1. Radiation Damage Studies for Solid State Sensors Subject to Mrad Doses
[T Follow-on]
Bruce Schumm
UC Santa Cruz
September 7, 2016

2. The Issue: ILC BeamCal Radiation Exposure
Covers between 5 and 40 miliradians
Radiation doses up to 100 MRad per year
Radiation initiated by electromagnetic particles (most extant studies for hadron –induced)
EM particles do little damage; might damage be come from small hadronic component of shower? 2 2

3. Radiation Damage in Electromagnetic Showers
Folk wisdom: Radiation damage proportional to non-ionizing component of energy loss in material (“NIEL” model)
BeamCal sensors will be embedded in tungsten radiator
Energy loss dominated by electromagnetic component but non-ionizing contribution may be dominated by hadronic processes

4. Hadronic Processes in EM Showers
There seem to be three main processes for generating hadrons in EM showers (all induced by photons):
Nuclear (“giant dipole”) resonances
Resonance at MeV (~Ecritical)
Photoproduction
Threshold seems to be about 200 MeV
Nuclear Compton scattering
Threshold at about 10 MeV;  resonance at 340 MeV
 These are largely isotropic; must have most of hadronic component develop near sample 4 4

5. Actual Setup In ESA Beamline
2 X0 pre-radiator; introduces a little divergence in shower
Sensor sample
Not shown: 4 X0 and 8 X0 radiators just before and after sensor

6. Daughter Board Assembly
Pitch adapter, bonds
Sensor
1 inch 6 6

7. Proposed split radiator configuration
5mm Tungsten “pre”
13mm Tungsten “post”
Separated by 1m
Fluence (particles per cm2)
1.0
2.0
3.0 7
Radius (cm) 7

8. Rastering
Need uniform illumination over 0.25x0.75 cm region (active area of SCIPP’s charge collection measurement apparatus).
Raster in 0.05cm steps over 1x1 cm, assuming fluence profile on prior slide (see next slide for result)
Exposure rate:
100 MRad at 0.75 nA and 15 GeV  ~ 6 Hours

9. Charge Collection Apparatus
Sensors
DAQ FPGA
with Ethernet
Sensor +
FE ASIC
Recently upgraded for multiple samples
P-type and N-type sensors
Float-zone and Magnetic Czochralski bulk
Will maintain 0-5o C during irradiation
Continue studies begin in 2013 9 9

10. Charge Collection Measurement
For pad sensors use single-channel readout
Daughter-board
Low-noise amplifier circuit (~300 electrons) 10 10

11. Charge Collection Apparatus
Readout: 300 ns
2.3 MeV e- through sensor into scintillator
Sensor +
FE ASIC
DAQ FPGA
with Ethernet 11 11

12. Pulse-height distribution for 150V bias Median pulse height vs. bias
Measurement time
Pulse-height distribution for 150V bias
Mean Pulse Shape
Single-channel readout example for, e.g., N-type float-zone sensor
Readout noise: ~300 electrons (plus system noise we are still addressing)
Median pulse height vs. bias 12 12

13. GaAs Charge Collection (21 Mrad Exposure)
 Try even higher annealing temperatures
 Higher exposure in next T506 run
21 Mrad Exposure
Vbias = 600 V
Slice at VB=600 vs. function annealing temp 13 13

14. PF Charge Collection after 270 Mrad
@600 V, ~20% charge collection loss (60C annealing) 14 14

15. Some Trends So Far Also, PF pad sensor irradiated to ~300 MRad
GaAs hasn’t done so well so far
SiC (not shown above) down by ~50% after 80 Mrad; maintains low current
Si Diode shows 20-60% charge loss after 300 Mrad
P-type Si diode sensors perhaps better than N-type (expected?)
Both N and P type develop substantial dark current, but probably very tolerable level (10W across entire instrument)
Irradiated with 5.7 and 21.0 Mrad doses of electromagnetically-induced showers
Also, PF pad sensor irradiated to ~300 MRad 15 15

16. But: Are electrons the entire picture?
G.P. Summers et al., IEEE Trans Nucl Sci 40, 1372 (1993)
NIEL e- Energy
2x MeV
5x MeV
1x MeV
2x MeV
Damage coefficients less for p-type for Ee- < ~1GeV (two groups); note critical energy in W is ~10 MeV
But: Are electrons the entire picture? 16 16

17. GOALS FOR THIS RUN A bunch of 300 Mrad exposures
Expose shard of N-type sensor already under development for use elsewhere in detector
New type of sensor: industrial sapphire
P-type sensor from 300 to 600 Mrad
SiC sensor to 300 Mrad
GaAs to higher exposure

18. BACKUP

19. Incorporate hadronic processes by placing
sensor at maximum of tungsten-induced shower
Up to 10W beam absorption; operate at about freezing to avoid annealing 19 19

20. Summer 2015: SiC and Further Si Exposure
SiC sensor array provided by Bohumir Zatko, Slovak Institute of Science
Irradiated to ~100 Mrad dose
Also, PF pad sensor irradiated to ~300 MRad 20 20