COLOR SENSORS BASED ON ACTIVE INTERFERENCE FILTERS USING SILICON-COMPATIBLE MATERIALS

Multilayer stacks of dielectric materials and polycrystalline silicon (with photodiodes therein) deposited on a silicon substrate can be use d to result in an 'active' structure that filters and detects light in its 'active' regions at the same time. Such a structure can be employ ed to design optical detectors with a programmable spectral response b y weighted summing of the photocurrents supplied by polysilicon and mo nocrystalline silicon photodiodes. Such thin-film colour sensors provi de improved response flexibility and fabrication compatibility with st andard microelectronic processing. Furthermore, such a realization fac ilitates the implementation of on-chip smart colour-imaging sensors an d features efficient area occupation by vertical stacking of the colou r detectors. This paper presents the design methods, the fabrication a nd the characterization of such a device. Results of the measured opti cal properties of the available silicon-compatible materials are also presented, together with the practical considerations required to impl ement photodetectors in polysilicon. The measurement results of a fabr icated colour sensor indicate that sufficient spectral selectivity can be achieved. (C) 1997 Elsevier Science S.A.