Demonstrations of Polarization Imaging Capability and Novel Functionality of Polarization-Analyzing CMOS Image Sensor with 65 nm Standard CMOS Process

Polarization sensing is one of the important optical measurement scheme used in various scientific and industrial applications. For instance, an optical rotation measurement is widely used to measure chirality of chemical species. The polarization of light is modulated when the light propagates the optically active material such as saccharide or protein. Polarization rotation reflects concentration and chirality of the measured materials. Not only as a single-beam measurement, but also in imaging, the polarization detection is expected to be an effective functional extension. Polarization mapping in captured images provides information of imaged objects such as reflectance, roughness, and relative angle of planes. Various technical approaches have been proposed and demonstrated to realize semiconductor photosensor and CMOS image sensor 1)-7). In order to realize polarization-analyzing CMOS image sensors, we have proposed and demonstrated a design strategy to use monolithically embedded polarizer within standard CMOS processes 8)-13). Fig. 1 shows concept of our works. Wire grid structure made of metal wiring layer in CMOS process were integrated on photodiodes of image sensor pixels. We demonstrated that the wire grid structure works as an on-pixel polarizer. This approach has technical advantages such as; 1. Since the polarizers are integrated in the CMOS fabrication process, no post-process is required to realize polarization detection function. 2. On-chip polarizers are accurately aligned to the pixel array, and it guarantees the angular datum. 3. Flexible pixel-by-pixel polarizer angle variation is available. In our previous works, taking the advantage 3, we designed an array of polarization-analyzing pixels with different polarizer angles (from 0 to 179 deg., in 1 deg. step) with 0.35 μm standard CMOS process8)-9). Combined with a linearly polarized light source with fixed polarization angle, we can obtain a polarization profile covering the whole angle in single frame measurement, without rotating the polarization of Abstract A polarization-analyzing CMOS image sensor with 65 nm standard fabrication process was designed and characterized. Polarization-analyzing image sensor pixel was realized using wire grid structures designed with a metal wiring layer within the standard CMOS process. Taking advantage of sub-100 nm CMOS process, a fine grid pitch was realized. Polarization-analyzing performance significantly higher than our previous sensors with 0.35 μm CMOS process was obtained. Polarization imaging capability was demonstrated for a scene with local polarization variation. With an aim of further performance improvement, subtraction readout scheme and multiple layer stacked on-pixel polarizer were proposed and discussed.