Fujifilm, Panasonic Develop Organic CMOS Sensor With Wide Dynamic Range (page 2)

Jun 12, 2013
Masahide Kimura, Nikkei BP Semiconductor Research

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.