Conventional semiconductors such as silicon and InGaAs based photodetectors have encountered a bottleneck in modern electronics and photonics in terms of spectral coverage, low resolution, non-transparency, non-flexibility and CMOS-incompatibility. New emerging 2D materials such as graphene, TMDs and their hybrid systems thereof, however, can circumvent all these issues benefitting from mechanically flexibility, extraordinary electronic and optical properties, as well as wafer-scale production and integration. Heterojunction-based photodiodes based on 2D materials offer ultrafast and broadband response from visible to far infrared range. Phototransistors based on 2D hybrid systems combined with other material platforms such as quantum dots, perovskites, organic materials, or plasmonic nanostructures yield ultrasensitive and broadband light detection capabilities. Notably the facile integration of 2D-photodetectors on silicon photonics or CMOS platforms paves the way towards high performance, low-cost, broadband sensing and imaging modalities.

Recent Progress and Future Prospects of 2D-based Photodetectors

The organic dye filters of conventional color image sensors achieve the red/green/blue response needed for color imaging, but have disadvantages related to durability, low absorption coefficient, and fabrication complexity. Here, we report a new paradigm for color imaging based on all-silicon nanowire devices and no filters. We fabricate pixels consisting of vertical silicon nanowires with integrated photodetectors, demonstrate that their spectral sensitivities are governed by nanowire radius, and perform color imaging. Our approach is conceptually different from filter-based methods, as absorbed light is converted to photocurrent, ultimately presenting the opportunity for very high photon efficiency.

Filter-Free Image Sensor Pixels Comprising Silicon Nanowires with Selective Color Absorption

Conventional semiconductors such as silicon- and indium gallium arsenide (InGaAs)-based photodetectors have encountered a bottleneck in modern electronics and photonics in terms of spectral coverage, low resolution, nontransparency, nonflexibility, and complementary metal-oxide-semiconductor (CMOS) incompatibility. New emerging two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and their hybrid systems thereof, however, can circumvent all these issues benefitting from mechanically flexibility, extraordinary electronic and optical properties, as well as wafer-scale production and integration. Heterojunction-based photodiodes based on 2D materials offer ultrafast and broadband response from the visible to far-infrared range. Phototransistors based on 2D hybrid systems combined with other material platforms such as quantum dots, perovskites, organic materials, or plasmonic nanostructures yield ultrasensitive and broadband light-detection capabilities. Notably the facile integration of 2D photodetectors on silicon photonics or CMOS platforms paves the way toward high-performance, low-cost, broadband sensing and imaging modalities.

Recent Progress and Future Prospects of 2D-Based Photodetectors

The rapid development of scientific CMOS (sCMOS) technology has greatly advanced optical microscopy for biomedical research with superior sensitivity, resolution, field-of-view, and frame rates. However, for sCMOS sensors, the parallel charge-voltage conversion and different responsivity at each pixel induces extra readout and pattern noise compared to charge-coupled devices (CCD) and electron-multiplying CCD (EM-CCD) sensors. This can produce artifacts, deteriorate imaging capability, and hinder quantification of fluorescent signals, thereby compromising strategies to reduce photo-damage to live samples. Here, we propose a content-adaptive algorithm for the automatic correction of sCMOS-related noise (ACsN) for fluorescence microscopy. ACsN combines camera physics and layered sparse filtering to significantly reduce the most relevant noise sources in a sCMOS sensor while preserving the fine details of the signal. The method improves the camera performance, enabling fast, low-light and quantitative optical microscopy with video-rate denoising for a broad range of imaging conditions and modalities. Scientific complementary metal-oxide semiconductor (sCMOS) cameras have advanced the imaging field, but they often suffer from additional noise compared to CCD sensors. Here the authors present a content-adaptive algorithm for the automatic correction of sCMOS-related noise for fluorescence microscopy.

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Fast and accurate sCMOS noise correction for fluorescence microscopy.

In the community of localization-based super-resolution microscopy (or called localization microscopy), it is generally believed that the emission of single molecules is so weak that an EMCCD (electron multiplying charge coupled device) camera is necessary to be used as the detector by eliminating read noise. Here we evaluate the possibility of a new kind of low light detector, scientific complementary metal-oxide-semiconductor (sCMOS) camera in localization microscopy. We demonstrate experimentally that sCMOS is capable of imaging actin bundles with FWHM diameter of 37 nm, evidencing the capability of sCMOS in localization microscopy. We further characterize the noise performance of sCMOS and find out that, with the use of a bright fluorescence probe such as d2EosFP, localization microscopy imaging is now working in the shot noise limited region.

Localization-based super-resolution microscopy with an sCMOS camera.

In this paper we describe a 55Mpixel 100 frames/sec wide-dynamic-range low-noise CMOS image sensor (CIS)
designed for scientific applications The sensor has 65μm pitch 5T pixels with pinned photodiodes and integrated
microlenses The 5T pixel architecture enables low noise rolling and global shutter operation The measured peak
quantum efficiency of the sensor is greater than 55% at 550nm, the Nyquist MTF is greater than 04 at 550nm, and the
linear full well capacity is greater than 35ke- The measured rolling and global shutter readout noise are 128e- RMS
and 254e- RMS respectively at 30 f/s and 20°C The pinned photodiode dark current is less than 38pA/cm2 at 20°C
The sensor achieves an intra-scene linear dynamic range in rolling shutter operation of greater than 86dB (20000:1) at
room temperature In global shutter readout the shutter efficiency is greater than 1000:1 with 500nm illumination

A 5.5Mpixel 100 frames/sec wide dynamic range low noise CMOS image sensor for scientific applications

This paper describes a CMOS image sensor technology suitable for the next generation of scientific cameras. We describe a prototype sensor with 320x240 pixels based on this technology. The sensor features 8 different types of 5T pixels with pinned photodiodes. All of the pixels have a 6.5um pitch and include an integrated micro-lens. The measured peak quantum efficiency of the sensor is greater than 50% at 550nm, and the read noise is less than 1e- RMS at room temperature. The linear full well capacity is greater than 40ke-, the dark current is less than 3.8pA/cm 2 at 20°C, and the MTF at 77 lp/mm is 0.4 at 600nm. The sensor also achieves an intra-scene linear dynamic range of greater than 92dB (40000:1) at room temperature.

Wide Dynamic Range Low Light Level CMOS Image Sensor

We present a CCD / CMOS hybrid focal plane array (FPA) for low light level imaging applications. The hybrid approach combines the best of CCD imaging characteristics (e.g. high quantum efficiency, low dark current, excellent uniformity, and low pixel cross talk) with the high speed, low power and ultra-low read noise of CMOS readout technology. The FPA is comprised of two CMOS readout integrated circuits (ROIC) that are bump bonded to a CCD imaging substrate. Each ROIC is an array of Capacitive Transimpedence Amplifiers (CTIA) that connect to the CCD columns via indium bumps. The proposed column parallel readout architecture eliminates the slow speed, high noise, and high power limitations of a conventional CCD. This results in a compact, low power, ultra-sensitive solid-state FPA that can be used in low light level applications such as live-cell microscopy and security cameras at room temperature operation. The prototype FPA has a 1280 x 1024 format with 12-um square pixels. Measured dark current is less than 5.8 pA/cm 2 at room temperature and the overall read noise is as low as 2.9e at 30 frames/sec.

CCD/CMOS hybrid FPA for low light level imaging

In this paper we present a VNIR solid state sensor technology suitable for next generation fused night vision systems.
This technology is based on a highly optimized low power 0.18um CMOS image sensor (CIS) process. We describe a
320(H) x 240(V) pixel prototype sensor based on this technology. The sensor features 5T pixels with pinned
photodiodes on a 6.5μm pitch with integrated micro-lens. The 5T pixel architecture enables both correlated double
sampling (CDS) and a lateral anti-blooming drain. The measured peak quantum efficiency of the sensor is greater than
50% at 600nm, and the read noise is less than 1e- RMS at room temperature. The sensor does not have any
multiplicative noise. The full well capacity is greater than 40ke-, the dark current is less than 3.8pA/cm2 at 20oC, and the
MTF at 77 lp/mm is 0.4 at 600nm. The sensor also achieves an intra-scene linear dynamic range of greater than 90dB
(30000:1) at room temperature.

Low-Light-Level CMOS Image Sensor For Digitally Fused Night Vision Systems

We present the design and test results of a prototype 4T CMOS image sensor fabricated in 0.18-µm technology featuring 20 different 6.5 µm pixel pitch designs. We review the measured data which clearly show the impact of the pixel topologies on sensor performance parameters such as conversion gain, read noise, dark current, full well capacity, non-linearity, PRNU, DSNU, image lag, QE and MTF. Read noise of less than 1.5e- rms and peak QE greater than 70%, with microlens, are reported.

Hung Do

Papers

A 5.5Mpixel 100 frames/sec wide dynamic range low noise CMOS image sensor for scientific applications

Wide Dynamic Range Low Light Level CMOS Image Sensor

CCD/CMOS hybrid FPA for low light level imaging

Low-Light-Level CMOS Image Sensor For Digitally Fused Night Vision Systems

Design of prototype scientific CMOS image sensors