Developments since 13 May meeting

1
RICH photodetectors status and planning

• 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

2
Developments since 13 May meeting

• Pixel chip measurements at 40MHz
• HPD absolute measurements of thresholds and
  photoelectron detection efficiency
• Bump bonding developments
• MaPMT magnetic field measurements

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 Restri
cted event size use LHCb mode 1024 pixels
4
Threshold and Noise scans at 40MHz
Threshold 1130e- RMS 110e-
Noise 140e- (130e- _at_ 10MHZ)
Noise and threshold characteristics satisfy LHCb
RICH requirements Threshold lt 2000e Noise lt
300e
5
PIXEL HPD
Pixel HPD (480 units) 80mm photocathode
window Electron Optics 20 kV 5 x
demagnification 1024 super-pixels 0.5mm x 0.5mm
6
Response to LED silicon bias and HV
? 1.741 _at_ 19kV, 80V
Detector bias scan
High voltage scan
7
HPD -Threshold distribution
Gaussian fit m 6.76kV (lt1880e)s 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)

8
Photoelectron detection efficiency(1)
? 1.74 _at_ 19kV,80V
Poisson fit
? 2.6_at_ 19kV,80V
Back-pulse spectrum ? average number of
photoelectrons per LED pulse inferred from
back-pulse fit
Number of firing pixels per LED pulse
9
Detached bump bonds
The principal cause of low efficiency is detached
bump bonds
Responding pixels 70 (Am, in HPD)
Responding pixels 94 (Sr, on bare anode)
10
Photoelectron detection efficiency(2)
Analyze event size, infer m from P(0)
Correct for double pixel clusters
LED shining smaller pixel area, where bump-bonds
are generally good
11
Photoelectron detection efficiency(2)
Record back-pulse spectrum, infer m from fit
problems at low ADC channels under investigation.
Compare values of m and m 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
12
Bump-bonding problem
Possible causes Three 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 mm at 300 C for 15mm-long die
goes with the square of the die size bump-bond
diameter is 32 mm BUT 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 (UBMUnder Bump
Metallization) ) resulting in degraded bump
adherence
13
New assembly measurements(1)
Before bake-out 6 missing bumps
Example with assembly 73
After bake-out 33 missing bumps
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
15
Bump bonding road map to solution
Bake out sensorchip assemblies IF detach
? Modify bonding process (VTT) IF
survive Bake out anode carrier assemblies IF
survive ? Resume HPD production (DEP) IF
detach Test following (4 month
programme) Stiffened ceramic carrier Ceramic with
lower thermal expansion coeff Different
glue Partial surface glueing
16
HPD project status

• First HPD prototype
• Systematic measurements with pulsed LED show
  expected photoelectron response with the
  exception of the missing bump-bonds
• New HPD preparation
• On 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

17
MaPMT - Magnetic Field Tests

• RICH 1 likely in magnetic field of 400 Gauss
• Measurements of MaPMT sensitivity to longitudinal
  and transverse magnetic fields up to 35 mT (350
  Gauss)
• LED light source, APVm read-out

Longitudinal axis
B mT vs I A
18
Longitudinal B-Field
?-metal shielding 0.9 mm thickness extension 13
or 20 mm
shielded MaPMT 13 mm extension
MaPMT with mumetal functions in longitudinal
field up to 10 mT (100 G)
19
Transverse B-Field
Transverse field in x-direction
MaPMT insensitive to transverse fields up to
25mT (250 G)
20
RICH Photon Detector review(24 june)

• June 2002 Milestone
• HPD with encapsulated LHCb-ALICE pixel chip
• 95 working channels
• Threshold lt 0.4 signal (2000e)
• Noise lt 0.15 threshold (300e)
• LHCb pixel chip working at 40MHz
• Threshold, noise performance as above
• If failure switch to MaPMT
• Small print review if LHC delayed

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

22
RICH Photon Detector history

• Dec 1999 Pixel HPD chosen as baseline from 3
  options
• Lowest risk within budget
• Dec 2000 Milestone Working HPD
• Missed Pixel chip limited to 10MHz
• Sept 2001 Milestone HPD with 10MHz chip
• Missed Delays in bump-bonding and anode
  assembly
• June 2002 Milestone HPD with 10MHz chip
• Working 40MHz chip
• Missed Bump bonds detached during bake-out

23
RICH Photon Detector history
Months (anticipated) To LHC collisions 66 54
54 57

• Dec 1999 Pixel HPD chosen as baseline from 3
  options
• Lowest risk within budget
• Dec 2000 Milestone Working HPD
• Missed Pixel chip limited to 10MHz
• Sept 2001 Milestone HPD with 10MHz chip
• Missed Delays in bump-bonding
• and anode assembly
• June 2002 Milestone HPD with 10MHz chip
• Working 40MHz chip
• Missed Bump bonds detached during bake-out

24
HPD planning short term
Short term tasks CERN group (3-4 FTE) RICH
team testing June 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 carrier Ceramic with
lower thermal expansion coeff Different
glue Partial surface glueing Milestone End
2002 Demonstrate HPD with 10MHz chip satisfying
all technical criteria IF Failure ? switch
to MaPMT
25
HPD planning medium/long term
Medium term tasks CERN group (3-4 FTE) RICH
team testing Jan March 2003 Complete small
(4HPDs) series production Produce and verify
40MHz anodes April October 2003 Complete 40MHz
HPD prototyping Prepare 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 HPDs Install
HPDs Milestone Sept 2006 commissioning
completed
26
MaPMT readout

• MaPMT (225k channels)
• Readout options
• Binary (as now) 5.5CHF/channel
• Digital (as ITR scheme) 7.5 CHF/channel
• 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 input
• Voltage attenuator at shaper input
• Reduced pre-amp gain
• Reduced PMT HV
• Reduced number of PMT dynodes

27
MaPMT planning
Tube production and testing March 2004-March
2006 is not on critical path Front end chip with
appropriate gain is critical component. PMT
readout demonstrated at 40MHz with APV chip, but
not LHCb compatible PMT with attenuator BEETLE
pre-amp/shaper demonstrated BEETLE 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
July Prepare designs for fully functional BEETLE,
adapted for MaPMT Submission 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 HPD Digital
- use Inner tracker readout scheme Analogue
- use VELO readout scheme Install
HPDs Milestone Sept 2006 commissioning completed
28
Summary

• The 40 MHz pixel chip appears to work
• The bump bonds intrinsically survive the bake out
• if 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.