Fujifilm, Panasonic Develop Organic CMOS Sensor With Wide Dynamic Range

Jun 12, 2013
Masahide Kimura, Nikkei BP Semiconductor Research
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Fujifilm Corp and Panasonic Corp developed an organic CMOS image sensor technology that realizes a wide dynamic range of 88dB.

The new technology prevents over exposure even in a bright place and enables to take vivid video even with a dark subject, Fujifilm said.

The details of the technology were announced at the 2013 Symposia on VLSI Technology and Circuits, which runs from June 11 to 14, 2013, in Kyoto, Japan (lecture number: T2-4, C2-3). The titles of T2-4 and C2-3 were "Thin Organic Photoconductive Film Image Sensors with Extremely High Saturation of 8500 electrons/μm2" and "An Ultra-low Noise Photoconductive Film Image Sensor With a High-speed Column Feedback Amplifier Noise Canceller," respectively.

In recent years, the resolutions of CMOS image sensors have been improving because of the increase in pixel count. But the expansion of dynamic range, improvement of sensitivity, reduction of color mixture between pixels, etc are becoming the next challenges.

Panasonic has been improving the image quality of image sensor by using its semiconductor device technologies. On the other hand, Fujifilm developed an organic photoconductive film (OPF) with a high optical absorption coefficient instead of the silicon (Si) photo diode for the light-receiving part and has been establishing new image sensor technologies.

This time, by combining Fujifilm's OPF technologies and Panasonic's semiconductor device technologies, they co-developed an organic CMOS image sensor technology that realizes a higher performance than conventional image sensor technologies. With the new technology, it becomes possible to achieve a wide dynamic range of 88dB, which the companies claim is the highest in the industry, 1.2 times higher sensitivity and wide range of incident light angle, enabling to make cameras with higher sensitivities, higher image qualities and smaller sizes.

Fujifilm and Panasonic plan to use the organic CMOS image sensor technology for a wide range of applications such as security cameras, automotive cameras, mobile devices, digital cameras, etc.

0.5μ-thick OPF

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0.5μ-thick OPF

Traditional image sensors consist of Si photo diode in the light-receiving area, metal wires, color filter and on-chip micro-lens. But the new organic CMOS sensor technology uses an OPF for the light-receiving area. The thickness of the OPF is 0.5μm, which is several times thinner than that of a Si photo diode.

With this structure and Panasonic's semiconductor device technologies, Fujifilm and Panasonic achieved a signal saturation value that is four times higher than those of conventional image sensors. Moreover, by newly developing a circuit that reduces noise, they realized a dynamic range of 88dB.

For conventional image sensors, it is necessary to form metal wires for each pixel and a light-blocking film to prevent light from entering areas other than the photo diode area, limiting the area of the light-receiving part. This time, however, it becomes possible to form an OPF on the whole surface, enabling to improve sensitivity by about 20%.

Also, conventional Si photo diodes require a thickness of about 3μm in the depth direction, limiting their incident light angles to about 30-40°. This time, an incident light angle of 60° was realized by reducing the thickness of OPF.

Because oblique light can be efficiently used, a high color reproducibility that does not cause color mixtures can be achieved, Fujifilm said. Furthermore, a lens can be designed more freely, contributing to reducing camera size.

Fujifilm developed a process technology to form an inorganic thin film that protects the OPF. It prevents moisture and oxygen from entering the OPF so that they do not deteriorate the performance of the image sensor. The new technology realizes an organic CMOS sensor that can pass temperature, moisture, voltage and light stress tests and can be used for a variety of applications.