Abstract
The modulation transfer function (MTF) characterizes the spatial frequency response of optoelectronic imaging devices and serves as a core indicator for evaluating imaging quality. The electron-bombarded active pixel sensor (EBAPS) is a new type of digital low-light-level imaging device. The electron emission from the photocathode, electron diffusion in the proximity region, and charge transport within the surface films of CMOS chips all exert remarkable effects on the device’s MTF. Therefore, establishing a physical MTF model for EBAPS is of important guiding significance for the optimal design of the proximity structure, surface films and overall structure of CMOS chips. Existing studies have investigated electron transport characteristics in the vacuum proximity region and solid-state substrate separately. However, the physical mechanism whereby the diffusion dynamics of multiplied electrons affect the MTF remains poorly understood. Based on the steady-state continuity equation, this paper constructs a full-link cascaded theoretical model for MTF. All physical processes, including photocathode electron emission, electron acceleration in the proximity region, as well as scattering and diffusion of multiplied electrons inside pixels, are integrated into a unified analytical framework and solved. Meanwhile, the validity of the proposed model is verified via resolution measurement results. Simulation results based on the established MTF model indicate that the doping concentration and thickness of the substrate primarily determine the charge collection boundary, while the initial lateral spread coefficient and surface recombination rate dominate the lateral diffusion range of electrons.