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GOSSIP/GridPix Review: Guidelines & Milestones for Enhanced R&D Progress in ATLAS for sLHC

This review aims to define a path for continued R&D work on the GOSSIP/GridPix technology, setting milestones for demonstrator placement and practical application in ATLAS for sLHC. It helps translate proponents' statements into achievable numbers, establishing thresholds in various aspects like spark rates, discriminator levels, and costs. Key goals include identifying target detector regions, covering essential research areas, and defining measurable milestones. The review questions claimed advantages, disadvantages, and technology feasibility, addressing aspects like material budgets, age/radiation tolerance, and neutron vulnerability. It also queries production logistics, chip integration, protection layers, and electronic signal tuning efficiency.

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GOSSIP/GridPix Review: Guidelines & Milestones for Enhanced R&D Progress in ATLAS for sLHC

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  1. Gossip/GridPix – guidelines, facts, and questions for review Version 1: Norbert Version 2: Tatsuo Version 3: Werner

  2. Goals of this review … • review shall define a path/milestones for continued R&D work that leads to • demonstrators that could place the GOSSIP/GridPix technology in a position • to become a serious option for an application in ATLAS for sLHC • help putting the (often optimistic) statements of the proponents into practically achievable numbers • define some (probably high) thresholds (e.g. max. spark rate in large volume • under realistic conditions, performance assuming much higher discriminator • thresholds, material budgets, ageing/radiation tolerance, costs) that must be • passed in order to be seriously considered as an option for sLHC • propose and agree with the proponents on a target detector region (most likely • outer tracker) to be addressed at first with focused R&D and manpower. • define which areas of research should be covered by this proposal (some of the ideas would be better in other programs (power, opto, readout…) • define milestones (with dates)

  3. some numbers to remember … • -400 V bias • avalanche gap = 50 µm • charge signal duration may be pretty long 20 – 50 ns … problem @ sLHC • shaping time 25 ns ? • DME/CO2 50:50 • gas gain < 104 (5000) • Drift field ~ 1000volts over 17mm or ?? Over 1mm for Gossip • Nprim= ~4.5 per mm 12.5? • 7 µm SiN • pixel cell = 50 x 165 µm2 • noise (w/o threshold dispersion) is 70 e • aimed threshold level is 350 e  is this achievable for a large system? • resolution ~ 13 µm in rphi, in z = 165 µm/sqrt(12) ? • …

  4. claimed (by authors) advantages/disadvantages • gas flow, no radiation damage • signal tunable • low capacitance compared to silicon  lower noise, lower power • measures track segments • no bump bonding  better price, but costs the ingrid • low mass…. how low ? • less neutron vulnerability • can identify delta rays • sparks • ageing • position resolution … what is the number ? • data volume x 3 • more services • long charge collection time, much longer than 25 ns

  5. comments to claimed advantages • not convinced by material estimate (recall Si sensor is < 10% of layer) • dE/dx … what do you mean ? why interesting ? why better than silicon ? • what‘s the point at all? • the delta-ray advantage is not obvious to us • we do not believe that the gas detector is better wrt to neutrons • if the hadr. interaction length is the same, the signal from the neutron background is not a problem anyway at small radii • claim that the power dissipation is smaller is not obvious to us – we might expect digital power to be higher as there is more data • we do not see that InGriD production is cheaper than bump bonding Gossip Review

  6. InGrid (most important questions in black) • how to put ingrid on a chip, wafer-scale process ? how to test single chips ? what is the yield to be expected ? • comparing costs of bump bonding with costs of ingrid-production, justify lower cost claim • mass production of InGrids  yield and costs • is the InGrid on the Chip or on something else ? • twin grid: is the yield multiplied ? • twin grid: what is the consequence of imperfections • how far is the twin grid technology advanced to date ? • 50 µm thick chip is claimed … how does this go along with having an InGrid or even a TwinGrid put on the CMOS side of the 50 µm thin wafer (handle wafer problematic etc.) • which temperature is involved the InGrid processing • what are the stresses involved in the InGrid processing and what limits the thickness ? Gossip Review

  7. protection layer • what is the favored approach for the protection layer ? which materials are considered • can there be pinholes in the protection material (as known in SiO2) where sparks can reach through? what is their likelihood? • temperature sensitivity of the protection layer ? • Why is the grid capacity so large ? 100 nF (page 7 of support document) • how does the thickness / resistivity of the layer affect the signal in pulse height and in spread • how can a Si3N4 layer on the InGrid make SiNProt superfluous? Does this also • apply for the TwinGrid ? • how many & which companies are capable of InGrid/protection processing? Gossip Review

  8. electronic signal • nice to tune the PH, but ageing? • same average signal does not mean the same efficiency • add threshold dispersion to noise (70 e  100 e) • threshold of 350 e seems unrealistic by factor ~5 or more, what does that change • in the conclusions • power reduction due to capacitance applies only to analog part (<50%) • dE/dx … what do you mean ? why interesting ? why better than silicon ? • what‘s the point at all. • Is the detection of TR a goal and how would this be achieved? • How is track segment information treated i.e. could a track trigger • be implemented at L1? What are implications on readout rate? Gossip Review

  9. rate capability • resistivity of protection layer versus rate capability • ion space charge and field distortions and their influence on the • rate capability Gossip Review

  10. ageing • ageing: how do you intend to study the ageing effects • how do you test ageing and radiation together Gossip Review

  11. sparks and radiation • sparks …  demonstrate „no problem“ in big volume • rate of sparks? Efficiency drop, and for how long? Neutrons signal (big)? • radiation  show operation in a radiation harsh environment, e.g. near • the LHC ring or behind the Very Forward Spectrometers

  12. material • X/X0 in reality probably is 1.5% or 2%, i.e. not any better than Si • how can you prove that this is not so ? Where does the difference • to silicon come from ? • Can one target an “outer” GridPix detector with ~50% the material of a silicon • detector ?

  13. Collaboration issues • understand how collaboration shares work (and costs) • understand what the collaboration can realistically achieve in terms of resources (is it realistic to prototype full wafers?) Gossip Review

  14. data volume • factor 3-10 larger data volume … how to cope with it Gossip Review 13

  15. Cooling • How does the needed cooling capacity compare to silicon detectors ? • Why should the anticipated power consumption be smaller than for silicon (p13 of support document. • Why does the operation temperature matter for the cooling performance ? Gossip Review 14

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