No.174 March 2019

Presentations

  • Dark Current Reduction in Crystalline Selenium-based Stacked-type CMOS Image Sensors
    Shigeyuki IMURA, Keitada MINEO, Kazunori MIYAKAWA, Masakazu NANBA,
    Hiroshi OHTAKE and Misao KUBOTA
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    ABSTRACT

    We have been studying crystalline selenium (c-Se)-based stacked-type CMOS image sensors. There is a possibility that highly sensitive imaging devices can be obtained by using avalanche multiplication in a c-Se, which is a material that is highly absorptive in the visible region. The increase of the dark current in c-Se even in the low-electric field region (non-avalanche region) has been an issue. In this study, we optimized the growth conditions of the tellurium (Te) nucleation layer which is used to prevent the Se film from peeling, resulting in a reduction of the dark current in the non-avalanche region by improving the Se crystallinity. We fabricated the test device on glass substrates and successfully reduced the dark current to below 100 pA/cm2 (by a factor of 1/100) at a reverse-bias voltage of 15 V.
  • Improvement in Performance of Photocells Using Organic Photoconductive Films Sandwiched Between Transparent Electrodes
    Toshikatsu SAKAI, Tomomi TAKAGI, Yosuke HORI, Takahisa SHIMIZU,
    Hiroshi OHTAKE and Satoshi AIHARA
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    ABSTRACT

    We have developed a novel type of image sensor that is overlaid with three different organic photoconductive films; each is sensitive to only one of the three primary colors. Toward highly sensitive image sensors, we have developed high performance photocells with quantum efficiencies of about 80%, for each R/G/B-sensitive photocell sandwiched between transparent ITO electrodes.
  • Development of Three-Dimensional Integrated Image Sensors with Pixel-Parallel Signal Processing
    Masahide GOTO, Yuki HONDA, Toshihisa WATABE, Kei HAGIWARA,
    Masakazu NANBA and Yoshinori IGUCHI
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    ABSTRACT

    We studied a three-dimensional integrated image sensor that is capable of pixel-parallel signal processing, thereby meeting the demand for high-resolution and high-frame-rate imaging. Photodiodes, pulse generation circuits and 16-bit pulse counters are three-dimensionally integrated within every pixel by direct bonding of silicon on insulator (SOI)layers with embedded Au electrodes, which provides in-pixel pulse frequency modulation A/D converters. The developed sensor has excellent linearity with a dynamic range of more than 96 dB, corresponding to a 16-bit value. Pixel-parallel video images with Quarter Video Graphics Array (QVGA) resolution were obtained, demonstrating the feasibility of these next-generation image sensors.