Gossip/GridPix – guidelines, facts, and questions for review

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