Archives for October 2021

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3D Backside-Illuminated SPAD Imager Sensors: Unlike the CMOS image sensors found in smartphones, which measure the amount of light reaching a sensor’s pixels in a given timeframe, single photon avalanche diode (SPAD) image sensors detect each photon that reaches the pixel. Each photon is converted into an electric charge, and the electrons that result are eventually multiplied in avalanche fashion until they form an output signal. SPAD image sensors hold great promise for high-performance, low-light imaging applications, for depth sensing, and for fully digital system architectures.

However, until now their performance has been limited by tradeoffs in pixel detection efficiency vs. pixel size, and by poor signal-to-noise ratios. Recently a charge-focusing approach was proposed to overcome these issues, but until now it remained to be implemented. In a late-news paper, Canon researchers will discuss how they did so, with the industry’s first 3D-stacked backside-illuminated (BSI) charge-focusing SPADs. The devices featured the largest array size ever reported for a SPAD image sensor (3.2 megapixels) and demonstrated a photon detection efficiency of 24.4%, and timing jitter below 100ps at 940 nm.

From the images below:

(a) is a full-resolution color intensity image captured by the 3.2megapixel SPAD image sensor at a high light level.

(b) is a monochrome intensity image captured by the device under a scene illumination of 2mlux (without post-processing)

(c) is a monochrome intensity image captured by the device under a scene illumination of 0.3mlux (without post-processing)

a full-resolution color intensity image captured by the 3.2megapixel SPAD image sensor at a high light level.

a monochrome intensity image captured  by the device under a scene illumination  of 2mlux (without post-processing)

a monochrome intensity image captured by the device under a scene illumination  of 0.3mlux (without post-processing)

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 ST reports at its Facebook page:

"ST’s Francois Roy succeeds in solid-state image sensors

The International Image Sensor Society recently gave François Roy the Walter Kosonocky Award for his paper entitled Fully Depleted Trench-Pinned Photo Gate for CMOS Image Sensor Applications. The Photo Gate pixel concept improves image quality and the manufacturing process.

‘’It is a great honor for ST, the ST Imaging teams, my PhD students and myself to receive this prestigious award and I thank them all,’’ said François.

At ST we are proud of our inventors. We nurture strong competences and encourage our distinguished senior experts to coach young engineers."

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IEDM 2021 presents many image sensor papers in its program:

• 20-1 A Back Illuminated 6 μm SPAD Pixel Array with High PDE and Timing Jitter Performance,
  S. Shimada, Y. Otake, S. Yoshida, S. Endo, R. Nakamura, H. Tsugawa, T. Ogita, T. Ogasahara, K. Yokochi, Y. Inoue, K. Takabayashi, H. Maeda, K. Yamamoto, M. Ono, S. Matsumoto, H. Hiyama, and T. Wakano.
  Sony
  This paper presents a 6μm pitch silicon SPAD pixel array using 3D-stacked technology. A PDE of 20.2% and timing jitter FWHM of 137ps at λ=940nm with 3V excess bias were achieved. These state-of-the-art performances were allowed via the implementation of a pyramid surface structure and pixel potential profile optimization.
• 30-1 Highly Efficient Color Separation and Focusing in the Sub-micron CMOS Image Sensor,
  S. Yun, S. Roh, S. Lee, H. Park, M. Lim, S. Ahn, and H. Choo.
  Samsung Advanced Institute of Technology
  We report nanoscale metaphotonic color-routing (MPCR) structure that can significantly improve the lowlight performance of a sub-micron CMOS image sensor. Fabricated on the Samsung's commercial 0.8μm pixel sensor, MPCR structures confirms increased quantum efficiency (+20%), a luminance SNR improvement (+1.22 dB@5lux), a comparably low color error and great angular tolerant response.
• 20-2 3.2 Megapixel 3D-Stacked Charge Focusing SPAD for Low-Light Imaging and Depth Sensing (Late News),
  K. Morimoto, J. Iwata, M. Shinohara, H. Sekine, A. Abdelghafar, H. Tsuchiya, Y. Kuroda, K. Tojima, W. Endo, Y. Maehashi, Y. Ota, T. Sasago, S. Maekawa, S. Hikosaka, T. Kanou, A. Kato, T. Tezuka, S. Yoshizaki, T. Ogawa, K. Uehira, A. Ehara, F. Inui, Y. Matsuno, K. Sakurai, T. Ichikawa.
  Canon Inc.
  We present a new generation of scalable photon counting image sensors for low-light imaging and depthsensing, featuring read-noise-free operation. Newly proposed charge focusing SPAD is employed to a prototype 3.2 megapixel 3D backside-illuminated image sensor, demonstrating the best-in-class pixel performance with the largest array size in APD-based image sensors.
• 23-4 1.62µm Global Shutter Quantum Dot Image Sensor Optimized for Near and Shortwave Infrared,
  J. S. Steckel, E. Josse, A. G. Pattantyus-Abraham, M. Bidaud, B. Mortini, H. Bilgen, O. Arnaud, S. Allegret-Maret, F. Saguin, L. Mazet, S. Lhostis, T. Berger, K. Haxaire, L. L. Chapelon, L. Parmigiani, P. Gouraud, M. Brihoum, P. Bar, M. Guillermet, S. Favreau, R. Duru, J. Fantuz, S. Ricq, D. Ney, I. Hammad, D. Roy, A. Arnaud , B. Vianne, G. Nayak, N. Virollet, V. Farys, P. Malinge, A. Tournier, F. Lalanne, A. Crocherie, J. Galvier, S. Rabary, O. Noblanc, H. Wehbe-Alause , S. Acharya, A. Singh, J. Meitzner, D. Aher, H. Yang, J. Romero, B. Chen, C.Hsu, K. C. Cheng, Y. Chang, M. Sarmiento, C. Grange, E. Mazaleyrat, K. Rochereau,
  STMicroelectronics
  We have developed a 1.62µm pixel pitch global shutter sensor optimized for imaging in the NIR and SWIR. This breakthrough was made possible through the use of our colloidal quantum Dot thin film technology. We have scaled up this new platform technology to our 300mm manufacturing toolset.
• 30-2 Automotive 8.3 MP CMOS Image Sensor with 150 dB Dynamic Range and Light Flicker Mitigation (Invited),
  M. Innocent, S. Velichko, D. Lloyd, J. Beck, A. Hernandez, B. Vanhoff, C. Silsby, A. Oberoi, G. Singh, S. Gurindagunta, R. Mahadevappa, M. Suryadevara, M. Rahman, and V. Korobov,
  ON Semiconductor
  New 8.3 MP image sensor for automotive applications has 2.1 µm pixel with overflow and triple gain readout. In comparison to earlier 3 µm pixel, flicker free range increased to 110 dB and total range to 150dB. SNR in transitions stays above 25 dB up to 125°C.
• 30-3 A 2.9μm Pixel CMOS Image Sensor for Security Cameras with high FWC and 97 dB Single Exposure Dynamic Range,
  T. Uchida, K. Yamashita, A. Masagaki, T. Kawamura, C. Tokumitsu, S. Iwabuchi,. Onizawa, M. Ohura, H. Ansai, K. Izukashi, S. Yoshida, T. Tanikuni, S. Hiyama, H. Hirano, S. Miyazawa, Y. Tateshita,
  Sony
  We developed a new photodiode structure for CMOS image sensors with a pixel size of 2.9μm. It adds the following two structures: one forms a strong electric field P/N junction on the full-depth deep-trench isolation side wall, and the other is a dual-vertical-gate structure.
• 30-4 3D Sequential Process Integration for CMOS Image Sensor,
  K. Nakazawa, J. Yamamoto, S. Mori, S. Okamoto, A. Shimizu, K. Baba, N. Fujii, M. Uehara, K. Hiramatsu, H. Kumano, A. Matsumoto, K. Zaitsu, H. Ohnuma, K. Tatani, T. Hirano, and H. Iwamoto,
  Sony
  We developed a new structure of pixel transistors stacked over photodiode fabricated by 3D sequential process integration. With this technology, we successfully increased AMP size and demonstrated backsideilluminated CMOS image sensor of 6752 x 4928 pixels at 0.7um pitch to prove its functionality and integrity.
• 35-3 Computational Imaging with Vision Sensors embedding In-pixel Processing (Invited),
  J.N.P. Martel, G. Wetzstein,
  Stanford University
  Emerging vision sensors embedding in-pixel processing capabilities enable new ways to capture visual information. We review some of our work in designing new systems and algorithms using such vision sensors with applications in video-compressive imaging, high-dynamic range imaging, high-speed tracking, hyperspectral or light-field imaging.

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Yole Developpement reports on CCM market:

"After the outbreak of the pandemic in 2020, society and enterprise including Compact Camera Module (CCM) industry were temporarily suspended, but swift action was taken, and CCM industry quickly recovered.

The multi-camera approach in mobile not only increases photography functions (such as macro, telephoto etc.) but also greatly improves the photographic effects. As a result, the multiple-camera strategy is applicable in most of smartphones, resulting in an increase in the number of mobile CCMs to increase from 4.9B to 5.4B units from 2019 to 2020, a Yearover- Year (YoY) growth of 10.4%.

From imaging to sensing, the 3D camera could be in the front or rear (the front also includes optical fingerprint recognition), it will positively affect the developmental direction of the multicamera approach in mobile phones.

The automotive market started with rear imaging and has now developed to 360 surround-view, going from one camera to at least four even more. The autonomous driving is also increasing the need for more cameras. In addition, cars also need in-cabin cameras, as well as cameras to replace rearview mirrors. They are the next wave of CCM market.

In the consumer sector, products are becoming intelligent – connected to everything – allowing vision to play a more significant role in applications such as robots and home surveillance cameras. These will need more cameras.

Yole Développement expects the revenue of the global camera module to expand from $34B in 2020 to $59B in 2026, at a 9.8% CAGR."

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 Zhuhai Cordy Electronic Technology publishes a video of its image sensor testing machine:

Teledyne e2v publishes a promotional video about its Emerald 36M and 67M sensors:

SCD publishes a video from its 5MP MSIR imager, said to be world's highest resolution MWIR sensor:

QinetiQ publishes an interview with Emberion and a short Q&A session:

Isorg posts a demo of its large area fingerprint sensor integrated into a smartphone display:

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MIPI Alliance announces a completion of the development of the next version of the MIPI A-PHY SerDes interface, which will double the maximum available downlink data rate from 16 Gbps to 32 Gbps to support evolving requirements of automotive displays and sensors (cameras, lidars and radars). The enhanced version, v1.1, also will double the data rate available for uplink control traffic and introduce options for implementing A-PHY’s lower speed gears over lower-cost legacy cables, providing additional flexibility for manufacturers to implement A-PHY.

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IEDM Press Kit shows few figures from STMicro presentation of its quantum dot NIR/SWIR imager paper:

Paper #23.4, “1.62µm Global Shutter Quantum Dot Image Sensor Optimized for Near and Shortwave Infrared,” J.S. Steckel et al, STMicroelectronics

Record Quantum Efficiency for NIR/SWIR Sensors: STMicroelectronics researchers will report a 1.62µm pixel-pitch global shutter sensor for imaging in the near-infrared (NIR) and shortwave infrared (SWIR) regions of the light spectrum. It demonstrated record optical performance: an unprecedented quantum efficiency of >50% and a shutter efficiency of >99.94%. The breakthrough was made possible by use of a novel colloidal PbS quantum dot thin-film technology, and the devices were fabricated on a 300mm manufacturing toolset.

• The top photo is of a qualification wafer showing (a) elementary quantum film (QF) test structures; (b) pixel matrix test chips; and (c) full image sensor products.
• Going from left to right in the middle set of images/drawings are a QF photodiode array integrated on top of a CMOS readout IC; the QF photodiode cross-section; and a graphical description of the device stack.
• At the bottom is an outdoor image taken with the 940nm NIR QF sensor (left) and with a high-end smartphone camera (right). The NIR image shows a significant difference in contrast, and the ability to clearly identify the black electrical wires hidden in the tree leaves, vs. the visible image.

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In a push to build a recurring revenue model, Sony Semiconductor Solutions announces that its AITRIOS edge AI sensing platform will launch in Japan, the U.S. and Europe starting from late 2021.

In May 2020, Sony announced an intelligent vision sensor, the IMX500, the world’s first image sensors to be equipped with AI processing functionality. Adding to the IMX500 intelligent vision sensor, AITRIOS offers partners a variety of features that help them craft solutions. Platform partners can include developers building AI that runs on cameras, developers building applications for AI-driven sensing applications, camera manufacturers/module integrators who produce AI cameras, and system integrators who build systems that integrate these AI cameras and sensing applications.

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PRNewswire: IDTechEx publishes a comparison of SWIR technologies:

"Arguably the most compelling attribute of imaging in the SWIR region is the reduced optical scattering of longer wavelengths of light. Reduced scattering means that SWIR cameras on vehicles and drones can see through fog and dust clouds, greatly improving visibility and hence safety.

Another benefit of SWIR imaging is distinguishing visually similar materials, which may have similar absorption (and thus reflection) spectra in the visible region but significant differences in the SWIR region. This ability is highly valuable for applications such as quality control in industrial processes, where it enables unwanted items such as rocks and metals to be spotted in food production for example, and sorting recycling.

Other benefits include thermal imaging for items with temperatures between 200 and 500 C, and the ability to see through materials that are opaque to visible light but transparent to SWIR. Silicon is a great example of this, with SWIR imaging used to check the quality of wafer attachment.

...at present short-wave infra-red (SWIR, 1000-2000 nm) imaging is dominated by expensive InGaAs (Indium Gallium Arsenide) sensors that can absorb light up to around 1800 nm. These can cost upwards of $10,000 due to the expense of producing the InGaAs layer via vapor deposition, low manufacturing yields, and limited pixel density that increases material consumption for a given resolution relative to standard silicon photodetectors.

The combination of commercially desirable attributes and an expensive incumbent technology creates a clear opportunity for a disruptive, low-cost alternative. As such, multiple competing approaches for SWIR imaging are being developed."

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Albert Theuwissen gives a "Masterclass on Developments In CMOS Image Sensors Since IS Europe 2021 Online" on October 14, 2021. 

The world of CMOS image sensors is changing at a pace that we never have seen before.  New applications, new technologies, new features are constantly added to the large portfolio of CMOS devices that are out in the market.  In this way the performance as well as the possibilities of the devices is constantly improved.

During Image Sensors Europe 2019 and 2020 conference, a masterclass was organised around the recent developments in the CIS world and due to the popular demand of them, Albert Theuwissen and Smithers will re-run the 3 hour online masterclass to review the year and report on the latest developments.

Several subjects will be discussed : small pixels, new colour filters, new ToF image sensors, new stacked devices, global shutter devices, high-dynamic range techniques, etc.  Some topics that are not yet announced at the moment of writing this abstract will be included as well, because one can be sure: further developments of the CIS technology will not stop on a short notice!  Still exiting times are ahead for the imaging engineers and the imaging community.

A lookback of the developments over the last 12 months will be given, including critical comments on the published papers and data-sheets.  In many cases the information made available to the general public contains a lot of rubbish and data that makes no sense.  The speaker will analyse the figures and numbers published and will compare them to data available from other companies.  A real, unbiased benchmark of performance data will be given in the workshop.

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IEEE Sensors keeps publishing old videos from its archives. Here is a recent bunch of such publications:

"Introduction to Time-of-Flight Imaging" by Edoardo Charbon from Technische Universiteit Delft, Netherlands

"In this paper, the most important architectures used in time-of-flight (TOF) imaging will be described, starting with global shutter image sensors, ultra-fast CCDs with 100ns frames, on to TOF-specific architectures, such as direct, or pulse-based TOF and indirect, or phase-based TOF, implemented both in CCD and CMOS processes with optimized optical stacks."

"A Fast Global Shutter Image Sensor Based on the VOD Mechanism" by Erez Tadmor, Idan Bakish, Shlomo Felzenshtein, Eli Larry, Giora Yahav, David Cohen from Microsoft

"In this paper the physical principles that allow a fast (ns scale) global shutter operation using the vertical overflow drain mechanism are explained and characterized. Several new measurement methodologies are developed in order to quantify the fast shutter temporal and spatial behaviour. Measurement results that highlight different physical properties of the shutter mechanism are surveyed, and the results are studied and analyzed. Process and device simulations of a pinned photodiode with a VOD mechanism are presented in order to give insights regarding the physical origins of the measured phenomena."

"Resolving Multipath Interference in Kinect: an Inverse Problem Approach" by Ayush Bhandari, Micha Feigin, Shahram Izadi, Christoph Rhemann, Mirko Schmidt, Ramesh Raskar from MIT and Microsoft

"Multipath interference (MPI) is one of the major sources of both depth and amplitude measurement errors in Time"of"Flight (ToF) cameras. This problem has received a lot of attention in the recent past. In this work, we discuss the MPI problem within the framework of inverse problems based on the Fredholm integral and multi"frequency measurements. As compared to previous approaches that consider up to two interfering paths, our model considers the general case of K"interfering paths. In the theoretical setting, we show that for the case of K"interfering paths of light, 2K + 1 frequency measurements suffice to compute the depth and amplitude images corresponding to each of the K optical paths. Our algorithm is practical, by providing a deterministic solution. Also, for the first time, we demonstrate the effectivity of our model on an off-the-shelf Microsoft Kinect. Theoretical findings and practical demonstration warrants future research and further experimentation."

"Depth-Range Extension with Folding Technique for SPAD-Based TOF LIDAR Systems" by Daniele Perenzoni, Leonardo Gasparini, Nicola Massari, David Stoppa from Fondazione Bruno Kessler, Italy

"Direct Time-of-Flight cameras can be implemented combining Single-Photon Avalanche Diodes (SPAD) with Time-to-Digital Converters (TDCs). Such a technology exhibits an intrinsic distance range limitation due to the TDC range, which is fixed by the TDC resolution and number of bits. Up to now it was not possible to extend this range without redesigning the TDC. In this work we propose a method to overcome this limitation thanks to a folding measuring technique. In our implementation the TDC is based on a ring-oscillator; the TDC starts when a photon is detected and stops when an external Stop signal is provided. As the number of bits is limited, the TDC restarts from 0 after reaching the final value (folding). In this paper, we show that it is possible to arbitrary extend the maximum detectable distance through repeated measurements by modifying the timing of the “stop” signal in multiples of the TDC’s maximum range."

"A Low-Power Pixel-Level Circuit for High Dynamic Range Time-of-Flight Camera" by Nicola Massari, David Stoppa, Lucio Pancheri from Fondazione Bruno Kessler, and Università degli Studi di Trento, Italy.

"Design of a low-power pixel-level circuit for extending the dynamic range of a ToF camera."

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W&W Sens Device together with Universities of California at Davis and Santa Cruz publishes Arxiv.org paper "Optimization of CMOS image sensors with single photon-trapping hole per pixel for enhanced sensitivity in near-infrared" by E. Ponizovskaya Devine, Ahasan Ahamed, Ahmed S. Mayet, Soroush Ghandiparsi, Cesar Bartolo-Perez, Lisa McPhillips, Aly F. Elrefaie, Toshishige Yamada, Shih-Yuan Wang, and M Saif Islam.

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