The invention refers to an electromagnetic radiation sensor micro device for detecting electromagnetic radiation, which device comprises a substrate and a cover at least in part consisting of an electromagnetic radiation transparent material, and comprising a reflection reducing coating and providing a hermetic sealed cavity and an electromagnetic radiation detecting unit arranged within the cavity. The reflection reducing coating is arranged in form of a multi-layer thin film stack, which comprises a first layer and a second layer arranged one upon the other. The first layer has a first refractive index and the second layer has a second refractive index different from the one of said first layer. First and second layer are of such layer thickness that for a certain wavelength there is destructive interference. The invention also refers to a wafer element as well as method for manufacturing such a device.