BTeV Silicon Pixel Detector

1
BTeV Silicon Pixel Detector

• Test beam results 1999-2000
• Talk given by G. Chiodini Fermilab
• Research Technique Seminar - Fermilab July 21,
  2000

2
Overview

• BTeV experiment
• Intersection region at the Tevatron
• Silicon pixel vertex detector
• Silicon pixel detector
• Test beam setup
• SSD telescope and DAQ
• Pixel planes tested
• Test beam results
• Pixel calibration
• Charge collection
• Charge-sharing
• Spatial resolution
• Magnetic field measurements
• 4 Plane pixel telescope
• Further studies
• 0.25mm radiation tolerant FPIX2
• Pixel module bench test
• Mechanics and cooling

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BTeV experiment

• BTeV is an experiment to study Heavy Quark
• Physics in the C0 IR of the Tevatron
• Mixing
• CP violation
• Rare Decays

• 1.6T Dipole magnet centered on the IR
• Forward geometry (1.9lthlt4.5)
• Symmetric two arm spectrometer
• Detached tracks in the 1stLevel trigger

4
BTeV experimentIntersection region at the
Tevatron
Luminosity21032cm-2s-1
BRlt1.510-5
L

• lt2 interactionsgt per BCO
• High density of tracks
• Hadronic decays

• 41011 b-hadrons/107sec
• B0, B, Bs (Lb, Bc)
• Forward region ltggt6

Resolution B decay length in BTeV
Ang. Correl. bb production
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BTeV experimentBTeV silicon pixel vertex detector

• Decay time resolution (CP studies) Þ
• good spatial resolution
• high statistics data samples
  
• 1st L trigger prim. vertex and detached tracks
  Þ
• high resolution points
• detector close to the interaction region
• low combinations and noise hits
• Pixel vertex detector Þ
• space points (x,y,z)
• radiation hard (21014 particles cm-2y-1)
• low occupancy and noise

Hybrid pixel detector
Planar pixel vertex detector
Readout chip
Sensor
bump
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BTeV experimentBTeV silicon pixel vertex
detector global layout
0.595m
1.482m
Pixel frame lateral view
cooling pipes
Pixel frame end view
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BTeV experimentBTeV silicon pixel vertex
detector half plane and module
Pin diode optical receiver
VCSEL optical driver
Data serializer
Control, monitoring, and, timing
track
beam

• Module
• 1Gbyte/s
• Rad-Hard components
• (maybe optical device out rad. Area)

• Half plane
• 20 overlap of sensors in a single plane
• 0.89 radiation length per plane

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BTeV experimentSilicon pixel detector - hybrid
detector

• Independent development and optimizations of
  readout chip
  and sensor
• Require 5000 bump-bonding per cm2 to connect
  the pixel cells to the
  readout cells
• Bump-bonding of flipped chip

• 2 acceptable bump metal (10-5 ltbump
  failurelt10-4)
  Indium (In) and solder (SnPb)
• Under Bump Metal (Cr, TiW, Cu, Au, )
  adhesion layer, diffusion barrier and oxide
  prevention
• Bonding process Indium Þ Metal bump both
  side, room T, pressure
• Solder Þ Metal bump one side, high T,
  reflow

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BTeV experimentSilicon pixel detector sensor
Vdepdepletion voltage , ddetector thickness,
eSi dielectric constant, Neffeffective
impurity concentration
Harsh radiation environment Þ p-type doping Þ
high Vdep Þ detector must operate partially
depleted after irradiation
n/n/p technology
type inversion
Inter-pixel isolation
p-side multi-guard ring
Surface current path Si-vacuum
0V
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BTeV experimentSilicon pixel detector sensor
Sensor radiation hardness can be improved by
defects engineering
According to the ROSE (RD48) Collaboration a
factor of 2 in the depletion voltage can be gain
using oxygen enriched silicon
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BTeV experimentSilicon pixel detector FPIXn
readout chip

• Three generations of readout chip each one with a
  specific goal
• FPIX0 Þ to establish a viable front-end
• Hewlett Packard (HP) 0.8mm CMOS process
• 12cols x 64 rows
• analog voltage output
• simple column based digital logic
• FPIX1 Þ to establish high speed digital logic
• HP 0.5mm CMOS process
• 18cols x 160 rows
• 2-bit flash ADC in each cells
• Complete column based digital architecture
• FPIX2 Þ Radiation tolerant design
• 0.25mm CMOS process (DSM) with Rad-Hard rules
  (guard rings and enclosed geometry transistors)
• Redesigned analog FE feedback and leakage
  compensation
• Simpler and faster digital section than FPIX1
• preFPIX2T (2cols x 160rows of FPIX2)
• FPIX2 submission in few months

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BTeV experimentSilicon pixel detector FPIX
readout chip
FPIX1 detailed block diagram

• 132 ns bunch crossing (BCO)
• Column-based and data driven architecture

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BTeV Silicon Pixel Detector
Test beam results 1999-2000 J.A. Appel, J.N.
Butler, G. Cardoso, H. Cheung, G. Chiodini, D.C.
Christian, E.E. Gottschalk, B.K. Hall, J. Hoff,
P. A. Kasper, R. Kutschke, S.W.Kwan, A.
Mekkaoui, R. Yarema, and S. Zimmermann Fermi
National Accelerator Laboratory C. Newsom -
University of Iowa A. Colautti, D. Menasce, and
S. Sala - INFN(Milan) R. Coluccia and M. Di
Corato - Universita di Milano M.Artuso and J.C.
Wang Syracuse University
Particular thanks to W. Baker, C. Brown, J.
Kilmer, T.Kobilarcik, beams division, operators,
MAB, SiDET
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Setup SSD telescope and DAQ
Magnet
DAQ
E T H E R N E T

• I/O Board
• - Controls and Initializes
• 4 pixel readout chips
• - GPIB controller HV,
• thresholds and pulser
• Automatic pixel calibration

VME COMPUTER
I/O BOARD
STAR
TFIB
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Setup Pixel planes tested
Samples of FPIX0 and FPIX1 readout chips
bump-bonded to ATLAS sensor prototypes
nnp
50x400 mm2 cells
indium bump-bonding
FPIX0 64x12cells 8 bit external ADC
FPIX1 160x18cells 2 bit internal FADC

• ST1-CiS p-stop
• ST2-CiS p-spray
• Bonded active area 3.2x4.4mm2

• Two ST1-Seiko p-stop
• ST2-Seiko p-spray
• Bonded active area 8x6.8mm2

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Setup Pixel planes tested
FPIX0 Inner Board
Analog Buffer
8 bit ADC
Pixel detector Light protected
FPIX1 Inner Board
PC Board Interface
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Setup Pixel planes tested
Close-up middle station
Slots at different angles 0, 5 10, 15, 20, 30
degrees
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Resultspixel calibration - pulse generator
FPIX0 bump-bonded to ST1 CiS p-stop
Qth2500400e- Qnoise10613e-
Qnoise,ADC40096e- Dynamic range 1.5MIP
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Results Pixel calibration - X ray sources
Vth0 Threshold knob
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Results Charge collection Single chip CiS
p-spray
ltQgt21500e- Qmp18300e-
Charge losses
400 mm
50 mm
Charge losses are thought not to be intrinsic to
the p-spray technology but a feature of this
particular sensor design.
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Results Charge collection Single chip CiS p-stop
ltQgt30100e- Qmp24700e-
Saturation bump for CS1

• The Landau distribution convoluted with a
  Gaussian function fit well the charge
  distribution.
• Only less than 0.7 of the events have a signal
  less than 15000 e-.

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Results Charge collection Single chip CiS p-stop
Landau distribution Single pixel
sQmp Qmp
4.2
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Results charge-sharing
Track inclination
Diffusion
Relative fraction of cluster sizes (CS)
FPIX0 CiS p-stop Qth2500e-
Vbias-140V Vdep-85V
c)
Delta rays emission
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Results charge-sharing Delta rays emission
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Results spatial resolutionPosition Finding
Algorithm
Charge Sharing
Q
Charge fluctuations
qR
qL
x
Track position is correlated to the charge of the
left and right hit in the cluster
Digital algorithm
Head-tail algorithm
where
It reduces to charge-weighting for N2 and
fpitch/2h
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Results spatial resolutionh distribution and
correlations
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Results spatial resolutionEta function f(h)
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Results spatial resolutionGaussian fit residual
distribution
ST1 CiS FPIX0 detector
Analog Pulse height used
x
y
50mm
400mm
CS1,,6

• Xpred projection of the kalman fit on the
  plane using all the planes, BUT
  the one under test (spred 2.1 mm) .
• Xmeas coordinate measured by the plane under
  test using the head-tail analog
  interpolation.

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Results spatial resolutionSpatial resolution vs
angle
ST1 CiS FPIX0 detector
Qth 2500e- Vbias 140V Vdep 85V
Excellent spatial resolution at all angles using
analog information
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Results spatial resolutionComparison between
detectors
Qth2500e- Qth2200e- Qth3780e-

• Most of the difference in spatial resolution
  between FPIX0 (nominal 8 bit) and FPIX1(2 bit)
  is due to the different readout threshold.
• The charge losses in FPIX0 p-spray degrades the
  spatial resolution
• BTeV requirement better than 9 mm

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Results spatial resolutionComparison with
simulation
Good agreement between data and BTeV pixel
detector simulation package with input parameters
describing the detector properties (such as
Vbias, Vdep, ) corresponding to the sensors used
in the test beam
Comparison FPIX0 beam test data and simulation
for binary and 8 bit analog readout
Comparison FPIX1 beam test data and simulation
for 2 bit analog readout and 2 values of threshold
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Results spatial resolutionComparison 8-bit ADC
and 2-bit ADC
FPIX0(8-bit) Qth3720e- FPIX1(2-bit) Qth3780e-
Going from nominal 8-bit to 2-bit analog
information the resolution degrade by less than
1mm
FPIX0(8-bit) Qth2500e-
Comparison nominal 8-bit FPIX0 and 2-bit FPIX0
degraded by software
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Results spatial resolutionBias voltage
For track angle gt 5 degrees no degradation of
the resolution when the detector is over
depleted.
ST1 CiS FPIX0 detector
Nominal bias voltage
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Results spatial resolutionThreshold
As expected, larger readout threshold degrades
the spatial resolution.
ST1 CiS FPIX0 detector
Nominal threshold
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Results spatial resolution2D spatial resolution
ST1 CiS FPIX0 detector
Sigma 4.650.10 mm
x
y
400400 mm
Good spatial resolution also when the charge
isshared between the long pixel dimension.
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Results spatial resolutionNon-Gaussian
resolution function
CS1 and track angle lt 10 degs Square convoluted
with a Gaussian
CSgt1 track angle lt 10 degs and all CS track angle
gt 10 degs Gaussian power law

• Non-Gaussian part
• 15 of events half in the constant
• term and half in the tails
• power law with an exponent ³2

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Results Magnetic field measurementFPIX0 p-stop
in the fringe field
Charge collection in magnetic field
Fringe field up to 0.6T
Ratio double/single
Vbias-190V
ageometry aLorentzmH,e B
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Results 4 plane pixel telescope
2.2mm thick diamond target
1mm
Excellent tracking capability even in high track
enviroment
Interaction vertex in the target
Thousands of triggered multiple interactions event
s
1mm
Interaction vertex in pixel plane
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Further studies Radiation Hard FE

• Radiation dose in BTeV near the beam
  comparable to ATLAS first layer (1014cm-2y-1)
• Pre-FPIX2 prototypes implemented in commercial
  0.25mm CMOS process from two vendors
• Pre-FPIX2 irradiation tests with Co60 at
  Argonne confirm the RD49 Collaboration results
  at CERN

ALICE/LHCb-RICH chip in DSM irradiated up to 30
Mrad (g,p) no large Single Event Upset rate and
no evidence of Gate Rupture Failure
preFPIX2T g irradiated at 33Mrad equivalent to
10 years running for BTeV at full luminosity of
21032cm-2s-1
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Further studies Module bench test
ATLAS 16 chips T1 p-stop
5 Fpix1 chips
HDI flex circuit
M1 M2 M3 M4
Upilex-SGA

• Multilayer Kapton High Density Interconnect
  cable.
• Very high density routing design
• Line center spacing 40 mm
• Via center spacing 208mm (350mm)

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Further studies Mechanics and cooling
Shingled detector
Nonporous carbon tubes, flocking carbon, and
fuzzy carbon
Heat exchanger test heated up by two aluminum
plates
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Conclusions

• The FPIX-type FE performs well as expected and
  needed
• GREAT data sample to gain operational experience
  with pixel silicon detectors (3M useful events)
• Primary features of the beam test results are
  clear
• Very good resolution at all angles
• 3 bit ADC good choice for FPIX2
• Little sensitivity to the bias voltage
• Excellent tracking capability
• Good agreement between simulation and real data
  indicates a good understanding of the detector
  performance
• Rapid progress in global systems issue
  bump-bonding, rad-hard sensor, rad hard
  front-end, modules, cooling, mechanical
  support,