In recent years, cellphone cameras have come to require much more diversification and increased functionalities, due to the strong growth of the smartphone market. In addition to the image quality, speed, and pixel counts that conventional image sensors require, there is high demand for new functions that can respond to various photo-taking scenes. We developed a stacked CMOS image sensor (CIS), composed of conventional back-illuminated (BI) image-sensor technology and 65nm standard logic technology.

A 1/4-inch 8Mpixel back-illuminated stacked CMOS image sensor

We study a new image sensor that is reminiscent of a traditional photographic film. Each pixel in the sensor has a binary response, giving only a 1-bit quantized measurement of the local light intensity. To analyze its performance, we formulate the oversampled binary sensing scheme as a parameter estimation problem based on quantized Poisson statistics. We show that, with a single-photon quantization threshold and large oversampling factors, the Cramer-Rao lower bound (CRLB) of the estimation variance approaches that of an ideal unquantized sensor, i.e., as if there were no quantization in the sensor measurements. Furthermore, the CRLB is shown to be asymptotically achievable by the maximum-likelihood estimator (MLE). By showing that the log-likelihood function of our problem is concave, we guarantee the global optimality of iterative algorithms in finding the MLE. Numerical results on both synthetic data and images taken by a prototype sensor verify our theoretical analysis and demonstrate the effectiveness of our image reconstruction algorithm. They also suggest the potential application of the oversampled binary sensing scheme in high dynamic range photography.

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Bits From Photons: Oversampled Image Acquisition Using Binary Poisson Statistics

We show how to construct and calibrate a full-Stokes imaging polarimeter system by combining the video data from two separate polarization cameras with a nonpolarizing beamsplitter and a waveplate. As a result, this system can capture the full Stokes vector at each pixel for 3 megapixel images at up to 60 Hz. To demonstrate some of the advantages of measuring the s 3 Stokes vector component that is normally not measured in polarization cameras, we show three experiments: viewing three-dimensional glasses, detecting a scarab beetle in a natural environment via the circular dichroism of its shell, and mixing an optically active liquid with a neutral liquid.

Video-rate full-Stokes imaging polarimeter using two polarization cameras

Overview and Outlook of Three-Dimensional Integrated Circuit Packaging, Three-Dimensional Si Integration, and Three-Dimensional Integrated Circuit Integration

We report on the IR sensitivity enhancement of back-illuminated CMOS Image Sensor (BI-CIS) with 2-dimensional diffractive inverted pyramid array structure (IPA) on crystalline silicon (c-Si) and deep trench isolation (DTI). FDTD simulations of semi-infinite thick c-Si having 2D IPAs on its surface whose pitches over 400 nm shows more than 30% improvement of light absorption at λ = 850 nm and the maximum enhancement of 43% with the 540 nm pitch at the wavelength is confirmed. A prototype BI-CIS sample with pixel size of 1.2 μm square containing 400 nm pitch IPAs shows 80% sensitivity enhancement at λ = 850 nm compared to the reference sample with flat surface. This is due to diffraction with the IPA and total reflection at the pixel boundary. The NIR images taken by the demo camera equip with a C-mount lens show 75% sensitivity enhancement in the λ = 700–1200 nm wavelength range with negligible spatial resolution degradation. Light trapping CIS pixel technology promises to improve NIR sensitivity and appears to be applicable to many different image sensor applications including security camera, personal authentication, and range finding Time-of-Flight camera with IR illuminations.

IR sensitivity enhancement of CMOS Image Sensor with diffractive light trapping pixels.

A 3.2-MP four-directional polarization image sensor with air-gap wire-grid polarizer is described. The image sensor was fabricated using a wafer process and incorporates back-illumination and an antireflection layer to minimize optical flaring and ghosting problems. In testing, the sensor achieved a polarization transmittance of 63.3% and an extinction ratio of 85 at 550 nm, thereby outperforming conventional polarization sensors. The proposed sensor also exhibited good oblique-incidence characteristics, even with small polarization pixels of $2.5~\mu \text{m}$ . Based on these results, the proposed image sensor is suitable for various megapixel fusion-imaging applications, such as reducing surface reflections, highly accurate depth mapping, and condition-robust surveillance.

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5- $\mu$ m Pixels

This paper presents a 1/2.3-inch 10.3Mpixel Back-Illuminated (BI) CMOS image sensor that targets both digital still camera (DSC) and high-definition camcorder applications. These applications require high-pixel-count, high-sensitivity, high saturation signal, low noise and high-speed imaging for image quality [1]. The sensor is scaled down to get a higher resolution due to higher pixel count. Several approaches such as a Cu process to reduce the pixel height and inner micro-lenses to gather rays of incident light have been proposed to overcome electro-optical challenges [2–4]. The BI process has been reported as one of the most promising technologies to improve optical performance [5,9]. This BI image sensor includes a 10b/12b analog-to-digital converter (ADC), an internal phase-locked loop (PLL) and a 10b serial LVDS interface to enable a data-rate up to 576MHz.

A 1/2.3-inch 10.3Mpixel 50frame/s Back-Illuminated CMOS image sensor

Polarization information is useful in highly functional imaging. This paper presents a four-directional pixel-wise polarization CMOS image sensor using an air-gap wire grid on 2.5-μm back-illuminated pixels. The fabricated air-gap wire grid polarizer achieved a transmittance of 63.3 % and an extinction ratio of 85 at 550 nm, outperforming conventional polarization sensors. The pixel-wise polarizers fabricated with the wafer process on back-illuminated image sensors exhibit good oblique-incidence characteristics, even with small polarization pixels of 2.5 μm. The proposed image sensor realizes mega-pixel various fusion-imaging applications, such as surface reflection reduction, highly accurate depth mapping, and condition-robust surveillance.

Four-directional pixel-wise polarization CMOS image sensor using air-gap wire grid on 2.5-μm back-illuminated pixels

There is provided a method of manufacturing an imaging device including a plurality of imaging elements in an imaging area, where each imaging element includes a photoelectric conversion unit in a substrate and a wire grid polarizer arranged at a light-incident side of the photoelectric conversion unit. The method generally includes forming the wire grid polarizer that includes a plurality of stacked strip-shaped portions, where each of the plurality of stacked strip-shaped portions includes a portion of a light-reflecting layer and a portion of a light-absorbing layer. The light-reflecting layer may include a first electrical conducting material that is electrically connected to at least one of the substrate or the photoelectric conversion unit. The light-absorbing layer may include a second electrical conducting material, where at least a portion of the light-absorbing layer is in contact with the light-reflecting layer.

Imaging element, method of manufacturing imaging element, imaging device, and method of manufacturing imaging device

PROBLEM TO BE SOLVED: To provide an imaging element having a constitution and a structure capable of suppressing the occurrence of discharge during the manufacture of a wire grid polarizing element.SOLUTION: An imaging element includes a wire grid polarizing element 50 including: a photoelectric conversion section 40; and a plurality of laminated structures 54 arranged side by side while being spaced from each other, each laminated structure including at least a strip-shaped light reflection layer 51 and a light absorption layer 53. The light reflection layer 51 is formed of a first conductive material, the light absorption layer 53 is formed of a second conductive material, and an extended portion 51a of the light reflection layer 51 is electrically connected to a substrate 31 or the photoelectric conversion section 40.SELECTED DRAWING: Figure 1

Yasushi Maruyama

Papers

3.2-MP Back-Illuminated Polarization Image Sensor With Four-Directional Air-Gap Wire Grid and 2.5- $\mu$ m Pixels

A 1/2.3-inch 10.3Mpixel 50frame/s Back-Illuminated CMOS image sensor

Four-directional pixel-wise polarization CMOS image sensor using air-gap wire grid on 2.5-μm back-illuminated pixels

Imaging element, method of manufacturing imaging element, imaging device, and method of manufacturing imaging device

Imaging element and manufacturing method therefor, and imaging device and manufacturing method therefor