Analysis and characterization of the spectral response of CMOS based integrated circuit (IC) photodetectors

This paper presents the analysis and characterization of the spectral response of CMOS based Integrated Circuit (IC) photodetectors. These detectors are driving the recent growth in CMOS based optical imaging and signal processing applications. A standard CMOS IC fabrication technology can support many different types of photodetectors. For example, a CMOS Nwell digital fabrication process can support three photodiode types (i.e. (1) n_well-p_sub , (2) n⁺-p_sub, and (3) p⁺-n_well), as well as a vertical p⁺-n _well-p_sub phototransistor. This paper will apply traditional semiconductor device analysis to approximate the spectral response of these CMOS IC photodetectors. It also includes experimental results obtained from several test photodetectors processed using a governmental MOSIS compatible fabrication facility. The measured visible region spectral response (i.e. varying the wavelength from 400 nm to 1 μm) and the static photoresponse (i.e. photocurrent versus light intensity) for the three CMOS photodiode types and vertical photo-bipolar transistor (photoBJT) will be presented