Displacement Damage Testing

Transcription

1 Displacement Damage Testing Christian Poivey Gordon Hopkinson

2 Outline Principle Standard, test methods Test Conditions Examples Bibliography

3 Principle Initial Measurement N p/cm 2 Irradiation CTR 0 /CTR Mitel 3C91C (device has no coupling medium) 5mA drive Vce=5V #20 initial CTR=98 #29 initial CTR=81 #49 initial CTR=54 Interim Measurement x x x x x10 11 CTR: Charge Transfer Ratio (Ioutput/Iinput) Fluence (32 MeV protons/cm 2 ) After R Reed, IEEE TNS vol 48-6, 2001

4 Test Standards There is no test standard Effects are application specific (depend on operating conditions) Annealing effects (particularly LEDs, laser diodes, optocouplers) Complex degradation modes ( particularly detector arrays) Some ASTM standards are useful for neutron testing (MIL-STD-883, method ) E Standard practice for conducting irradiations at accelerator based sources F Standard guide for neutron irradiation of unbiased electronic components F980M-96 Standard guide for measurement of rapid annealing of neutron-induced displacement damage in silicon semiconductor devices Test programme will need to be tailored to requirements

5 Irradiation Conditions Beam energy : precision << 10%. Purity : mass analyser selecting the right element Beam uniformity : scattering foils and/or sweeping the beam (e.g. 10% over the die) Dosimetry (particle counting): low flux for heavy ions, high flux for protons

6 European Test Facilities - Protons Paul Scherrer Institute, Switzerland Low energy PIF Energy range: 6 to 70 MeV Proton flux: < p/cm 2 /sec Beam spot: circle, up to 9 cm diameter, Beam uniformity: > 90% over 5 cm diameter High energy PIF Initial proton energies: 254, 212, 150, 102 and 60 MeV. Energies available with PIF degrader: quasi continuously from 35 MeV up to 300 MeV Gaussian-form initial beam profiles with minimum FWHM=6 cm. (Can be flattened) The maximum diameter of the irradiated area: φ 9 cm. Neutron background: less than 10-4 neutrons/proton/cm 2. CYCLONE, Universite catholique de Louvain, Louvain-la- Neuve, Belgium Proton beam line (LIF) 10 to 75 MeV, either by cyclotron adjustment or using plastic degrader 10% uniformity over 10 cm diameter neutron fluence/proton fluence 1-5E-4 (depending on neutron energy) Many others in Netherlands, France,

7 European Test Facilities - Neutrons CYCLONE, Universite catholique de Louvain, Louvain-la-Neuve, Belgium Monoenergetic Neutron Beam Line Energy range 25 to 75 MeV, via protons on lithium target Collimated beam Many others in France, Belgium, Sweden,

8 Choice of Particle Type and Energy If particle type can be representative of the environment then less reliance on NIEL scaling Protons for most space environment Electrons or low energy protons for solar cells Protons give both DD and TID - may need to separate the effects, but usually not so bad since: CCDs and detectors arrays can usually separate DD and TID effects LEDs (lens), optocouplers TID effects relatively small Photodiodes, laser diodes TID effects negligible, unless high dose Can do proton plus separate Co-60 test (if needed) Or else can use neutrons for DD plus separate Co-60 test Care needed to make sure NIEL scaling is valid Some neutron facilities also give gammas

9 Choice of Particle Type and Energy Protons can be used for both DD & TID, however: Bias dependence DD usually is not bias dependent, TID is bias dependent would have to do a biased proton irradiation, may anyway for photonics (to simulate annealing) but can be awkward for detector arrays TID will be sensitive to dose rate annealing mechanisms are different - not easy to do accelerated anneals. but if TID effects are small and dose is reached (or exceeded) during proton testing and biasing is representative, then it may be acceptable to perform just proton testing - but need care of overtest margin if effects are inter-dependent or non-linear with proton fluence in bipolar ICs TID can affect DD so may have to simulate with protons

10 Choice of Particle Type and Energy If particle energy can be representative of the environment then, again, less reliance on NIEL scaling choose an energy close to the peak damage energy 800 km polar orbit Differential Flux*10-4 (/MeV/cm²/day) mm Al Shielding Solar Minimum 800 km Polar Orbit 10 mm Al Shielding Proton Energy (MeV) For shielded proton environments the main energy of interest is MeV

11 Choice of Particle Type and Energy MeV is a good proton test energy particularly for GaAs devices (NIEL scaling uncertain) there is a case for using < 30 MeV because of NIEL uncertainties also good penetration depth (> 10 mm Al), but masking difficult 10 MeV also a good energy for detector arrays can mask using thin (1.5 mm) Al plates comparison with existing data For solar cells the shielding is reduced and most of the damage comes from low energy protons and electrons 1-3 MeV electrons and 3-10 MeV protons are common dependence on NIEL is different for electrons and protons, advisable to do separate tests Always ideal to test at several energies - but not always practical (e.g. funding issues)

12 Choice of Particle Energy Often can tune the beam for different energies - but takes time (recalibration etc.) or can use degraders blocks of material, e.g. Al, lexan, copper reduce energy but also produce straggling (spread in energy) can do calculations using Monte Carlo or SRIM2003 code ( set up ion and target data, number of ions and output data for transmitted ions - calculate mean and standard deviation e.g. 100 MeV protons degraded by 1 cm Al gives a mean transmitted energy of 83.6 MeV and a straggling (RMS) of 0.5 MeV

13 Number of devices/fluence steps/flux Number of test devices needs to be sufficient to cover the number of fluence steps, bias conditions and annealing tests number of irradiation steps depends on whether a general evaluation or specific for a project for imager arrays can reduce by masking the device into several fluence regions for projects, fluence should be derived from environment document (including margins). some device types show significant device-to-device variations so need to increase the number of devices (e.g. to ~10) to get good statistics e.g. LEDs, VCSELs, optocouplers usually arrange each proton irradiation step to take a few minutes particle flux ~ 5 x 10 8 /cm 2 /s no evidence for flux rate effects in this regime

14 Example of masking a CCD 60 MeV Protons 10 MeV protons

15 Irradiation Bias / Temperature No evidence for defect creation being bias dependent for DD can usually irradiate unbiased at room temperature short pins together using sockets or conducting foam sometimes irradiate at low temperatures if there is a need e.g. high flux fast neutron facility at Louvain la Neuve Annealing effects in LEDs, optocouplers, laser diodes depends on operation (injection current) can irradiate unbiased and do a separate annealing test LED Laser Diode Johnston & Miyahira, IEEE Trans. Nucl. Sci., vol. 49, no. 3 pp , 2002.

16 Device Mounting Decide how many devices can be irradiated at the same time (typical beam size: 5x9 cm) beam uniformity, masking Cables/feedthroughs air or vacuum irradiation (for < 20 MeV protons) consider noise induced by long cables Materials - some (e.g. heavy metals) become activated affects timescales for device interchange and return to the lab use low density materials where possible foam rather than sockets for shorting former materials for fibre optics nearby materials affect neutron environment (reflections etc)

17 Post Irradiation Measurements Aim is to determine damage constants, k damage depend on parameter measured and on conditions temperature, bias etc May need specialized optical equipment can t always do in situ, or within 1 hour usually OK, as long as annealing is considered Often some prompt annealing (first few minutes) maybe also some minor changes over the first few days or weeks (so recommend wait > 2 days) Recombination-enhanced annealing (LEDs etc) High temperature anneals First level analysis in real time

18 Post Irradiation Measurements Usually test for data sheet parameters but some devices are complex imager example: random telegraph signal (RTS) dark current fluctuations - not often tested for but severely limits possibilities to calibrate dark signal 4000 Dark Signal (electrons/pixel/s) E2V CCD C Baseline Level (overscanned pixels) Time (hours)

19 Example Wide Field Camera 3 E2V 2k x 4k n-ccd in front of Proton Beam at UCDavis

20 Bibliography NASA Guidelines Proton Test Guidelines Development Lessons Learned, RADECS 2003 short course notes Gordon Hopkinson, Component Characterization and Testing, Displacement Damage. IEEE NSREC 1999 short course notes Cheryl Marshall, Proton Effects and Test Issues for Satellite Designers, Part B: Displacement Effects.