Production and Tests of Hybrid Photon Detectors for the LHCb RICH Detectors
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Transcript of Production and Tests of Hybrid Photon Detectors for the LHCb RICH Detectors
Production and Tests of Hybrid Photon Production and Tests of Hybrid Photon Detectors for the LHCb RICH DetectorsDetectors for the LHCb RICH Detectors
Introduction Hybrid Photon Detectors Production Test results Conclusions
RICH 2007, Trieste, 17.10.2007RICH 2007, Trieste, 17.10.2007
Stephan Eisenhardt, University of EdinburghStephan Eisenhardt, University of EdinburghOn behalf of the LHCb experimentOn behalf of the LHCb experiment
RICH2RICH1
LHCb
HPD
RICH 2007, Trieste, 17.10.2007 Stephan Eisenhardt 2
RICH Photondetector RequirementsRICH Photondetector Requirements
C4F10 (small)
Aerogel (large)
CF4
RICH1 RICH2
photodetector area: 3.3 m2
single photon sensitivity: 200 - 600 nm
quantum efficiency: >20%
good granularity: 2.5 x 2.5 mm2
active area fraction: 65%
# of electronic channels: 500k
LHCb DAQ rate: 40MHz
rad. tolerant: 3kRad/year
single event full LHCb simulation used in performance studies
answer: 484 Hybrid Photon Detectors
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Hybrid Photon Detector (HPD)Hybrid Photon Detector (HPD) Photon detector:
– Quartz window, S20 photocathode• Typical QE dE > 0.7eV
– Cross-focussing optics (tetrode structure):• De-magnification by ~5
• Active diameter 75mm
484 tubes for overall RICH system
– 20 kV operating voltage (~5000 e– [eq. Si])
Anode:– 25632 pixel Si-sensor array (“Alice mode”)
small pixels low noise– bump-bonded to binary readout chip– assembly encapsulated in vacuum tube– “LHCb readout mode”: 8-fold binary OR
effective 3232 pixel array– pixel size 500m500m sufficient
Anode
Vacuumphoton detector
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HPD manufacture – AnodeHPD manufacture – Anodechallenge:– 7 companies/institutes
– 6 countries
– coordinated by LHCb
tests by LHCb
Readout chip (IBM)
Detector chip (Canberra)
Wafer probing
Ceramic carrier (Kyocera)
High T bump-bonding (VTT)
Assembly probing
20 m
Brazing (DEP) and gold-plating
(CERN)
Visual inspection and plating control
Packaging (HCM) Anode testing
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HPD manufacture – Tube (@DEP)HPD manufacture – Tube (@DEP)
Tube body assembly Photo-cathode deposition and vacuum sealing
Anode incoming inspection and testing
Anode testing Final HPDtesting by LHCb
HPD cabling and potting
QE measurement and anode testing
Vacuum bake-out@ 300°C
HPD tube production (DEP)
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Photon Detector Test FacilitiesPhoton Detector Test Facilities Photon Detector Test Facilities (PDTF): (Edinburgh & Glasgow)
– 2 test stations per site
– design test rate: 1 HPD / day / site
– standard preparation and automated test programme per HPD: ~6hrs
– extended tests: on ~10% of HPDs• Quantum Efficiency (Edinburgh)• Backpulse Signal (Glasgow)
HPD Storage:– under He-free atmosphere: N2 gas flow (0.2 l/min)
Dark box
HPD
Electronics & Power supplies DAQ PC
flat & pointinglight source
PDTF station
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PDTF – TestsPDTF – Tests Comprehensive test of every function and parameter of the HPD:
Readout ChipConnectionsCommunicationsDAC linearityReadout modesDead ChannelsNoisy ChannelsPixel maskingThresholdNoise
PhotocathodeDark CountResponse to lightQuantum Efficiency
HPD BodyDimensionsQuartz windowPin Grid ArraySensor position
Electron Optics /Tube VolumeImagingDemagnificationHV StabilityField DistortionsIon Feed BackVacuum Quality
Silicon SensorIV CurveDepletionBump-BondingEfficiency (Backpulse)
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PDTF – Automation of TestsPDTF – Automation of Tests
automation:– parameter setting
– data taking
– logging
– data analysis
– report generation
human control:– parameter choice
– online displays
– offline reports
Initialisation
HV monitor
Bias V monitor
Temp monitor
LED monitor
PDTF Taskflow
Power ON
IV Scan
Threshold Scan
HV ramp up
Strobe Scan
Bias Voltage Scan
HV ScanLED light – Alice mode
LED light - LHCb mode
Dark Count – Alice mode
Dark Count - LHCb mode
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Testing Programme – SummaryTesting Programme – Summary
result:pass: 547 ~98%fail: 12 ~ 2%
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Mechanical TestsMechanical Tests
t 555 HPD passed 2 HPD failed on first test
– leaned by ~0.4mm
tubes repaired to pass as well
gap: 0.1mm
point of first possible contact
any contact = failure
PDTF:mechanical test jig
HPD : 83.0mm +0.0mm -0.1mmTeflon tape: 0.1mmJig : 83.4mm
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Pixel Chip – Threshold and NoisePixel Chip – Threshold and Noise
excellent signal over noise: specification<measured>– average signal charge @ 20kV: C = 5000 e-
– average threshold: T = < 2000 e- 1065 e-
– average electronic noise: N = < 250 e- 145 e-
– signal over noise: S/N = (C-T)/N > 12 27
(min, max) = (21,33)
electonic noise of pixel chip
0
20
40
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16050
65
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noise [e-]
HPD
.
global threshold setting
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threshold [e-]
HPD
.
signal-over-noise of pixel chip
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S/N
HPD
.
<threshold>:1065 e-
<noise>:145 e-
<S/N>:27
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Anode – Channel YieldsAnode – Channel Yields development of Flip-Chip bump-bonding
for O(104) channels:
excellent yields for response of individual pixels:– in “Alice mode” 8192 pixels / HPD
– spec: > 95% working
(< 400 pixels dead)
– all HPD within spec
– noisy pixels: negligible
noisy pixels per HPD
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0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
pixels
HPD
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noisy pixels / HPD
dead pixels per HPD
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pixels
HPD
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dead pixels / HPD20 m
Alice mode:fine resolution
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Anode Leakage Current: at 80V bias
0
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0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000Leakage Current [A]
HPD
.
Leakage Current @ 80V bias
# H
PD
Leakage Current [nA]
Anode – Leakage CurrentAnode – Leakage Current
HPD - IV curves
-1000
-500
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908580757065605550454035302520151050
Bias Voltage [V]
Lea
kage
Curr
ent [n
A]
.
goal: typical value of: LC ~ 1A achieved for all bare chips when unpowered in powered HPD: 1W heat dissipation
– anode heat up by ~12-15 °C
– increase in leakage current: ~*2 for 6 °C
IV scans for sample of HPDs
Bia
s C
urr
en
t [n
A]
Bias Voltage [V]
found two classes:– low current @ 80V (<1A):
quadratic behaviour up to 90V bias
– medium current @ 80V (~1A…3A):
turn up point between: 40…60V
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HPD linear demagnification
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5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2
linear demagnification
HPD
.
xlinear demagnification: <D> = 5.45
fit for image diameter
# H
PD
linear demagnification
ImagingImaging
Distribution of image centres
-1500
-1000
-500
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1500
-1500 -1000 -500 0 500 1000 1500
X Deviation from centre of chip [m]
Y D
evi
ati
on
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m c
en
tre
of
ch
ip
[m
]
.
batch 1-7
batch 8-25
y = -46.732x + 6649.5
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circles: LHCb pixel Ø
sensor displacement:due to positioning error
>1mm (2 LHCb pixel):signal loss possiblein magnetic field
fit for sensor position
d
isp
lac
em
en
t in
y [m
]
displacement in x [m]
pulsed LED run(200k events, ~3 npe/event)
cylindrical reflection:reflection on Al coating
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Photoelectron ResponsePhotoelectron Response
HV scan: look for photon yield– onset of response
– onset of charge sharing between pixels
– slope due to increasing efficiency
for back-scattered e-
(only partial energy deposit)
all accepted HPD pass
pixel hit rate
cluster hit rate
HV [kV]
ph
oto
ele
ctr
on
s /
ev
en
t
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Anode Response – Bias Voltage Anode Response – Bias Voltage ScanScan
Bias voltage scan: look for photon yield– onset of response
– bias of full depletion
– plateau of over-depletion >50V
all accepted HPD pass
workingpoint
pixel hit rate
cluster hit rate
Anode Bias [V]
ph
oto
ele
ctr
on
s /
ev
en
t
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Dark Count ResponseDark Count Response
Dark Count settling after first HV ramp up:– observation of signals without light source
– typical decay:
factor 2 in 30min after initial ramp-up
– time constants vary
all accepted HPD pass
pixel hit rate
cluster hit rate
Time [min]
da
rk c
ou
nts
/ e
ve
nt
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Dark CountDark Count all accepted HPD have a very low
dark count < 20kHz/cm2
– DC = 5 kHz/cm2 :
1% probability for 1 hit / HPD / event
– 497 HPD with DC < 5 kHz/cm2
H516009: 7.3 kHz/cm2
high red sensitivity
H516018: 10.0 kHz/cm2
increased IFB prob.
Dark Count from 5M events
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Dark Count [kHz/cm2]
HP
D .
settled Dark Count from high statistics run
# H
PD
Dark Count [kHz/cm2]
in the range 5…20 kHz/cm2:– two types:
• high red sensitivity• increased IFB probability
– perfectly fine to be used in RICH
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Ion Feed Back from Strobe Scan
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HP
D .
Ion Feed BackIon Feed Back due to e- ionising residual gas atoms
ion produces bunch of photoelectrons at photocathode
cluster of hits with 200-300ns delay we find: very low IFB very good tube vacuum at fabrication
Strobe Scan H524004
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Delay [ns]
Hit
s P
er
Ev
en
t
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Clusters
Poisson estimate
Ion Feedback x 100
Very low IFB <<1%
<IFB> = 0.04% spec:
max. 1%
hit
s /
ev
en
t
Delay [ns]
HPD response to 15ns LED pulses with varied delay Ion Feed Back from delayed cluster signals
#
HP
D
Ion Feed Back [%]
50ns strobe signal
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Quantum Efficiency – DEP DataQuantum Efficiency – DEP Data Excellent sensitivity:
– increase due to process tuning at DEP
– single most helpful improvement to RICH performance
– <QE @ 270nm> = 30.8%
>> typical QE = 23.3%
<QE> @ 270 nm (per batch)
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aver
age
QE
[%
] .
<QE> per batch
running <QE> (batch 0-25)
more tuning improvements:– fill of sensitivity dip between UV and visible
– reduction of red sensitivity @ 800nm• anti-correlated to blue sensitivity• cause of thermal e--emission (dark count)
QE
[%
]
Wavelength [nm]
RMS ofbatch spread
<QE> per delivery batch
QE
[%
]
Batch number
<QE> (DEP Data): across delivery batches
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QE – LHCb VerificationQE – LHCb Verification
PDTF measurement:– 7 wavelengths, 10nm bandpass filter
– error: 2%
– 76 HPD measured
PDTF QE measurements typically
matches DEP values within 3%
QE PDTF vs DEP
-0.050
0.000
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0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400
DEP QE, hq (no units)
PD
TF Q
E, h q (no u
nits)
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y=x
PDTF measurements confirm
shape of spectra & absolute values full trust in DEP measurements
Quantum Efficiency - typical HPD sample
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Wavelength l / nm
QE
, hq , (no u
nits)
.
H648005: DEP
H648005: PDTF
H612011: DEP
H612011: PDTF
H650003: DEP
H650003: PDTF
H545002: DEP
H545002: PDTF
4 tests across QE range
Q
E
wavelength [nm]
all tests: PDTF vs. DEP
Q
E –
PD
TF
QE – DEP
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ConclusionsConclusions
Production & testing of >550 HPDs has finished Rigorous test programme with: ~98% of HPDs accepted
pass: 547 HPD
fail: 12 HPD
HPDs meet requirements of LHCb RICH detectors Very good results for vacuum quality and Dark Count Excellent results on Quantum Efficiency and S/N DEP Quantum Efficiency results confirmed by PDTF Commissioning is underway
with 288 HPD installed in RICH2
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Backup SlidesBackup Slides
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guideline for usability in RICH:– 161x class A+ : exceed specifications significantly
– 282x class A : clear pass in all aspects
– 60x class B : may fail specs, but recommended for usage• HPDs with slightly increased dark count
– 42x class E : flagged with an issue, still usable in RICH• HPDs with increased LC or 1…5% dead pixels
– 12x class F : clear fail reject
12 failed HPDs:– 9x replaced with good HPD
– 3x accepted as failure within LHCb responsibility misc:
– 4x repaired, retested and accepted as good
– 2x anode problem, but usable,
under study, not classified
Classification SystemClassification System
pass: 545+2 of 559~ 98%
fail: 12 of 559~ 2%
HPD category
161
282
60
42
12
0
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A+ A B E F
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QE – PDTF Test SetupQE – PDTF Test Setup measurement of the photocurrent, referenced with calibrated photodiode
)(
)()()(
lllhlh
PD
HPDPDq
HPDq I
I
differing DEP parameters:– Bias: 900V
– Ø: 10-15mm
– large photo currents
default: 100V
cross-check: 22V (just below He ionisation threshold)
Quartz-TungstenHalogen Lamp
Fused SilicaLens
FilterSystem
ReferencePhotodiodeHPD
IPD [pA]
Shutter , 10nm BP filter , IR or VIS block , ND filterRL
Dark Box
Interlock
IHPD [pA]
Bias [V]
photocurrent: <160nAimage Ø:~ 50mm
RICH 2007, Trieste, 17.10.2007 Stephan Eisenhardt 27
QE – Effect of degrading VacuumQE – Effect of degrading Vacuum
degraded vacuum causes:– increase of Ion Feed Back
– increase of charge per photoelectron
– increase of measured photo current
– fake increase in determined QE
cure:– measure photo current below
He ionisation threshold
– PDTF : IV curves 0…500V
– PDTF : bias = 100V, 22V
– DEP : bias = 900V22V
case of extreme
vacuum degradation
for good illustration
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Photoelectron Efficiency – Photoelectron Efficiency – BackpulseBackpulse
comparison of binary to analog event yield with constant light source– binary: through readout chip npe
– analog: measurement of the charge pulse on the bias line Poisson <>
capacity of whole chip: noise*104 wrt. single pixel
Poisson fit to analog spectrum Results: efficiency = npe / <>
strobe length
efficiency 25ns 50ns
PDTF 2007 88% 94%
(production HPDs)
CERN 2004 84% 92%
(prototype HPDs)
error estimation pendingADC counts
even
ts
analog ph.el. spectrum
data fitan almost
perfect match
1
2 34
5
photo electrons
pedestal
subtracted
fit yields Poisson <>