SPAD Imagers in Biophotonics Review

Arxiv.org paper "Single-photon SPAD imagers in biophotonics: Review and Outlook" by Claudio Bruschini, Harald Homulle, Ivan Michel Antolovic, Samuel Burri, and Edoardo Charbon from EPFL and TU Delft presents an excellent overview of the recent advances in the field:

"Single-photon avalanche diode (SPAD) arrays are solid-state detectors offering imaging capabilities at the level of individual photons, with unparalleled photon counting and time-resolved performance. This fascinating technology has progressed at very high pace in the past 15~years, since its inception in standard CMOS technology in 2003. A host of architectures has been explored, ranging from simpler implementations, based solely on off-chip data processing, to progressively "smarter" sensors including on-chip, or even pixel-level, timestamping and processing capabilities. As the technology matured, a range of biophotonics applications has been explored, including (endoscopic) FLIM, (multi-beam multiphoton) FLIM-FRET, SPIM-FCS, super-resolution microscopy, time-resolved Raman, NIROT, and PET. We will review some representative sensors and their corresponding applications, including the most relevant challenges faced by chip designers and end-users. Finally, we will provide an outlook on the future of this fascinating technology."

Credit Suisse on Smartphone CIS Market: 108MP and 64MP Sensors are Coming

IFNews: Credit Suisse update dated by March 13, 2019, reports on CIS market:

"We note a sustained shift toward higher image resolution and multi-camera imaging systems in CIS. In Oct–Dec 2018, the multi-camera adoption rate fell briefly to 43% due to a slump in Apple’s dual-camera-equipped OLED models (vs. 65% in Jul–Sep and 58% in Oct–Dec 2017). However, we note the trend accelerating in non-Apple Android devices with 52% (43%, 21%). The multi-camera system adoption rate across smartphones finished at 40% in 2018 (vs. our initial outlook for 40%). We raise our estimate for the multi-camera system adoption rate to 60% in 2019 (prev. 50%). Within multi-camera systems, we raise our estimate for triple-camera systems to 15% in 2019 (10%) and forecast 70% and 22%, respectively in 2020. Sony’s image sensors registered a sales decline in Oct–Dec 2018 due to production adjustments in iPhones and Chinese smartphones, but we forecast an upturn in YoY momentum from Jan–Mar. Our outlook for profit growth at the business in FY3/20 and FY3/21 remains intact due to product mix improvement driven by faster uptake for multi-camera systems and the shift to larger/higher-resolution images.

- Cameras: OLED models for 2019 will likely feature a triple-lens rear camera (12mp) and we expect liquid crystal models to be upgraded to a dual-camera configuration. As in our previous survey, we think OLED models will very likely use Dual OIS and fixedfocus actuators and LCD models will use Dual OIS. Apple is apparently considering larger lenses for 2020 models and SMA (Shape Memory Alloy) for OIS. We also expect 2020 models to feature Dual OIS and actuators for front-facing cameras.

- ToF: We expect ToF for rear-facing cameras to be adopted after 2020 rather than in 2019, and think Apple will very likely use UWB (ultra-wide band) microwave for distance measuring sensors. We expect indirect ToF to feature after 2020."

"New features and technologies in Chinese smartphones

We had forecast in the previous survey that adoption of triple-camera systems and 48MP sensors would accelerate in CY19, and our latest survey confirms this. ...Sony will likely be the sole supplier of these for spring models. Samsung’s LSI 12MP/48MP re-mosaic technology is lagging and had been slated for launch in 2H CY19, but we think Samsung will skip real 48MP and concentrate instead on developing 64MP sensors for a 2H release. We also see an increasing possibility of 108MP sensors launching in 2020.

We estimate that Chinese demand for 24MP CIS, mainly for phones with two front-side cameras, reached around 100mn units in CY18 and look for 150mn units of rear-side 48MP demand in CY19.

Companies like Huawei, Oppo, and Xiaomi are considering adopting 5x-zoom folded optics systems. The issue with folded optics is low production yields on actuator module assembly. Sensor size is meanwhile limited by considerations of phone thickness, making higher resolutions difficult as well.

We sense that demand is increasing for shape memory alloy (SMA) OIS over VCM-type actuators/OIS in response to the increasing size and number of lenses. Phone makers are also considering using a glass lens in the lens unit for f/1.4 and smaller and 108MP sensors, with the resulting increase in weight another factor likely to drive demand for SMA and ball-guide OIS.

Pop-up selfie cameras have also begun appearing on at least one model from each manufacturer, but not so far on their mass-produced flagships."

Another Credit Suisse report talks about multi-camera adoption and sensor resolution trends:

• Demand from Huawei (32MP CIS mass production) and Xiaomi (long-term contract) has helped Samsung to gain market share in CIS.
• Multi-camera smartphones are expected to comprise 65–70% of all models in 2019, up from 40% in 2018. Triple-camera models are expected to account for as much as 20% of all smartphone handsets (up from 1.5% in 2018).
• The multi-camera percentage for Samsung Mobile is expected to reach 70% in 2019 (up from 21% in 2018).
• Demand for 5MP CIS is booming due to the trend toward multi-camera smartphones (the 5MP CIS is an essential component of triple-camera handsets).
• The CIS technology roadmap calls for further evolution towards higher megapixels, with development expected to bring 64MP in 2H 2019 and 100MP in 2020. The trend will increase the number of lenses required (though weight is an issue), demanding higher levels of cooperation between lens, module and AP manufacturers to achieve incremental improvements in image resolution.
• With Line 11 undergoing conversion, Samsung is planning to boost the total monthly capacity of its CIS 300mm production lines to 75,000 units by end-2019 and 85,000 units by end-2020. No decision has been taken yet on whether to convert Line 13 to CIS production, but the general plan is to continue expanding capacity steadily.
• CIS 300mm line development is underway at SK Hynix.

The smartphone market size in terms of units has started to shrink from the end of 2017, according to Credit Suisse:

Velodyne Cumulative Sales Reached $500M

Forbes: Velodyne has shipped 30,000 LiDARs since 2007 when it started making them, generating cumulative sales of $500M, according to the company CEO and founder David Hall.

Velodyne sees demand for shorter-range units for ADAS safety tech, monitoring road conditions, blind spots and objects in a driver's path. “The market is changing a little bit, and we're trying to aim a little bit toward the ADAS end now, where we have lower product costs and higher volume,” David Hall said. “We’re not convinced that the ultimate lidar has been invented by anybody yet. We still have an active program to try to hammer this thing into its final shape.”

Velodyne has formed strategic alliances with three key investors in the past few years, with Ford, China’s Baidu and Nikon investing a combined $200M in the company.

The company built an automated 200,000-square-foot LiDAR “megafactory” in San Jose, CA, in 2017. Nikon is also setting up a LiDAR assembly line in Japan in partnership with Velodyne, and it has a strategic licensing deal with Veoneer, a unit of Swedish Autoliv, to help boost production of its sensors to millions of units a year worldwide.

Yole on Smartphone Front Camera Market

Yole Developpement publishes its analysis of MWC 2019 smartphone camera announcements "Is the smartphone full display trend taking over from front selfie cameras and biometric 3D sensing?"

"There are obviously two main trends conflicting right now: one favors sensing on the front display side of smartphones; the other favors display.

The display strategy is driven by a ‘wow effect’, by increasing screen-to-body ratio, showing immersive videos that are one of the drivers of 5G adoption. The foldable trend is also an extension of this, and may end up in a compromise between a smartphone and a tablet. It is not clear right now if this could convert into additional revenues or volume for the industry, knowing what we know about smartphones and tablets.

The sensing strategy is using 3D as a biometric interface, where biometry and Human Machine Interface (HMI) are combined. This one conflicts with the full display aesthetic and is constrained by handset design and camera and display technologies. Apple is actively working on the ideal technical solution, which should reach the market before the year’s end."

Color Photon Counting Sensor

Arxiv.org paper "Megapixel Photon-Counting Color Imaging using Quanta Image Sensor" by Abhiram Gnanasambandam, Omar Elgendy, Jiaju Ma, and Stanley H. Chan from Purdue University and Gigajot presents first color photon counting sensor:

"Quanta Image Sensor (QIS) is a single-photon detector designed for extremely low light imaging conditions. Majority of the existing QIS prototypes are monochrome based on single-photon avalanche diodes (SPAD). Color imaging has not been demonstrated with single-photon detectors due to the intrinsic difficulty of shrinking the pixel size and increasing the spatial resolution while maintaining acceptable intra-pixel cross-talk. In this paper, we present image reconstruction of the first color QIS with a resolution of 1024×1024 pixels, supporting both single-bit and multi-bit photon counting capability. Our color image reconstruction is enabled by a customized joint demosaicing-denoising algorithm, leveraging truncated Poisson statistics and variance stabilizing transforms. Experimental results of the new sensor and algorithm demonstrate superior color imaging performance for very low-light conditions with a mean exposure of as low as a few photons per pixel."

Mitsubishi Develops MWIR and LWIR Graphene Sensors

Nikkei: Mitsubishi claims it has developed a MWIR sensor having the world's highest responsivity among graphene sensors. Due to an internal graphene FET gain, the responsivity is 10x higher than that of quantum-type IR sensors with no internal amplification. Mitsubishi uses graphene FET and leverages its high electron mobility.

Other than a graphene-based FET, there is "a light-amplifying part" that produces photoelectrons and photoholes and is placed under the graphene. At a very low temperature of, for example, 80K, the responsivity increases even more, by a factor of 100x:

Mitsubishi is also developing a LWIR sensor using a dielectric for the light-amplifying. Existing quantum-type LWIR sensors reduce thermal noise by cooling down to liquid nitrogen temperature. Mitsubishi claims that with its new method, the sensor might be able to work at room temperature:

The original article in Japanese has few more figures:

Here is an earlier Nikkei article on the same topic. Mitsubishi is going to present its work at IDTechEx Show in Berlin, Germany on April 10-11, 2019.

Terahertz Imaging Pixel

Japanese Journal of Applied Physics publishes a paper "Wideband terahertz imaging pixel with a small on-chip antenna in 180 nm CMOS" by Yuri Kanazawa, Sayuri Yokoyama, Shota Hiramatsu, Eiichi Sano, Takahiro Ikegami, Yuma Takida, Prasoon Ambalathankandy, Hiroaki Minamide, and Masayuki Ikebe from Hokkaido University, Sony, and RIKEN. The new paper appears to be a further development of their previous paper presented at ISW 2017.

"We propose a Si-CMOS terahertz image sensor to resolve paucity of low-cost and small-size detectors. The imaging pixel consists of an on-chip antenna and an amplifier acting as envelope detector. The pixel uses a microstrip patch antenna for receiving THz waves. However, the antenna's narrow bandwidth and large ground plane size causes major problems. A low-resistivity Si substrate degrades the gain of planar antennas besides the microstrip patch antenna. We introduce an on-chip folded-slot antenna to reduce the pixel size and prevent gain degradation due to the Si substrate. The antenna has a broader bandwidth and higher gain than conventional on-chip slot antenna. We fabricated the patch/folded-slot types of the pixel circuits by using 0.18 μm CMOS process. Measurement results show that the folded-slot antenna has a broader bandwidth from 850 GHz to 1.05 THz."

Venturebeat: In an unrelated news, FCC has started issuing 10-year licenses to experiment in 95GHz to 3THz spectrum range for the companies that are trying to find "the next big thing."

Yantai Raytron Prepares IPO

Reuters: Yantai Raytron Technology Co, a Chinese developer of LWIR imaging and sensors technology is one of the first companies preparing the IPO at Shanghai’s Nasdaq-style Science and Technology board, announced by President Xi Jinping in November 2018. The board’s registration-based listing procedure is supposed to take 3 months and allow start-ups that have yet to turn a profit to list.

Yantai Raytron is developing a low-cost thermal imagers based on microbolometric technology.

Light Co. CEO Keynote at MWC

Light Co. publishes its CEO Dave Grannan talk at MWC 2019 Keynote Session "The Next Unicorn".

IHS Markit on ToF Market

Semiconductor Engineering publishes IHS Markit article on ToF sensing market:

"IHS Markit forecasts that global revenue for ToF sensors in the 3D optical sensing market will surpass $500 million in 2019, up from $370 million last year. We also predict that the ToF market will grow in the coming years, spurred by combo solutions integrated with other light sensors in the same package. This will lead to a cheaper bill of materials (BOM) compared to the BOM for the SL method.

At the same time, IHS Markit forecasts that the total market potential for light sensors will be worth much more, reaching $1.5 billion by year 2022. That’s because after a solid start with gaming consoles, 3D sensing has matured and consolidated in the massive smartphone arena.

A segment of 3D sensing’s future growth will come from other use cases and applications that are emerging outside consumer electronics and mobile. These include people-counting and -tracking in consumer and industrial applications, landing-aid and obstacle-avoidance functions in drones, and car-trunk (boot) opening with foot gestures, as well as gesture recognition and passenger detection in automotive.

All told, the ToF approach appears to have a greater chance than the SL method in gaining a larger market share, leading to a cheaper and smaller BOM along with reduced integration costs in system assembly and calibration."