Types of Infrared Detectors

1
Types of Infrared Detectors

• Photon
• photoconductors
• photovoltaic
• high performance requires cooling to minimize
  dark current
• Thermal
• Bolometers - R(T) resistance changes with
  temperature
• Pyroelectric - Ps(T) spontaneous electric
  polarization changes with temperature
• Thermopile - junction potential changes with
  temperature
• do not require cooling

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Why Uncooled Infrared Detectors?

• Applications of Thermal Imagery
• Nightvision
• transportation- consumer market cars, trucks,
  boats, aircraft
• firefighting - see through smoke, detect hot
  spots
• military, security and policing - surveillance
  and target tracking
• Radiometry
• medicine - thermal imagery - blood flow, tumor
  detection
• manufacturing - monitor temperature
• Demand for Low Cost IR Cameras

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Medical Imaging
Transportation and Security
Human Chest
Photo from Raytheon VOx FPA
4
First generation uncooled infrared cameras
developed by Raytheon appeared in the 2000 model
year Cadillac to provide a nightvision drivers
aide.
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Blackbody Spectral Radiance
6

• Thermal Model

• Micromachined thermal isolation structures to
  reduce thermal conductance

7
Noise Effects on Temperature Resolution

• Background Noise Limited Detectivity for TDTBT
  is 1.8 x 1010 cm Hz1/2/W at 300 K.
• Noise Equivalent temperature difference where
  (DP/DT)l1-l2 2.6x10-4 W/cm2K for 8-14 mm
  atmospheric window

NETDmin 1 mK
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NETD
Comparing the background noise limited NETD to
the detector temperature for different scene or
background temperatures shows that there is
little benefit to cooling the detector if 300K
scenes are being imaged.
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NETD
Comparing NETD versus the thermal isolation shows
that reducing the detector temperature means less
thermal isolation is required.
10
Uncooled Detector Issues

• Use Si-micromachining techniques to fabricate
  suspended detector structures - polyimide
  sacrificial layer Tplt 500C
• Use CMOS substratesTplt400C
• Thermal budget problem since many good uncooled
  detector material require high temperature
  processing
• VOx, lead titanate pyroelectric materials, MnO
  CMR, a-Si