Application of the Quanta image sensor concept to linear polarization imaging-a theoretical study.

Research efforts in linear polarization imaging have largely targeted the development of novel polarizing filters with improved performance and the monolithic integration of image sensors and polarization filter arrays. However, as pixel sizes in CMOS image sensors continue to decrease, the same limitations that have an impact on color and monochrome CMOS image sensors will undoubtedly affect polarization imagers. Issues of low signal capacity and dynamic range in small pixels will severely limit the useful polarization information that can be obtained. In this paper, we propose to leverage the benefits of the relatively new Quanta image sensor (QIS) concept to mitigate the anticipated limitations of linear polarization imaging as pixel sizes decrease. We address, by theoretical calculation and simulation, implementation issues such as alignment of polarization filters over extremely small pixels used in the QIS concept and polarization image formation from single-bit output of such pixels. We also present design innovations aimed at exploiting the benefits of this new imaging concept for simultaneous color and linear polarization imaging.

The Quanta Image Sensor: Every Photon Counts.

The Quanta Image Sensor (QIS) was conceived when contemplating shrinking pixel sizes and storage capacities, and the steady increase in digital processing power. In the single-bit QIS, the output of each field is a binary bit plane, where each bit represents the presence or absence of at least one photoelectron in a photodetector. A series of bit planes is generated through high-speed readout, and a kernel or "cubicle" of bits (x, y, t) is used to create a single output image pixel. The size of the cubicle can be adjusted post-acquisition to optimize image quality. The specialized sub-diffraction-limit photodetectors in the QIS are referred to as "jots" and a QIS may have a gigajot or more, read out at 1000 fps, for a data rate exceeding 1 Tb/s. Basically, we are trying to count photons as they arrive at the sensor. This paper reviews the QIS concept and its imaging characteristics. Recent progress towards realizing the QIS for commercial and scientific purposes is discussed. This includes implementation of a pump-gate jot device in a 65 nm CIS BSI process yielding read noise as low as 0.22 e- r.m.s. and conversion gain as high as 420 µV/e-, power efficient readout electronics, currently as low as 0.4 pJ/b in the same process, creating high dynamic range images from jot data, and understanding the imaging characteristics of single-bit and multi-bit QIS devices. The QIS represents a possible major paradigm shift in image capture.

Color filter array patterns for small-pixel image sensors with substantial cross talk.

Digital image sensor outputs usually must be transformed to suit the human visual system. This color correction amplifies noise, thus reducing the signal-to-noise ratio (SNR) of the image. In subdiffraction-limit (SDL) pixels, where optical and carrier cross talk can be substantial, this problem can become significant when conventional color filter arrays (CFAs) such as the Bayer patterns (RGB and CMY) are used. We present the design and analysis of new color filter array patterns for improving the color error and SNR deterioration caused by cross talk in these SDL pixels. We demonstrate an improvement in the color reproduction accuracy and SNR in high cross-talk conditions. Finally, we investigate the trade-off between color accuracy and SNR for the different CFA patterns.

Ultra-high-resolution quanta image sensor with reliable photon-number-resolving and high dynamic range capabilities.

Superior low-light and high dynamic range (HDR) imaging performance with ultra-high pixel resolution are widely sought after in the imaging world. The quanta image sensor (QIS) concept was proposed in 2005 as the next paradigm in solid-state image sensors after charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) active pixel sensors. This next-generation image sensor would contain hundreds of millions to billions of small pixels with photon-number-resolving and HDR capabilities, providing superior imaging performance over CCD and conventional CMOS sensors. In this article, we present a 163 megapixel QIS that enables both reliable photon-number-resolving and high dynamic range imaging in a single device. This is the highest pixel resolution ever reported among low-noise image sensors with photon-number-resolving capability. This QIS was fabricated with a standard, state-of-the-art CMOS process with 2-layer wafer stacking and backside illumination. Reliable photon-number-resolving is demonstrated with an average read noise of 0.35 e- rms at room temperature operation, enabling industry leading low-light imaging performance. Additionally, a dynamic range of 95 dB is realized due to the extremely low noise floor and an extended full-well capacity of 20k e-. The design, operating principles, experimental results, and imaging performance of this QIS device are discussed.