Characterization and performance evaluation of a APS pixel in a standard 2μm CMOS technology

The characterization of an active pixel sensor (APS) fabricated with the 2μm CMOS process entirely developed in the Center of Semiconductor Components of UNICAMP is presented. The transistors were manufactured with channel length and width of L=2 μm and W=10 μm, respectively. The CMOS process parameters used were: gate SiO₂ thickness of 30nm, junction depths (X _Jn and X_Jp) of 0.45μm and gate of Si-poly n ⁺. The obtained threshold voltages were Vt_n=0.8V and Vt_p=-0.7V for n and p MOSFETS, respectively. The photodetectors are n⁺-diodes on a p-type substrate with the same junction depth of X_jn=0.45μm. The fill-factor is about 44% and consumed power for pixel is roughly 2mW. The devices show responsivity peaks (38 mA/W) located around 500 nm. Measurements of the photocurrent show a linear relation with the light optical power. When operated at a reverse bias of 5.0 V, the photodetector achieve a dark current density of μA/cm² at 25°C, and a gain factor Γ= 0.03 μV/e. These results are in good agreement with those found in the literature.