Mitsuyoshi Mori

1/4-inch 2-mpixel MOS image sensor with 1.75 transistors/pixel

This paper presents new MOS image sensor technologies that realize ultra-small pixel size, i.e., 2.25/spl times/2.25 /spl mu/m/sup 2/, with high sensitivity and low supply voltage. A 1/4-inch 2-Mpixel MOS image sensor has been developed by a new pixel configuration and by a new pixel design with a 0.25-/spl mu/m CMOS process. In the new pixel configuration, a unit pixel consists of one photodiode (PD), one transfer transistor, and an amplifier circuit with three transistors which are shared by four pixels. As a result, the unit pixel has 1.75 transistors. High sensitivity has been achieved by a high aperture ratio of 25%. In the new pixel design, the low supply voltage of 2.5 V has been realized by optimizing both the potential profile in the PD and the gate length of the transfer transistor.

A 2.0-/spl mu/m pixel pitch MOS image sensor with 1.5 transistor/pixel and an amorphous Si color filter

In this paper, an ultrafine pixel size (2.0/spl times/2.0 /spl mu/m/sup 2/) MOS image sensor with very high sensitivity is developed. The key technologies that realize the MOS image sensor are a newly developed pixel circuit configuration (1.5 transistor/pixel), a fine 0.15-/spl mu/m design rule, and an amorphous Si color filter (Si-CF). In the new pixel circuit configuration, a unit pixel consists of one photodiode, one transfer transistor, and an amplifier circuit with two transistors that are shared by four neighboring pixels. Thus, the unit pixel has only 1.5 transistors. The fine design rule of 0.15 /spl mu/m enables reduction of wiring area by 40%. As a result, a high aperture ratio of 30% is achieved. A newly developed Si-CF realizes the 1/10 thickness of that of the conventional organic-pigment CF, giving rise to high light-collection efficiency. With these three technologies combined, a high sensitivity of 3400 electrons/lx/spl middot/s is achieved even with a pixel size of 2.0/spl times/2.0 /spl mu/m/sup 2/.

A 1/4in 2M pixel CMOS image sensor with 1.75 transistor/pixel

A 2.5V CMOS image sensor using a pixel configuration of four photodiodes in one unit sharing seven transistors is presented. This image achieves a 2.25/spl mu/m pixel pitch with 25% aperture ratio in a 0.25/spl mu/m IP2M CMOS process.

A 2.0 /spl mu/m pixel pitch MOS image sensor with an amorphous Si film color filter

A CMOS image sensor with an amorphous Si film color filter is implemented on a standard Si process. The color filter thickness is less than 100 nm. The sensor achieves a 30% aperture ratio by a 1.5 transistor/pixel architecture and a 0.15 /spl mu/m design rule.

6.6 A 1280×720 single-photon-detecting image sensor with 100dB dynamic range using a sensitivity-boosting technique

Continuous improvements in sensitivity have opened up applications for image sensors such as camcorders, digital still cameras, mobile phones, and surveillance cameras. Even though leading-edge image sensors have reached the noise floor of a few electrons [1,2], a thrust towards darker levels still continues down to an illumination level equivalent to being under a crescent moon (i.e., 10-2 down to 10-4 lux). This requires single-photon detection with typical digital cameras pixel size, i.e., 1.5 to 5μm. Although huge-size pixel [3] or single-photon avalanche photodiode (SPAD) based image sensors [4] have been presented for such a purpose, in general, both have to pay area and dark current penalties. Thus, an image sensor capable of both single-photon detection and normal imaging providing us with a high dynamic range is a huge technological challenge.

An APD-CMOS image sensor toward high sensitivity and wide dynamic range

We present a sensitivity-boosting technique by incorporating an avalanche photodiode into a normal photo-conversion region. Under a dark scene, an avalanche photodiode operation is selected, where the photo-electrons are multiplied up to 105 electrons. Under a bright scene, a photodiode operation is selected, where photo-electrons in proportional to light intensity are generated in a similar way to conventional CMOS image sensors. Alternating the two operations enables wide operational range extending to dark conditions.