Marko Mikuž University of Ljubljana & J. Stefan Institute Diamond Pixel Modules for the High Luminosity ATLAS Inner Detector Upgrade ATLAS Tracker Upgrade

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


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


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


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


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


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


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


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


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

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v1


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


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


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 %


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


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


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

Documents

Marko Mikuž University of Ljubljana & J. Stefan Institute Diamond Pixel Modules for the High Luminosity ATLAS Inner Detector Upgrade ATLAS Tracker Upgrade