Improvement of on-pixel polarizer with 0.35 μm CMOS process for electro-optic imaging systems

Abstract

In this paper, we propose an improved on-pixel polarizer structure for an image sensor, which was fabricated using the 0.35 μm standard CMOS process with dual metal layers (Metal 1 and Metal 2), i.e. two layers of gratings with metal-wiring layers were stacked. By designing the line/space ratio as 0.7/0.7 μm, the extinction ratio was significantly improved at a wavelength of 780 nm, which was over 1.4 times higher than that of a single-layer grating, and the detection sensitivity of the polarization change was enhanced by more than 1.8 times. We also demonstrated electro-optical imaging at radio frequency using this image sensor.

THz near-field intensity distribution imaging in the 0.3 THz band using a highly sensitive polarization CMOS image sensor using a 0.35 μm CMOS process

“…5. [15][16][17] In general, the photodiodes of image sensors are small; thus, they are not suitable for detecting weak polarization changes owing to their low upper limit of incident light intensity. Furthermore, the extinction ratio of on-pixel polarizers fabricated on polarization image sensors is lower than that of uniform polarizers because polarizers with different polarization angles are arranged at each pixel.…”

“…By using two layers of on-pixel polarizers, one can realize a higher extinction ratio than with a single layer. 17,18) By using this polarization image sensor and the dual-layer polarization imaging system, we can calculate the polarization angle from the signal difference between 0°and 90°polarizers of 50 × 50 pixels was averaged. The standard deviation of the polarization measurement over 30 s was estimated to be 3.81 × 10 −4• .…”

“…The standard deviation of the polarization measurement over 30 s was estimated to be 3.81 × 10 −4• . 31) 3. Demonstration of THz intensity distribution imaging…”

“…dual-polarizer system. 17) We fabricated this system using M2 and M3 as the on-pixel polarizers, but the extinction ratio can be further improved by fabricating three layers of on-pixel polarizers from M1 to M3. This method can achieve 80% of the theoretical measurement sensitivity by achieving an extinction ratio of 10.…”

“…We previously demonstrated a method for imaging the distribution of weak polarization changes using polarization image sensors. [15][16][17][18] This high-sensitivity polarization imaging system combined with a THz detector makes it possible to measure the THz near-field intensity distribution with high sensitivity. In this study, we developed an intensity distribution imaging method for the power density distribution evaluation in the 0.3 THz band in real time.…”