An 8K4K-resolution 60fps 450ke − -saturation-signal organic-photoconductive-film global-shutter CMOS image sensor with in-pixel noise canceller

There is a growing demand for high-resolution and high-reality cameras for use in broadcasting, surveillance, and various other systems. Conventional papers report on research and development of 8K ultra-high-definition television (UHDTV) systems, 8K full-resolution cameras [1], and 8K 240fps cameras that employ stacked sensors [2]. In these camera systems, a rolling-shutter method is used for scanning, since a global-shutter method has an area tradeoff between the photoelectric conversion region and the charge storage region [3-5]. However, this leads to a shutter distortion problem during the high-speed imaging and synchronization of multi-viewpoint imaging. To overcome this problem, a CMOS image sensor is developed that has an 8K4k resolution, a 60fps frame rate, and a 450ke − saturation signal, with an organic photoconductive film (OPF) laminated on the pixel circuits. Even with small (e.g., 3μσι) pixels, a global shutter can be realized without degradation of the saturation signal [6]. However, there still remains a requirement to achieve 8K4K resolution at 60fps readout speed. There are three potential strategies to achieve this: 1) high-speed cancellation of reset noise in single storage-type global shutter pixels, 2) high-speed readout with a long vertical signal line, and 3) high-saturation in global-shutter mode. For 1), in the conventional case, a feedback amplifier (FBAMP) is allocated to each column to affect noise cancellation, but there is a long noise suppression time due to the large time constant of the vertical signal line. An in-pixel noise canceller is developed to shorten the noise suppression time even when the length of the vertical signal line becomes four times longer than with a Full High Definition (FHD) sensor. Moreover, to utilize the advantages of the OPF image sensor's stacked structure, high-capacitance Metal-Insulator-Metal (MIM) capacitors are allocated in the metal interconnect area. For 2), since the photoelectric conversion film is present at the upper layer, the photoelectric conversion characteristics are not affected, even if the number of vertical signal lines is increased. Therefore, two pairs of quadruple vertical signal lines are used for each vertical 8 pixels, and 16 sample-and-hold (S/H) capacitors are provided in each column. For 3), a high saturation circuit is developed without increasing the pixel size.