Blue-enhanced and bandwidth-extended photodiode in standard 0.35-pm CMOS

In this paper, a photodiode structure based on N×N junctions is presented to enhance responsivity in the blue region and provide optical-bandwidth extension. The use of subsections or multiple junctions increases the number of generated blue photo-carriers as well as the collection speed of photo-carriers at the depletion regions edges. An NWell/Psub photodiode formed of 5×5 subsections is designed and fabricated in standard AMS 0.35 pm CMOS technology with the OPTO process option. The photodiode is compared to a solid structure with a single section having the same optical window area of 100 pm × 100 pm. A responsivity improvement of around 10% ~ 15% is measured between 400 nm to 550 nm wavelength. The normalized AC-responsivity shows a 2× increase in bandwidth and at least 2 dB improvement around the cut-off frequency of the reference PD at 1 V reverse bias voltage.