Floating Source/Drain Enabled Linear–Linear–Logarithmic Self-Adaptive One-Transistor Active Pixel Sensor

In this work, a novel one-transistor active pixel sensor (1T-APS) with adjustable self-adaptive sensitivity enabled by floating source/drain (S/D) is demonstrated on 22-nm fully depleted Si-on-insulator (FD-SOI) platform. Additional control gates (CGs) with floating S/Ds are incorporated into the sensor, which are parallel to the sensing gate (SG). For weak illumination, the CG channel keeps closed so that the photoresponse is only active for SG controlled region, resulting in high linear sensitivity, while the CG channel will automatically turn on when the illumination is strong enough. Correspondingly, the CG controlled region is connected with SG controlled region for photoresponse together, resulting in a relatively lower linear sensitivity. For very strong illumination, the 1T-APS will automatically switch to logarithmic response mode due to the activated virtual photodiode in the FD-SOI substrate. The sensitivity transition points in the linear–linear region and the linear–logarithmic region can be further adjusted by the bias of CG and back gate, respectively. The adjustable self-adaptive sensitivity indicates the great potential of the proposed 1T-APS for high-quality image sensing.