Advanced CMOS Pixel Technology - Yashashree Wase

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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


• 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


Eric R. Fossum

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Photogate-Type (PG) APS

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A Photogate type APS schematic


• 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


• 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


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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


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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


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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


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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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