Advances in CMOS Solid-state Photomultiplier Detectors

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Advances in CMOS Solid-state Photomultiplier
Detectors
 
Christopher Stapels, RMD Inc., 44 Hunt St
Watertown, MA 02472

• Topic Outline
• Low light detection and detectors
• Radiation spectroscopy with SSPMs
• Component integration
• Advanced devices

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Low light detection

• Biology (fluorescence detection, fluorescence
  lifetime imaging bacteria, DNA, and spore
  detection)
• Chemistry (chemiluminescence, laser spectroscopy)
• Physics (Particle detection, radiation
  monitoring)
• Border Security, automotive sensors, personal
  dosimetery, optical signaling (telecom)
• Space Solar particle monitoring and Dosimetry

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Low light detectors

• PMT low dark current, high gain, Vacuum, large
  form factor, low QE, high voltage
• Photodiode small form factor, low power, low
  gain, high noise
• CCD High QE, high fill factor, low gain, slow
  readout, not CMOS compatible
• APD medium gain, large area, small form factor
  medium noise, excess noise, dark current, high
  voltage
• SSPM High gain, small form factor, CMOS
  compatible, low power, dark noise,
  excess noise, fill factor limits.

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Geiger Photodiodes

• Geiger photodiode Avalanche photodiode biased
  above reverse bias breakdown voltage
• Integrated resistor provides passive quenching
• Each individual pixel has a binary output
• Large gain (gt106), fast rise time

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Solid-State Photomultiplier

• Parallel array of Geiger Photodiodes is an SSPM
  Solid-State Photomultiplier
• SSPM output is proportional to the number of
  photons detected
• Low power, small form factor, robust detector
• CMOS fabrication provides process control and
  cost gains with quantity

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SSPM-based Spectrometer

• Scintillator illuminates high-gain photodetector
• SSPM provides spectral information
• Solid-state solution eliminates PMT
• CMOS environment allows on-chip integration of
  readout components

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Radiation Detection

• Particle detection determined by scintillator
  material
• High-energy charged particles, gamma-rays,
  neutrons

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Signal output

• Signal size depends on
• Nttl Number of incident photons
• QE Quantum efficiency
• Pg Geiger probability (excess bias)
• CJ Junction capacitance (temperature)
• VA-VBExcess bias (temperature)

p - n well - p-epi
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SSPM Noise Sources

• Readout noise (negligible due to high gain)
• Dark noise from thermally generated events (not
  time correlated)
• Excess noise
• Crosstalk
• After pulsing
• Gain fluctuations

?nd? number from dark ?nt? total pixels
triggered
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Integrated Signal Processing

• Comparator at each pixel controls gain
  fluctuations
• Pulse height determined by comparator, not excess
  bias
• Adjustable gate output allows integration and
  reduced afterpulsing

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Photon Counting

• Clearly delineate from 0 to 200 photons
  (compared to 30 without conditioning)

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Circuit integration

• Dosimeter on-a-chip
• 300 conditioned pixels
• Seven 16-bit counters and a slow clock
• Pulse height determination
• Temperature feedback

SSPM
Encoder
Out MUX
RAM
32-bit chip
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Large Area Devices

• 10 x 10 mm monolithic device, 46 fill factor
• 50k pixels for large dynamic range
• Integrated temperature monitor

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Position Sensitive Devices

• Provides position sensitivity using charge
  division on four readout wires
• 50 mm position resolution

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Back Illumination Improved active area

• 3 mm x 3 mm devices thinned to 50 mm and 20 mm.
• Surface scan with focused illumination shows fill
  factor improvement
• Dark count rate unaffected

Bulk Si
P-epi
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Back Illumination Improved QE
Depth (mm)

• Quantum efficiency increase shifts to shorter
  wavelengths
• Net improved QE in long wavelengths from FF and
  QE improvement
• Front side Etalon effect removed

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Summary

• Single photon detectors in CMOS can work for low
  light detection applications
• CMOS environment allows integrated processing and
  ancillary circuitry
• SSPMs can allow low cost nuclear spectroscopy on
  a chip
• Fill factor and sensitivity improvements expected

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Acknowledgement

• NASA, DOE, DOD, and NIH
• CMOS layout by Augustine Engineering

Jim Christian, Erik Johnson, Eric Chapman,
Sharmistha Mukhopadhyay, J Chen, Mikel McClish,
Kanai Shah, Purushottam Dokhale
Instrument Research Development
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Low T
Instrument Research Development
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Dosimeter on a chip

• Pulse-height information required for accurate
  calculation of dose
• Dosimeter-on-a-chip distills and stores pulses in
  on-board RAM

241Am 60 keV 57Co - 122 keV
22Na 511 keV
32-bit chip