Sony has developed back-illuminated CMOS image sensor stacked directly on a signal processing chip instead of the substrate typically used.
“Conventional CMOS image sensors mount the pixel section and analogue logic circuit on top of the same chip, which require numerous constraints when wishing to mount the large-scale circuits such as measures to counter the circuit scale and chip size, measures to suppress noise caused by the layout of the pixel and circuit sections, and optimising the characteristics of pixels and circuit transistors,” said the firm.
By using stacking, the product is smaller and the two die can be produced on processes optimised for their function.
The firm is also claiming faster signal processing and lower power consumption.
At the same time, the firm is introducing ‘RGBW coding’ to cut image noise in poor lighting conditions, and ‘HDR (high dynamic range) movie’ to retain colour in bright light.
RGBW coding adds white pixels to the conventional RGB pattern.
“While the addition of white pixels improves sensitivity, it has the problem of degrading image quality,” said Sony, claiming: “Our device technology and signal processing realises superior sensitivity without hurting image quality.”
“Furthermore, while the individual pixels of the newly developed models are extremely minute at 1.12µm, the incorporation of RGBW coding has realised a signal-to-noise ratio equivalent to that of a conventional 1.4µm pixel.”
There is an RGB mode for more traditional image processing.
A technique borrowed from high-end stills cameras, HDR movie sets two different exposure conditions, then combines the exposures to create a single image with wider dynamic range.
Planned product include:
Stacked 1/4 CMOS sensor with ~8Mpixel(effective) - sampling March
Stacked 1/3.06 CMOS sensor with ~13Mpixel(effective) plus RGBW coding and HDR movie - sampling June
Stacked 1/4 CMOS sensor with ~Mpixel(effective) plus RGBW coding and HDR movie - sampling August.