High-sensitivity and no-crosstalk pixel technology for embedded CMOS imagesensor

A high-photosensitivity and no-crosstalk pixel technology has been develope d for an embedded active-pixel CMOS image sensor, by using a 0.35-mum CMOS logic process. To increase the photosensitivity, we developed a deep p-well photodiode and an antireflective film, consisting of Si3N4 film, for the p hotodiode surface. To eliminate the high voltage required for the reset tra nsistor in the pixel, we used a depletion-type transistor as the reset tran sistor. The reset transistor also operates as an overflow control gate, whi ch enables antiblooming overflow when excess charge is generated in the pho todiode by high-illumination conditions. To suppress pixel crosstalk caused by obliquely incident light, a double-metal photoshield was used, while cr osstalk caused by electron diffusion in the substrate was suppressed by usi ng the deep p-well photodiode. A 1/3-in 330-k-pixel active-pixel CMOS image sensor was fabricated using this technology. A sensitivity improvement of 110% for 550-nm incident light was obtained by using the deep p-well photod iode, while an improvement of 24% was obtained by using the antireflective film. The pixel crosstalk was suppressed to less than 1% throughout the ran ge of visible light.