Diamond Pixel Modules
for the High Luminosity ATLAS Inner Detector Upgrade
Marko Mikuž
University of Ljubljana & J. Stefan Institute
ATLAS Tracker Upgrade Workshop
Valencia 12-14 December 2007
Diamond as sensor material
Property
Diamond
Silicon
Band gap [eV]
5.5
1.12
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
0.9(e)-1.4(h)x 107
0.82x 107
3.52
2.33
6
14
Dielectric constant - ε
5.7
11.9
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
Aver. Signal Created / 0.1 X0 [e0]
4401
8323
Saturation velocity [cm/s]
Density [g/cm3]
Atomic number - Z
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
 Low leakage
 Low capacitance
 Low signal
Marko Mikuž
2
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
All photographs courtesy of Element Six
Surface view of growth side
Side view
Test dots on 1 cm grid
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
3
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
4
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
 Qcol 
CCD 
 mean not
most probable
e
36 0
μm
• CCD = average distance e-h pairs move apart
• Coincides with mean free path in infinite
(t ≫ CCD) detector
d
t
d  d e  d h  distance e - h move apart
Qcol  Qcreated
CCD measured on recent
1.4 mm thick pCVD wafer
t - detector t hickness
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
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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
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6
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
scCVD measured in Ljubljana
~ same CCD
as pCVD
Current
e-injection with α-particles
Transient time
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
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7
Radiation Damage - Basics
Radiation induced
effect
Leakage current
Operational
consequence
Diamond
small &
none
decreases
Space charge
Charge trapping
~ none
Operational
consequence
I/V = αΦ
Heating
α ~ 4x10-17 A/cm
ΔNeff ≈ -βΦ
Thermal runaway
β ~ 0.15 cm-1
Increase of full
depletion voltage
Charge loss
1/τeff = βΦ
Charge loss
Polarization
β ~ 5-7x10-16 cm2/ns
Polarization
none
Yes
Silicon

Charge trapping the only relevant radiation damage effect

Egap in diamond 5 times larger than in Si

 NIEL scaling questionable a priori
 Many processes freeze out
 Typical emission times order of months
Like Si at 300/5 = 60 K – Boltzmann factor
 Lazarus effect ?
 Time dependent behaviour
1
 eff
  N t (1  Pt ) t vth
t
 A rich source of effects and (experimental) surprises !
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
8
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









Two 500 mm thick detectors, CCD0 190
& 215 mm
Irradiated to 6 and 18x1015 p/cm2





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)
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
1 V/ mm
2 V/ mm
Radiation homogenizes diamond –
bulk damage starts to dominate
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
9
Radiation damage parameterization and NIEL
W. de Boer et al.
arXiv:0705.0171v1
 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
 For mean free path in infinite detector expect
1
1

 k 
CCD CCD0
 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 6x10 14 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
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
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10
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
Module after bump bonding
C-sensor in carrier
Complete module under test
1 single-chip scCVD module

CERN SPS test beam

Irradiated to 5x1014 p/cm2

SPS test beam in August & October
Pattern with In bumps
1 single-chip pCVD module

Irradiated to 2x1015 p/cm2
 Electronics heavily damaged
Valencia, December 12-14, 2007
scCVD diamond
ATLAS Upgrade Workshop
scCVD module
Marko Mikuž
11
pCVD full module
Tests show no change of threshold and noise
from bare chip to module – low sensor C & I



Data from DESY test beam plagued by
multiple scattering



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
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



CERN preliminary
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
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Noise = 137 e
Thr = 1450 e
 = 18 mm

Full module

Bare chip
Diamond pCVD Pixel Module – Results
DESY
Eff = 97.5 %
Marko Mikuž
12
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 mm


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Cluster signal

Track distribution
Diamond scCVD Pixel Module – Results
Eff = 99.98 %
Charge sharing shows most of charge
collected on single pixel – optimal for
performance after (heavy) irradiation
edge = 7 mm
Looking forward to data of irradiated module !
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
13
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
Pixel
BCM-stations
Noise rate vs. thr2
Beam pipe
Eff vs. thr
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
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14
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
15
Backup – going edgeless

scCVD module pattern

scCVD single-chip module is edgeless – patterning right
up to the edge
Data exist on performance – needs to be analyzed
Valencia, December 12-14, 2007
ATLAS Upgrade Workshop
Marko Mikuž
16