Continuous fabrication technology for improving resolution in RGB-stacked organic image sensor

Abstract

With the goal of developing a compact, high-resolution color camera, we have been studying about a novel image sensor with three stacked organic photoconductive films: each film is sensitive to only one of the primary color components, and each has a signal readout circuit. In this type of image sensor, the acceptable focal depth is roughly estimated to be shorter than about 20 μm when the pixel pitch of the sensor is several μm. To reduce the total thickness of the stack-type sensor, a continuous fabrication technology that entails stacking continuously all layers from the bottom to the top of the sensor is necessary. In the continuously stacked sensor, the three organic layers separated by interlayer insulators are formed close to each other on a single glass substrate. In this paper, we describe the elemental technologies for the continuous fabrication of a stack-type organic image sensor consisting of improving the heat resistance of organic films and decreasing the fabrication temperature of the interlayer insulators and signal readout circuits. A 150°C heat-resistant organic photoconductive film can be obtained by using organic materials possessing high glass-transition temperatures, and low-temperature fabrication of the interlayer insulator can be accomplished by metal oxides using atomic layer deposition (ALD) at 150°C. The amorphous In-Ga-Zn-O thin-film transistors (TFT) are fabricated at a maximum temperature of 150°C by using Al 2 O 3 gate insulator via ALD and a post-treatment. The resulting TFT has good transfer characteristics. A continuously-stacked organic image sensor can be fabricated by integrating these technologies.