AMEYA360:Panasonic Develops Organic Photoconductive Film (OPF) CMOS Image Sensor Technology

　　Panasonic Holdings Corporation announced that it has developed excellent color reproduction technology that suppresses color crosstalk by thinning the photoelectric conversion layer using the high light absorption rate of the Organic Photoconductive File (OPF) and by using electrical pixel separation technology.   

     In this technology, the OPF part that performs photoelectric conversion and the circuit part that stores and readouts the electric charge are completely independent.   This unique layered structure dramatically reduces the sensitivity of each pixel in green, red, and blue in wavelength regions outside the target range.   As a result, color crosstalk is reduced, excellent spectral characteristics are obtained, and accurate color reproduction is made possible regardless of the type of light source.

　　Conventional Bayer array-type silicon image sensors do not have sufficient color separation performance for green, red, and blue.   Therefore, for example, under light sources that have peaks at specific wavelengths, such as cyan light and magenta light, it has been difficult to accurately reproduce, recognize, and judge colors.

　　Our OPF CMOS image sensor has a unique structure in which the photoelectric conversion part that converts light into an electric signal is an organic thin film, and the function of storing and reading out the signal charge is performed in the circuit part, which are completely independent from each other (Figure 1). As a result, unlike with conventional silicon image sensors,   it is possible to provide photoelectric conversion characteristics that do not depend on the physical properties of silicon.   The OPF with its high light absorption rate enables the thinning of the photoelectric conversion part ((1) Photoelectric conversion film thinning technology).    

       By providing a discharge electrode at the pixel boundaries, the signal charge due to the incident light at the pixel boundaries is discharged, and the signal charge from adjacent pixels is suppressed ((2) Electrical pixel isolation technology).   In addition, since the under part of the OPF is covered with the pixel electrode for collecting the signal charge generated in the OPF and the electrode for discharging the charge, incident light that cannot be absorbed by the OPF does not reach the circuit side.   This suppresses the transmission ((3) Light transmission suppression structure).   With the above three technologies, it is possible to suppress light and signal charges that enter from adjacent pixels.   As a result, color crosstalk can be reduced to an almost ideal shape, as shown in the spectral characteristics shown in Figure 2, and accurate color reproduction is achieved regardless of the color of the light source (Figure 3).

　　This technology enables accurate color reproduction and inspection even in environments where it is difficult for conventional image sensors to reproduce the original colors, such as plant factories that use magenta light.   It is also possible to accurately reproduce the colors of substances with subtle color changes, such as living organisms.   It can also be applied to managing skin conditions, monitoring health conditions, and inspecting fruits and vegetables.   Furthermore, in combination with the high saturation characteristics and global shutter function of our OPF CMOS image sensor*, it can contribute to highly robust imaging systems that are highly tolerant of changes in light source type, illuminance, and speed.