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Imaging beyond the visible An Overview of Short-Wave Infrared (SWIR) Technology for Machine Vision
Paul Maria Zalewski, Business Development Manager5th November 2014, Stuttgart
Contents
Short-wave Infrared Technology
Differences between SWIR and CCD/CMOS cameras
Industrial Applications & Benefits of Short-wave Infrared- Semiconductor- Photovoltaics- Glass Industry- Plastic Sorting with Hyperspectral Imaging
Conclusion
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What is Short-wave Infrared?
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SWIR900-2500nm
Visible400-750nm
NIR750-1000nm
2,500400 750 1,700900 1,000Wavelength [nm]
CCD/CMOS
NIR Enhanced CCD/CMOS
Standard InGaAs
2,200
Extended InGaAs
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What differs a SWIR camera from a classic Machine Vision camera?
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Cooling CapabilityDue to the higher Dark Current of InGaAs sensors, cooling is necessary
InGaAs DetectorSensitivity between 900 and 1,700 nmHigh complexity level in the production processDefect pixels on every sensorNon-uniform pixel behavior Higher dark current than CCD, CMOS
More IntelligenceAdvanced image correction featuresNon-uniformity correction (NUC)Defect Pixel CorrectionBackground Correction
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2
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Basic Structure of a SWIR Camera
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InGaAsSensor
Optics&
Filters
Sensor Cooling
Intelligence &
Electronics
Interface&
I/O Control
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Effect on the Image Quality with Cooling and more Intelligence
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Sensor Temp. +40°C 100ms Exposure Time1
Apply Cooling Sensor Temp. -5°C2
Increase Exposure Time 800ms3
Apply IntelligenceNon-Uniformity Correction (NUC)4
Apply more IntelligenceDefect Pixel Correction5
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A Selection of SWIR Applications
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Industrial Machine Vision
Semiconductor Photovoltaics Chemical (gas, plastic, foil) Pharmaceutical Glass Production Agriculture Food
Scientific & Medical
Optical Coherence Tomography Microscopy Hyperspectral Imaging Laserbeam Profiling Airborne Remote Sensing Art Inspection
Security & Traffic
Surveillance Vision Enhancement Night Vision Homeland Security
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Semiconductor Industry
Applications
Silicon Crystal & Ingot Inspection
Wafer Inspection
Wafer Level Packaging
3D-IC Defect Inspection with Infrared Microscopy
Photon Emission Microscopy
Photovoltaics
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What makes SWIR so special for Semiconductor Inspection?
Silicon gets transparent at wavelengths above 1,100 nm
SWIR has a great sensitivity at 1,000 nmInGaAs CameraQE of ≈ 76% at 1,000 nm
CCD/CMOS NIR Enhanced CameraQE of ≈ 3% at 1,000 nm
The higher the thickness of the wafer (≈ >20µm), the more reasonable is an InGaAs camera
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76%
3%
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Luminescence imaging helps to identify non-uniformities in the silicon wafer or solar cell by forcing it to emit light:
Electroluminescence (EL)
Photoluminescence (PL)
Some emission effects to characterize photovoltaics intermediates are only visible in SWIR …
… or partially with CCD/CMOS, but with extreme long exposure times (Seconds instead of Milliseconds)Thinfilm based solar cells show other effects
- e.g. Copper Indium Diselenide (CIS) at a wavelength of 1,330 nm
What makes SWIR so special for Photovoltaics Inspection?
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Glass Production
Hot-End Glass InspectionMonitoring of glass temperatureuniformities and cooling rate
Interior and exterior inspection
Improvement of yield and quality
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What makes SWIR so special for Hot-End Glass Inspection?
Typical: Temperature Measurement between 250°C to 800°C
Based on the Planck’s radiation lawExtended Temperature Measurements possibleSWIR cameras can image through glass
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Reference temps:White hot steel ~1200 °CMelting point of aluminum 660 °CWater boils at 100 °CUncooled camera at 38 °CHuman body at 37 °C, radiates at ~ 10 μmWater freezes at 0 °C
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Hyperspectral Imaging (HSI)
HSI combines digital imaging with spectroscopy to obtain detailed information across multiple ranges of the electromagnetic spectrum
Applications:Recycling & Plastic Sorting
Geology & Mineral Inspection
Pharmaceutical Quality Control
Food & Agriculture
Medical e.g. Disease Diagnosis
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What makes SWIR so special for Hyperspectral Imaging?
Each inorganic material has a differentchemical composition and crystallinestructure resulting in an unique spectralresponse corresponding to its specificlight absorption characteristics
Illustration shows the unique information content of five different sorts of plastic starting with 1,000 nm
In general, the higher the wavelength in the application, the higher the spectral information content
- 400 nm to 1,000 nm (basic information)
- 900 nm to 2,500 nm (extended or unique information)
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Source: Middleton Research
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Conclusion
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There are basically three technical differences between SWIR and CCD/CMOS cameras
Photon detector material (InGaAs vs. Si)
Cooling capabilities needed to reduce noise
More Intelligence: Advanced image correction features
Take SWIR into consideration and explore your application with new eyes!
SWIR cameras offer new physical effects in the Short-wave Infrared spectrum
SWIR helps you to improve the yield in terms of quality, as well as productivityDetect defects more accurately and much faster
Extraordinary reduction of exposure times
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Thank you very much!
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Paul Maria ZalewskiBusiness Development Manager– Infrared & Scientific –
Allied Visionwww.alliedvision.com
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