STI Based Trench Capacitor for High Sensitivity and High dynamic range in CMOS Image Sensor

The application of shallow trench isolation (STI) as trench capacitor is proposed in CMOS image sensor (CIS) to provide variable conversion gain. This provides higher sensitivity without degrading the dynamic range (DR) of the pixel. The proposed structure uses in-built isolation trenches as capacitors. In case of low light, trench capacitor (TC) is disconnected from the floating diffusion (FD) node which makes it possible to detect the low light signals due to lower FD capacitance. In high light, TC is connected in parallel to the FD node increasing the overall capacity to collect charges from photodiode, thus enhancing the DR.