Inorganic Phosphor Coatings for Ultraviolet Responsive Image Detectors

Abstract

Typical CCD digital imaging sensors are insensitive to ultraviolet ( UV ) radiation by virtue of the very shallow ( 2 nm ) penetration depth in silicon. This warrants the use of a post-packaging coating to up-covert the UV radiation to longer wavelengths. In this thesis, A light-converting inorganic coating has been developed to improve the responsivity of gated CCD image sensors in the UV ( from 250 - 400 nm ). The coating consists of a plastic acrylic layer doped with inorganic phosphors. The coating is deposited using a spin-coater typically used by the IC fabrication industry. Inorganic phosphors were selected over organic phosphors since they are quite well established and are typically used to coat light bulbs, an application that requires a long lifetime. In contrast, organic phosphors rapidly degrade upon exposure to UV radiation. The parameters associated with the coating and coated sensor are presented here. They include coating conversion effciency, penetration depth, photostability; and coated sensor quantum effciency, contrast transfer function and photo-response non-uniformity. The coatings presented here are a viable, cost-effective alternative to other UV response CCD designs.