Dark Current Sharing and Cancellation Mechanisms in CMOS Image Sensors Analyzed by TCAD Simulations

Technology computer aided design (TCAD) simulations are conducted on a 4T PPD pixel, on a conventional gated photodiode (PD), and finally on a radiation hardened pixel. Simulations consist in demonstrating that it is possible to reduce the dark current due to interface states brought by the adjacent gate (AG), by means of a sharing mechanism between the PD and the drain. The sharing mechanism is activated and controlled by polarizing the AG at a positive OFF voltage, and consequently the dark current is reduced and not compensated. The drawback of the dark current reduction is a reduction of the full well capacity of the PD, which is not a problem when the pixel saturation is limited by the readout chain. Some measurements performed on pixel arrays confirm the TCAD results.