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This paper presents a time-resolved (TR) CMOS image sensor (CIS) using two-tap near-infrared (NIR) lock-in pixels with background light (BGL) cancelling capability for remote heart rate (HR) detection. Aimed to the application, the sensor features a 1024 (V) $\times $ 1280 (H) spatial resolution with 412 (V) $\times $ 1280 (H) region-of-interest-readout (ROI-readout) at 30 fps, a high sensitivity of 134.8 ke−/lux $\cdot $ s, and an ultra-low temporal random noise of 1.13 $\mathrm {e}_{\mathrm {rms}}^{\mathrm {-}}$ at analog gain of 64. A maximum charge modulation ratio of 90.1% is obtained for realizing lock-in operation by means of in-pixel lateral electric field charge modulator (LEFM). The remote HR detection is achieved by capturing the heart-beat-induced temporal variation of the oxy-hemoglobin (HbO2) concentration by the developed TR CIS with NIR lock-in technique, and larger than 98% detection accuracies are attained under both non-visible-light condition and fluctuant brightness ambient-light environments. This remarkable feature demonstrates the superiority of the proposed method for driver monitoring applications in particular.

Controlling and engineering the particle composition of semiconductor alloys is one of the topmost targets in the field of semiconductor materials science and technology. Quantum dot (QD) nanocrystals offer an unmatched opportunity to obtain a wide range of composition-controlled alloys and have captivated a great deal of interest recently. Herein, we report on band gap engineering via tuning and controlling the sulphur molar fraction (ternary shell layer) of quaternary/ternary core/shell alloyed CdZnSeS/ZnSeS QDs. Varying optical properties were exhibited by the alloyed QDs but a uniform particle size distribution was maintained across all the compositions. The alloyed QDs displayed bright emission colours under UV irradiation, whereas the photoluminescence quantum yields (PL QY) were in a remarkable range of 36–98%. Non-linearity of the lattice parameter was an indication of gradient alloying of the nanocrystals, whereas the kinetics of the optical properties unravelled the effect of intrinsic optical bowing. Displacement of bond length and anion mismatch influenced the optical properties of the QDs with respect to the variation in the PL QY. Alloyed CdZnSeS/ZnSe1.0S1.3 QDs with a spectacular PL QY were exploited as an ultrasensitive fluorescence reporter in a conjugated molecular beacon (MB) assay to detect influenza virus H1N1 RNA. Our detection system was rapid and highly sensitive for detecting extremely low concentrations of H1N1 RNA (down to 2 copies per mL), specific and versatile (detects H1N1 RNA in human serum). For proof of concept, the alloyed CdZnSeS/ZnSe1.0S1.3 QD-MB bioprobe exhibited a superior 12-fold sensitivity over an alloyed CdZnSeS-MB probe, while a conventional CdSe/ZnS-MB probe could not detect extremely low concentrations of influenza virus H1N1 RNA.

A programmable sub-nanosecond time-gated four-tap CMOS lock-in pixel (LIP) image sensor that uses an in-pixel pulse generator (PG) is developed for time-resolved (TR) biomedical imaging applications, such as a fluorescence lifetime imaging microscopy (FLIM). We demonstrate the system’s effectiveness with simulations and measurements. Using pixel-level PG circuits, very narrow time windows (TWs) that are less than 0.8 ns can be used for charge modulation. This rapid gating allows very weak signals from living cells to be captured with a high signal-to-noise ratio (SNR). The prototype CMOS imaging system displays a fast intrinsic response of 170 ps at 472 nm and a very low temporal random noise of 0.85 e-rms at 45 frames/s under truly correlated-double-sampling operation using two-stage charge transfer. Four outputs from the LIPs allow real-time fluorescence lifetimes (FLTs) measurement, even from samples with multiple FLT components.

A large full well capacity (FWC) for wide signal detection range and low temporal random noise for high sensitivity lock-in pixel CMOS image sensor (CIS) embedded with two in-pixel storage diodes (SDs) has been developed and presented in this paper. For fast charge transfer from photodiode to SDs, a lateral electric field charge modulator (LEFM) is used for the developed lock-in pixel. As a result, the time-resolved CIS achieves a very large SD-FWC of approximately 7ke-, low temporal random noise of 1.2e-rms at 20 fps with true correlated double sampling operation and fast intrinsic response less than 500 ps at 635 nm. The proposed imager has an effective pixel array of ${\text{128}}{\text{(H)}}\times {\text{256}}{\text{(V)}}$ and a pixel size of ${\text{11.2}}\times {\text{11.2}}\, \mu {\text{m}}^{2}$ . The sensor chip is fabricated by Dongbu HiTek 1P4M 0.11 $\mu {\text{m}}$ CIS process.

In this paper, a wide dynamic range (WDR) CMOS image sensor (CIS) with a charge splitting gate (SG) and two storage diodes (SDs) is presented. By using single-gate on/off control with the SG, photocurrent path to the first (SD1) or second storage diodes (SD2) is switched alternatively and periodically during exposure and signal electrons generated in a photodiode (PD) are transferred to and accumulated in the SD1 or SD2. By setting a large ratio of the off-time to on-time of the SG, two different sensitivity signals, which are originated by the same photodiode, are generated and a WDR image signal is obtained. This technique has a distinct advantage on mitigating the problem of motion artifact in WDR imaging with high and low sensitivity signals and flexible dynamic control of the dynamic range. An experimental WDR CMOS image sensor with 280 (H) &times, 406 (V)-pixel array consisting of 14 sub-arrays, each of which have 20 (H) &times, 406 (V) pixels, was implemented and tested. For the SG on/off-time ratio of 30 and 279, the DR of 93 dB and 104 dB, respectively, was demonstrated. The effect of the proposed WDR imaging operation on the reduced motion artifact was experimentally confirmed.

A CMOS lock-in pixel image sensor with embedded storage diodes and lateral electric field modulation (LEFM) of photo-generated charge is developed for fluorescence lifetime imaging. The time-resolved CMOS image sensor (CIS) with two-tap lock-in pixels achieves a very high time resolution of 10 ps when images are averaged over 30 frames, a very short intrinsic response time of 180 ps at 374 nm, and a low temporal random noise of $1.75{\text{e}}^{-}_{\text{rms}}$ with true correlated double sampling (CDS) operation. In addition, by using the LEFM and optimized process, a very high extinction ratio of approximately 94% at 472 nm laser diode is achieved. The usefulness of the proposed CIS is demonstrated for fluorescence lifetime imaging with the simulation and measurement results.

We propose a novel full-electronically controlled laser confocal microscope in which a liquid-crystal-on-silicon spatial light modulator and a custom CMOS imaging sensor are synchronized for performing multi-beam confocal imaging. Adaptive wavefront modulation for functional multi-beam excitation can be achieved by displaying appropriate computer generated holograms on the spatial light modulator, in consideration of the numerical aperture of the focusing objective. We also adopted a custom CMOS imaging sensor to realize multi-beam confocal microscopy without any physical pinhole. The confocality of this microscope was verified by improvements in transverse and axial resolutions of fluorescent micro-beads.

A low temporal read noise and high conversion gain reset-gate-less CMOS image sensor (CIS) has been developed and demonstrated for the first time at photoelectron-counting-level imaging. To achieve a high pixel conversion gain without fine or special processes, the proposed pixel has two unique structures: 1) coupling capacitance between the transfer gate and floating diffusion (FD) and 2) coupling capacitance between the reset gate and FD, for removing parasitic capacitances around the FD node. As a result, a CIS with the proposed pixels is able to achieve a high pixel conversion gain of $220~\mu \text{V}/\text{e}^{ {{-}}}$ and a low read noise of 0.27e $^{-}_{\text {rms}}$ using correlated multiple-sampling-based readout circuitry.

We have developed and evaluated the large full well capacity (FWC) for wide signal detection range and low temporal noise for high sensitivity lock-in pixel CMOS image sensor (CIS) embedded with two storage-diodes (SDs). In addition, for fast charge transfer from photodiode (PD) to SDs, a lateral electric field charge modulator (LEFM) is used for the developed lock-in pixel. As a result, the time-resolved CIS achieves a very large FWC of approximately 7000e-, low temporal random noise of 1.17e-rms at 45fps with true correlated double sampling (CDS) operation, and fast intrinsic response less than 500ps at 635nm. The proposed imager has an effective pixel array of 128(H)×256(V) and a pixel size of 11.2×11.2μm2. The sensor chip is fabricated by a Dongbu HiTek 1P4M 0.11μm CIS process.

Recently, CMOS time-resolved imaging devices are being widely used for scientific and medical applications. A fluorescence lifetime imaging microscopy (FLIM), which is a powerful analysis tool in fundamental physics as well as in the life science, is a typical application for the time-resolved imaging devices. For better time-resolution in the lock-in pixel design, a multi-tap pixel architecture is very effective and useful. In this paper, we have proposed an 8-tap CMOS lock-in pixel with lateral electric field charge modulator (LEFM) and demonstrated the effectiveness of designed pixel by CAD simulation. The proposed pixel makes possible to measure the highly time-resolved images with a high signal to noise ratio (SNR) and to observe various images of cells even if a sample has a multi-lifetime component. An 8-tap time-resolved CMOS image sensor chip is developed by 0.11μm 1P4M CIS process technology.

Fluorescence-based time-resolved (TR) analysis techniques are fundamental and effective methods in life science and medicine. Among others, fluorescence lifetime imaging microscopy (FLIM) is one of the representative measurement techniques for biomedical applications. Recently, advanced all-solid-state imaging devices for FLIM, e.g., a CCD with optional electron-multiplication (EM) readout, a single-photon avalanche diode (SPAD), and a TR CMOS image sensor (CIS), have been reported [1–3]. These devices can be implemented compactly in comparison with the typical FLIM systems such as a time-correlated single-photon counting (TCSPC) system [4]. However, imaging devices based on the CCD or SPAD still have some issues, including the need for specialized fabrication processes, use of higher voltages, and greater circuit complexity. The recent TR CIS with two taps in a pixel [3] shows us a way to realize real-time lifetime imaging, but the two-tap CIS has a limitation that a sample's lifetime cannot be measured in real time if the sample has multi-exponential decay components.

In the past several years, CMOS image sensors (CISs) with sub-single-electron noise level, particularly, deep sub-electron read noise (less than 0.5e-rms), have been reported. Such an ultra-low noise level is realized with a reduced floating diffusion (FD) node capacitance for attaining the high pixel conversion gain (CG) [1,2], and a high-gain readout circuitry with noise-reduction capabilities [3,4]. Recently, a reset-gate-less (RGL) CMOS image sensor has been reported [5]. It shows an excellent read noise performance using an optimized pixel structure for high CG and high-gain column ADC with multiple sampling. In this technique, however, a very high pulsed voltage of approximately 25V for the FD reset is essential to cause a punch-through effect. It is not suitable for image sensors with high pixel resolution and high-speed signal readout.

A CMOS lock-in pixel image sensor with embedded storage diodes in a pixel and lateral electric field modulator (LEFM) is developed for time-resolved measurements such as a fluorescence lifetime imaging microscopy (FLIM) and near-infrared spectroscopy (NIRS). The time-resolved CMOS image sensor (CIS) with two-tap lock-in pixels achieves a very high time resolution of 10ps when images are averaged over 30 frames, a very short intrinsic response time of 180ps at 374nm, and a low temporal random noise of 1.75e-rms with true correlated double sampling (CDS) operation. In addition, by using the LEFM and optimized process, a very high extinction ratio of approximately 94% at 472nm laser diode is achieved. The usefulness of the proposed CIS is demonstrated by the device simulations and the measurements. Then, we confirmed that the developed imager is very suitable for the scientific applications such as a biomedical imaging and multifunctional cameras.

A CMOS image sensor with deep sub-electron read noise and high pixel conversion gain has been developed. Its performance is recognized through image outputs from an area image sensor, confirming the capability of photoelectroncounting- level imaging. To achieve high conversion gain, the proposed pixel has special structures to reduce the parasitic capacitances around FD node. As a result, the pixel conversion gain is increased due to the optimized FD node capacitance, and the noise performance is also improved by removing two noise sources from power supply. For the first time, high contrast images from the reset-gate-less CMOS image sensor, with less than 0.3e− rms noise level, have been generated at an extremely low light level of a few electrons per pixel. In addition, the photon-counting capability of the developed CMOS imager is demonstrated by a measurement, photoelectron-counting histogram (PCH).

In the work described in this paper, an image reproduction scheme with an ultra-high-speed temporally compressive multi-aperture CMOS image sensor was demonstrated. The sensor captures an object by compressing a sequence of images with focal-plane temporally random-coded shutters, followed by reconstruction of time-resolved images. Because signals are modulated pixel-by-pixel during capturing, the maximum frame rate is defined only by the charge transfer speed and can thus be higher than those of conventional ultra-high-speed cameras. The frame rate and optical efficiency of the multi-aperture scheme are discussed. To demonstrate the proposed imaging method, a 5×3 multi-aperture image sensor was fabricated. The average rising and falling times of the shutters were 1.53 ns and 1.69 ns, respectively. The maximum skew among the shutters was 3 ns. The sensor observed plasma emission by compressing it to 15 frames, and a series of 32 images at 200 Mfps was reconstructed. In the experiment, by correcting disparities and considering temporal pixel responses, artifacts in the reconstructed images were reduced. An improvement in PSNR from 25.8 dB to 30.8 dB was confirmed in simulations.

Background It is important to devise efficient and easy methods of detecting colorectal tumours to reduce mortality from colorectal cancer. Dual-wavelength excitation autofluorescence intensity can be used to visualize colorectal tumours. Therefore, we evaluated dual-wavelength excitation autofluorescence images of colorectal tumours obtained with a newly developed, high-sensitivity complementary metal-oxide-semiconductor (CMOS) imager. Methods A total 107 colorectal tumours (44 adenomas, 43 adenocarcinomas with intramucosal invasion, and 20 sessile serrated adenoma/polyps [SSA/Ps]) in 98 patients who underwent endoscopic tumour resection were included. The specimens were irradiated with excitation light at 365 nm and 405 nm, and autofluorescence images measured with a 475 ± 25-nm band pass filter were obtained using a new, high-sensitivity CMOS imager. Ratio images (F365ex/F405ex) were created to evaluate the lesion brightness compared with that of normal mucosa, and specimens were categorized into a no signal or high signal group. Results Adenomas and adenocarcinomas were depicted in 87 ratio images, with 86.2 % (n = 75) in the High signal group. SSA/P was depicted in 20 ratio images, with 70.0 % (n = 14) in the High signal group. Conclusions Dual-wavelength excitation autofluorescence images of colorectal tumours can be acquired using our high-sensitivity CMOS imager, and are useful in detecting colorectal tumours.

To demonstrate the low-noise performance of the multi-aperture imaging system using a selective averaging method, an ultra-high-sensitivity multi-aperture color camera with 2×2 apertures is being developed. In low-light conditions, random telegraph signal (RTS) noise and dark current white defects become visible, which greatly degrades the quality of the image. To reduce these kinds of noise as well as to increase the number of incident photons, the multi-aperture imaging system composed of an array of lens and CMOS image sensor (CIS), and the selective averaging for minimizing the synthetic sensor noise at every pixel is utilized. It is verified by simulation that the effective noise at the peak of noise histogram is reduced from 1.44 e- to 0.73 e- in a 2×2-aperture system, where RTS noise and dark current white defects have been successfully removed. In this work, a prototype based on low-noise color sensors with 1280×1024 pixels fabricated in 0.18um CIS technology is considered. The pixel pitch is 7.1μm×7.1μm. The noise of the sensor is around 1e- based on the folding-integration and cyclic column ADCs, and the low voltage differential signaling (LVDS) is used to improve the noise immunity. The synthetic F-number of the prototype is 0.6.

Ultra-high-speed cameras are a powerful tool for biology as well as physics and mechanics to analyze the process of ultra-high-speed phenomena. The frame rate of the state-of-the-art burst-readout ultra-high-speed silicon imagers has reached approximately 20Mfps [1,2]. To observe faster phenomena such as plasma generation in laser processing, the state of electrons in a chemical reaction, and so on, much faster cameras are desired. There are several factors that prevent the speed-up of the ultra-high-speed imager: high gate control voltages and high power dissipation for high-efficiency multi-stage charge transfer in CCD imagers, and the current density limit of the power and ground lines and RC-constant of the vertical readout lines in CMOS imagers. Computational imaging can be a promising option to break the design limit of solid-state ultra-high-speed imagers. Several dedicated CMOS imagers have been demonstrated [3,4]. This paper presents a demonstration of a single-chip ultra-high-speed multi-aperture CMOS imager based on compressive sampling. The imager performs single-shot burst-readout image acquisition at a frame rate of 200Mfps.

This paper presents the design and implementation of a time-resolved CMOS image sensor with a high-speed lateral electric field modulation (LEFM) gating structure for time domain fluorescence lifetime measurement. Time-windowed signal charge can be transferred from a pinned photodiode (PPD) to a pinned storage diode (PSD) by turning on a pair of transfer gates, which are situated beside the channel. Unwanted signal charge can be drained from the PPD to the drain by turning on another pair of gates. The pixel array contains 512 (V) × 310 (H) pixels with 5.6 × 5.6 µm2 pixel size. The imager chip was fabricated using 0.11 µm CMOS image sensor process technology. The prototype sensor has a time response of 150 ps at 374 nm. The fill factor of the pixels is 5.6%. The usefulness of the prototype sensor is demonstrated for fluorescence lifetime imaging through simulation and measurement results.