Monday, December 11, 2017

12nm Pixel Size

There is a funny mistake in Xiaomi Redmi 5 Plus smartphone promotional video:

2-step Column-Parallel Delta-Sigma ADC

CentraleSupelec, France, publishes a paper "A 14-b Two-step Inverter-based Σ∆ ADC for CMOS Image Sensor" by Pierre Bisiaux, Caroline Lelandais-Perrault, Anthony Kolar, Philippe Benabes, and Filipe Vinci dos Santos presented at IEEE International NEWCAS Conference, in June 2017 at Strasbourg, France.

"This paper presents a 14-bit Incremental Sigma Delta (IΣ∆) analog-to-digital converter (ADC) suitable for a column wise integration in a CMOS image sensor. A two-step conversion is performed to improve the conversion speed. As the same Σ∆ modulator is used for both steps, the overall complexity is reduced. Furthermore, the use of inverter-based amplifiers instead of operational transconductance amplifier (OTA) facilitates the integration within the column pitch and decreases power consumption. The proposed ADC is designed in 0.18 µm CMOS technology. The simulation shows that for a 1.8 V voltage supply, a 20 MHz clock frequency and an oversampling ratio (OSR) of 70, the power consumption is 460 µW, achieving an SNR of 83.7 dB."

Sunday, December 10, 2017

Imec Quantum Dot Sensor

MDPI Special Issue on the 2017 International Image Sensor Workshop (IISW) publishes Imec, KU Leuven, and Ghent University paper "Thin-Film Quantum Dot Photodiode for Monolithic Infrared Image Sensors" by Pawel E. Malinowski, Epimitheas Georgitzikis, Jorick Maes, Ioanna Vamvaka, Fortunato Frazzica, Jan Van Olmen, Piet De Moor, Paul Heremans, Zeger Hens, and David Cheyns. The paper describes a somewhat similar to Invisage IR image sensor:

"This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10−6 A/cm2 at −2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors."

Saturday, December 09, 2017

Canon Global Shutter Sensor Paper

MDPI Special Issue on the 2017 International Image Sensor Workshop (IISW) publishes Canon paper "Development of Gentle Slope Light Guide Structure in a 3.4 μm Pixel Pitch Global Shutter CMOS Image Sensor with Multiple Accumulation Shutter Technology" by Hiroshi Sekine, Masahiro Kobayashi, Yusuke Onuki, Kazunari Kawabata, Toshiki Tsuboi, Yasushi Matsuno, Hidekazu Takahashi, Shunsuke Inoue, and Takeshi Ichikawa.

"CISs with GS function have generally been inferior to the rolling shutter (RS) CIS in performance, because they have more components. This problem is remarkable in small pixel pitch. The newly developed 3.4 µm pitch GS CIS solves this problem by using multiple accumulation shutter technology and the gentle slope light guide structure. As a result, the developed GS pixel achieves 1.8 e− temporal noise and 16,200 e− full well capacity with charge domain memory in 120 fps operation. The sensitivity and parasitic light sensitivity are 28,000 e−/lx·s and −89 dB, respectively. Moreover, the incident light angle dependence of sensitivity and parasitic light sensitivity are improved by the gentle slope light guide structure."

Friday, December 08, 2017

Huawei is Reported Preparing Triple Rear Camera Smartphone

XDA Developers quotes Venturebeat reporter Evan Blass twitted about the oncoming Huawei smartphone featuring triple rear camera smartphone with 40MP resolution and 5x zoom:

Yole: Camera is Among Major Heat Sources in Smartphones

Yole Developpement report "Smartphones: a significant challenge for thermal management companies" points to camera and LED flash on one of the complex thermal management problems in smartphones:

Thursday, December 07, 2017

Recent ON Semi CCD Advances

MDPI Special Issue on the 2017 International Image Sensor Workshop (IISW) publishes ON Semi paper "Recent Enhancements to Interline and Electron Multiplying CCD Image Sensors" by Eric G. Stevens, , Jeffrey A. Clayhold, Hung Doan, Robert P. Fabinski, Jaroslav Hynecek, Stephen L. Kosman, and Christopher Parks.

"This paper describes recent process modifications made to enhance the performance of interline and electron-multiplying charge-coupled-device (EMCCD) image sensors. By use of MeV ion implantation, quantum efficiency in the NIR region of the spectrum was increased by 2×, and image smear was reduced by 6 dB. By reducing the depth of the shallow photodiode (PD) implants, the photodiode-to-vertical-charge-coupled-device (VCCD) transfer gate voltage required for no-lag operation was reduced by 3 V, and the electronic shutter voltage was reduced by 9 V. The thinner, surface pinning layer also resulted in a reduction of smear by 4 dB in the blue portion of the visible spectrum. For EMCCDs, gain aging was eliminated by providing an oxide-only dielectric under its multiplication phase, while retaining the oxide-nitride-oxide (ONO) gate dielectrics elsewhere in the device."

Queen Elizabeth Prize for Engineering Handed to Image Sensor Inventors

Queen Elizabeth Prize for Engineering has been presented to Eric Fossum, Nobukazu Teranishi and Michael Tompsett. Together with George Smith, who is unable to attend the ceremony, this year’s winners are honored for their contribution to creating digital imaging sensors:

From left to right: Prince Charles, Fossum, Tompsett, Teranishi

Qualcomm Snapdragon 845 Imaging Features

PRNewswire: The new Snapdragon 845 Platform is designed to capture cinema-grade videos and for AR applications:

Spectra 280 ISP:

  • Ultra HD premium capture
  • Qualcomm Spectra Module Program, featuring Active Depth Sensing
  • MCTF video capture
  • Multi-frame noise reduction
  • High performance capture up to 16MP @60FPS
  • Slow motion video capture (720p @480 fps)
  • ImMotion computational photography
  • Dual 14-bit ISPs
  • Hybrid Autofocus
  • Hardware Accelerated Face Detection
  • HDR Video Recording
Adreno 630 Visual Processing Subsystem:

  • 30% improved graphics/video rendering and power reduction compared to previous generation
  • Room-scale 6 DoF with SLAM
  • Adreno foveation, featuring tile rendering, eye tracking, multiView rendering, fine grain preemption
  • Improved 6DoF with hand-tracking and controller support

Hexagon 685 DSP:
  • 3rd Generation Hexagon Vector DSP (HVX) for AI and imaging

Wednesday, December 06, 2017

Leti SPAD Presentation

Leti publishes a presentation on SPAD image sensors it develops together with ST: "Avalanche Diodes for 3D Imaging at Large Distances" by Norbert Moussy. A few slides from the presentation:

Image Sensor Design Tutorials

CMOS Chip Designer site publishes a number of nice tutorials on image sensor design:

CMOS Image Sensors Overview - general Q&A
CMOS Pixel Design - starts from basics, does not go very far but still useful
Image Sensor Readout Circuits - ROIC - basic introduction, although some of the circuits do not represent the best practices, such as this one:

Column PGA and single-slope ADC with auto-zero

Update: The site owner took it offline. The content is still accessible for the next couple of days through Google cache by typing in the Google search field.

Update #2: The image sensor tutorials are back on-line.

Tuesday, December 05, 2017

Google on 3D Sensing in AR Applications

Google AR/VR head Clay Bavor comes up with a remarkable statement emphasizing imaging importance in AR applications:

Gigajot Licenses Binary Pixel Technology from Rambus

BusinessWire: Rambus announces that Dartmouth College-based startup Gigajot Technology has licensed Rambus Binary Pixel technology and patents for use in Gigajot’s next-generation image capture solutions. Gigajot’s Quanta Image Sensor (QIS) enables high-speed counting of single photons of light at gigapixel resolution. The new features enabled by QIS and Binary Pixel Technologies can benefit imaging applications such as scientific, automotive, security, defense, encryption, AR/VR, 3D and consumer photography, among others. Rambus has supported the early work at Dartmouth on the technology.

Rambus Binary Pixel technology combines an imager and a processor architectures to enable high quality images and video from small form factor imagers for compact solutions. The technology senses the photons using discrete thresholds to avoid pixel saturation and enable better light sensitivity. Binary Pixel also employs special oversampling methods, which subdivide pixels, exposure and digitization to capture more data and extend the dynamic range of the imager.

Traditionally, it has been difficult to achieve acceptable signal-to-noise ratio in low-light situations for quality images,” said Saleh Masoodian, CEO, Gigajot. “Combining the Rambus Binary Pixel technology with Gigajot’s QIS devices enables development of highly sensitive imaging technology via mainstream commercial CMOS fabrication processes for not only consumer devices such as smartphones, tablets and cameras, but also for more high-end commercial pursuits such as scientific, medical, security and surveillance sensors and cameras.

Rambus Binary Pixel technology enables improved performance for small, compact image sensors, allowing unprecedented image quality for consumer devices,” said Laura Stark, SVP and general manager, Emerging Solutions of Rambus. “Combining the Gigajot and Rambus cutting-edge imaging technologies will dramatically improve the image capture experience for the next generation of consumers and professionals.

As a matter of fact, Rambus Emerging Solutions web page does not list imaging technologies anymore. Neither the company product page lists any of the imaging technologies that Rambus developed in the past: HDR sensors, binary pixels, lensless imagers.

Yole Talk on TSV Technology

Most of the Yole Developpement webcast on TSV technology is devoted to stacked memory integration, but there is also some image sensor content, especially from 28:00 to 38:00 time:

TSMC 0.8um-0.9um Pixel Paper

MDPI Special Issue on the 2017 International Image Sensor Workshop (IISW) gets one more TSMC paper "A 45 nm Stacked CMOS Image Sensor Process Technology for Submicron Pixel" by Seiji Takahashi, Yi-Min Huang, Jhy-Jyi Sze, Tung-Ting Wu, Fu-Sheng Guo, Wei-Cheng Hsu, Tung-Hsiung Tseng, King Liao, Chin-Chia Kuo, Tzu-Hsiang Chen, Wei-Chieh Chiang, Chun-Hao Chuang, Keng-Yu Chou, Chi-Hsien Chung, Kuo-Yu Chou, Chien-Hsien Tseng, Chuan-Joung Wang, and Dun-Nien Yaung.

"In this work, we demonstrated a low dark current of 3.2 e−/s at 60 °C, an ultra-low read noise of 0.90 e− rms, a high full well capacity (FWC) of 4100 e−, and blooming of 0.5% in 0.9 μm pixels with a pixel supply voltage of 2.8 V. In addition, the simulation study result of 0.8 μm pixels is discussed."

A unit pixel circuit and device partition.
A 45 nm stacked CIS test vehicle.
TG area device optimizations
(a) Regular pixel; (b) crosstalk-improved pixel.

Espros Announces New Generation ToF Sensor

Espros announces epc611, a new generation 8×8 pixel ToF sensor. The epc611 is said to establish a new industry standard in terms of photon sensitivity, distance measurement frame rate and versatility for a wide range of applications. The small footprint of 2.6 x 2.6mm and bare die packaged epc611 will be produced in cooperation with TSMC.

Sensitivity: epc611 has a 30% enhanced sensitivity in comparison to previous generation ESPROS TOF sensors due to the latest generation TOF pixel design. Only 7.5 nW per millimeter-square of optical power is needed to measure accurately distance. And this under full sunlight condition.

Frame Rate: The epc611 allows up to 8’000 distance measurements per second.

Versatility: epc611 can be configured to operate in 7 different TOF modes. From an 8×8 imager to binning of all pixels into a single large pixel almost anything is possible. Groups of pixels can be configured to operate at different integration times or at different phase angles. In this way the imager can achieve a wide dynamic distance range or catch fast moving objects without generating motion blur.

«We put our entire experience in this new generation sensor», says Beat De Coi, CEO and founder of ESPROS Photonics. «I built sensors my whole life and know about the quite individual requirements that need to be satisfied. Therefore I wanted this chip to come with all configuration options that we could think of. And now its here!».

The new epc611 TOF sensor is available now. Several pilot customers have epc611 already in their labs. A first distance measurement module is under development and will be released soon.

Monday, December 04, 2017

IEDM Image Sensor Presentations

IEDM Image Sensor session has a nice selection of 6 papers. IEDM publishes figures from two of the presentations:

16.4 Near-infrared Sensitivity Enhancement of a Back-illuminated Complementary Metal Oxide Semiconductor Image Sensor with a Pyramid Surface for Diffraction Structure,
I. Oshiyama, S. Yokogawa, H. Ikeda, Y. Ebiko, T. Hirano, S. Saito, T. Oinoue, Y. Hagimoto, H. Iwamoto, Sony Semiconductor

Boosting Near-Infrared Sensitivity in CMOS Imagers: Backside-illuminated CMOS image sensors are ubiquitous in camera phones, and there is a growing demand for them to be able to handle near-infrared (NIR) light frequencies so that they can be used in iris scanning, facial recognition and motion-sensing applications. However, the NIR-sensitivity of silicon CMOS image sensors has been inadequate. The simplest way to enhance it would be to make the photo-absorption layer thicker, but that would require substantial capital investment in manufacturing equipment like high-energy ion implanters to be able to work with the thicker layer. Instead, Sony researchers developed a way to increase the NIR sensitivity of a 2-megapixel backside imager by building pyramidal light-diffraction structures on its surface. These 400nm structures diffract and trap the light coming to each pixel. The researchers also isolated each 1.12µm pixel from its neighbors by means of a special treatment process and used deep trench isolation to reduce crosstalk. They achieved a 50% increase in NIR sensitivity and a quantum efficiency of 30% at 850nm. Image resolution and levels of dark current (i.e., electrical “noise”) were not compromised.

The image is a photomicrograph of a section of a backside-illuminated CMOS image sensor with a cell size of 1.12µm and pyramid surfaces for diffraction (PSD) and deep-trench isolation (DTI) structures. The PSD pitch was 400 nm.

16.3 Back-side Illuminated GeSn Photodiode Array on Quartz Substrate Fabricated by Laser-induced Liquid-phase Crystallization for Monolithically-integrated NIR Imager Chip,
H. Oka, K. Inoue, T. T. Nguyen*, S. Kuroki*, T. Hosoi, T. Shimura and H. Watanabe, Osaka University, *Hiroshima University

Back-side illuminated single-crystalline GeSn photodiode array has been demonstrated on a quartz substrate for group-IV-based NIR imager chip. Owing to high crystalline quality of GeSn array formed by laser-induced liquid-phase crystallization technique, significantly enhanced NIR photoresponse with high responsivity of 1.3 A/W was achieved operated under back-side illumination.

Record Performance from GeSn Backside Imager: An Osaka University-led team will report on a backside-illuminated germanium-tin (GeSn) photodiode array with a high responsivity of 1.3 A/W at 1550nm, a record high on/off ratio of 5 decades, and low dark current of 10-3 A/cm2. They formed the large-area, tensile-strained and single-crystal GeSn device on a quartz substrate by using laser-induced liquid-phase crystallization. Because quartz has a high transparency to NIR frequencies, and can be combined directly with silicon, this work opens up the possibility to monolithically integrate high-performance GeSn NIR imagers with silicon CMOS circuitry.

In the schematic on the left, (a) is an illustration of lateral liquid-phase crystallization of GeSn wire on a quartz substrate by rapid thermal annealing, while (b) is an in-situ observation of lateral liquid-phase growth of GeSn wire.

At right is a schematic of the fabrication process and an optical image of a single-crystal GeSn n+/p photodiode array on a quartz substrate. P+ implantation was performed to form the n+ regions of the diodes.

Chronocam CEO on Bio-Inspired Vision

Chronocam CEO Luca Verre talks about the company's bio-inspired approach to vision at Hello Tomorrow Summit 2017:

33-Mpixel 240-fps Stacked Sensor

NHK, Brookman, TSMC, and University of Tokyo publish an open-access IEEE TED paper "A 1.1- μm 33-Mpixel 240-fps 3-D-Stacked CMOS Image Sensor With Three-Stage Cyclic-Cyclic-SAR Analog-to-Digital Converters" by Toshiki Arai, Toshio Yasue, Kazuya Kitamura, Hiroshi Shimamoto, Tomohiko Kosugi, Sung-Wook Jun, Satoshi Aoyama, Ming-Chieh Hsu, Yuichiro Yamashita, Hirofumi Sumi, and Shoji Kawahito. The paper describes, basically, a 1-inch 8K video sensor with a slow-motion function:

Sunday, December 03, 2017

Omnivision Applies for SiGe Image Sensor Patent

Omnivision patent application US20170345851 "Graded-Semiconductor Image Sensor" by Dajiang Yang, Gang Chen, Duli Mao, and Dyson Tai propose SiGe graded epi doping to enhace IR response:

"Detection of infrared (IR) light is useful in automotive and night vision applications. However, conventional image sensor devices may poorly absorb infrared light due to the band structure of semiconductor materials used in modern microelectronic devices. Even if conventional image sensors can absorb IR light, the semiconductor may need to be sufficiently thick. Additional semiconductor thickness may complicate other fabrication steps and/or reduce performance."

1MP Photon-number-resolving Sensor

OSA Optica publishes a paper "Photon-number-resolving megapixel image sensor at room temperature without avalanche gain" by Jiaju Ma, Saleh Masoodian, Dakota Starkey, and Eric Fossum, Dartmouth College, NH, USA. From the abstrac t:

"Termed a quanta image sensor, the device is implemented in a commercial stacked (3D) backside-illuminated CMOS image sensor process. Without the use of avalanche multiplication, the 1.1 μm pixel-pitch device achieves 0.21e−  rms average read noise with average dark count rate per pixel less than 0.2e−/s, and 1040 fps readout rate. This novel platform technology fits the needs of high-speed, high-resolution, and accurate photon-counting imaging for scientific, space, security, and low-light imaging as well as a broader range of other applications."