Measurements on Single and Poly Crystal CVD Diamond Sensors

1
Measurements on Single and Poly Crystal CVD
Diamond Sensors

• Christian Grah, Desy
• FCAL Workshop
• 12-13 February
• Cracow

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Contents

• Low dose rate irradiation of polycrystalline CVD
  sensors, measure the Charge Collection Distance,
  CCD vs dose
• E64
• Desy7
• Single crystal diamond
• IV
• Individual spectra
• CCD vs HV/time
• Summary outlook

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Low Dose Rate Irradiation

• Usually irradiation in our laboratory is done by
• Irradiation with closest possible distance
  between source and sensor (typically 2.6 cm) to
  achieve high dose rate.
• Measure the CCD of the sensor in regular time
  intervals with a reasonable distance to prevent a
  high double hit rate (typically 7.5cm).
• This enables for reproducible measurements on a
  timescale of several days to get into the 100 Gy
  range of accumulated dose.
• BUT need of an operator
• LOW DOSE RATE IRRADIATION gt automatic CCD
  measurement at low dose rate, but needs much more
  time.
• Did this at the time of the TAU workshop 2005.

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CCD Measurement

• Use the high energetic part of a Sr90-ß- source
  gt MIP spectrum.

?t 30min
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E64 Irradiations

• Have done 2 irradiation periods with different
  dose rates

29.8. 5.9. (7d)
6.9. 9.11. (64d)
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Desy7 and Desy8

• Got these two new samples in Nov. 06.
• The samples are 300 µm thick and 12x12 mm in
  size.
• The metallization is 10x10 mm in size divided
  into 4 pads on one side.
• 100 nm Ti 200 nm Pt 500 nm Au.
• Material selection was with focus on avoiding
  micro cracks.

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Desy7 and Desy8 (cont.)

• pCVD Diamonds from Freiburg (Fraunhofer IAF)
• Main issue from former samples
• micro cracks
• IV behavior
• CCD performance
• CCD vs irradiation
• Large part of the measurements were presented by
  K. Afanaciev. Much better performance than
  earlier samples.
• Issue of signal decreasing with time.

FAP7 series
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Spectra of Desy7
Shortly after switching the high voltage a large
signal is measured.
Took pedestal as determined by the early
measurements and fixed it for the rest.
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Low Dose Rate Result
switching voltage
Stable signal!
22.12.05- 11.1.06
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BDS7 - IV

• Started to investigate a sCVD Diamond.
• Got the sample (BDS7) in December from the GSI
  Darmstadt.
• 5 x 5 x 0.318 mm3 Cr(50 nm)Au (100 nm) or
  Ti(30nm)Pt(50nm)Au(100nm)

known breakthrough
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Mip signal of BDS7
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BDS7 CCD
thickness
The single crystal diamond shows a high (100)
and stable (t) signal even at low E-field.
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Summary

• Have tested sensors from E6 and IAF (Freiburg) up
  to highest doses so far in our lab (gt250 Gy).
• Desy7 and Desy8 show a small but stable signal
  and did not show any microcrack related problem.
• Started to test a single crystal diamond (sCVD)
  from E6.
• Superior efficiency at low E-field and very
  stable behaviour of the sCVD sample.

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Outlook

• We will get pCVD samples back from Freiburg with
  annealed (10min_at_500C) metallization. Expected
  this week.
• Waiting for new thin samples from Freiburg from a
  dedicated wafer with reduced nitrogen
  concentration during growth.
• We will have a testbeam period (end of April) at
  the TU Darmstadt DALINAC (10MeV and 15Gy/s) and
  will investigate high dose behavior of diamonds.
• sCVD diamonds are interesting but they are not
  (yet) available on waferlevel. Will follow the
  development of this technology.