Opto Electronic Readout Systems of Inner Detectors at the LHC and SLHC

Cigdem Issever

University of Oxford

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Outlook – Readout Systems at (S)LHC

1. ATLAS

2. CMS

3. SLHC

SCT Barrel 3

Inner Tracker Barrel , L4+

3

ATLAS Inner Detector

Area

[m2]

Resolution

[μm]

Channels

[106]

Pixel 2.3 12/66-77 140

SCT 61.1 16/580 6.2

TRT 170 per straw 0.42

TRT

Pixels SCT

Performance

• |η| < 2.5• high pt tracks: σ(1/pt,|η|<2) = 0.4 TeV-1

σ(1/pt,|η|=2.5) = 1.2 TeV-1

• Impact parameter (high pt) σr-φ< 20 m, σz< 100 m

• ε ~ 95%, 90% in jets• Lifetime ~10 LHC years

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ATLAS SCT Opto Readout System

•2 VCSEL/1 PIN opto-package for data and TTC.

•VDC & DORIC4A ASICs.

•Kapton flex circuits

Fujikura SIMM(50/60/125) fibres

•12 way arrays of VCSEL and PINs.

•BPM-12 and DRX-12 ASICs

Data

L1, clockcommands

~17500 links (SCT+pixel)

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ATLAS SCT Optical Readout System

• Readout of modules:• binary readout• Transfer data from 4088 modules @ 40Mbits/sec to

ReadOut Drivers (RODs).• Two links per module (redundancy) to the ROD

• BC Clock & L1 Trigger & commands to the modules:• Transfer TTC data from RODs to modules @

40Mbits/sec. • Biphase mark encoding (same fibre for clock and

commands).• One link per module, in case of failure redundancy

link to neighbouring module.

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ATLAS SCT Readout Summary

• ATLAS SCT links built and do work. Used successfully for readout of barrels and End Caps.

• Main concerns:

• Breaking of Al LMTs during installation

• ESD damage may have reduced the lifetime of the VCSELs.

• Need to design simpler more modular systems for SLHC.

• Very complicated system design:

• 16 flavours of barrel opto-flex cables

• 42 flavours of barrel harnesses

• Large and non-modular system

• Difficult to produce with high yield

http://atlas.web.cern.ch/Atlas/GROUPS/INNER_DETECTOR/inner_detector.html

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CMS Tracker analogue optical link

• Transmitter : 1310nm InGaAsP EEL

• Fibres and connectors : Ge-doped SM fibre

• Receivers : InGaAs 12-way p-i-n

• plus analogue electronics : rad-hard deep sub-micron

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CMS Tracker Readout and Control Links

PLL Delay

MUX 2:1

Timing

APVamplifierspipelines

128:1 MUX

Detector Hybridprocessingbuffering

TTCRx

ADC

Rx Hybrid

FED

TTCRx

FEC

CCUCCU

CCU CCU

DCU

Control

processingbuffering

Front-EndRadiation zone

Back-End,Controll room

TTC

DAQ

Analogue Readout50000 links @ 40MS/s 3 x ATLAS

Digital Control2000 links @40MHz

Tx Hybrid

redundancy

FrontEnd AOH

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CMS’s Ansatz: COTS

• Extensive use of Commercial Off-The-Shelf components (COTS) in CMS optical links

• Benefit from latest industrial developments

•cheaper

• “reliable” tested devices

• However COTS not made for CMS environment

•no guarantees of long-life inside CMS

• validation testing of COTS mandatory before integration into CMS

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CMS Readout Summary

• CMS Tracker Optical links project

• 50000 analogue + 1000 digital links

• COTS components

• Extensive validation testing of radiation hardness necessary

• ionization damage (total dose) & SEU

• displacement damage (total fluence), annealing, reliability

• Accumulated knowledge of radiation damage effects • compensation built into optical link system

• confidence of capacity to operate for 10 years inside CMS Tracker

• If CMS would build it again:

• simplify logistics, delegating even more to even fewer industries, 

• enforce common solutions and reduce the number of variants. 

• would also include hybrids and cables into the system design before freezing the components design.

http://cern.ch/cms-tk-opto/

Performance of CMS/ATLAS Lasers

CMS, EEL: no annealing shown, threshold shifts ~70% will anneal at low flux.Optical Readout and Control Systems for the CMS Tracker, J. Troska et al., IEEE 2002

ATLAS, VCSELs: annealed for 1 week, threshold shifts ~20% @ 1.5E+15n/cm2.Radiation hardness and lifetime studies of the VCSELs for the ATLAS SemiConductor Tracker, P.K. Teng et al., NIMA 497(2003)294

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SLHC Inner Detector Readout

Schedule

• Luminosity upgrade of LHC (SLHC) ~2015

• Start of construction ~ 2009/2010

• R&D for ID at SLHC is starting.

5 years SLHC @ 10^35 cm-2 sec-1 with a safety factor of 2

1.0E+14

1.0E+15

1.0E+16

1.0E+17

1.0E+18

0 20 40 60

Radius [cm]

1 M

eV

ne

utr

on

Flu

en

ce

[n

/cm

^2

]

SiGaAs

Estimation based on IM. Gregor, Optical Links for ATLAS Pixel Detector, Thesis, WUB DIS 2001 - 03, 2001, Wuppertal

•100 Mrad

SLHC: challenging radiation environment!!

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SLHC Inner Detector Readout Challenges

• 10 x more radiation

• ≤ 10 x channels

• Space and material constraints

• 2 – 10 GBits/sec O(100) x faster

• Very short time for R&D and construction

Readout for the SLHC: high-speed, radhard and efficient to build

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• Can some devices be reused (e.g. cable plants)

• How much fluence can the current devices tolerate:• Lasers, PIN diodes

• 0.25 micron technology, which no option for SLHC but gives an estimate for the radiation hardness of submicron technology.

(i.e. GOL, QPLL-chip used by LHCb & CMS)

• Fibres

• Are there radhard COTS for the SLHC?

• Test of custom-made devices.

• What is the SEU cross section @ GBits/sec?

SLHC : Early Questions to be Answered

Answers will determine which devices

to use and where to place devices.

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SLHC: Light Output after Irradiation -- VCSELs

0

20

40

60

80

100

120

0.10 1.00 10.00 100.00 1000.00

Fluence [1014 n/cm2]

Lig

ht

Ou

tpu

t [%

]

VCSELs annealed for 21h – 35h

Fatal failures

~70% of pre-irradiated VCSELs

50%

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-10

10

30

50

70

90

0.1 1 10 100 1000

Fluence [1014 n/cm2]

Fa

tal

Fa

ilu

res

[%

]SLHC: Fatal Failures -- VCSELs

>5E+15 n/cm2 first fatal failures.

Failures needs to be further investigated.

Could be mechanical.

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SLHC: Fujikura SIMM(50/60/125) Fibre Gamma Irradiations

High Dose Rate = 12 kGy/h (H) fibre length = 20.15 m Low Dose Rate = 4 kGy/h (L)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 20 40 60 80 100 120 140 160

Dose (Mrad)

Los

s (d

B/m

)

HA HB

HC HD

LA LB

LC LDVery good performance

≤1.33%/m loss

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SLHC: ATLAS & CMS

• CMS • digital? under discussion• tracker into trigger 10GBits/sec

• ATLAS • digital ? under discussion• ~1-2 GBits/sec

• Same system is unlikely, but groups organized themselves to share as much as possible. • Develop same radiation procedures,• Share beam time,• Communicate! And use expertise of both

experiments!• www.-pnp.physics.ox.ac.uk/~issever/Homepage/Opto/

opto.html

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Summary

ATLAS CMS

~17500 links ~50000 links

Custom-madeExtensive use of COTS

Binary Analogue

• For LHC ATLAS and CMS have two different solutions for readout

•SLHC much more challenging! Radiation, Time and Costs

• For Future: Simpler and include hybrids and cables into the system design early on!

•Even if CMS and ATLAS end up with two different solutions, Collaboration is needed to gain from extensive expertise on both sides.

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Backup Slides

The next slides are from A. Weidberg’s LECC 2005 talk: “The Production of the SCT Optical Links”

C. Issever 22Bare Opto-flex

Module Connector

Location for opto-package

Connector to Power Tape

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Opto-flex on barrel

Cover for ASICs and VCSEL/PIN

Fibres in furcation tubing

Al Power tapes

Module Connector

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Harnesses on Barrel 3

1 of 384 flex circuits

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Barrel 3 with harness & Cooling Loops

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EC Opto and Power

• Similar components but more modular system (possible because of clearances). Separate

• Fibre harnesses with opto-packages

• Power tapes

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Forward Fibre Harness Assembly

Opto-package on PCB with connector

Infineon and MT 12 way fibre ribbon connector

Fibres in furcation tubing and Al foil for ribbon

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End Cap Flex Circuits

CCA twisted pair for high current (DC power)

Stiffener

CuKapton for HV and control signals

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Disk With Electrical/Optical/Cooling Services

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Cooling pipe

Opto-package Fibres in furcation tubing

Dummy module

siliconModule with ASICs

Opto-package with fibres

Redundancy links

Flex Circuits

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Off-Detector Opto-Electronics

• Based on novel packaging for 12 way VCSEL and PIN arrays.

• BPM-12 ASIC to encode data and drive VCSELs for TTC data modules.

• DRX-12 ASIC to discriminate optical data from modules.

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Opto-Array Sub Assembly

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RX/TX Plugins

12 way PIN array

12 way VCSEL array

M-L. Chu et al. NIM A 530 (2004) 293-310.

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VCSEL performance

VCSEL Power

0

100

200

300

400

500

600

700

015

030

045

060

075

090

010

5012

0013

50

Power @ 50% duty cycle (uW)

Fre

qu

ency Cut

Links used successfully in readout of barrels and End Caps.

> 99.7% (99.7%) working channels for Barrels (EC-C)

BER < 10-12 for data and TTC links.

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Problems

• Complexity and yield

• Cracks on kapton flex circuits

• (Light leakage)

• ESD

• Resonant bond wire vibrations

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Complexity

• Very complicated system design:

• 16 flavours of barrel opto-flex cables

• 42 flavours of barrel harnesses

• Large and non-modular system

• Difficult to produce with high yield

• Mistake in geometry opto-flex cables for barrels 4 and 6 had the module connectors out by 2.8 mm couldn’t connect to the modules.

• tPCB added to solve problem.

• Conclusion: much simpler design would have achieved same physics performance but would have been much easier to build.

tPCB (bricolage)

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Cracks Barrel kapton flexes

• Layout of opto-flexes not optimised because there were too many flavours to design!

• Added ceramic stiffeners behind connectors.

Crack!

39

Cracks End Cap Flex Circuits

• Cu/kapton alone and Al t.p. alone robust.

• Problem is Al much more rigid than Cu/kapton cracking during bending.

Kapton tape over t.p. and flex circuit.

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Cracks in Al LMTs

• Al/kapton LMTs used to bring in power/control lines to modules.

• Al is ~ 4 times better than Cu for X0/.

• Al/kapton was reasonably robust

• Cracks found on exposed Ni plated regions ( photos).

PbSn Solder ~ 10 mNi ~ 5 m

Al 50 m Kapton 50 m

Glue 25 m

Cover layer

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500 m

Cracks appear to form on grain boundaries

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Cracks on Al LMTs: Conclusion

• Believe that cracks are due to hydrogen released during Ni plating leading to hydrogen embrittlement of Al.

• Rate of cracks on barrel harnesses: ~ 1%.

• Much higher rate of cracks found on End Cap LMT harnesses (probably because there was insufficient room for mechanical protection).

• New Cu/Espanex LMTs being produced for the End Caps.

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ESD Deaths

• ESD and DORIC4A ASIC

• ESD and VCSELs

• One strike and you are out

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ESD On DORIC4A ASIC

Damaged tracks

Cause of ESD identified as bad handling procedure procedures improved and all suspect chips removed.

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VCSEL ESD Failures• Neitzert et al, Sensitivity of Proton Implanted VCSELs to ESD Pulses, IEEE Journal Selected Topics in Quantum Electronics, Vol

7, No 2 March 2001.

• ESD causes optical and electrical degradation

• High optical power local heating of the DBR mirror increased absorption decreased light o/p.

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VCSEL ESD Failures (2)

• ESD causes electrical degradation

• Further local heating creates defects which change the IV characteristics of the diode.

Small but significant change in diode forward voltage

Seen with our tests with ESD simulator confirms that dead VCSELs on disks with altered IV are due to ESD.

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VCSEL ESD Deaths

• Estimate ESD deaths for VCSELs in End Cap fibre harnesses

• 10 out of 1976 for EC-C at Liverpool

• Deaths occurred during operation on disks when it is very difficult to change a harness rely on redundancy scheme.

• ESD precautions checked at all assembly sites and improved but origin of problems not localised.

• Question: have we reduced the lifetime for many VCSELs by low level ESD damage?

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Resonant Wire Bond Breaking

• Force on bond wire F=B*I*L negligible unless frequency ~ resonant frequency of a bond wire wire bonds will break after ~ minutes (seen by CDF SVXII).

• Amplitude

• Length scaling: long bonds much more vulnerable a ~ l4

• 2 orders of magnitude larger for oscillations out of plane of bond wire loop than in plane.

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Resonant Wire Bond Vibrations and SCT Links

• Potentially dangerous wire bonds are VDC VCSEL as current increases on receipt of an L1 trigger. However

• Barrel has wire bonds with the safer orientation with the B field.

• End Cap has very short wire bonds.

• Additional precaution: implement fixed frequency trigger veto in the TIM.

• T.J. Barber et al, NIM A 538(2005) 442-457.

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Conclusions

• ATLAS SCT links built and do work. Used successfully for readout of barrels and End Caps.

• Main concerns:

• Breaking of Al LMTs during installation

• ESD damage may have reduced the lifetime of the VCSELs.

• Need to design simpler more modular systems for SLHC.

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VCSELs

• Very radiation hard ( see new data on Truelight VCSELs).

• 850 nm matched to rad-hard Si PIN diodes.

• Cheap to test and produce.

• Easy to couple into fibres.

• Easy to drive.

• Low thresholds (~4 mA).

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SCT Barrel Readout

• Electrical and optical services for barrel silicon modules.

• Opto-flex cable

• Connects to low mass Al power tapes.

• Connects to silicon module.

• Fibres fusion spliced to ribbons.

• Mechanical challenges

• Hermeticity tight clearances ~ 1 mm.

• Transfer heat to cooling tube.

• Allows for contraction of LMTs and cooling tube (~0.5 mm)

30 mmSi modules

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SCT Barrel Harness

• Electrical and optical services for 6 modules.

Redundancy connection

TTC & Data fibres

Opto & ASICs

Module connector

Cu/kapton cable

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Taiwan Opto-Packages

• MITEL 1A444 bare chip VCSELs and Centronic epitaxial Si PIN diodes. Also tried Truelight VCSELs & PINs.

• Simple/cheap components used (PCBs).

• 45o angle polished fibre used to reflect light from(to) VCSEL(PIN) to(from) fibre.

• Active alignment of fibres to VCSEL/PINs

• use red laser to inject light into fibre and illuminate VCSEL/PIN. Adjust fibre position until light spot is above active region, then glue.

• Good performance when integrated into SCT links:

• No cross talk between emitters and receiver.

• BER within specs.

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Taiwan Opto-package

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Back emf

• If bond wires can be directly connected to the pulse generator (not the case for barrel dogleg) can see back emf from vibrations.

• Pulse the wire with a step at low frequency and observe the voltage at the bond wire on the scope.

• FFT gives peaks at resonance frequency.

Resonance ~ 18 kHz

Test bond wire 3 mm. B in plane of bond wire loop.

-110

-105

-100

-95

-90

-85

-80

-75

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-65

-60

0 5000 10000 15000 20000 25000 30000

Frequency / Hz

Am

plitu

de /

dB

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Results with ATLAS tests

• Barrel dogleg VDCVCSEL bonds with correct orientation of B field.

• No resonances seen with camera in scan of 10-100 kHz.

• Amplitude << 25 m.

• K5 VDC hybrid bonds.

• No resonances seen with camera in scan 10-100 kHz.

• Amplitude << 25 m.

• Forward opto PCB VCSEL.

• No resonances seen with camera in scan 50-110 kHz.

• No resonances seen with back emf.

• Amplitude << 25 m.

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Next slides are from Jan Troska

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COTS components for CMS Tracker links

• Some examples:

single fibre and MU connector

1-way InGaAsP edge-emitting lasers on Si-submount with ceramic lid

12-way optical ribbon and MT-connector

96-way cable

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CMS System Considerations

• Build in radiation damage compensation into optical link system

• Lasers

• provide adjustable d.c. bias to track threshold increase

• provide variable gain to compensate for efficiency loss (and other gain factors)

• Fibres and connectors

• No significant damage

• Photodiodes

• provide leakage current sink

• provide adjustable gain

• use sufficient optical power (~100W) to avoid significant SEU effects

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The following slides are from Oliver Pooth, RWTH Aachen

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