1. Micropattern on CMOS pixels NIKHEFMaximilien Chefdeville Auke-Pieter Colijn Alessandro Fornaini Harry van der Graaf Peter Kluit Jan Timmermans Jan Visschers Saclay CEA-DAPNIAPaul Colas Yannis Giomataris Arnaud Giganon Univ. Twente/Mesa+Jurriaan Schmitz CERN/Medipix ConstmErik Heijne Xavie Llopart Michael Campbell Thanks to: Wim Gotink Joop Rovenkamp Arnaud Giganon Harry van der Graaf NIKHEF SECOND WORKSHOP ON LARGE TPC FOR LOW ENERGY RARE EVENT DETECTION LPNHE - Paris VI and VII Universities PARIS, France 20 December 2004

2. Time Projection Chamber (TPC): 2D/3D Drift Chamber The Ultimate Wire (drift) Chamber E-field (and B-field) Wire Plane + Readout Pads track of charged particle Wire plane Pad plane

3. Giomataris & Charpak 1995: Micromegas Ideally: a preamp/shaper/discriminator channel below each hole…. Let us eliminate wires: wireless wire chambers better granularity

4. 1996: F. Sauli: Gas Electron Multiplier (GEM)

5. The MediPix2 pixel CMOS chip 256 x 256 pixels pixel: 55 x 55 μm 2 per pixel:- preamp - shaper - 2 discr. - Thresh. DAQ - 14 bit counter - enable counting - stop counting - readout image frame - reset We apply the ‘naked’ MediPix2 chip without X-ray convertor!

6. Problem With wires: measure charge distribution over cathode pads: c.o.g. is a good measure for track position; With GEMs or Micromegas: narrow charge distribution (only electron movement) wire avalanche Cathode pads GEM Micromegas Solutions:- cover pads with resistive layer - ‘Chevron’ pads - many small pads: pixels

7. Drift Space GEM foils MediPix CMOS pixel sensor Brass spacer block Printed circuit board Aluminium base plate Our GEM-equipped TPC We have constructed a small test TPC equipped with three GEM foils which can be read out by means of the MEDIPIX2 CMOS pixel sensor.MEDIPIX2 The GEM foils were obtained from the CERN/Sauli/GEM group; hole-to-hole distance (hexagonal geometry): 140 µm, hole diameter 85 µm, fiducial surface 100 mm x 100 mm, thickness 50 µm. The drift volume (vol. 100x100x100 mm 3 ) is surrounded by square wire loops, spaced 6.3 mm, put at decreasing potential. Three GEM foils are placed 7.4 mm behind the plane of the bottom wire loop; the distance between GEM foils is 1.6 mm. The anode plane, at ground potential, is 6.6 mm below the third GEM foil. A new readout for the TESLA TPC: Each GEM hole gets its own preamp/shaper/discriminator:

8. Cathode foil Gem foils Support plate Medipix 2 Drift Space The MediPix2 pixel CMOS chip We apply the ‘naked’ MediPix2 chip without X-ray convertor!

9. First events, recorded on March 29, 2003. Drift space irradiated with 55 Fe quanta Gas: Ar/Methane 90/10

10. No source; exposed 0.01 sNo source; exposed 2 s No source; exposed 0.1 s 90 Sr source; exposed 0.01 s Fiducial field: 14 x 14 mm 2 Collected ionisation in 14 x 14 x 100 mm 3 during exposure time Gas: Ar/Isobutane 90/10 Feb 9, 2004

11. MediPix2 pixel sensor Brass spacer block Printed circuit board Aluminum base plate Micromegas Cathode (drift) plane 55 Fe Baseplate Drift space: 15 mm With Paul Colas & Yannes Giomataris: MediPix2 & Micromegas Very strong E-field above (CMOS) MediPix!

12. MediPix modified by MESA+, Univ. of Twente, The Netherlands Pixel Pitch: 55 x 55 μm 2 Bump Bond pad: 25 μm octagonal 75 % surface: pacivation SiN New Pixel Pad: 45 x 45 μm 2 Insulating surface was 75 % Reduced to 20 %

15. We always knew, but never saw: the conversion of 55 Fe quanta in Ar gas No source, 1s 55 Fe, 1s 55 Fe, 10s Friday 13 (!) Feb 2004: signals from a 55 Fe source (220 e- per photon); 300  m x 500  m clouds as expected 14 mm The Medipix CMOS chip faces an electric field of 350 V/50 μm = 7 kV/mm !!

16. Eff = e -Thr/G Thr: threshold setting (#e-) G: Gas amplification Prob(n) = 1/G. e -n/G no attachment homogeneous field in avalanche gap low gas gain  No Curran or Polya distributions but simply: Single electron efficiency

17. New trial: NIKHEF, March 30 – April 2, 2004 Essential: try to see single electrons from cosmic muons (MIPs) Pixel preamp threshold: 3000 e- Required gain: 5000 – 10.000 New Medipix New Micromegas Gas: He/Isobutane 80/20 Ar/Isobutane 80/20 He/CF4 80/20 …… It Works!

18. He/Isobutane 80/20 Modified MediPix Sensitive area: 14 x 14 x 15 mm 3 Drift direction: Vertical max = 15 mm

19. He/Isobutane 80/20 Modified MediPix

20. He/Isobutane 80/20 Modified MediPix

21. He/Isobutane 80/20 Non Modified MediPix Amaricium Source

22. He/Isobutane 80/20 Modified MediPix

23. He/Isobutane 80/20 Modified MediPix δ-ray!

24. For TPCs: all primary electron info is used, only diffused by diffusion! Simulations: TPC performance in view of single electron detection: spatial resolution (= momentum resolution) precision dE/dX by cluster counting (M. Hauschild) multi track separation corrections for scattering δ-ray suppression Low diffusion low number of clusters? Form collaboration to develop TimePix CMOS pixel chip: based on MediPix: change pixel counters into TDCs require full scale! Submit costs 150 kE for 6 wafers… MediPix Consortium (CERN based) likes to design TimePix1

25. INtegrate (Micromegas) GRID and pixel sensor ‘ Micromegas ’ By ‘wafer post processing’ at MESA+, Univ. of Twente InGrid InGrid + Pixel chip = GridPix

26. Integrate GEM/Micromegas and pixel sensor: InGrid ‘GEM’ ‘Micromegas’ By ‘wafer post processing’

30. First InGrid has been delivered Wafer dia.: 100 mm 30 fields with a variety of pillar (spacer) geometry

31. HV breakdowns: issue for InGrid 2 4) Protection Network 1) High-resistive layer 2) High-resistive layer 3) ‘massive’ pads

32. Vernier, Moire, Nonius effect Pitch MediPix: 55 μm Pitch Micromegas: 60 μm Periodic variation in gain per 12 pixels Focussing on (small) anode pad Continues anode plane is NOT required Reduction of source capacity! Non-modified MediPix Modified MediPix has much less Moire effect No charge spread over 2 or 4 pixels

35. Modified Non Modified InGrid: perfect alignment of pixels and grid holes! Small pad: small capacitance! focusing De-focussing Low E-field Low gas gain

36. GridPix could become a general way to readout gaseous chambers Other applications of GridPix: - μ-TPC - Transition Radiation Detectors - GOSSIP: vertex detector for intense radiation environment

37. CMOS pixel array MIP Micromegas (InGrid) GOSSIP: Gas On Slimmed SIlicon Pixels Drift gap: 1 mm Max drift time: 15 ns MIP CMOS chip Cathode foil

38. GOSSIP? Ageing Efficiency Position resolution Rate effects Radiation hardness HV breakdowns Power dissipation Material budget

39. Ageing Remember the MSGCs…… Little ageing: the ratio (anode surface)/(gas volume) is very high w.r.t. wire chambers little gas gain: 5 k for GOSSIP, 20 – 200 k for wire chambers homogeneous drift field + homogeneous multiplication field versus 1/R field of wire. Absence of high E-field close to a wire: no high electron energy; little production of chemical radicals Confirmed by measurements (Alfonsi, Colas) But: critical issue: ageing studies can not be much accelerated! Now being set-up with X-ray generator (Panalytical/Philips)

40. Spatial resolution: pixels down to 20x 20 μm 2 may be useful After all: TPC! 3D track info Counting rate in Super LHC (no Si Vertex compatitor) : 10 tracks/ (cm 2 25 ns): ions reach grid within 10 – 30 ns Radiation hardness: - Replace electron-hole pair generation in Si by gas + gas amplification - Sufficient signal charge to eliminate low-noise amplifiers in pixels - CMOS readout circuit: only digital gates (130 nm technology) Material budget: only slimmed Si (40 μm), 1 mm gas Cooling: CMOS chip power < 0.1 W/cm 2 : use gas flow as cooling….. If it works: interesting for ATLAS, CMS, LHCb, ALICE, D0 etc

41. How to proceed? - InGrid 1 available for tests: - rate effects (all except change in drift direction) - ageing (start of test)  Proof-of-principle of signal generator: Xmas 2004! - InGrid 2: HV breakdowns, beamtests with MediPix (TimePix1 in 2005) - TimePix: convincing 5 institutes to participate (we have 3 already!) - GOSSIPO: CMOS chip for Multi Project Wafer test chip in 130 nm tech. - Apply InGrid 2 on ATLAS FE Pixel chip: GOSSIP proof-of-principle Dummy wafer

42. Micropattern on CMOS pixels NIKHEFMaximilien Chefdeville Auke-Pieter Colijn Alessandro Fornaini Harry van der Graaf Peter Kluit Jan Timmermans Jan Visschers Saclay CEA DAPNIAPaul Colas Yannis Giomataris Arnaud Giganon Univ. Twente/Mesa+Jurriaan Schmitz CERN/Medipix ConstmEric Heijne Xavie Llopart Michael Campbell Thanks to: Wim Gotink Joop Rovenkamp Arnaud Giganon Harry van der Graaf NIKHEF SECOND WORKSHOP ON LARGE TPC FOR LOW ENERGY RARE EVENT DETECTION LPNHE - Paris VI and VII Universities PARIS, France 20 December 2004