CMS Tracker Upgrade for Super-LHC. Fabrizio Palla INFN Pisa

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1 CMS Tracker Upgrade for Super-LHC Fabrizio Palla INFN Pisa 1

2 Outline CMS workshops on SLHC Current layout Radiation issues Pixel system Strip system Electronic issues Tracker Trigger DISCLAIMER the comments presented here are not an official view from CMS but are (hopefully) representative of our thinking 2

3 SLHC & CMS CMS has held three workshops on SLHC Feb General startup July Mostly Tracker, Trigger and Electronics July Trigger upgrades Many discussions, many ideas, no detailed proposal yet! Important starting point Most CMS systems will survive and continue to operate without changes to inaccessible electronic systems Implies some constraints on future machine operation Major exceptions Tracker - which is expected to be entirely replaced for SLHC Trigger - rebuild L1 processors + there is a strong belief that Tracker information is necessary for L1 trigger 3

4 The CMS Silicon Tracker TOB 220 cm TIB PD TOB TIB TID TEC PD 270 cm 210m 2 micro-strip silicon detectors modules µm thick and µm thick sensors (all from 6 wafers) APV chips analog strip channels. About 25M wire bonding. 4

5 The CMS Pixel Detector 3 barrel layers r = cm, cm, cm ~ 60 x 10 6 pixels 2 pairs of Forward/Backward disks Radial coverage 6 < r < 15 cm Average z position: 34.5 cm, 46.5 cm Later update to 3 pairs possible (<z> ~ 58.2 cm) Per Disk: ~3 x 10 6 pixels 3 high resolution space points for η < 2.2 Pixel size: 100 µm x 150 µm driven by FE chip Hit resolution: r-φσ ~ µm (Lorentz angle 23 in 4 T field) r-z σ ~ 17 µm Modules are the basic building elements 800 in the barrel in the endcaps NB system designed to be replaceable 5

6 The CMS Silicon Strip Tracker Outer Barrel (TOB): 6 layers Thick sensors (500 µm) Long strips Radius ~ 110cm, Length z view ~ 270cm Endcap (TEC): 9 Disk pairs r < 60 cm thin sensors r > 60 cm thick sensors η~1.7 6 layers TOB 4 layers TIB η~ disks TID 9 disks TEC Inner Barrel (TIB): 4 layers Thin sensors (320 µm) Short strips Inner Disks (TID): 3 Disk pairs Thin sensors Black: total number of hits Green: double-sided hits Red: ds hits - thin detectors Blue: ds hits - thick detectors 6

7 Modular mechanical structures: Shells, Rods, Petals TIB mechanics (Shells) TOB (Rods) TOB Mechanics TEC (Petals) TEC Mechanics 7 Pixel Module

8 Module components Kapton pig-tail Pins Front-End Hybrid APV and control chips Pitch Adapter Kapton Bias Circuit Carbon Fiber/Graphite Frame Silicon Sensors The coordinated procurement of the needed components (including quality control procedures) can be critical. Try to simplify the most and to reduce the number of variants. 8

9 Thick modules variants 9

10 How does it looks in reality 10

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12 Tracker Upgrade issues Higher granularity and more pixels are required Power requires major effort & new ideas Chip voltages reduce with technology evolution, currents may (??), but number of channels will not Need to bring increased total currents through volumes which can t expand Material budget should not increase Large systems are hard to build Qualification must be taken seriously True industrial production is likely to be required Sensors are one of many issues Any new material technology must be large-scale commercial within ~5 years Electronic technology evolution will bring benefits and also more complexity and much difficult work 12

13 Radiation Issues for SLHC 13

14 Radiation issues LHC Cumulative effects (NIEL, TID) increase by a factor 5 Instantaneous effects (occupancy, SEU) increase by a factor SLHC

15 PIXEL System 15

16 Pixel system Use 5xTDR fluencies Old fluence limit 6x10 14 /cm 2 r min ~26 cm!! Problem What can we do? Change detector more often Improve fluence limit of sensor Need to study sensors more! RD50 16

17 INFN Group V activity SMART (Structures and Materials for Advanced Radiation hard Trackers) Sezioni INFN di Bari, Firenze, Perugia, Pisa Coll. Esterni: Sez INFN Padova ITC-IRST Trento Research Objective Development of detector systems Silicon based (pixel and micro strips) with radiation tolerances up to cm -2 (fast hadrons) and doses up to 4 MGy. 17

18 Fluence limits of Silicon Pixel Sensors Double sided processed, n + on n-silicon Expensive but high quality detectors So far many investigations for fluences ~1x10 15 cm -2, still quite ok! Reduced signal collection Partial depletion depth Controlled by high Voltage capability Oxygenation Czochralski (lower costs) Epitaxial silicon Thinner detectors (e.g. 200 µm-> Leakeage current?) Reverse polarity?? Trapping So far not engineerable -> final fluence limit for silicon detector Fluence ~ 3x10 15 cm -2 -> Q IR =25% Q NIR (very speculative!) 18

19 Fluence limits Oxygenated CMS pixel sensors Double sided processed n + on n Silicon 285 µm thickness At 450 V ~ fully depleted even with large fluences CMS Pixel test beam at CERN Summer 2003 Shallow track method 19

20 Towards outer radii Cost of pixel module limits very much the use at large radius Very rough costs of current pixel module Readout chip 0.25 µm (16x) Sensor (DS, n + on n Si) HDI Bump Bonding Baseplate (SiN) Cable (40 cm & TBM) etc Module area 10 cm 2 Optical links, FED, PS +~20% Costs ~400 SFr/cm SFr 1000 SFr 300 SFr 1200 SFr Costs ~3300 SFr 200 SFr 200 SFr 20

21 Low cost pixel for intermediate radii 15 to 25 cm radii need cheaper technology Pixel System 2 Single sided pixel detectors, n+ on p Silicon (Czochralski) (partial depleted operation possible, although HV issue at guard ring need R&D) Large Module size, e.g. 32 x 80 mm sensitive area Pixel area ~ 160 µm x 650 µm Large bumps (90 mm lead tin, IBM C4) for cheap bump bonding Large ROC s (16 mm x 20 mm) for fewer bump bonding placements ROC in 0.13 µm technology (lower production costs/cm2) Estimated cost ~100 SFr/cm 2 2 layers at 18 and 22 cm 21

22 Larger radii 25 to 60 cm radii need to deal with SLHC rates Silicon strips (actual) have sensor element area of 10 to 15 mm 2 10 fold increase in the luminosity would need a 10 fold decrease of it Macro pixel detectors of 1 mm x 1 mm/ Micro strips of 200 µm x 5 mm Simple DC coupled p+ on n Silicon detector Route signals on thick polyimide (~40 µm) insulation to periphery and bump bond to modified pixel ROC for cost efficient zero suppressed readout ~ 40 SFr/cm 2 Could cover 3 Layers 30, 40 and 50 cm 22

23 Cost & Power estimate for new Tracker Pixel Systems 1-3 : Costs & Power.vs. eta (barrel/disks) Pix Sys #1 : 3 layers 330 mw/cm 2 High φ pix 400 SFr/cm Pix Sys #2 : 2 layers 130 mw/cm 2 Large pix 100 SFr/cm 2 Pix Sys #3 : 3 layers 45 mw/cm 2 Macro pix 40 SFr/cm 2 Eta =1.4 Area = 18.3 m 2 Power [Watts] Costs [KSFr] Costs Power Mechanics etc. not in costs! Strip detector ~25 mw/cm 2 eta 23

24 Strip System 24

25 What will remain the same? Specifications - no obvious reason for major change momentum resolution & spatial resolution no specific physics to justify tracker parameters, unlike, eg, ECAL Volume available so geometry will resemble present system Space in control room & cavern is also limited increased off-detector electronics must be compensated by density power supplies, cables, readout and control total power constraints will also not relax much Ability to cool system No major technology improvements Budget? Value unknown but should expect it to constrain design 25

26 What will not remain the same? No of channels will increase M channels for R>60? (~x5) Detector (sensitive) thickness may change Noise specification will depend on signal size - but won t be higher Particle density => improved granularity to maintain track separation Off-line computing power will increase will it scale faster than increase in channel count or reconstruction requirements? can occupancy increase? (present limit defined by DAQ switch) On-line processing on-detector (ASIC) processing - will be limited by power dissipation off-detector (FED) processing - will increase but benefits may be limited by increase in channels and complexity of data 26

27 Tracker to Stracker scaling Increased channel and module count has consequences N SAPV ~ 3x N APV reduce test time (60s) to <20s, or more parallel stations N Sbonds ~ 5x N bonds N Smodules ~ 5x N modules N Srod ~ N rod N Spetal ~ N petal What limits throughput? Assume similar Stracker modules to Tracker SAPV test x2 stations ok, control electronics Bonding is time known? mechanics, no. stations, quality (?) Module construction: gantries, staff? testing: staff? Srod, Spetal assembly: handling, staff? test: equipment? Power - dominated by SAPV - may scale favourably - but If new functions (trigger, ADC, logic, ) : expect more power More optical links or multiplexing needed - fibre/connector volume also an issue Total tracker power should not increase or more space needed for cables Material Not clear yet if any gains are possible 27

28 System issues CMS has pioneered automated module assembly But Almost fully proven, and module assembly should go quite fast in ~2 years Significant development time to reach this point Many crucial, detailed, labour intensive tasks Developing specialised or automated tools Hybrids, noise & irradiation studies, engineering of cooling, controls, Connectivity System assembly, installation and commissioning still ahead Much less adaptable to automation SLHC tracker will be different - more modules & 28

29 Mechanical issues Two levels of mechanics Modules and assembly Support structure, cooling and integration Module construction Effort influenced by multiple geometries, and significant customisation Greater degree of automation, compared to past but Many labour-intensive tasks are limiting factors Bonding, testing, low-t qualification, Structure and integration As expected heat removal is difficult as well as crucial Present tracker has variants of cooling systems Planning cabling is difficult until late stage FEA studies - sufficient expertise and tools available? Other specific challenges? 29

30 Sensor material Radiation for outer region: ~5x present worst levels, or replace at intervals Outer layers, silicon looks promising Oxygen doped, Magnetic Czochralski silicon investigated (see next slide) Inner region - no proven alternative to silicon yet - but are other materials possible? Performance Series noise (C det ) can decrease but parallel (I leak ) may not, even if reduce τ I leak ~ strip length, thickness, particle fluence Power dissipation leakage current increase could dominate module power? requires review of planning of current to sensors Manufacturability & R&D required will unusual materials be acceptable? are they available in required quantities? any special processing requirements? work in close collaboration with major sensor manufacturers from an early stage 30

31 Sensor design Dimensions is finer pitch than present design essential? bonding task is enormous if done conventionally pitch adapter is simple but troublesome element can we better match electronics pitch to sensor? present designs optimise sensor pitch to location in tracker should we sacrifice for manufacturability? how much is lost if all sensors have, eg, 100µm or 200µm pitch? Ease of handling and assembly since modules will be shorter, there will be many more. We must minimise handling and tracking - could this be done by industry? Cost present design originates in bottom-up approach underestimates many costs and difficulties 31

32 Straw man module Adapt sensor for commercial bump bonding 100µm Bond pads 200µm pitch (staggered) Heat sink + substrate to deliver service signals Silicon? SAPV: 2 per die Outputs in middle Power rails bump bond to substrate services via substrate surface service chips at periphery Many questions to answer But might be candidate for commercial assembly on large scale? Is it possible with more conventional assembly? 32

33 Front-end power example Scaled APV-type circuit 0.25µm -> 0.13µm (M. Raymond) simplest assumptions eg. supply voltages scale, 80MHz Power/channel 0.25µm 0.13µm Preamp 0.65mW 0.10mW Total analogue Digital power Total 1.90mW 0.41mW 2.31mW 0.30mW 0.09mW 0.39mW ENC ~ 700e for 2cm strip (+ leakage current..) Good news factor 6 gain [digital ~4 (?)] Bad news no of channels probably scale similarly 33

34 Intermediate prototype Installation of modest prototype system at t p = t 0 + 5y Less cost and lower risk Less substantial case for support needed More chance of resources, on short time scale Allows trial of components or devices, which may still evolve Human time-scale Prototype contained in the volume from pixel layer 0 to 4 Need to use/reuse service space for pixels Will allow the study of New technologies Occupancy/rates Beam backgrounds Trigger Data links 34

35 Trigger at SLHC Occupancy Degraded performance of algorithms Larger event size to be read out New Tracker: higher channel count & occupancy large factor Reduces the max level-1 rate for fixed bandwidth readout. Trigger Rates Try to hold max L1 rate at 100 khz by increasing readout bandwidth Avoid rebuilding front end electronics/readouts where possible Rebuild L1 processors to work at 80 MHz Already few cases use 160 MHz processing Use 40 MHz sampled data to produce trigger primitives with 12.5 ns resolution Radiation damage -- Increases for part of level-1 trigger located on detector 35

36 Tracker Trigger at L1 Muon L1 Trigger rate at L = cm -2 s -1 Note limited rejection power (slope) without tracker information Must develop Tracker Trigger at L1 Export some HLT algorithms to L1? Lot of activities going on 36

37 backup 37

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39 Level-1 Latency Present Latency of 3.2 µsec becomes 256 crossings Assuming rebuild of tracking & preshower electronics will store this many samples Do we need more? Yield of crossings for processing only increases from ~70 to ~140 It s the cables! Parts of trigger already using higher frequency How much more? Justification? Combination with tracking logic Increased algorithm complexity Asynchronous links or FPGA-integrated deserialization require more latency Finer result granularity may require more processing time ECAL digital pipeline memory is MHz samples = 6.4 µsec Propose this as SLHC Level-1 Latency baseline 39

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42 Magnetic Czochralski silicon One example of recent progress (ROSE, RD50) 300µm? For L.dt = 2500 fb -1 R (cm) Hadrons [cm -2 ] 8 x x x Dose [kgy]

43 On-detector electronic issues Analogue readout was a good choice Investigating major design variants is lengthy and costly often introduces new features, needing verification Modified specifications based on experience Improve vulnerability to HIPs (and leaky strips?) Can t yet be sure if common mode is solved or can be improved What dynamic range is required? - it must be lower? (V supply ) Power dissipation was successfully limited but total is still large Re-evaluate asymmetric power rails Radiation tolerance Qualification is time consuming (x-ray systems & SEU) Automated testing successful, but detailed tests only refinable during pre-production hard to track components 43

44 Optical data transmission Tracker is first large scale system good choice and very beneficial material, power, interference immunity many components adapted widely in CMS linear analogue data links are unique digital is industry standard all tracker components specially selected and customised into assemblies must satisfy requirement to be miniature, robust, non-magnetic, low power Optical links are largest single part of tracker electronics budget we should examine technology developments reconsider implementation - even though very successful 44

45 Off-detector electronic issues Manufacturability - will be proven only in 2005 Assembly technology & commercial testing looks promising Details of quality will be crucial for time, cost, commissioning Special components (optical Rx, TTCrx, ) need care Processing power will increase but constraints are harder to anticipate power, density, impact on manufacture Components evolve fast (~5 years lifetime) Functionality will increase & design time Like ASICs, many possible solutions to single problem Manufacture -Pb free solder, fpbga assembly, Power hard to predict reliably until design is well advanced 45

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