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Design and Characterization of a Highly Miniaturized Radiation Monitor

This project aims to develop a chip-sized prototype radiation monitor for spacecraft, focusing on efficiency and miniaturization. The monitor uses Active Pixel Sensors for low-cost and low-energy particle detection. The ASIC design includes specifications for radiation tolerance and performance metrics for electron and proton ranges. The mechanical elements of the monitor include LID, BODY, and BASE components made from Titanium. The ASIC design features a CMOS sensor with 4T pixels in a compact array, with high radiation tolerance and low noise levels.

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Design and Characterization of a Highly Miniaturized Radiation Monitor

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  1. Design and characterisation of a Highly Miniaturised Radiation Monitor (HMRM)N. Guerrini1, R. Turchetta1, D. Griffin1, T. Morse1, A. Marshall1, O. Poyntz-Wright1, S. Woodward1, E. Daly2, A. Menicucci2, H. Araujo3, E. Mitchell31.STFC - Rutherford Appleton Laboratory, UK 2.ESA - Noordwijk, The Netherlands3.Imperial College London, UK International Workshop on Semiconductors Pixel Detectors for Particles and ImagingPIXEL 2012 – Inawashiro, Japan 6th September 2012

  2. Introduction • Application and scope • Radiation monitor architecture • ASIC design and characteristics • First results • What’s next • Conclusions Outline

  3. Data on the ionising radiation environment are very important to ensure an efficient design and operation of spacecrafts. Monitors currently in use weight more than 2Kg, require several Watts of power, are quite large (>10cm in each dimension) • STFC and IC (within the framework of a ESA technology development contract) aim to develop a “chip sized” (that is smaller, lighter and less power hungry) prototype radiation monitor suitable for application in: • Coarse radiation housekeeping • Save and alerting function • Support to platform and payload systems Introduction

  4. Radiation Monitor requirements: • Minimum number of external components • Dosimeter function • Particle Rate Meter function • Particle Species Identification function • In-flight calibration procedure • Power dissipation < 200mW • Weight <20 g • Radiation TID tolerance of at least 100kRad • Latch up free • Operating temperature range from -40 to +80°C Introduction Monitor based on Active Pixel Sensors Low cost (CMOS process) Low complexity (functionalities on integrated circuit )

  5. Low energy particle High energy Particle (MIP) Low energy particle High energy Particle (MIP) - - - - - - - + + + + + + + • When the energy deposited in the detector by a low energy particle is the similar to the energy deposited by a MIP Ambiguity • With APS sensors and judicious selection of silicon substrate thickness we can think to sample the dE/dxcurve and uniquely identify the particle species and energy. APPLICATION

  6. Conceptual design: APS telescope with low threshold for e/p discrimination • Parameters: number of sensors and shields, aperture size • Variables: energy thresholds, sensitive area, particle ranges • Optimisation with preliminary simulation geometry of particle telescope • Parameters: dimensions/materials for wafers, shields, casing, window, algorithms • Variables: thresholds, effective area, efficiency and purity for PID • Validation with full simulation geometry in 5 reference orbits • Parameters: algorithm tables (on-board and ground segment) • Variables: ID purity, pile-up probabilities, dosimetry functions, spectral reconstruction 1 2 3 APPLICATION CAD G4HMRM v1.0

  7. electrons SIMULATED PERFORMANCE SUMMARY • Electron range: 0.063 to 6 MeV • Proton range: 1.3 to 500 MeV • Maximum omni/d flux: 1x108 cm-2s-1 • Dosimetry • Count rate on front sensor • Dose rate on all sensors • Also cumulative lifetime doses • On-board alerting functions • 3 programmable particle ‘channels’ • Offline spectral reconstruction • Electron/proton energy spectra protons APPLICATION

  8. Three main mechanical elements of the HMRM chassis LID: Provides the prescribed geometry for detector telescope. Mounts the window (for visible blindness) BODY: Main structural housing around electronics BASE: structural interface to spacecraft ARCHITECTURE Fabricated in Titanium - Mass 52g (including fasteners and connector)

  9. Flex rigid PCB design • Four rigid boards • Interface PCB • Interface connector PCB • FPGA PCB • Detector PCB ARCHITECTURE

  10. ASIC DESIGN CMOS sensor for a Highly Miniaturised Radiation Monitor (HMRM). Main specifications. • 0.18 µm CMOS Image Sensor technology • 20 µm 4T-pixels in a 50 x 51 array • Snapshot and correlated double sampling (CDS) • Frame rate up to 10,000 fps • Column-parallel 3-bit single-ramp ADC, with in-column trimming • Digital readout, plus analogue readout for debugging • Integrated DAC for voltage/current generation • Band gap • Temperature sensor 

  11. ASIC DESIGN 3T vs 4T • Simplest active pixel • Higher noise • Well proven, high radiation tolerance • Most popular active pixel • Low noise • Good radiation tolerance The radiation tolerance requirements for HMRM are well within the 4T pixel measured range.

  12. ASIC DESIGN FORTIS CMOS 0.18 µm – 4T sensor 12 µm epi thickness with 1kWcm resistivity 15 µm pixel Most probable noise: 3.6e- Noise histogram (measured with Photon Transfer Curve) Average noise: 4.5e- S/N =118 Conversion gain at output: 65.0μV/e- Linear full well capacity: 17,900e- Landau distribution (from beam test results) Noise (in e-, before board noise correction)

  13. ASIC DESIGN Radiation Hardness

  14. ASIC DESIGN • 60 sensors manufactured on 12 µm, low resistivity epitaxial substrates • 60 sensors manufactured on 12 µm, high resistivity (>1kOhm cm) epitaxial substrates • Design for radiation tolerance: • Total dose • Single event upset immunity

  15. ASIC DESIGN The sample values from the pixels and the reset values are readout in snapshot mode and stored onto sampling capacitances at the top and at the bottom of the array. The sampling control logic allows to sample and reset the pixels independently, hence controlling the pixel shuttering.

  16. ASIC DESIGN • One comparator per column (readout on both sides) • Seven 7-bit programmable thresholds • One 8-bit DAC for each comparator trimming adjusting The ADC ramp is generated from the 7 programmable thresholds. The comparator output is sampled 7 times (for each ramp level). The result is then converted into a 3 bits value. In this way the output data will tell us between which thresholds the pixel value is.

  17. ASIC DESIGN • 3-bit encoder per comparator • Data read on a 9 bit bus  2*17=34 clock cycles for readout • plus one clock cycles for temperature sensor data (9-bit) • Test input to the entire shift register • Triple majority voting (TMV) system for single event upset immunity. • TMV used for programming and readout shift registers, except in shift register controlling the analogue readout. • Enclosed geometry layout for total dose tolerance (entire chip).

  18. Photon Transfer Curve method, measured through analogue test output: • Gain = 59.9 µV /e- (exp. 51.2) • Noise = 16.8 e-rms (exp. 13.5) • Cin = 2.1 fF (exp 2.3) • Full well = 14,600 e- • Full well (lin) = 6600 e- • Expected performance on data path: • Gain = 40.3 µV /e- • Noise = 13.9 e- rms • S/N (m.i.p.) = 69 RESULTS

  19. Complete digital characterisation with light • Test of 2nd iteration (end of September) • Tests under irradiation (2nd iteration) • Temperature tests (2nd iteration) FUTURE WORK

  20. CMOS image sensors provide new solutions to radiation detection • High radiation tolerance • Highly Miniaturised Radiation Monitor (HMRM) based around a CMOS image sensor now in development • Measured noise = 16.8 e- rms S/N (m.i.p.) = 69 • HMRM instrument about to be tested • with sources • 2nd iteration on (end of September) its way with reduced power consumption and improved cross-talk and reliability. CONCLUSIONS

  21. Thanks!!! http://dsc.stfc.ac.uk/Default.aspx

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