Stacked Image Sensor With Green- and Red-Sensitive Organic Photoconductive Films Applying Zinc Oxide Thin-Film Transistors to a Signal Readout Circuit

A vertically stacked image sensor composed of green (G)- and red (R)-sensitive organic photoconductive films, each having a thin-film transistor (TFT) that uses a transparent zinc oxide (ZnO) channel to read out a signal generated in the organic film, was fabricated. The effective number of pixels of the ZnO-TFT circuits was 1410 (47 times 30), and their pitch was 600 mum. The current on/off ratio and turn-on voltage of the ZnO-TFT were over 10⁵ and 1.5 V, respectively. The G- and R-sensitive organic photoconductive films showed excellent wavelength selectivity: the peak wavelength of the G-sensitive film was 540 nm, and that of the R-sensitive one was 700 nm. A color image with a resolution corresponding to the number of pixels was obtained by a shooting experiment with the fabricated image sensor, which clearly demonstrated color separation in the depth direction of the image sensor, using a stacked structure of wavelength-selective organic films with ZnO-TFT readout circuits.