Opto Electronic Readout Systems of Inner Detectors at the LHC and SLHC Cigdem Issever University of Oxford

C. Issever2 Outlook – Readout Systems at (S)LHC 1. ATLAS 2. CMS 3. SLHC SCT Barrel 3 Inner Tracker Barrel, L4+

3 ATLAS Inner Detector Area [m 2 ] Resolution [μm] Channels [10 6 ] Pixel2.312/ SCT61.116/ TRT170 per straw0.42 TRT PixelsSCT 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) σ r-φ < 20  m, σ z < 100  m ε ~ 95%, 90% in jets Lifetime ~10 LHC years

C. Issever4 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, clock commands ~17500 links (SCT+pixel)

C. Issever5 ATLAS SCT Optical Readout System Readout of modules: binary readout Transfer data from Mbits/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 40Mbits/sec. Biphase mark encoding (same fibre for clock and commands). One link per module, in case of failure redundancy link to neighbouring module.

C. Issever6 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

C. Issever7 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

C. Issever8 CMS Tracker Readout and Control Links PLL Delay MUX 2:1 Timing APV amplifiers pipelines 128:1 MUX Detector Hybrid processing buffering TTCRx A D C Rx Hybrid FED TTCRx FEC CCU DCU Control processing buffering   Front-End Radiation zone Back-End, Controll room  TTC DAQ Analogue Readout MS/s 3 x ATLAS Digital Control 2000  Tx Hybrid    redundancy FrontEnd AOH

C. Issever9 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

C. Issever10 CMS Readout Summary CMS Tracker Optical links project analogue 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.

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 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

C. Issever12 SLHC Inner Detector Readout Schedule Luminosity upgrade of LHC (SLHC) ~2015 Start of construction ~ 2009/2010 R&D for ID at SLHC is starting. Estimation based on IM. Gregor, Optical Links for ATLAS Pixel Detector, Thesis, WUB DIS , 2001, Wuppertal 100 Mrad SLHC: challenging radiation environment!!

C. Issever13 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

C. Issever14 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 GBits/sec? SLHC : Early Questions to be Answered Answers will determine which devices to use and where to place devices.

C. Issever15 SLHC: Light Output after Irradiation -- VCSELs VCSELs annealed for 21h – 35h Fatal failures ~70% of pre- irradiated VCSELs 50%

C. Issever16 SLHC: Fatal Failures -- VCSELs >5E+15 n/cm2 first fatal failures. Failures needs to be further investigated. Could be mechanical.

C. Issever17 SLHC: Fujikura SIMM(50/60/125) Fibre Gamma Irradiations Very good performance ≤1.33%/m loss

C. Issever18 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! pnp.physics.ox.ac.uk/~issever/Homepage/Opto/opto.html

C. Issever19 Summary ATLASCMS ~17500 links~50000 links Custom-made Extensive use of COTS BinaryAnalogue 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.

C. Issever20 Backup Slides

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

C. Issever22 Bare Opto-flex Module Connector Location for opto-package Connector to Power Tape

C. Issever23 Opto-flex on barrel Cover for ASICs and VCSEL/PIN Fibres in furcation tubing Al Power tapes Module Connector

C. Issever24 Harnesses on Barrel 3 1 of 384 flex circuits

C. Issever25 Barrel 3 with harness & Cooling Loops

C. Issever26 EC Opto and Power Similar components but more modular system (possible because of clearances). Separate Fibre harnesses with opto-packages Power tapes

C. Issever27 Forward Fibre Harness Assembly opto-packages on plug- in PCB Splice protector Ribbon fibre Opto-package on PCB with connector Infineon and MT 12 way fibre ribbon connector Fibres in furcation tubing and Al foil for ribbon

C. Issever28 End Cap Flex Circuits CCA twisted pair for high current (DC power) Stiffener CuKapton for HV and control signals

C. Issever29 Disk With Electrical/Optical/Cooling Services

C. Issever30 Cooling pipe Opto-packageFibres in furcation tubing Dummy module

siliconModule with ASICs Opto-package with fibres Redundancy links Flex Circuits

C. Issever32 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.

C. Issever33 Opto-Array Sub Assembly

C. Issever34 RX/TX Plugins 12 way PIN array 12 way VCSEL array M-L. Chu et al. NIM A 530 (2004)

LECC VCSEL performance Cut Links used successfully in readout of barrels and End Caps. > 99.7% (99.7%) working channels for Barrels (EC-C) BER < for data and TTC links.

C. Issever36 Problems Complexity and yield Cracks on kapton flex circuits (Light leakage) ESD Resonant bond wire vibrations

C. Issever37 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)

LECC 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.

40 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

C. Issever  m Cracks appear to form on grain boundaries

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C. Issever46 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.

C. Issever47 ESD Deaths ESD and DORIC4A ASIC ESD and VCSELs One strike and you are out

C. Issever48 ESD On DORIC4A ASIC Damaged tracks Cause of ESD identified as bad handling procedure  procedures improved and all suspect chips removed.

C. Issever49 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 ESD causes optical and electrical degradation High optical power  local heating of the DBR mirror  increased absorption  decreased light o/p.

C. Issever50 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.

C. Issever51 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?

C. Issever52 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 ~ l 4 2 orders of magnitude larger for oscillations out of plane of bond wire loop than in plane.

C. Issever53 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)

C. Issever54 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.

C. Issever55 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).

C. Issever56 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 mm Si modules

C. Issever57 SCT Barrel Harness Electrical and optical services for 6 modules. Redundancy connection TTC & Data fibres Opto & ASICs Module connector Cu/kapton cable

C. Issever58 Taiwan Opto-Packages MITEL 1A444 bare chip VCSELs and Centronic epitaxial Si PIN diodes. Also tried Truelight VCSELs & PINs. Simple/cheap components used (PCBs). 45 o 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.

C. Issever59 Taiwan Opto-package

C. Issever60 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.

C. Issever61 Results with ATLAS tests Barrel dogleg VDC  VCSEL bonds with correct orientation of B field. No resonances seen with camera in scan of kHz. Amplitude << 25  m. K5 VDC  hybrid bonds. No resonances seen with camera in scan kHz. Amplitude << 25  m. Forward opto PCB  VCSEL. No resonances seen with camera in scan kHz. No resonances seen with back emf. Amplitude << 25  m.

C. Issever62 Next slides are from Jan Troska

C. Issever63 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

C. Issever64 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 (~100  W) to avoid significant SEU effects

C. Issever65 The following slides are from Oliver Pooth, RWTH Aachen

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