PowerPointPrsentation

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Timing measurements with Silicon Drift Detectors
Gabriele Schächner
25.04.2006
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Outline

• Introduction on Silicon Drift Detectors (SDD)
• operating principle
• properties of SDDs
• Timing measurements
• my Diploma thesis

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Introduction

• SDDs were proposed in 1984 by Gatti and Rehak
• position-sensitive detectors with high resolution
• ? position determined trough drift time and
  segmentation of the charge collecting electrode
• detectors for fast ionising particles and X-ray
  spectroscopy

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Sideward depletion concept

• starting point reverse biased pn-junction (a)
• depletion of n-type silicon bulk through a small
  anode on one side and two p contacts (b,c)

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Operation Principle

• for high enough voltages bulk fully depleted ?
  no free charge carriers in bulk
• incoming photon / particle generates free
  electrons
• ? free electrons move to potential minimum
  (position depends on applied voltages)

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Drift Field

• transport of signal charges to anode through
  drift field parallel to surface
• ? voltage difference between drift rings /
  stripes applied

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Integrated J-FET

• good energy resolution because of small anode
  capacitance(? low noise)
• capacitance independent of active area
• J-FET integrated on chip to minimize
  capacitance between anode and first
  amplification step

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Fe55-Spectrum
5.9 keV

• spectrum of Fe55 source obtained by SDD at -10C

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Different types of SDDs
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Properties of SDDs

• energy resolution 125 eV _at_ 5.9 keV
• quantum efficiency gt 90 _at_ 0.3-10 keV
• peak to background ratio 103-104 (depending on
  detector type)
• count rate capability up to 106 cps
• radiation hardness gt 1013 photons _at_ 18 keV
• low bias voltage

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Timing Measurements

• good time resolution important for coincidence
  measurements and drift time measurements
• time resolution limited by
• noise
• SDD drift time
• preamplifier rise time
• timing measurements with electron signal (only
  small detectors) and hole signal from backside
  possible

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Time Jitter

• Equivalent Noise Charge
• zero-crossing derivative

• time jitter

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n order of semi-gaussian filter
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Experimental Setup
Schematic of the chain used for the timing
coincidence measurement
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Time Resolution
Timing resolution with a signal of about 65.000
electrons

• Measured timing resolution with signal charge
  created by laser pulses

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Timing with hole signal
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Results

• measured time resolution with an IR laser (l
  904 nm)

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My Diploma-Thesis

• goal measure time and energy resolution with
  electron and hole signal of SDDs as a function
  of
• position
• power
• temperature
• statusexperimental setup nearly ready for first
  measurements

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box with x-y-desk
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board inside the box
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mounted SDDs
cap and socket
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Summary

• operation principle
• photons / fast particles generate free charges in
  fully depleted bulk of detector
• drift field move signal charges to anode
• detector capacitance is small (i.e. noise is low)
  and independent of active area
• SDDs have a good energy resolution
• position determined with the drift time of the
  electrons
• SDDs show also good timing properties, but
  further measurements are necessary

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References

• talks from L. Strüder, H. Soltau, P. Lechner and
  C. Fiorini
• E. Gatti, P. Rehak, Nucl.Instr. and Meth. A 541
  (2005) 47
• A.Castoldi, E. Gatti, Ch. Guazzoni, Nucl. Instr.
  and Meth. A 518 (2004) 429
• C. Fiorini, et al., IEEE Trans. Nucl. Sci. 51
  (2004) 1091