High-performance silver-dielectric interference filters for RGBIR imaging.

New architectures of interference silver-dielectric multilayer filters inspired from induced transmission designs are investigated with the prospect of high-performance red-green-blue (RGB) complementary metal oxide semiconductor imaging. The optimized designs provide combined colorimetric, signal-to-noise ratio and sensitivity performances similar to the traditional organic color filters, but without the equirement of an external infrared (IR)-cut filter, which enables the integration of additional channels such as white or IR, in addition to RGB. Due to the sub-micrometer thickness of the stacks, this is a unique solution for fully integrated, high-performance multispectral filters patterned in very small pixels. The concept is demonstrated by a wafer-scale prototype with RGBIR filters patterned down to 1.4 µm adjacent pixels with up to 80% transmission.

Multispectral interference filter arrays with compensation of angular dependence or extended spectral range.

Thin film Fabry-Perot filter arrays with high selectivity can be realized with a single patterning step, generating a spatial modulation of the effective refractive index in the optical cavity. In this paper, we investigate the ability of this technology to address two applications in the field of image sensors. First, the spectral tuning may be used to compensate the blue-shift of the filters in oblique incidence, provided the filter array is located in an image plane of an optical system with higher field of view than aperture angle. The technique is analyzed for various types of filters and experimental evidence is shown with copper-dielectric infrared filters. Then, we propose a design of a multispectral filter array with an extended spectral range spanning the visible and near-infrared range, using a single set of materials and realizable on a single substrate.

On-chip copper-dielectric interference filters for manufacturing of ambient light and proximity CMOS sensors.

Filter technologies implemented on CMOS image sensors for spectrally selective applications often use a combination of on-chip organic resists and an external substrate with multilayer dielectric coatings. The photopic-like and near-infrared bandpass filtering functions respectively required by ambient light sensing and user proximity detection through time-of-flight can be fully integrated on chip with multilayer metal-dielectric filters. Copper, silicon nitride, and silicon oxide are the materials selected for a technological proof-of-concept on functional wafers, due to their immediate availability in front-end semiconductor fabs. Filter optical designs are optimized with respect to specific performance criteria, and the robustness of the designs regarding process errors are evaluated for industrialization purposes.