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PImMS a fast event-triggered pixel detector with storage of multiple timestamps

PImMS a fast event-triggered pixel detector with storage of multiple timestamps.

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PImMS a fast event-triggered pixel detector with storage of multiple timestamps

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  1. PImMSa fast event-triggered pixel detector with storage of multiple timestamps Mark Brouard, Ewen Campbell, Edward Halford, Alex Johnsen, Jason Lee, Craig Slater, Claire Vallance, Edward Wilman, Benjamin Winter, Weihao Yuen Chemistry, University of OxfordIris Friedli, Laura Hill, Jaya John John, Andrei Nomerotski, Robert PisarczykPhysics, University of OxfordAndy Clark, Jamie Crooks, Iain Sedgwick, Renato TurchettaSTFC Rutherford Appleton Laboratory 14 September 2011 - PSD9, Aberystwyth 1

  2. Outline PImMS: Pixel Imaging Mass Spectrometry PImMS1 sensor Context / requirements Design Initial results Future directions PImMS 1

  3. Context: time of flight mass spectrometry Mass spectrum for human plasma ~ 100 µs duration

  4. Context: ion imaging Use a position sensitive detector to obtain x-y distributions – learn about reaction dynamics Need to tune the timing to select one ion S atom ion images for OCS photodissociation at 248nm

  5. Pixel Imaging Mass Spectrometry Combines time of flight MS with 2D ion imaging Takes advantage of recent advances in silicon to image multiple ions in one cycle

  6. Initial proof of concept Proof of concept experiments with a fast framing camera (Dalsa CCD) in 2007-8 for dimethyldisulfide Required prior knowledge of timing of mass peaks CH3S2CH3 M. Brouard, E.K. Campbell, A.J. Johnsen, C. Vallance, W.H. Yuen, and A. Nomerotski, Rev. Sci. Instrum. 79, 123115, (2008)

  7. Towards sensor requirements Want a fast sensor, flexible to analyse any mass spectrum Sparse events consider time-stamping approach To record both early and late ions, need multiple memories. How many? Simulate: 1 register 2 registers 3 registers 4 registers p (ion detected) n (ions flown) all 40 ions simulated p (ion detected) p (ion detected) n (ions flown) n (ions flown)

  8. PImMS1 sensor: specifications 72 by 72 pixel array 70 µm by 70 µm pixel 5 mm x 5 mm active area < 50 ns timing resolution 12 bit time stamp storage 4 memories per pixel adjustable experimental period, up to ~1ms programmable threshold and trim – 4 bits per pixel one test pixel with access to intermediate analogue points PImMS 1

  9. Overview of the sensor Column bias and timecode distribution Pixel configuration + row addressing Pixel configuration read-back 72 x 72 pixel array Digital Sense Amplifiers Digital Readout Path 12 Analogue Readout Path

  10. PImMS1 sensor: technology • Light is detected in the thin epitaxial layer, < 20µm • With only NMOS transistors, obtain limited functionality • PMOS transistors would compete for charge • INMAPS process developed at RAL • Isolated N-well Monolithic Active Pixel Sensors – p+ shield • Gain full CMOS capabilities

  11. PImMS1 sensor: technology • 0.18µm CMOS fabrication • INMAPS process • 615 transistors per pixel • over 3 million transistors in all 7.2 mm Sensor design: Andy Clark and Jamie Crooks, STFC Rutherford Appleton Laboratory

  12. PImMS pixel Preamplifier Shaper Charge Collection Diodes hit Comparator 12-bit timecodes

  13. Pixel operation diode preamplifier shaper crossing => hit crossing => hit comparator inputs hit indicator timecode 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 0 0 0 0 0 6 6 6 6 6 6 6 6 6 6 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 1414 14 14 14 memory 1 memory 2 13

  14. Pixel layout

  15. Readout: camera USB control and readout F-mount SLR lens • Cooling system • Option for nitrogen/dry air

  16. Readout: software The camera is controlled and read out by bespoke LabView software. Data can be saved to disk for offline analysis. A growing library of online and offline visualisation tools is available. Software design: Jason Lee, Oxford Chemistry

  17. Analogue readout Corresponds to the output of the pre-amplifier Represents the total charge stored in each pixel, cumulative for all hits during a given experiment Mainly used for focusing an optical lens onto the phosphor screen

  18. Digital readout – multiple hits 5 laser hits, 30µs apart A = analogue image, integrated over all hits 1 = 1st memory 2 = 2nd memory 3 = 3rd memory 4 = 4th memory A 1 2 3 4

  19. Digital readout – 3D visualisation 1st four pulses: • 5 laser pulses, 25ns long, at 405nm • 40µs apart = 800 timecodes (50ns/timecode) # of hits # of hits Timecode # of hits # of hits Pixel position - y Pixel position - x Timecode

  20. Threshold • The threshold for experiments is set by two adjustable analogue voltages (generated on the camera) • This shows the spot produced by a defocused class 1 laser at increasing threshold levels. 400 mV 200 mV 100 mV 55 mV 0.1 mV

  21. Sensor calibration • Each pixel has 4 bits of trim and can be masked • Maximum trim ~50mV • Dispersion (sigma) before and after calibration: 12.5 -> 4.5 mV (this plot). • With subsequent improvements to the software, the current dispersion is 2.3 mV. net threshold trim

  22. Optical testing Quantum efficiency 8-9% for visible light Max @ 470 nm Fill factor 20% for front illuminated Full well capacity 24,000 e-

  23. Mass spectrometry rig (Oxford Chemistry)

  24. Comparison of PImMS and PMT • Same mass peaks seen with PImMS as with a photomultiplier tube (PMT) • 2 fragments of CHCA

  25. Velocity map imaging • N,N-dimethylformamide (DMF) is a prototype molecule for studying peptide bond cleavage. • Early PImMS data on the 193 nm fragmentation of DMF is shown below.

  26. First PImMS spatial imaging results 1 2 3 4 • Comparison:conventionalcamerato PImMS # of hits timecode

  27. PImMS2 Larger array: 324 by 324 pixels 23 mm by 23 mm active area 380 experiments/sec Potential 400,000 measurements per experimental cycle Designed to also work directly after MCP – reduced pin count for vacuum applications Improved power supply, routing and trim Submission this autumn, ready by early 2012

  28. Future work and directions Sensor characterisation: Currently working on: noise, time resolution Next: spatial resolution, time walk versus light power In Chemistry, further spatial and velocity map imaging Possible new applications: Atomic probe tomography (alloy analysis) Fluorescence imaging Larger, improved sensor PImMS2 Submission this autumn; testing in early 2012

  29. Summary PImMS is both a new technique in mass spectrometry and a specialised sensor for MS The first sensor has been proven for mass spectrometry Adding 2D sensing to a time-of-flight mass spectrum adds structural information and can increase throughput Multiple memories capture different mass peaks within one experimental cycle The second generation sensor will be ready in early 2012

  30. Thank you Acknowledgements The support of the EPSRC through Grant EP/G00224X/1, of the STFC through PNPAS award, of the RC-UK through MI-3 programme (GR/S85733/01) and a `proof of concept' grant from ISIS Innovation Ltd. are gratefully acknowledged. 30

  31. Back-up material 31

  32. Sensor calibration • Masking assists calibration by handling subsets of pixels. • 1 configuration bit per pixel disables the comparator. • Arbitrary masks are possible. Three laser pulses have been recorded here. Pixels are characterised by plotting threshold voltage versus number of noise hits. Limited floor space and manufacturing tolerances mean that pixel responses vary. Number of hits Number of hits Global mean

  33. Sensor calibration Number of hits After trimming of pixels Number of hits Global mean

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