arX
iv:0
705.
0171
v1
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 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
Complete module under test
Module after bump bonding
scCVD diamond scCVD module
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
Bar
e ch
ip
Fu
ll m
odu
le
=
18
m
Eff = 97.5 %
Thr = 1450 e Noise = 137 e
CERN preliminary DESY
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 !C
lust
er s
ign
al
edge = 7m
Tra
ck d
istr
ibu
tion
Eff = 99.98 %
Valencia, December 12-14, 2007 ATLAS Upgrade Workshop Marko Mikuž 14
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
BCM-stations
Beam pipe
Pixel
Noise rate vs. thr2
Eff vs. thr
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 1016 represents a quantum leap in challenge Current electronics not suitable for tests much above 1015
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
scC
VD
mod
ule
pat
tern