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

Goals of this review … 1 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)

some numbers to remember … V bias avalanche gap = 50 µm charge signal duration may be pretty long 20 – 50 ns … sLHC shaping time 25 ns ? DME/CO 2 50:50 gas gain < 10 4 (5000) Drift field ~ 1000volts over 17mm or ?? Over 1mm for Gossip N prim = ~4.5 per mm  12.5? 7 µm SiN pixel cell = 50 x 165 µm 2 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) ? …

claimed (by authors) advantages/disadvantages 3 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

comments to claimed advantages 4 Gossip Review 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

InGrid (most important questions in black) 5 Gossip Review 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 ?

protection layer 6 Gossip Review what is the favored approach for the protection layer ? which materials are considered can there be pinholes in the protection material (as known in SiO 2 ) 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?

electronic signal 7 Gossip Review 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?

rate capability 8 Gossip Review resistivity of protection layer versus rate capability ion space charge and field distortions and their influence on the rate capability

ageing 9 Gossip Review ageing: how do you intend to study the ageing effects how do you test ageing and radiation together

sparks and radiation 10 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

material 11 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 ?

Collaboration issues 12 Gossip Review 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?)

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

Cooling 14 Gossip Review 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 ?