CMOS image sensor development at Sony began in 1996 and led to the launch of our first CMOS image sensor (IMX001) in 2000. At the time, CMOS image sensors produced noisy images under low light and were also inferior to CCD image sensors in the number of pixels. However, the lower readout speed of CCD image sensors convinced us that they would be unable to support high-resolution data as the industry moved from SD to HD video. In 2004, we therefore changed course greatly by shifting our focus from CCD to CMOS image sensor development. It was a bold decision. Instead of holding the world’s number one share in CCD image sensors, we would be building on a negligible market share in CMOS image sensors.
Later in 2007 we commercialized CMOS image sensors with an original column A/D conversion circuit for fast, low-noise performance, followed in 2009 by back-illuminated CMOS image sensors with twice the sensitivity of conventional image sensors – beyond the human eye.
Further examples of technical innovation that has enabled us to constantly lead the industry include stacked CMOS image sensors in 2012 – with higher image quality and multiple functions in a smaller package, thanks to layering of the pixel and signal-processing sections – and, in 2015, the world’s first image sensors with a Cu-Cu connection, enabling smaller packages, higher performance, and greater productivity in manufacturing.
Column-Parallel A/D conversion circuit-equipped CMOS image sensors (commercialized in 2007)
These sensors use original Column-Parallel A/D conversion technology, with an A/D converter for each vertical row of pixels, arranged in a parallel configuration.
In this arrangement, analog signals read from the vertical signal lines can be conveyed directly to each row’s ADC across a minimal distance, which reduces loss of image quality from noise entering the signal during analog transmission and accelerates signal readout. Noise is also reduced through dual noise cancellation, with high-precision cancellation applied to both analog and digital circuits.
Back-illuminated CMOS image sensors (commercialized in 2009)
These image sensors adopt an innovative back-illuminated structure that offers lower noise and nearly double the sensitivity of conventional front-illuminated CMOS image sensors.
Without interference from wiring or transistors, light is received from the back side of silicon substrate, which increases the amount of light entering each pixel and reduces loss of sensitivity relative to light entering at various angles. This enables smooth, clear images even at night or in other low-light conditions.
Stacked CMOS image sensors (commercialized in 2012)
In the stacked structure adopted by these image sensors, the pixel section where back-illuminated pixels are formed is layered over a chip (instead of the supporting substrate used in conventional back-illuminated CMOS image sensors) where signal processing circuits are formed.
One advantage is that large-scale circuits can be mounted on a small chip. Since each section is formed on a separate chip, specialized manufacturing processes can be used to produce a pixel section with high image quality and a circuit section with high performance, enabling higher resolution, multi functionality, and a compact size.
Stacked CMOS image sensor with Cu-Cu connections (commercialized in 2015)
Cu-cu connections involve direct connections between the copper pads formed on the layering surfaces of pixel chips and logic circuit chips. Without the need to provide electrical connections through pixel chips or special areas for connections, manufacturers can make smaller image sensors at a higher rate of productivity. Offering greater freedom in pin layout and higher density, the technology will help enable stacked CMOS image sensors with expanded functionality.