Design of Small-Molecular Organic Photo-Diode CMOS Image Sensor for High Photo-Current by Absorbing Red-Light

Abstract

In the era of the 4th industrial revolution, as the market for smartphones and autonomous vehicles grew, the market size of image sensors also increased. Compared to charge-coupled devices, CMOS image sensors can be fabricated in a CMOS process and are rapidly growing due to their low power advantage. Currently, one of the biggest problems of CMOS image sensors is that the pixel size is reduced in order to realize high resolution in the same sensor size, and the light-receiving area is reduced, making it difficult to detect signals. In an effort to solve this problem, it changed from front-illuminated type to rear-illuminated type from 2 microns or less, and increased light-receiving efficiency by increasing light-receiving efficiency by using technologies such as Samsung Electronics ‘ISOCELL’ and 'TETRACELL' at less than 2 microns. We are continuing our efforts to make it. In this study, organic photodiode design was carried out as one of various methods to increase light-receiving efficiency. Search for low-molecular organic substances with an absorption rate of 80% or more in the red wavelength, find the donor material TiOPc and the acceptor material ZnPC, calculate the band gap using Tauc plot, and verify organic photodiodes that can be used in both front-illuminated and back-illuminated types. The structure test was carried out. In addition, in order to find the optimal thickness of the organic material, the donor material is fixed at 100nm and the acceptor material is deposited at 125nm, 150nm and 175nm to design a red organic photodiode with a sensing margin of 1.13V at 175nm through current voltage characteristics and pulse operation. Thus, it achieved 1.37 times the RED light absorption efficiency compared to the existing silicon photodiode (0.84V). Through this study, it was confirmed that organic materials can absorb a specific wavelength and replace the color filter of conventional silicon photodiodes.