Analysis of electron scattering in thin dielectric films used as ion barriers in Generation III image tubes

Abstract

In Generation III image intensifier (I 2 ) tubes, the input of the microchannel plate (MCP) is typically coated with a thin dielectric film to prevent ions generated in the MCP during operation from migrating back to the cathode and damaging the delicate (Cs:O) activation layer. While dramatically improving operational life, the presence of the film serves as a scattering center for the signal electrons and significantly reduces the signal-to-noise ratio (SNR) of the image tube. To prevent or minimize the impact of the ion barrier film (IBF) on tube performance the night vision industry has focused on reducing the thickness of the IBF or more preferably in developing a process that completely removes the film (unfilmed) to improve the SNR while maintaining operational life. In this paper, we present an overview of the role of the ion barrier in Generation III image intensifiers and present the results of a Monte Carlo simulation on electron transport through dielectric films with varying stoichiometry, thickness, and accelerating voltage.