One direction taken by sensor manufacturers for years is to maximize the surface sensitive to light, to optimize its capture. In this sense, first the back-illuminated sensors and then the “stacked” ones brought great innovations.
sony is among the leaders in this field and presented another innovation, which promises to raise the performance bar once again. Sony Semiconductor Solutions Company succeeded, in fact, in developing the first stacked CMOS image sensor with 2-Layer Transistor Pixel technology. Unlike normal CMOS image sensors, in which the photodiodes and pixel transistors occupy the same substrate, Sony’s new technology separates the photodiodes from the pixel transistors by placing them on different layers, maximizing the area dedicated to image capture. photons.
The transistor area still takes up a lot of space today, although circuits have already been moved “downstairs” in stacked sensors. A stacked CMOS image sensor adopts a layered structure: the pixel chip, composed of back-illuminated pixels, is superimposed on a logic layer, which houses the signal processing circuits. Inside the pixel chip, the photodiodes, which convert light into electrical signals, and the pixel transistors, which control the signals, are placed next to each other on the same layer.
Sony’s new architecture represents an evolution from today’s stacked CMOS image sensors. Still taking advantage of its exclusive stacked technology, Sony has managed to arrange the photodiodes and pixel transistors on separate substrates, positioned one above the other, adding a layer to the silicon sandwich. Moreover, as all the transistors, except the TRG (Transfer Gate), that is to say those of reset (RST), selection (SEL) and amplification (AMP), no longer have to share the layer with the photodiodes, it becomes possible increase the size of amplifier transistorscan work better on noise reduction.
The new architecture brings great advantages, practically succeeding in double the sensitive area: this also doubles the level of the saturation signal compared to conventional image sensors, widens the dynamic range and reduces noise thanks to the increased space for the amplifier transistors – all with the aim of improving the overall characteristics of capture of the sensor and the final quality of the images.
With the new technology, the pixels have a structure that allows them to maintain or improve their current properties, not only with the same dimensions, but also in the case of smaller pixels, and therefore also in the event of an increase in resolution and the number of pixels packed on the sensor.
According to the press release, the technology will likely be applied to smartphone sensors first, but as has already happened with the stacked BSI Exmor R and Exmor RS sensors, it could also land on cameras with large sensors.
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