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Advanced CMOS Pixel TechnologiesPresented
by
Yashashree WaseGraduate Student, Electrical Engineering
Contact: [email protected]
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Outline• CMOS image sensor (CIS) technology - Review• CMOS pixel types• Comparison between pixel architectures• Recent technologies and developments• Future prospects
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CMOS Image Sensor (CIS)
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CMOS image sensor (CIS) Floorplan
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
•“Achilles’ Heel” of CCD technology – The need for perfect charge transfer•Low power consumption•High integration capability•System-on-chip: miniaturization•Cost-effective
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CMOS Image Sensors Classification• Charge integration sensors• Passive pixel sensors(PPS)• Active pixel sensors(APS)
• Non-integrating sensors• Retina-like sensors• Other functions
• So many other architectures based on the applications
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CMOS Image Sensor (CIS)
Passive Pixel
Active Pixel
Hybrid Pixel
PD-APS PPD-APSPG-APS
HPDPG Dual PixelHybrid IRPD-PPS PG-PPS
Log-APS CTIA-APS CAPS
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First CMOS Imagers
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A Photodiode type PPS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
• PPS pixel structure is similar to DRAM
• Large fill factor• PPS are based on photodiodes
without internal amplification• External readout circuitry on chip• Large smear• Large kTC noise• Large column FPN
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Active Pixel Sensor (APS)
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• Active amplifier within a pixel• 3T PD APS and 4T PD APS• Transversal signal line (TSL)• Overcomes SNR issue of PPS• kTC noise exists• Photodetection and
photoconversion regions are sameA 3T Photodiode type Active Pixel Sensor schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
Eric R. Fossum
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Photogate-Type (PG) APS
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A Photogate type APS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
• Combines CCD charge transfer• Readout inside a pixel• Signal charge is integrated under
photogate• Correlated Double Sampling (CDS)• High performance and low-light
applications
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Quick Comparison
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Source: Photobit Tech., Eric Fossum, “CMOS Image Sensors.pdf”, http//:www.ericfossum.com
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PPD APS and PPG APS• Pinned Photodiode and Pinned Photogate APS• Physical p+ layer – complex fabrication• Fixed VPIN voltage based on doping concentration• High quantum efficiency• Low dark current• Lower pixel noise• Widely used in industry• Low light imaging – astronomy and biotechnology
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Photodiode-Type Logarithmic APS
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A Photodiode type logarithmic APS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
• Non-integrating pixel• Logarithmic response – non-linear
output• Increase on intrascene DR• High dynamic range Applications• Retina like sensors – silicon retinas• Slow response under low light • Large FPN
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Comparison Between Pixel ArchitecturePPS 3T-APS 4T-APS(PD) 4T-APS(PG) Log
SensitivityDepends on the
performance of a charge amp
Good Good Fairly Good Good but poor at low light level
Area consumption Excellent Good Fairly Good Fairly Good Poor
Noise Fairly good Fairly good (no kTC reduction) Excellent Excellent Poor
Dark Current Good Good Excellent Good Fairly good
Image LAG Fairly good Good Fairly good Fairly good Poor
Process Standard Standard Special Special Standard
Note Very few commercialized
Widely commercialized
Widely Commercialized
Very few Commercialized
Recently Commercialized
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Source: Jun Ohta, “Smart CMOS Inage Sensors and Applications,” CRC, 2008
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Shared Pixel
• Two-way shared PPD-APS – 2.5 T architecture• Four-way shared PPD-APS – 1.75 T architecture• Eight-way shared – 1.35 T architecture• PPD APS – 3T, 4T, 2.5T, 1.5T, 1T
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PD-Type Shutter APS
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• Addition of shutter transistor• High speed applications• Shutter efficiency is very
high• Shutter node active pixel
(SNAP)• CMOS SNAP
(Efficiency>99.9%)• Global Shutter
A Photodiode type shutter APS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
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Thin Film on ASIC (TFA) Pixel
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• Higher absorption coefficient• Improve sensitivity• High dynamic range and high fill factor
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
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PD-Type CAPS APS
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• Complimentary active pixels sensors
• Reset transistor replaced by PMOS
• Complimentary outputs Voutp & Voutn
• Highly integrated• High performance• Alternative to conventional APS
A Photodiode type CAPS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
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PD-Type CTIA APS
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• Capacitive transimpedance amplifier APS
• Achieve low FPN by using divider circuit with switched capacitor voltage feedback
A Photodiode type CTIA APS schematic
Source: M. Bigas, E. Cabruja, J. Forest, and J. Salvi, “Review of CMOS image sensors.” Microelectronics Journal, 37(5):433-451, 2006
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Differential APS
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Differential APSSource: Jun Ohta, “Smart CMOS Image Sensors and Applications”, CRC 2008
• Suppress common mode noise• Uses pinned PD and PMOS SF• In-pixel CDS to reduce noise• Increased reset and readout
noise• Ultra low light detection
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Geiger Mode APD
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APD in standard CMOS technologySource: Jun Ohta, “Smart CMOS Image Sensors and Applications”, CRC 2008
• Single photon avalanche diode (SPAD)
• Ultra low light detection
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CMOS APS SFG
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J. Nakamura, S. E. Kemeny, and E. R. Fossum, “A CMOS active pixel image sensor with simple floating gate pixels,” IEEE Trans. Electron Devices, vol. 42, pp. 1693–1694, Sept. 1995
• Simple floating gate• No kTC noise and no image lag• High blooming overload
protection• Non-destructive readout (NDRO)• Drawbacks of floating gate
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Hybrid CMOS Pixels• Hybrid Photodiode-Photogate Pixel (HPDPG)
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Standard Photodiode
Pixels
Source: SIIMPEL, Eric Fossum, “Adventures with Image Sensors.pdf”, http//:www.ericfossum.com
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Recent Technologies and Development
• Dual Pixel Sensors• EOS 70D: Dual Pixel CMOS AF• Dual Sensitivity Pixel Technology
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Source: www.imaging-resource.com
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Future Prospects
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• JOT based sensors• Quantum Image Sensors• Quantum dots
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Thank you!
Your questions are valuable!
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