180nm gate length amorphous InGaZnO thin film transistor for high density image sensor applications

In this article, we propose a novel hybrid complementary metal oxide semiconductor (CMOS) image sensor architecture utilizing nanometer scale amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFT) combined with a conventional Si photo diode. This approach will overcome the loss of quantum efficiency and image quality due to the downscaling of the photodiode. The 180nm gate length a-IGZO TFT exhibits remarkable short channel device performance including a low 1/f noise and a high output gain, despite fabrication temperatures as low as 200°C. The excellent device performance has been achieved by a double layer gate dielectric (Al₂O₃/SiO₂) and a trapezoidal active region formed by a tailored etching process. A self aligned top gate structure was employed for low parasitic capacitance. 3D process simulation tools were applied to optimize a four pixel CMOS image sensor structure. The results demonstrate how our stacked hybrid device approach contributes to new device strategies in image sensor architectures. We expect that this approach is applicable to numerous devices and systems in future micro- and nano-electronics.