Sony Corporation today announced the development of a back-illuminated CMOS image sensor (pixel size: 1.75µm square pixels, five effective mega pixels, 60 frames/s) with significantly enhanced imaging characteristics, including nearly twofold sensitivity*1 and low noise. This improved performance has been achieved by illuminating the backside of the silicon substrate, in contrast to conventional CMOS image sensors based on front-illumination technology.
The newly developed CMOS image sensor achieves a signal-to-noise ratio of +8dB(+6dB sensitivity, -2dB noise) in comparison to existing Sony CMOS image sensors of the same pixel size. Sony will apply this back-illuminated CMOS technology in consumer digital video camcorders and digital still cameras to deliver an even higher quality image experience. Conventionally, consumer digital video camcorders and digital still cameras have been required to combine high resolution capable of capturing every detail of the subject matter, and miniaturization oriented to portability. In order to meet these needs, image sensor development has focused on miniaturizing pixel size, while maintaining imaging characteristics. However, in addition to these ongoing requirements, in recent years demand for improved levels of minimum subject illuminance and rapid image capture has also increased. This has led to the requirement of image sensors with improved signal-to-noise ratio and other features capable of realizing improved overall picture quality.
Sony has retained the advantages of CMOS image sensors such as low power consumption and high-speed operation, while radically realigning their fundamental pixel structure from front-illumination to back-illumination to successfully develop a prototype, back-illuminated CMOS image sensor (pixel size: 1.75µm square pixels, five effective mega pixels, 60 frames/s) with improved sensitivity and noise reduction - the key factors to enhancing image quality.
With a conventional front-illumination structure, the metal wiring and transistors on the surface of the silicon substrate that form the sensor's light-sensitive area (photo-diode) impede photon gathering carried out by the on-chip lens, and this has also been an important issue in the miniaturization of pixels and widening optical angle response.