1. Arachnid: A CMOS MAPS R&D programme Adrian Bevan (a.j.bevan@qmul.ac.uk)

2. Overview 2  What is an INMAPS device?  The Cherwell chip  Characterisation work  Test beam  Applications  Chip design for ALICE  Outlook

3. What is an INMAPS device? 3

4. INMAPS: 4  Charge collection inefficiency across a pixel is detrimental to efficient system design:  Want to have smart pixels  Requires circuitry in pixel for rudimentary signal processing  Use a deep p-well to shield the N-well in chip electronics Isolated N-well Monolithic Active Pixel Sensors STANDARD CMOSINMAPS e.g. See J.P. Crooks et al., Proc. IEEE Symp on Nucl. Sci (2007), 2, 931-935. M. Stanitzki et al., Proc. IEEE Symp. on Nucl. Sci. (2007), 1, 254-258 J. A. Ballin et al. Pixels,Sensors 2008, 8(9), 5336-5351.

5. TPAC 1.X Results F B Pixel profiles Using 55 Fe sources and IR lasers  Using the test pixels (analog output)  IR laser shows impact of deep p-well implant Marcel Stanitzki, Pixel 2010

6. ) Typical resistivity ~ 10-100 Ω cm High resistivity ~ 1-10k Ω cm Standard / Hi-res EPI Layers 6  Testing devices with standard and high resistivity to compare properties:  Standard:  Slow  Radiation soft devices  High Res:  Faster charge collection  Reduced charge spread  Increased radiation tolerance

7. 3T vs 4T architecture 7  3T:  Read out and charge collection are in the same area.  4T:  3 additional elements  Readout and charge collection area are at different points  Benefits  Low Noise via in-pixel correlated double sampling (CDS)  High Gain 3T 4T

8. INMAPS Roadmap 8 Calorimetry Tracking Vertexing Deep p-well TPAC 1.0TPAC 1.2TPAC 1.1 High Res & 4T INMAPS FORTIS 1.0FORTIS 1.1 TODAY Stitching TPAC for ALICE CHERWELLCHERWELL2 FuturePast DECAL

9. The Cherwell chip 9

10. The Cherwell Chip 10 Cherwell Digital Calorimetry (DECAL) “4T” pixels with triggered global shutter and in-pixel CDS 25um pixel pitch 2x2 pixel summing at column base 50um pixel pitchVertex/Tracking Standard “4T” pixels Reference pixel array 12 bit ramp ADC implemented at column base “Strixel” array 12 bit ramp ADC embedded in pixel array

11. Cherwell Floorplan 11  There are two sides to the chip:  Vertexing:  Reference pixels: 4T structure with 25 ✕ 25μm pixels [48 ✕ 96].  Strixels: Reference style pixel with in column ADC [48 ✕ 96].  Calorimetry  DECAL 25: 4 of these can be ganged together to make a 50 ✕ 50μm pixel [96 ✕ 192].  DECAL 50: 50 ✕ 50μm pixel for calorimetry [48 ✕ 96]. (Reference)

12. Cherwell Floorplan 12  There are two sides to the chip:  Vertexing:  Reference pixels: 4T structure with 25 ✕ 25μm pixels [48 ✕ 96].  Strixels: Reference style pixel with in column ADC [48 ✕ 96].  Calorimetry  DECAL 25: 4 of these can be ganged together to make a 50 ✕ 50μm pixel [96 ✕ 192].  DECAL 50: 50 ✕ 50μm pixel for calorimetry [48 ✕ 96]. Reference 4T structures: similar to FORTIS. These provide a baseline for us to test the integrity of the chip design, and investigate the different types of chip produced.

13. Cherwell Floorplan 13  There are two sides to the chip:  Vertexing:  Reference pixels: 4T structure with 25 ✕ 25μm pixels [48 ✕ 96].  Strixels: Reference style pixel with in column ADC [48 ✕ 96].  Calorimetry  DECAL 25: 4 of these can be ganged together to make a 50 ✕ 50μm pixel [96 ✕ 192].  DECAL 50: 50 ✕ 50μm pixel for calorimetry [48 ✕ 96]. Strixels. Similar to the reference pixel array, however there is an in column 12 bit ADC. Aims: Increase fill factor for a sensor. dE/dx measurement for rudimentary PID. Reduce need for ancillary electronics.

14. Cherwell Floorplan 14  There are two sides to the chip:  Vertexing:  Reference pixels: 4T structure with 25 ✕ 25μm pixels [48 ✕ 96].  Strixels: Reference style pixel with in column ADC [48 ✕ 96].  Calorimetry  DECAL 25: 4 of these can be ganged together to make a 50 ✕ 50μm pixel [96 ✕ 192].  DECAL 50: 50 ✕ 50μm pixel for calorimetry [48 ✕ 96]. DECAL 25 4T pixel variant for calorimetry studies Potentially of interest for Higgs factory digital calorimetry. We are concentrating our efforts on understanding the reference and strixel part of the chip first.

15. Cherwell Floorplan 15  There are two sides to the chip:  Vertexing:  Reference pixels: 4T structure with 25 ✕ 25μm pixels [48 ✕ 96].  Strixels: Reference style pixel with in column ADC [48 ✕ 96].  Calorimetry  DECAL 25: 4 of these can be ganged together to make a 50 ✕ 50μm pixel [96 ✕ 192].  DECAL 50: 50 ✕ 50μm pixel for calorimetry [48 ✕ 96]. DECAL 50 4T pixel variant for calorimetry studies Potentially of interest for Higgs factory digital calorimetry. We are concentrating our efforts on understanding the reference and strixel part of the chip first.

16. Maximising the fill factor 16  The efficiency of a detector is dependent on how much of the surface area is occupied by dead space.  Core part of the design of Cherwell is to use islands of electronics within the pixel array – avoid having dead regions at the edge of a sensor to maximise sensitive area. 4T4T SELECT COL RESET COL 1x SR AM BIAS COL 4T4T 4T4T 4T4T 4T4T 4T4T 4T4T 4T4T 4T4T

17. The Cherwell Chip 17 Cherwell Digital Calorimetry (DECAL) “4T” pixels with triggered global shutter and in-pixel CDS 25um pixel pitch 2x2 pixel summing at column base 50um pixel pitchVertex/Tracking Standard “4T” pixels Reference pixel array 12 bit ramp ADC implemented at column base “Strixel” array 12 bit ramp ADC embedded in pixel array This seminar will mostly concentrate on tests of the reference pixel part of Cherwell.

18. Characterisation work Results on the reference and strixel parts of Cherwell 18

19. Basic readout set-up 19  Use a PC to drive a source (LED/laser/radiation source) to illuminate sensor.  Same PC drives DAQ via custom USB interface that talks directly to main board that chip is mounted on.

20. Characterisation work 20  Basic understanding of the chips has been achieved over the past 6 months.  Pedestals, noise, gain of pixels  Temperature response over a nominal range [-50, +50] °C Pedestal Value (ADC counts)

21. Photon Transfer Curve results (PTC) 21  Noise and Gain characterisation PTC performed using IR illumination Results show good uniformity across the pixels Gain ≈ 0.17 ADC/e Noise ≈ 12e rms Linear full well ≈ 11500e Maximum full well ≈ 14700e Log(Signal) Log(Noise 2 ) Signal Noise 2

22. Characterisation work 22  Noise and gain are uniform across the sensor  Average noise value ~12 e RMS  Average gain value 0.17 => 51V/e Noise from each pixel RMS Noise(e) Gain from each pixel Gain(ADCs/e)

23. Source tests 23  Work is on going to fully understand the response of these devices to radiation sources:  55 Fe spectrum endpoint has a sharp cut-off at about 150.  Consistent with expectations from the PTC characteristics of devices.  Good S/N up to 150.  No K α or K β observed, we think this is understood given the geometry of the pixel

24. Temperature variation 24  Performance of the pixels changes as a function of temperature:  Want to understand how things vary over a sufficient range for a viable system: T = [-50, +50] °C. Onset of thermal excitation swamping signal at about 50°C. Any fast systems would need to be maintained below this temperature in order to ensure reliable operation. Have done some preliminary thermal studies using water cooling mock-ups to explore system integration. High Res Epi Layer Expected behavior up to ~50°C Above that – noise escalates Good operating range Thermal runaway

25. Test beam 25

26. 26 Test beam  November 2012  T4 beamline at H6 at CERN  1 week of π beam time  + a few days of parasitic data taking.  Aim: understand resolution, charge sharing, and efficiency of Cherwell. p ~ 120 GeV/c Δ p/p ~1.5%

27. Test beam 27  Analysis is ongoing... more results to come  So far we have pedestal corrections implemented, correcting for common mode noise.  Work is on going with regard to tracking, and clustering – but we can clearly see correlations between hits in different planes of the stack.  alignment constants are stable, indications are that the efficiency is high for these devices, but work needs to be finalised.  Planning further test-beam runs at DESY this year. Aim: start testing DECAL side of the chip.

28. Correlation plot between rows in adjacent sensors. 28  Implemented an SVD based tracking algorithm.  Working on computing hit resolution and efficiency.

29. Applications A few potential uses for this technology (there are many) 29

30. 30  Vertexing:  Fast, precision, low mass detection of charged particles in the vicinity of the interaction region of a detector.  Can be used with one or more layers.  X 0 is dominated by two things:  Thickness of silicon: can back-thin sensors to ~20μm giving a very low mass system  Speed of readout: fast readout requires active cooling and adds mass  Projects pursuing this technology:  SuperB: Particle physics experiment at the Cabibbo Lab in Italy.  Searching for new physics at the intensity frontier.  ALICE: Nuclear Physics experiment at the LHC.  Searching for a deeper understanding of matter at the energy frontier. e.g. See Bevan et al., NIMA 643 (2011), pp. 29-35

31. 31  Vertexing:  Fast, precision, low mass detection of charged particles in the vicinity of the interaction region of a detector.  Can be used with one or more layers.  X 0 is dominated by two things:  Thickness of silicon: can back-thin sensors to ~20μm giving a very low mass system  Speed of readout: fast readout requires active cooling and adds mass  Projects pursuing this technology:  SuperB: Particle physics experiment at the Cabibbo Lab in Italy.  Searching for new physics at the intensity frontier.  ALICE: Nuclear Physics experiment at the LHC.  Searching for a deeper understanding of matter at the energy frontier.  Next generation chip design based on ALICE tracker upgrade. e.g. See Bevan et al., NIMA 643 (2011), pp. 29-35 τ -C ???

32. 32  Calorimetry  High granularity large area detector for particle flow reconstruction and identification algorithms:  Use the shower shape to distinguish between particle species based on how they interact in the calorimeter  e.g. pixel-W sandwich based calorimeter concept: CALICE (Higgs Factory/CLIC)  Variant of a standard CMOS process makes this technology cheap enough to be of interest for such applications. e.g. See J A Ballin et al 2011 JINST 6 P05009

33. 33  Other uses  Characterisation of these devices over a range of temperatures is driven by a desire to understand:  the maximum operating temperature of a functional device.  how devices work over a "normal" range of actively cooled temperatures.  how they work in a regime of interest for ground based astronomy  (here you want to cool sufficiently to be able to eliminate IR background from your detector: need to operate at LN2 temperatures).  Also of interest to T2K Re: LAr calorimetry.  how low can you go?  These issues are all related to building a "system".

34. Work in progress 34  Temperature characterisation is being performed systematically for several variants of the device:  In addition to preliminary results shown, we are preparing our infrastructure to use a low temperature cryostat. Preparing to test performance of chips, mounted on a 40pin DIL socket, down to a few K later this year. Study charge carrier freeze out, and understand operation in high B fields using this (up to 7T). Goal: Understand limits of the technology for future design work, and develop generic infrastructure for future testing.

35. CMOS Image Sensor for the ALICE ITS Work in progress 35

36. Basic concept. 36 To subdivide the full array into smaller sub-arrays, the size to be defined in order to match specifications, in particular in terms of speed and power. Column circuitry Front end (see later) The pixel Front-end based on ‘imaging’ pixels Column-circuitry: ‘end-of-column’ circuitry, folded back into the columns by using deep P- islands Similar concepts under test in the Cherwell sensor designed for Arachnid. 36

37. 37 Building the array 37 Column circuitry Front end The pixel The strixel The sub-array or

38. 38 Pixel schematic SEL RST1 VRST1 I bias0 V bias0 OUT WRITE 250 fF 38 Based on the schematic shown here, and presented in 2009. See http://www.imagesensors.org/Past%20W orkshops/2009%20Workshop/2009%20P apers/066_paper_turchetta_ral_reset_noi se.pdf http://www.imagesensors.org/Past%20W orkshops/2009%20Workshop/2009%20P apers/066_paper_turchetta_ral_reset_noi se.pdf This pixel allow CDS, but not snapshot. Pixel studied in depth.

39. 39 Timing SEL RST VRST OUT WRITE SEL WRITE RST Integration Sample Reset Sample Signal Reset pixel

40. 40 PTC 40 Log-log plot Linearity

41. 41 Per pixel noise 41 Gain 33 µV/e- Full well 18,000 e- Dynamic range 2,900 or 69.5 dB

42. 42 Pixel optimisation for Alice-ITS 42 Based on the previous experimental results, we optimised the pixel for the Alice application. Results below based on a 128-pixel strixel and for different timings (trade-off between noise and power)

43. 43 Strixel circuitry 43 + - OUT_S OUT_R ROW COUNTER CK Memory 1 Memory 2 Counter status Counter status bus State machine Digital output Counter status bus Row decoder In the strixel Each strixel will be independently working in rolling shutter mode. Hits recorded in strixel memories. Two memories should be enough based on occupancy.

44. 44 Dies 44 Sensors Two dies with 256 strixels Each strixel with 128 pixels Readout architecture LVDS chip (with PLL) already prototyped (back from fab Feb 2013) LVDS speed: minimum target 500 Mbit/sec (simulated up to 800Mbit/sec) Submission Chip submission should occur any day now. Expect to be testing this device summer/autumn 2013.

45. Outlook 45

46. 46  Cherwell is functioning well  Bench-test characterisation yielded interesting initial results so far.  First results from test beam are promising  Reference/Strixel parts of the chip  Basic operational requirements are understood  plan to continue exploring these aspects.  DECAL needs more investigation  planning a test beam at DESY to study this half of the chip.  One step closer to being able to build a fully integrated INMAPS based detector system.

47. To Do 47  Test beam analysis is ongoing:  Aim to get efficiency and a better understanding of clustering.  Requires tracking software refinement.  Bench-top characterisation:  Laser hit maps to study uniformity of response across pixels.  Radiation hardness  The pinned photodiode is suspected to be radiation soft, want to investigate this device in more detail.  Further our understanding of the operational envelope:  crucial if we want to be able to map out a wider range of possible applications for devices based on this technology.  Continuing to develop infrastructure to this end.  Chip design:  Expect a new chip submission this week for a next generation device for vertexing (ALICE Tracker prototype).

48. ALICE Specs (1) 48

49. ALICE Specs (2) 49