Smartphone camera is the most frequently used device for taking pictures today.
Photographs with family or friends, or shots of beautiful landscape or townscape―whatever the scene, image sensors are the crucial element that makes it possible for smartphone cameras to capture those scenes just like they appear to our eyes.
Though hidden from our view, the performance of this component directly influences the image quality. Smartphone cameras need to produce images as expected and offer stress-free operation. Sony‘s image sensors make it a reality with an array of functionality to support such requirements as great photos taken against a light source, accurate focusing, and clear image rendering even in a low luminosity environment.
One of the ways to improve the image quality of smartphone cameras is to increase the resolution by mounting more pixels, which requires miniaturization of the pixels. However, reducing the pixel size compromises the device sensitivity. Addressing this problem, Sony has developed what we call Quad Bayer structure, which minimizes the sensitivity loss due to physical size reduction of a pixel. It combines data signals from four adjacent pixels into one larger unit when the camera operates in a low luminosity environment, such as when capturing nightscapes. This effectively increases the pixel capacity four-fold, compensating the sensitivity, and makes clearer, noise-free still/movie images possible.
The auto focus feature is one of the essential components for ensuring the best shot moments. Sony’s all-pixel AF (Auto Focus) technology enables to mobilize all pixels to obtain focus information. This facilitates high-precision auto focus under a multitude of environmental conditions.
Precise focus is achieved by zooming in to the focus point even if it is a small area, such as small area of person's eyes or subject with blurred edges.
The all-pixel AF handles a variety of focus information, so it offers a reliable and highly accurate performance even in dark places.
In an environment with high contrast, taking a picture can be tricky. For example, a bright background can overshadow the face of the person in the frame. In such a situation, advanced HDR (High Dynamic Range) function automatically adjusts the brightness. It reduces the blowout or blackout and helps the rendering to be as close as how the scene appears to the human eyes. Scenes with a high dynamic range, such as an bright outdoor scenery seen from a dark indoor environment, can be captured as naturally as they appear to our eyes by resolving blowouts and blackouts.
In fact, nightscapes are also high-contrast images. The HDR function reduces the blowout effect of neon signs, making it possible to capture an image just like we see it.
The slow motion feature with the capacity up to 960 frames per second makes it easy to shoot scenes in slow motion just like we see it on TV or in cinema. It facilitates smooth slow-motion videos even of non-linear movements, such as a running animal. It is also useful to study your body movements, for example, to check your golf swing, tennis serve, etc.
Sony has always pursued high image quality, multi-functionality, and smaller sensor sizes ever since the advent of image sensors. Image sensors for smartphones are another area where the system developed by Sony are diffused worldwide.
Conventional CMOS image sensors adopt a so-called “front-illuminated structure,” in which the incident light passes through the metal wiring layer before reaching the photodiode. This structure has an issue of compromised light efficiency.
To address this issue, an idea of “back-illuminated structure” was explored, reversing the order of the photodiode and metal wiring. After overcoming great technical difficulties, this idea was finally commercialized in 2009. The back-illuminated CMOS image sensor is formed by attaching a substrate onto ready-formed circuit layer, reversing and polishing the surface, followed by mounting the color filter and micro lens on top. This structure enables to maximize the utilization of incident light without metal wiring and transistors obstructing its passage. As a result, the sensor sensitivity, which is crucial to the image quality, has been drastically improved.
In 2012, Sony made a successful breakthrough in mass-production of “stacked” image sensors, the first of the kind in the world. The stacked structure is based on the back-illuminated CMOS image sensor, with its supporting substrate replaced with a signal processing LSI, onto which a pixel section is “stacked.”
The structure comprises two components, a signal processing LSI with high performance capability that supports functionality enhancement, and a pixel section specially designed to improve photo quality, which are fabricated independently and stacked. This makes it possible to improve the sensor‘s functionality while reducing its size. Future enhancement includes the integration of intelligence (AI) features into the signal processing LSI, adding further value to Sony’s image sensors.