D.Websdale, LHCC referees meeting, CERN, 1-7-2002 1

Developments since 13 May meeting Outcome of review on 24 June HPD planning MaPMT planning

D.Websdale

Meeting with LHCC referees

CERN, 1st July 2002

RICH photodetectors – status and planning

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 2

Pixel chip measurements at 40MHz HPD: absolute measurements of thresholds and

photoelectron detection efficiency Bump bonding developments MaPMT – magnetic field measurements

Developments since 13 May meeting

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 3

LHCb pixel chip tests Ken Wyllie at al

40MHz lab system to be adopted as global system for all tests – chips, wafers, assemblies, anodes, HPDs

Limited functions at the moment – problems with memory access on FLIC, under investigation

Restricted event size – use LHCb mode = 1024 pixels

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 4

Threshold and Noise scans at 40MHz

Threshold ~ 1130e-RMS ~ 110e-

Noise ~ 140e-

(~130e- @ 10MHZ)

Noise and threshold characteristics satisfy LHCb RICH requirementsThreshold < 2000eNoise < 300e

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 5

Pixel HPD (480 units)

80mm photocathode window

Electron Optics:20 kV5 x demagnification

1024 super-pixels 0.5mm x 0.5mm

PIXEL HPD

PGA ceramic carrier

Kovar ring

Bump-bonded chip assembly

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 6

Response to LED – silicon bias and HV

Detector bias scan High voltage scan

´= 1.741 @ 19kV, 80V

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 7

HPD -Threshold distribution

Gaussian fit:

m = 6.76kV (<1880e) = 0.82kV (230e)

Gaussian distribution reflects the comparator threshold distribution of the ALICE1LHCb chip (without threshold adjust)

Differential number of firing pixels as a function of HPD HV (Si det. bias = 80V)

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 8

Photoelectron detection efficiency(1)

Poisson fit

= 2.6@ 19kV,80V

´= 1.74 @ 19kV,80V

Number of firing pixels per LED pulse

Back-pulse spectrum

= average number of photoelectrons per LED pulse inferred from back-pulse fit

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 9

Detached bump bonds

Responding pixels: 70%

(Am, in HPD)

Responding pixels: 94%

(Sr, on bare anode)

The principal cause of low efficiency is detached bump bonds

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 10

Photoelectron detection efficiency(2)

LED shining smaller pixel area, where bump-bonds are generally good:

Analyze event size, infer ’ from P(0)

Correct for double pixel clusters

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 11

Photoelectron detection efficiency(2)

Record back-pulse spectrum, infer from fit; problems at low ADC channels under investigation.

Compare values of ’ and ; present estimates range from 81% to 83%; not corrected for LED drift with time, LED tail, missing bump-bonds, masked pixels, photoelectron pile-up

Error estimates:LED drift: 5-10%

Fit parameters: 5%

LED tail: a few %

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 12

Bump-bonding problem

Possible causesThree main differences between Omega3 (half-scale prototypes) and

ALICE1LHCb (full-scale prototypes):

bake-out temperature lower, dwell time shorter

elongated bump shape

increased die size and thickness

elongated bump shape does not correspond to relaxed shape when bumps re-melt

expansion coefficient mismatch between Si (3.5 ppm/C) and alumina (7 ppm/C) results in electronics chip downwards bending:

calculated sagitta with 2D bimetallic strip model: ~30 m at 300 ° C for 15mm-long die; goes with the square of the die size

bump-bond diameter is 32 mBUT no major degradation of bumps after silver glass curing process (dwell plateau

400 °C, dwell time ~10 min.)

incomplete curing process of silver glass, which could possibly experience further non-uniform retraction during subsequent bake-out cycle

metallurgy problems (UBM=Under Bump Metallization) ) resulting in degraded bump adherence

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 13

New assembly measurements(1)

Example with assembly 73:

Before bake-out: 6 missing bumps

After bake-out: 33 missing bumps

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 14

Testing new bump bonded assemblies

Sr source: response table:

Number of Responding pixels from 8192 [%]

Before bake-out After bake-out

8186 [99.93%] 8159 [99.60%]

8178 [99.83%] 8179 [99.84%]

8191 [99.99%] 8191 [99.99%]

8171 [99.74%] NA

8188 [99.95%] NA

New bump-bonding process better than ever;

New, unpackaged, bump-bonded assemblies completely survive bake-out cycle;

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 15

Bump bonding – road map to solution

Bake out sensor–chip assembliesIF detach Modify bonding process (VTT)

IF survive:

Bake out anode carrier assembliesIF survive Resume HPD production (DEP)

IF detach:Test following (4 month programme)

Stiffened ceramic carrierCeramic with lower thermal expansion coeffDifferent gluePartial surface glueing

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 16

HPD project – status

First HPD prototypeSystematic measurements with pulsed LED show expected photoelectron response… with the exception of the missing bump-bonds

New HPD preparationOn hold at DEP

Bake-out tests of bare new LHCb assemblies from VTT successful

Wait for bake-out tests of packaged new LHCb assemblies from VTT to proceed

New LHCb chip functional at 40 MHz;

Detector order approved and to be placed, mask and wafer layout to be started soon

New ceramic carrier mechanical draft design delivered; routing design underway

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 17

Longitudinal axis

MaPMT - Magnetic Field Tests

RICH 1 likely in magnetic field of 400 GaussMeasurements of MaPMT sensitivity to

longitudinal and transverse magnetic fields up to 35 mT (350 Gauss)

LED light source, APVm read-out

B [mT] vs I [A]

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 18

-metal shielding0.9 mm thicknessextension13 or 20 mm

shielded MaPMT 13 mm extension

Longitudinal B-Field

MaPMT with mumetal functions in longitudinal field up to 10 mT (100 G)

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 19

Transverse B-Field

Transverse field in x-direction

MaPMT insensitive to transverse fields up to 25mT (250 G)

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 20

RICH Photon Detector review(24 june)

June 2002 Milestone:HPD with encapsulated LHCb-ALICE pixel chip

95% working channelsThreshold < 0.4 signal (2000e)Noise < 0.15 threshold (300e)

LHCb pixel chip working at 40MHzThreshold, noise performance as above

If failure – switch to MaPMTSmall print – review if LHC delayed

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 21

RICH Photon Detector review(24 june)

Outcome of Review:- Recommendations

HPD: Solve bump bonding problem Delay HPD Milestone until end 2002

If failure – switch to MaPMT If success – produce small series of HPDs

- prepare 40MHz anode assemblies

MaPMT: Front-end chip is critical item Prepare fully functional BEETLE designs

for submission in October 2002

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 22

RICH Photon Detector history

Dec 1999: Pixel HPD chosen as baseline from 3 options“Lowest risk within budget”

Dec 2000: Milestone: Working HPDMissed: Pixel chip limited to 10MHz

Sept 2001: Milestone: HPD with 10MHz chipMissed: Delays in bump-bonding and anode

assembly

June 2002: Milestone: HPD with 10MHz chip + Working 40MHz chip

Missed: Bump bonds detached during bake-out

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 23

RICH Photon Detector history

Dec 1999: Pixel HPD chosen as baseline from 3 options“Lowest risk within budget”

Dec 2000: Milestone: Working HPDMissed: Pixel chip limited to 10MHz

Sept 2001: Milestone: HPD with 10MHz chipMissed: Delays in bump-bonding

and anode assembly

June 2002: Milestone: HPD with 10MHz chip + Working 40MHz chip

Missed: Bump bonds detached during bake-out

Months (anticipated)To LHC collisions

66

54

54

57

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 24

HPD planning – short term

Short term tasks: CERN group (3-4 FTE) + RICH team testingJune – Dec 2002:

Solve bump bonding problems:Bake out anode carrier assemblies

IF survive Resume HPD production (DEP)IF detach:

Test following (4 month programme)Stiffened ceramic carrierCeramic with lower thermal expansion coeffDifferent gluePartial surface glueing

Milestone: End 2002Demonstrate HPD with 10MHz chip satisfying all technical criteria

IF Failure switch to MaPMT

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 25

HPD planning – medium/long term

Medium term tasks: CERN group (3-4 FTE) + RICH team testingJan – March 2003:

Complete small (~4HPDs) series production:Produce and verify 40MHz anodes

April – October 2003:Complete 40MHz HPD prototypingPrepare specs/invite tenders for anodes and tubes

Milestone: Dec 2003 place orders for tubes

Long term tasks: CERN group (3 FTE) + Glasgow/Edinb. (4-5FTE)

March 2004-March 2006:Produce and test HPDsInstall HPDs

Milestone: Sept 2006 commissioning completed

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 26

MaPMT readout

MaPMT: (225k channels)

Readout options:

1. Binary (as now) 5.5CHF/channel2. Digital (as ITR scheme) 7.5 CHF/channel3. Analogue (as VELO scheme) 10 CHF/channel

Critical item for all is the front-end chip BEETLE is preferred LHCB compatible chip

BEETLE needs reduced (x ~50) gain Options to reduce gain:

Charge attenuator at pre-amp inputVoltage attenuator at shaper inputReduced pre-amp gainReduced PMT HVReduced number of PMT dynodes

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 27

MaPMT planning

Tube production and testing: March 2004-March 2006 is not on critical pathFront end chip with appropriate gain is critical component.PMT readout demonstrated at 40MHz with APV chip, but not LHCb compatiblePMT with attenuator + BEETLE pre-amp/shaper demonstratedBEETLE is preferred chip – valid for binary, digital or analogue readout schemes

Next steps: Short term tasks: Edinburgh, Oxford (+Heidelberg), Cambridge

July – Dec 2002:Planning meeting 15 JulyPrepare designs for fully functional BEETLE, adapted for MaPMTSubmission for Multi-Project Wafer run in October 2002

Medium term tasks:Decision on readout mode (costs are compared to HPD + readout chain)

Binary preferred - uses same readout chain as HPDDigital - use Inner tracker readout schemeAnalogue - use VELO readout scheme

Install HPDsMilestone: Sept 2006 commissioning completed

D.Websdale, LHCC referees meeting, CERN, 1-7-2002 28

Summary

•The 40 MHz pixel chip appears to work

•The bump bonds intrinsically survive the bake outif a problem remains it is related to the packaging in the carrier

•The prototype HPD functions as expected in all respects (modulo detached bonds)

•Sufficient time remains to complete the project provided the bump bonding is solved by end 2002

•Resources will be found to produce and test a fully functional BEETLE, with appropriate gain for MAPMT, for early 2003.

•The MaPMT remains a viable backup.