Problem
Multipixel image sensors are widely used in digital camera, LIDAR, medical imaging devices, and other equipment. For color image sensors, typically arrays of pixel elements are used for each pixel position. Light reaches each pixel element through a respective color filter, so each pixel element responds primarily to a single color, for example red, green, or blue. Spatial resolution of such sensors has improved over the years to make it practical to pack millions of pixel positions in a single sensor, with pitch from several microns (micrometers) down to less than a micron. The size of the individual color filters needs to be reduced accordingly. Multispectral imaging is an imaging variation that involves not only spatial but also spectral imaging and may use more than four photodiodes per pixel position. Consequently, the filter complexity is increased for multispectral imaging. At present, there are limited manufacturing options for efficiently creating high-performance on-chip filters.
Solution
We have invented on-chip CMOS compatible bandpass filters which are predicted to achieve less than 40 nm Full-Width-Half-Maximum bandwidth with a transmission of greater than 50%. Each wavelength specific bandpass filter has the same layer material sequence, and maintains the same total physical thickness for filter wavelengths over the 350 nm - 950 nm wavelength range. Our technology will allow image sensor manufacturers to optimize their multispectral camera systems achieving new levels of performance and resolution.