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


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


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


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)


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


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)


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


Testing Programme – SummaryTesting Programme – Summary

result:pass: 547 ~98%fail: 12 ~ 2%


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


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

60

80

100

120

140

16050

65

80

95

110

125

140

155

170

185

200

215

230

noise [e-]

HPD

.

global threshold setting

0

20

40

60

80

100

120

140

160

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

threshold [e-]

HPD

.

signal-over-noise of pixel chip

0

20

40

60

80

100

120

140

12

15

18

21

24

27

30

33

36

39

42

45

48

S/N

HPD

.

<threshold>:1065 e-

<noise>:145 e-

<S/N>:27


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

0

50

100

150

200

250

300

350

400

450

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

pixels

HPD

.

noisy pixels / HPD

dead pixels per HPD

0

20

40

60

80

100

120

140

160

0 2 4 6 8

10

12

14

16

18

20

22

24

26

28

30

pixels

HPD

.

dead pixels / HPD20 m

Alice mode:fine resolution


Anode Leakage Current: at 80V bias

0

50

100

150

200

250

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

0

500

1000

1500

2000

2500

3000

3500

4000

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


HPD linear demagnification

0

20

40

60

80

100

120

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

0

500

1000

1500

-1500 -1000 -500 0 500 1000 1500

X Deviation from centre of chip [m]

Y D

evi

ati

on

fro

m c

en

tre

of

ch

ip

[m

]

.

batch 1-7

batch 8-25

y = -46.732x + 6649.5

5600

5800

6000

6200

6400

6600

6800

7000

0.00 0.50 1.00 1.50 2.00 2.50 3.00

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


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


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


workingpoint

pixel hit rate

cluster hit rate

Anode Bias [V]

ph

oto

ele

ctr

on

s /

ev

en

t


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


pixel hit rate

cluster hit rate

Time [min]

da

rk c

ou

nts

/ e

ve

nt


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

0

50

100

150

200

250

300

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

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


Ion Feed Back from Strobe Scan

0

50

100

150

200

250

300

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20Ion Feed Back [% ]

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

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 100 200 300 400 500

Delay [ns]

Hit

s P

er

Ev

en

t

Raw hits

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


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)

19

21

23

25

27

29

31

33

35

37

0 2 4 6 8 10 12 14 16 18 20 22 24batch no.

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


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

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

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)

.

270

340

400

440

520

640

800

y=x

PDTF measurements confirm

shape of spectra & absolute values full trust in DEP measurements

Quantum Efficiency - typical HPD sample

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 100 200 300 400 500 600 700 800 900 1000

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


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


Backup SlidesBackup Slides


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

50

100

150

200

250

300

A+ A B E F


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


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


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 <>

production and tests of hybrid photon detectors for the lhcb rich detectors

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