The monolithic active pixel sensor (MAPS) technology is widely used for high-energy particle-collision experiments. When the serious radiation damage near the collision points in the experimental environment is considered, a study on the radiation hardness of the MAPS chip is an essential part of the chip R&D process. Especially, study on the details of the non-ionizing energy loss (NIEL) effect on the chip has not shown much progressed because the electron trap processes in the silicon pixel chips are not well known. In this research, the charge collection efficiency (CCE) was studied for various MAPS chips irradiated by neutrons of a few 10$^{13}\cdot$1 MeV n$_{\mathrm{eq}}$/cm$^2$ with $^{55}$Fe in the laboratory chip test system built in the Heavy Ion Physics Experiment (HIPEx) Laboratory of Pusan National University.

Keywords: Silicon pixel detector, CMOS imaging sensor, Non-ionizing energy loss (NIEL) effect, Pixel chip characterization, Charge collection efficiency