A 0.4 e-rms Temporal Readout Noise 7.5 µm Pitch and a 66% Fill Factor Pixel for Low Light CMOS Image Sensors

This paper explores a new way to reduce the readout noise for CMOS image sensors by using a typical 4T pixel embedding a PMOS source follower with reduced oxide thickness and gate dimensions. This approach is confirmed by a test chip designed in a 180 nm CIS CMOS process, and embedding small arrays of the proposed new pixels together with state-of-the-art 4T pixels for comparison. The new pixels feature a pitch of 7.5 µm and a fill factor of 66%. A 0.4 erms input-referred noise and a 185 µV/e- conversion gain are obtained. Compared to stateof-the-art pixels, also present onto the test chip, the RMS noise is divided by more than 2 and the conversion gain is multiplied by 2.2.