CMOS-integrated photodetectors for neuromorphic and smart imaging applications: A low-cost design and measurement method

Several on-chip photodetecting device structures are designed using a low-cost standard 0.18μm CMOS process. The comparison in terms of measured light responsivity and the response speed is presented between conventional and comb-shaped Nwell-Psubstrate photodiodes, conventional and comb-shaped, vertical and lateral bipolar-junction phototransistors and a Darlington pair of bipolar-junction phototransistors. The photodetectors are embedded in a conventional three transistor active pixel topology and measured using a customized low-cost measurement setup. The presented comparative study targets neuromorphic and smart imaging applications where the pixel light responsivity and the response speed are crucial performance merits. The study demonstrates the benefits of using standard-CMOS-compatible bipolar-junction structures in these applications. Therefore, the pixel responsivity and response speed are measured for each structure and the results are presented in detail.