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This paper presents a dynamic range expansion technique for CMOS image sensors using dual charge storage in a pixel and multiple exposures. Each pixel contains two photodiodes, PD1 and PD2 whose sensitivity can be set independently by the accumulation time. The difference of charge accumulation time in both photodiodes can be widely controlled to expand the dynamic range of the sensor. It allows flexible control of the dynamic range since the accumulation time in the PD2 signal is adjustable. The multiple exposure technique used in the sensor reduces the motion blur in the synthesized wide dynamic range image when capturing fast-moving objects. It also reduces the signal-to-noise ratio dip at the switching point of the PD1 signal to the PD2 signals in the synthesized wide dynamic range image. To reduce the read out time, a comparator-controlled selective readout of the PD1 and PD2 signals has been tested. The synthesis of the captured images to produce wide dynamic range image is also described. A wide dynamic range image sensor with 320x240 pixels has been implemented and tested. It is found that the use of 4 exposures in one frame for the short accumulation time signals is sufficient for the reduction of motion blur in the synthesized wide dynamic range image, and the signal-to-noise ratio dipping at the switching point of the PD1 to PD2 signals is reduced by 6 dB using 4 short-time exposures.

A CMOS active pixel sensor has been designed and fabricated using standard 2-poly and 4-metal CMOS processing technology. The CMOS active pixel sensor has been made up of a unit pixel having a highly sensitive PMOSFET photo-detector and electronic shutters that can control the light exposure time to the PMOSFET photo-detector, correlated-double sampling (CDS) circuits, and an 8-bit two-step flash analog to digital converter (ADC) for digital output. This sensor can obtain a stable photo signal in a wide range of light intensity. It can be realized with a special function of an electronic shutter which controls the light exposure-time in the pixel. Moreover, this sensor had obtained the digital output using an embedded ADC for the system integration. The designed and fabricated image sensor has been implemented as a pixel array. The area of the unit pixel is and its fill factor is about 35 %.

We report on the first implementation of a single-photon avalanche diode (SPAD) in 90nm complementary metal oxide semiconductor (CMOS) technology. The detector features an octagonal multiplication region and a guard ring to prevent premature edge breakdown using a standard mask set exclusively. The proposed structure emerged from a systematic study aimed at miniaturization, while optimizing overall performance. The guard ring design is the result of an extensive modeling effort aimed at constraining the multiplication region within a well-defined area where the electric field exceeds the critical value for impact ionization. The device exhibits a dark count rate of 8.1 kHz, a maximum photon detection probability of 9% and the jitter of 398ps at a wavelength of 637nm, all of them measured at room temperature and 0.13V of excess bias voltage. An afterpulsing probability of 32% is achieved at the nominal dead time. Applications include time-of-flight 3D vision, fluorescence lifetime imaging microscopy, fluorescence correlation spectroscopy, and time-resolved gamma/X-ray imaging. Standard characterization of the SPAD was performed in different bias voltages and temperatures. (C) 2010 Optical Society of America

In this paper, a CMOS image sensor for fluorescence lifetime imaging (FLIM) is presented. The fluorescence lifetime is a powerful tool to analyze molecules because the fluorescence lifetime reflects a molecule's structure, dynamics, and environments. The proposed CMOS FLIM sensor consists of pixel array to realize the sifting ability for fluorescence, noise canceling column readout amplifiers, and output buffers. The pixel has a photodiode and an image intensifier to sift fluorescence from the excited light pulses. A prototype CMOS FLIM sensor with 320(H) times 80(V) pixels is designed and implemented in 0.18 mum CMOS technology. The results show that the CMOS FLIM sensor has the ability to sift fluorescence from the excited light pulses using a blue and an ultraviolet light-emitting diodes. It also shows that the CMOS FLIM sensor can measure the lifetime in a wide range of fluorescence lifetime.

In this paper, a novel photodetector using an N-channel metal oxide semiconductor field effect transistor (NMOSFET) with a 30 nm-wide silicon nano-wire is described. The photodetector was fabricated on silicon-on-insulator (SOI) substrate and its wire was patterned by optical lithography, electron beam lithography and thermal oxidation. At room temperature, the device has similar I DS-V DS characteristics to a general NMOSFET when incident light is supplied instead of the gate voltage. A maximum responsivity of higher than 1×102 A/W and optical transient time of 80 µs have been obtained. Additionally, for the purpose of demonstrating the feasibility of the new device application, a 1×16 complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) connected with the novel photodetector array was also designed and fabricated using 1-poly and 2-metal 1.5 µm CMOS technology. It is confirmed that this photodetector with high sensitivity as well as nano-scaled area could be applied to an image acquisition system for low illumination level.

We present the first avalanche photodiode (APD) successfully fabricated in standard 65nm CMOS technology. The APD operates both in proportional and Geiger mode at -60C to +60C temperature range. The device comprises an octagonal n+p-well junction surrounded by an n-tub guard-ring; its photon detection probability peaks at 450nm with 200mV excess bias and it is above 1% between 350 and 750nm. The dark count rate is 1.5kHz/μm2 at 200mV excess bias, while afterpulsing is less than 1% for a dead time longer than 5μs and timing jitter is better than 235ps. Applications include low-power, ultra-high-speed quantum number generators, time-of-flight 3D image sensors, LIDAR detectors, and time-resolved spectroscopy.