Sensitivity estimation of CMOS optical BDJ detector

We report the characterisation of the CMOS optical Buried Double p–n Junction (BDJ) detector in terms of sensitivity, with the aim of developing micro-systems for biochemical analysis. We have first used a statistical approach with pA-meters for signal and noise measurements. The obtained results show a minimum noise level limiting the sensitivity performance, due to noise contributions of the coupled measuring instruments. Then we have adopted another approach with implementation of noise-reduction techniques, including low-noise preamplification and synchronous detection. This has allowed the sensitivity estimation much closer to the achievable performance of the detector. The CMOS BDJ detector has two outputs, and its detectivity depends on the used output signals. When the detector is employed as a photodetector with its output current (I1+I2) as response, the evaluated detectivity is 2.4×1012 cm Hz1/2 W−1. When choosing the other output signal I1, or using both outputs for wavelength detection, the corresponding detectivity is 1.9×1012 cm Hz1/2 W−1. By using the synchronous detection technique, an optical signal of less than 10 fW (10−14 W) is still detectable.