Nanoplasmonic filters for image sensors

As pixels shrink in CMOS detectors, scaling effects could lead to potential issues with existing colored filters because of their thickness (approx. 1μm). In this paper, we propose to investigate a new generation of filters that are potentially thinner by approximately a decade. Several years ago [1], nanometric metallic gratings have been found to have very unusual transmission properties. Especially, unexpected high transmission has been measured at specific wavelengths. Since these first experiments, studies have shown that very different optical processes can be responsible for these resonant transmissions, depending on the geometry of the grating. This has led to the demonstration of first applications in imaging[2]. With our designs, we show that such components are suitable for RGB color filters. We first discuss the theoretical performances and the integration of these components through modeling with rigorous electromagnetical techniques (RCWA and FDTD) in 2D and in 3D. As an example we evaluate the impact of the pixelization, the technological errors and the illumination conditions on the filter performances. Thanks to an algorithm that can optimize color correction matrix, we show that we have a satisfactory color rendering (dE=4.3). In a second part we realize these samples. We sputter Al layers on glass substrates and structure them with Focused Ion Beam technology that enables approximately 30 nm resolution. These structures are compatible in size with pixel dimensions (1.5 μm X 1.5 μm) and are tested with a dedicated micro-spectrometer.