Displacement Damage Mechanism and Effects

Transcription

1 Displacement Damage Mechanism and Effects Christian Poivey Gordon Hopkinson

2 Outline Introduction Mechanism NIEL concept Terms and units Effect of Defects Device Effects, examples System Level Effects Bibliography

3 Introduction Semiconductor materials (Si, GaAs,..) are usually crystalline Space environment consists of energetic particles which can pass through shielding Leads to disruption in the lattice structure and device damage Damage degrades electrical performances of the device

4 Displacement Damage Vacancies and interstitials migrate, either recombine ( ~90%) or migrate and form stable defects (Frenkel pair) I V V Stable Defect

5 Displacement Damage Energy of recoils (PKA spectrum) is determined by the collision kinematics electrons produce low energy PKAs low energy protons (< 10 MeV in Si, higher in GaAs) : Coulomb (Rutherford) scattering dominates low energy PKAs isolated (point) defects E neutrons and higher energy protons - nuclear elastic scattering and nuclear reactions (inelastic scattering) flat PKA spectrum E cascades & multiple cascades above ~ 20 MeV in silicon, inelastic collisions tend to dominate

6 Cascades 50 kev PKA is typical of what can be produced by a 1MeV neutron or high energy proton Threshold displacement energy in Si: 21 ev After Johnston, NSREC short course 2000

7 Non Ionizing Energy Loss (NIEL) Final concentration of defects depends only on NIEL (total energy that goes into displacements, about 0.1% of total energy loss) and not on the type an initial energy of the particle Number of displacements (I-V pairs) is proportional to PKA energy Kinchin-Pease: N=T/2T D ; T: PKA energy; T D : threshold energy to create a Frenkel pair) In cascade regime the nature of the damage does not change with particle energy- just get more cascades nature of damage independent of PKA energy

8 Non Ionizing Energy Loss (NIEL) Assume underlying electrical effect proportional to defect concentration (Shockley Read Hall theory) Damage constant depends on device and parameter measured damage = k damage x displacement damage dose NIEL( E) dφ( E) de de

9 Terms and Units NIEL (displacement kerma = Kinetic Energy Released to MAtter) kevcm 2 /g or MeVcm 2 /g displacement damage dose DDD DDD= NIEL(E)dΦ(E)dE (kev/g or MeV/g) de Displacement damage equivalent fluence DDEF (monoenergetic beam) F E0 = (NIEL(E) dφ(e)de NIEL(E0) de e.g. 10 MeV protons/cm 2 or 1 MeV neutrons/cm 2

10 NIEL - Silicon Protons Protons Neutrons Dale et al. Huhtinen and Arnio Akkerman et al. Jun Vasilescu & Lindstroem ASTM E 722 NIEL, (kevcm2/g) 10 1 Neutrons Electrons Summers et al. Akkerman et al. 0.1 Electrons Particle Energy (MeV) Si

11 NIEL - GaAs NIEL (kevcm 2 /g) Protons Neutrons Summers et al. Akkerman et al. Summers et al. Akkerman et al. Akkerman et al. ASTM E Electrons GaAs Energy (MeV)

12 Effect of Defects Conduction Band E DONOR E C E t E V Valence Band Generation Recombination Trapping Compensation Tunneling Leakage Current Minority Carrier Lifetime CTE in CCDs also Carrier Removal Carrier Removal Leakage Current especially if narrow bangap and high electric field Also: scattering at defects reduces carrier mobility, but only at vey high fluences

13 Device Effects Lifetime Damage Minority carrier lifetime 1 = τ 1 τ 0 + φ K affects bipolar ICs (e.g. wide base regions in lateral & substrate pnp transistors, > MeV p/cm 2 ) reduces detector responsivity (decrease in diffusion length, (Dτ) 1/2 ) reduces efficiency of solar cells reduces light output of LEDs (non-radiative recombination) threshold current increase in laser diodes reduction of current transfer ratio (CTR) in optocouplers LED, phototransistor and coupling medium can be affected sensitive devices can degrade at MeV protons/cm 2

14 Device Effects Majority Carrier Removal approximate carrier removal rates Particle Silicon GaAs 1 MeV 0.15/cm 0.6/cm electrons 50 MeV 12/cm 30/cm protons effect depends on doping (and whether n- or p- type) for doping of /cm 3, carrier removal starts to be important for 50 MeV proton fluences ~ p/cm 2 but lightly doped structures can degrade at lower fluence (e.g. i- region of a p-i-n diode: due to leakage currents p/cm 2 ) but p-i-n diodes harder than conventional diodes since not sensitive to lifetime effects - collection by drift rather than diffusion type inversion (n- to p-type) in detectors & increase in depletion voltage carrier removal important for solar cells at high fluence

15 Device Effect - Summary Technology category sub-category Effects General bipolar BJT hfe degradation in BJTs, particularly for low-current conditions (PNP devices more sensitive to DD than NPN) diodes Increased leakage current increased forward voltage drop Electro-optic sensors CCDs CTE degradation, Increased dark current, Increased hot spots, Increased bright columns Random telegraph signals APS Photo diodes Photo transistors Increased dark current, Increased hot spots, Random telegraph signals Reduced responsivity Reduced photocurrents Increased dark currents hfe degradation?? Reduced responsivity?? Increased dark currents?? Light-emitting diodes LEDs (general) Reduced light power output Laser diodes Reduced light power output Increased threshold current Opto-couplers Solar cells Silicon GaAs, InP etc Reduced current transfer ratio Reduced short-circuit current Reduced open-circuit voltage Reduced maximum power Optical materials Alkali halides Silica Reduced transmission

16 Device Effects - Examples Voltage Regulator Rax et al. IEEE Trans. Nucl. Sci. vol 46(6), pp , 1999

17 Device Effects, Example 1.20 Mitel 3C91C (device is made no coupling medium) mA drive Vce=5V #20 initial CTR= #29 initial CTR=81 #49 initial CTR=54 CTR 0 /CTR Optocoupler E+00 2.E+10 4.E+10 6.E+10 8.E+10 1.E+11 Fluence (32 MeV protons/cm 2 ) Reed et al. IEEE Trans. Nucl. Sci. vol 48(6), pp , 2001

18 Device Effects - Examples LED Johnston NSREC200 Short CourseNotes

19 Device Effects - Examples CCD Dark Image: dark spikes & CTI damage 1.8E10 10 MeV p/cm 2

20 Materials Effects Effects in materials (insulators, optical glasses, biological samples) are usually considered to be dominated by ionization processes only a small fraction of the particle energy goes into displacements materials like insulators and glasses are disordered with no well defined crystal structure (will contain many defects before irradiation) However displacement damage effects cannot be ruled out, particularly at the end of the particle track Displacement damage effects in photonic crystals tend to occur only at very high fluences

21 Photonic Crystal

22 NIEL deviations: GaAs devices Walters et al., IEEE Trans. Nucl. Sci., vol. 48, pp , 2001 But NIEL scaling is a good first approximation removes most of the energy (and particle) dependence without it, testing/prediction would be much more complicated

23 System Level Effects Sensor degradation important for payloads and star trackers but usually a gradual change in performance but difficult to calibrate (e.g. RTS and CTI effects in CCDs) CTI effects for Chandra CCDs Optocouplers have failed in space applications Topex Poseidon, failures in optocouplers in thruster monitoring circuits at 2 x p/cm 2 optocouplers used in many types of circuit (e.g. DC- DC converters) Solar cell degradation or failure

24 Bibliography RADECS short course notes 2003 Gordon Hopkinson Radiation Engineering Methods for Space Applications, part 3B: Radiation Effects and Analysis, Displacement Damage IEEE NSREC short course notes 1999 Cheryl Marshall Proton Effects and Test Issues for Satellite Designers, Part B: Displacement Effects 2000 Allan Johnston Optoelectronic Devices with Complex Failure Modes