BTeV Silicon Pixel Detector

BTeV Silicon Pixel Detector

Test beam results 1999-2000

Talk given by G. Chiodini – FermilabResearch Technique Seminar - Fermilab – July 21, 2000

July 21, 2000 G. Chiodini - Fermilab 2

Overview 1. BTeV experiment

– Intersection region at the Tevatron– Silicon pixel vertex detector– Silicon pixel detector

2. Test beam setup– SSD telescope and DAQ – Pixel planes tested

3. Test beam results– Pixel calibration– Charge collection– Charge-sharing– Spatial resolution– Magnetic field measurements– 4 Plane pixel telescope

4. Further studies– 0.25m radiation tolerant FPIX2– Pixel module bench test– Mechanics and cooling

5. Conclusions


BTeV experimentBTeV is an experiment to study Heavy QuarkPhysics in the C0 IR of the Tevatron:

• Mixing• CP violation• Rare Decays• …

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


BTeV experimentIntersection region at the Tevatron

• <2 interactions> per BCO• High density of tracks• Hadronic decays

Luminosity=2cms

• 41011 b-hadrons/107sec• B0, B+, Bs (bBc)• Forward region

BR<1.510-5L

Resolution B decay length in BTeVAng. Correl. bb production


BTeV experimentBTeV silicon pixel vertex detector

• Decay time resolution (CP studies) • good spatial resolution• high statistics data samples

• 1st L trigger: prim. vertex and detached tracks • high resolution points• detector close to the interaction region• low combinations and noise hits

• Pixel vertex detector • space points (x,y,z)• radiation hard (21014 particles cm-2y-1)• low occupancy and noise

Hybrid pixel detector

Readout chip

Sensor

Planar pixel vertex detector

bump


BTeV experimentBTeV silicon pixel vertex detector –

global layout

Pixel frame end view

Pixel frame lateral view

1.482m

0.595m

cooling pipes


BTeV experimentBTeV silicon pixel vertex detector –

half plane and module

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

Pin diode optical receiver

VCSEL optical driver

Data serializer

Control, monitoring, and, timing

track


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 <bump failure10-4): Indium (In) and solder (SnPb) • Under Bump Metal (Cr, TiW, Cu, Au, …): adhesion layer, diffusion barrier and oxide prevention • Bonding process: Indium Metal bump both side, room T, pressure Solder Metal bump one side, high T, reflow


Harsh radiation environment p-type doping high Vdep detector must operate partially depleted after irradiation

BTeV experimentSilicon pixel detector – sensor

0V

Surface current

path Si-vacuum

Inter-pixel isolation

p-side multi-guard ring

2

2dqNV eff

dep Vdep=depletion voltage , d=detector thickness, Si dielectric constant, Neff=effective impurity concentration

21310 cmfluence

type inversion

n+/n/p technology


BTeV experimentSilicon pixel detector – sensor

According to the ROSE (RD48) Collaboration a factor of 2 in the depletion voltage can be gain using oxygen enriched silicon

Sensor radiation hardness can be improved by defects engineering


Three generations of readout chip each one with a specific goal:• FPIX0 to establish a viable front-end

• Hewlett Packard (HP) 0.8m CMOS process• 12cols x 64 rows• analog voltage output• simple column based digital logic

• FPIX1 to establish high speed digital logic• HP 0.5m CMOS process• 18cols x 160 rows• 2-bit flash ADC in each cells• Complete column based digital architecture

• FPIX2 Radiation tolerant design • 0.25m 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

BTeV experimentSilicon pixel detector – FPIXn readout chip


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

BTeV experimentSilicon pixel detector – FPIX readout chip

FPIX1 detailed block diagram


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 toW. Baker, C. Brown, J. Kilmer, T.Kobilarcik,beams division, operators, MAB, SiDET …


VME COMPUTE

R

I/OBOARD STAR TFIB

ETHERNET

Setup: SSD telescope and DAQ

Magnet

DAQ

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


Setup: Pixel planes tested

FPIX0 64x12cells

8 bit external ADCFPIX1 160x18cells

2 bit internal FADC

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

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

Samples of FPIX0 and FPIX1 readout chips bump-bonded to ATLAS sensor prototypes

50x400 m2 cellsindium bump-bonding

n+np



FPIX0Inner Board

Pixel detectorLight protected

Analog Buffer

8 bit ADC

FPIX1Inner Board

PC Board Interface



Close-up middle station

Slots at different angles : 0, 5 10, 15, 20, 30 degrees


Results:pixel calibration - pulse generator

Qth=2500e-

Qnoise=106e-

Qnoise,ADC=400e-

Dynamic range MIP

FPIX0 bump-bonded to ST1 CiS p-stop


Results: Pixel calibration - X ray sources

Vth0 = Threshold knob


Results: Charge collection Single chip CiS p-spray

<Q>=21500e-

Qmp=18300e-

400 m

50 m

Charge losses are thought not to be intrinsic to the p-spray technology but a feature of this particular sensor design.

Charge losses


Results: Charge collection Single chip CiS p-stop

<Q>=30100e-

Qmp=24700e-

• 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-.

)'

(

2')(

0

2

2

)'(2

2

MP

g

EE EEe

dENEfg

Saturation bump for CS=1


Results: Charge collection Single chip CiS p-stop

Landau distributionSingle pixel

Qmp

Qmp


Results: charge-sharing

Angle

[degs]

CS=1 CS=2 CS=3 CS=4 CS=5 CS6

0 .639 .328 .017 .009 .0034 .0025

5 .433 .527 .022 .010 .0041 .0028

10 .090 .846 .040 .015 .0055 .0029

15 - .635 .332 .022 .0080 .0034

20 - .209 .741 .031 .0124 .0060

30 - - .178 .769 .041 .0115

FPIX0 CiS p-stopQth=2500e- Vbias=-140V Vdep=-85V

Track inclinationDiffusion

Delta rays emission

c)

Relative fraction of cluster sizes (CS)


Results: charge-sharing Delta rays emission


Results: spatial resolutionPosition Finding Algorithm

Digital algorithm

x

Q Charge fluctuations

qLqR

Head-tail algorithm

Charge Sharing

2,1

,1 RL

Nj

Njj

digital

xx

j

x

x

)(_ fxx digitaltailhead LR

LR

qq

qq

where

Track position is correlated to the charge of the left and right hit in the cluster

LRtailhead q

qpitch

It reduces to charge-weighting for N=2 and f=pitch/2

22

RLLR qqq

qqq

nfluctuatio-qnoise

12

fraction Sharingpitchrmsdigital


Results: spatial resolutiondistribution and correlations


Results: spatial resolutionEta function f


Results: spatial resolutionGaussian fit residual distribution

ST1 CiS FPIX0 detector

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

CS=1,…,6

xy

400m

50m

Analog Pulse height used


Results: spatial resolutionSpatial resolution vs angle


Excellent spatial resolution at all angles using analog information

Qth= 2500e- Vbias= 140V Vdep= 85V


Results: spatial resolutionComparison between detectors

Qth=2500e-

Qth=2200e-

Qth=3780e-

• 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 m


Results: spatial resolutionComparison with simulation

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

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


Results: spatial resolutionComparison 8-bit ADC and 2-bit ADC

Comparison nominal 8-bit FPIX0 and “2-bit” FPIX0 degraded by software

FPIX0(8-bit) Qth=3720e-


Going from nominal 8-bit to 2-bit analog information the resolution degrade by less than 1m



Results: spatial resolutionBias voltage


For track angle > 5 degrees no degradation of the resolution when the detector is over depleted.

Nominal bias voltage


Results: spatial resolutionThreshold


As expected, larger readout threshold degrades the spatial resolution.

Nominal threshold


Results: spatial resolution2D spatial resolution


xy

Sigma=4.650.10 m

400+400 m

Good spatial resolution also when the charge isshared between the long pixel dimension.


Results: spatial resolutionNon-Gaussian resolution function

offcutpl

offcutoffcut

pl

pl

rxx

A

rxr

A

xF

||||

||||

)(

W

xt

W

bgpW

pWbg e

AdtxF

2

2)(

2)(

CS=1 and track angle < 10 degs:Square convoluted with a Gaussian

CS>1 track angle < 10 degsand all CS track angle > 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 2

)()()( xFxFxF plGauss


Results: Magnetic field measurementFPIX0 p-stop in the fringe field

Fringe field up to 0.6T

Charge collection in magnetic field

Ratio double/singleVbias=-190V

geometry

Lorentz=,eB


Interaction vertex in the target

Interaction vertex in pixel plane

2.2mm thick

diamond target

Thousandsof triggeredmultipleinteractionsevents

Results: 4 plane pixel telescope

Excellent tracking capability even in high track enviroment

1mm

1mm


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 0.25m CMOS process from two vendors• Pre-FPIX2 irradiation tests with Co60 at Argonne confirm the RD49 Collaboration results at CERN

preFPIX2T irradiated at 33Mrad equivalent to 10 years running for BTeV at full luminosity of 21032cm-2s-1

ALICE/LHCb-RICH chip in DSM irradiated up to 30 Mrad (,p): no large Single Event Upset rate and no evidence of Gate Rupture Failure


Further studies: Module bench test

ATLAS 16 chips T1 p-stop

5 Fpix1 chips

HDI flex circuit

Layer Pair 1

Layer pair 2 Conductor

Dielectric Cu / Ni / Au

L AYER PAIR

Upilex-SGA

M1

M2

M3

M4

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


Shingled detectorNonporous carbon tubes, “flocking” carbon, and “fuzzy” carbon

Further studies: Mechanics and cooling

Heat exchanger test heated up by two aluminum plates


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, …

BTeV Silicon Pixel Detector

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