Sony Unveils New CMOS Sensor

June 27, 2008: Sony has developed a new CMOS sensor that collects light through its silicon substrate and provides higher sensitivity and lower noise than previous sensors, according to a report in JPEA International PEN News Weekly.

With a photosite surface area of 1.75-by-1.75 micrometers and resolution of 5-megapixels, the new sensor supports frame rates up to 60 fps. 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 advises it will apply this back-illuminated CMOS technology in consumer digital video camcorders and digital still cameras ‘to deliver an even higher quality image experience’.

The diagram above shows the structure of the new sensor. (Source: Sony.)
According to the report, in conventional sensor design, the amount of light reaching photosites is limited by the wiring, transistors and dielectric layers in the sensor chip, which enable photons to be converted into electrons. Together they can prevent the light collected by the on-chip microlenses from reaching the photosites, thereby reducing the fill factor and causing additional problems such as cross talk between the photosites.

Conventional sensor design, showing the light path through metal wiring. (Source: Sony.)

Sony’s new sensor design in which the wiring is below the light-sensitive area. (Source: Sony.)
By allowing light to reach the silicon substrate directly, the new sensor design minimises these problems. At the same time, according to Sony, it doubles the sensor’s sensitivity and reduces noise to half that of similar-sized conventional front side illuminated CMOS sensors. No details have been provided about when the new sensors will be released in cameras.