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Sony redesigns back-lit CMOS for improved smartphone cameras

Jan 23, 2012 at 23:59 GMT

Sony has developed CMOS designs to offer improved performance on small sensors and is planning three such sensors for smartphones and similar devices. The 'Stacked CMOS' design builds on the backlit CMOS idea by building the light-sensitive photo element on top of the processing circuitry, rather than combining them in a single layer. This creates a greater light-sensitive area while also making more space for processing circuitry. The company has also demonstrated two feaures that use the extra circuitry space of the design.

The first of these features is what Sony is calling RGBW Coding, which appears to be another attempt at including clear (white) pixels in the sensor's color filter array. Sony has already used the idea to create brighter LCD panels and Kodak had previously promoted it for use in sensors (though we don't remember seeing it used).

The concept is to have some photosites featuring no color filter in front of them, so that they are exposed to more light (and therefore are less prone to noise), but lose the ability to distinguish between colors. This promises to improve low light performance but at the theoretical cost of some color resolution.

The HDR Video feature, meanwhile, attempts to boost dynamic range during video capture. Details from Sony are limited, beyond saying that the sensor works by 'setting two different exposure conditions within a single screen shooting' and then processing the different regions accordingly. We have requested more information.

Examples of an 8MP, 1/4" type sensor without either RGBW Coding or HDR video will become available from March 2012 with a larger, 13MP 1/3.06" type sensor following in June and a 8MP 1/4" sensor with both features arriving in August.

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CMOS Technology Press release

Sony Develops Next-generation Back-Illuminated CMOS Image Sensor which Embodies the Continuous Evolution of the Camera

Tokyo, Japan - January 23, 2012 - Sony Corporation (“Sony”) today announced that it has developed a new next-generation back-illuminated CMOS image sensor which embodies the continuous evolution of the camera. This image sensor layers the pixel section containing formations of back-illuminated structure pixels onto chips containing the circuit section for signal processing, which is in place of supporting substrates for conventional back-illuminated CMOS image sensors. This structure achieves further enhancement in image quality, superior functionalities and a more compact size that will lead to enhanced camera evolution.

Hereafter, Sony will position it as the next generation back-illuminated CMOS image sensors, and unwaveringly strive to further develop this image sensor and expand its product lineup, thereby contributing to the further development of user-friendly cameras and to shooting enjoyment.

Features of stacked CMOS image sensor

Background of development

The popularization of smartphones and other devices in recent years has been accompanied by an increasingly diverse use of camera functionality. This has brought heightened demand for more sophisticated cameras, to ensure adaptability to a wider range of scenes and Sony developed this stacked CMOS image sensor to meet such demand. In addition to the higher pixel numbers, superior image quality and faster speeds which conventional image sensors pursued, the newly-developed image sensors further achieve more highly-advanced functionalities and a more compact size, thus paving the way for enhanced camera evolution.

As the first step towards the commercialization of its new CMOS image sensors, Sony has developed a model with built-in signal processing functionality, an element that usually requires external embedment. Samples will be shipped from March, 2012. Accordingly, models have been developed with Sony’s unique “RGBW Coding” function, which facilitates low noise, high quality image capture even in low light condition, and the proprietary “HDR (High Dynamic Range) Movie” function, which achieves brilliant color even when taking pictures against bright light.

About stacked CMOS image sensors

Conventional CMOS image sensors mount the pixel section and analog 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 optimizing the characteristics of pixels and circuit transistors.

Sony has succeeded in establishing a structure that layers the pixel section containing formations of back-illuminated structure pixels over the chip affixed with mounted circuits for signal processing, which is in place of supporting substrates used for conventional back-illuminated CMOS image sensors. By this stacked structure, large-scale circuits can now be mounted keeping small chip size. Furthermore, as the pixel section and circuit section are formed as independent chips, a manufacturing process can be adopted, enabling the pixel section to be specialized for higher image quality while the circuit section can be specialized for higher functionality, thus simultaneously achieving higher image quality, superior functionality and a more compact size. In addition, faster signal processing and lower power consumption can also be achieved through the use of leading process for the chip containing the circuits.


Feature press release:

Sony Develops New “RGBW Coding” and “HDR Movie” Functions

Tokyo, Japan - January 23, 2012 - Sony Corporation (“Sony”) today announced the development of two CMOS image sensor models designed for use in smartphones and other devices. They are equipped with Sony's unique “RGBW Coding” function which allows images to be captured with low noise and high picture quality even in low-light conditions. They also contain Sony's “HDR (High Dynamic Range) Movie” function which allows brilliant color to be captured even in bright settings. Sony has also developed a model with built-in signal processing functionality, an element that usually requires external embedment.

Sony has successfully developed new stacked CMOS image sensor technology that realizes higher image quality and superior functionality in a more compact size. The three newly developed next-generation back-illuminated CMOS image sensor models will be the first to utilize this technology. Samples will begin to successively ship starting March 2012.

Background of development (new functions)

The recent proliferation of smartphones and other devices has increased casual shooting opportunities and there is demand for the evolution of cameras to be able to shoot in a diverse range of settings. In particular, consumers want to easily take pictures in low light conditions or those with both low and bright lights. Sony has incorporated its two newly developed models with its unique “RGBW Coding” function which enables high-sensitivity shooting even in low-light conditions and its “HDR Movie” function which can capture images or video across a broad dynamic range of low-light to bright-light conditions.

About the key functions incorporated in the new CMOS image sensors

1. Sony's unique “RGBW Coding” function enabling clear shooting in dark rooms or at night

The built-in “RGBW Coding” function which adds W (White) pixels to the conventional range of RGB (Red-Green-Blue) pixels has realized higher sensitivity, enabling high-quality shooting with low noise even in dark indoor or night settings.

While the addition of W (White) pixels improves sensitivity, it has the problem of degrading image quality. However, Sony's own device technology and signal processing realizes 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 the “RBGW Coding” function has realized a SN ratio (signal-to-noise ratio) equivalent to that of a unit pixel size of 1.4μm under conventional methods, which in turn has enables the image sensors to achieve a higher resolution at a more compact size.

The new models are also able to output signals through the conventional RGB method, thus there is no need to change the signal processing adopted in existing devices.

2. “HDR (High Dynamic Range) Movie” function which enables brilliant colors to be captured even in bright settings

The built-in “HDR Movie” function enables brilliant colors to be captured even in settings with a wide range of light including bright light.

Typically, when shooting with differing light levels, such as an indoor setting against a bright outdoor background, there can easily be blocked up shadows for dark areas or blown out highlights for bright areas. Such phenomena are a result of the combination of low-light and bright-light which have different optimal exposure conditions in the same shot. This function reduces this by setting two different exposure conditions within a single screen shooting and conducts the appropriate signal processing for the captured image information under each optimal exposure condition. This process generates an image with a broad dynamic range and enables shooting of both the background and subject matter with brilliant colors even in a bright environment.

Upcoming product launches (plan)

*1 Not equipped with “RGBW Coding” or “HDR Movie” functions