Diamond Module Prototypes
for the ATLAS SLHC Pixel Detector
Marko Mikuž
University of Ljubljana & J. Stefan Institute
PIXEL 2008 Workshop
Fermilab, September 23-26 2008
Diamond tracker upgrade proposal
Collaboration
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Bonn
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Carleton
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CERN
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Ljubljana
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Ohio State
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Toronto
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Submitted May’07
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Updated Dec’07
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Approved by ATLAS EB Mar’08
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EDMS: ATU-RD-MN-0012
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
2
R&D proposal goals
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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:
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Diamond sensors
Bump-bonding contracts
200 FE-I3 + 25 MCC’s
Module support prototypes
Three year beam-test program (2008-2010)
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
3
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]
6.07
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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
 Low leakage
 Low capacitance
 Low signal
Marko Mikuž
4
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
→ ~500-700 μm thick detectors
– Base-line diamond material for pixel sensor
Surface view of growth side
Photo HK@OSU
Side view
Test dots on 1 cm grid
Fermilab, September 23-26, 2008
Photograph courtesy of E6
PIXEL 2008 Workshop
Marko Mikuž
5
Diamond sensor types - scCVD
• 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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
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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
Q 
col
 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
Qcol  Qcreated
t
d  d e  d h  distance e - h move apart
t - detector t hickness
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
CCD measured on recent
1.4 mm thick pCVD wafer
CCD of recent 0.5 mm
thick pCVD detectors
CCD 
@ 2 V/ mm
Marko Mikuž
7
Radiation Damage - Basics
Radiation induced
effect
Leakage current
Space charge
Diamond
small &
decreases
~ none
Charge trapping
Yes
Operational
consequence
none
Silicon
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

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 !
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
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W. de Boer et al.
 In Si most damage
scales with NIEL
 NIEL in C at high E an
order of magnitude
smaller than in Si
 NIEL violation
observed for n vs. p
damage in diamonds
phys. stat. sol. (a) 204, No. 9 (2007)3009
Radiation damage parameterization and NIEL
 For mean free path in infinite detector expect
1
1

 k 
CCD CCD0
 With CCD0 initial trapping on grain boundaries, k a damage constant
 Larger CCD0 performs better (larger collected charge) at any fluence
 Can turn 1/ CCD0 into effective “initial” fluence, expect CCD0 ~ ∞ for SC
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
9
Diamond irradiations in 2007-08
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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 → testbeam …
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scCVD (4) and pCVD (2) with PS 24 GeV
protons up to 6x1015 p/cm2 (in 3 steps); k ~
10-18 μm-1cm-2, ~same as old pCVD proton data
pCVD (2) with reactor neutrons up to 1.3x1016
neq/cm2 (in 6 steps); k ~ 3-5x10-18 μm-1cm-2,
discrepancy between source and test-beam
pCVD with PSI 200 MeV pions up to 6x1014
π/cm2; k consistent with ~1-3x10-18 μm-1cm-2
Re-measured pCVD at 1.8x1016 p/cm2 result
consistent with previous measurements
KEK 70 MeV
Pion vs. proton looks roughly consistent with NIEL, neutron damage appears high
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Radiation homogenizes diamond – bulk damage starts to dominate, k appears universal
Analysis ongoing, k have 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)
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
10
Diamond Pixel Modules
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modules built with ATLAS pixel
chips @ OSU, IZM and Bonn
Module after bump bonding
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1 full (16 chip) pCVD
module
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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
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Analysis in progress
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C-sensor in carrier
Complete module under test
Pattern with In bumps
1 single-chip scCVD module
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CERN SPS test beam
Irradiated complete module to
1 and 7 x1014 p/cm2
SPS test beam 2007, 2008
Fermilab, September 23-26, 2008
scCVD diamond
PIXEL 2008 Workshop
scCVD module
Marko Mikuž
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pCVD full module
Tests show no change of threshold and noise
from bare chip to module – low sensor C & I
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Data from DESY test beam plagued by
multiple scattering
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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
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
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CERN
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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Noise = 137 e
Thr = 1450 e
DESY
 = 18 mm
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Full module
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Bare chip
Diamond pCVD Pixel Module – Results
Eff = 97.5 %
Marko Mikuž
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Benefit of low C and I on pixel operation
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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)
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
13
Analysis (M. Mathes PhD, Bonn) of SPS test beam
data exhibits excellent module performance
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Cluster signal nice Landau
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Efficiency 99.98 %, excluding 6/800
problematic electronic channels
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Unfolded track resolution using η-algorithm
from TOT exhibits  ≈ 8.9 mm
Charge sharing shows most of charge collected
at high voltage on single pixel – optimal for
performance after (heavy) irradiation
100 V
400 V
 = 8.9 mm
TOT - η
Track distribution
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Track resolution
scCVD single chip module
Cluster signal
Diamond scCVD Pixel Module – Results
Long side
binary
Data of irradiated (7x1014 p) module
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Preliminary analysis A. La Rosa, H. Pernegger
Very sensitive
to calibration !
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
14
Strawman 2008 of ATLAS ID inner part @ sLHC
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Pixel layer 1: stave about 60 cm long at r ~ 3cm
Radiation for 3000 fb-1
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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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
15
Any technology fit for layer 1 ?
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Not really with current FE
Peak Q @ ~ 900V
25000
Collected Charge Q [e-]
20000
Casse NIM A n-on-p FZ p irr
.Casse IEEE07 n-on-p FZ n irr
Affolder n-on-p FZ p irr
Diamond
3D 2E ~150V, 210 um
3D 3E ~150V, 210 um
3D 4E ~150V, 210 um
H. Sadrozinski, SLAC 6/08
2nd
15000
1rst Pixel
Layer
Pixel
Layer
3D
4E 11800
3E 10600
2E 8600e
10000
5000
Signal required with
present Pixel ASIC
(= 2 x In-time threshold):
Planar Si
7600e
p/cm2
p/cm2
Diamond
4600e
0
0.0E+00
Fermilab, September 23-26, 2008
5.0E+15
1.0E+16
Fluence [neq/cm2]
PIXEL 2008 Workshop
1.5E+16
Marko Mikuž
16
Sensors - Diamond Detectors Ltd
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All results shown obtained with their sensors
(RD42 has research contract with DDL)
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Outstanding purchase orders for three
ATLAS pixel sensors
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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
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Waiting to see
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
17
Sensors - Alternative Suppliers
Large wafer growth and
processing capability
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
18
Thermo-mechanical considerations
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Have brain-stormed a number of options to thin readout layers
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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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
19
Summary
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Good progress on all fronts, despite late
start with ATLAS approval in March’08
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Goals for 2009
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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
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 !
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
20
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Backup slides
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
21
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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
22
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
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
23
Single crystal irradiation results
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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%.
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
24
Going edgeless
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scCVD module pattern
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scCVD single-chip module is edgeless – patterning right
up to the edge
Data exist on performance – needs to be analyzed
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
25
Diamonds in ATLAS
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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
Pixel
BCM-stations
Noise rate vs. thr2
Beam pipe
Eff vs. thr
Fermilab, September 23-26, 2008
PIXEL 2008 Workshop
Marko Mikuž
26