An integrated silicon colour sensor using selective epitaxial growth

Abstract

Abstract An integrated silicon colour sensor using selective epitaxial growth (SEG) of silicon is presented. The sensor concept is based on the strong wavelength dependence of the photon absorption coefficient in silicon in the visible spectral range. Photocurrents of three vertically stacked photodiodes, with the desired position and thickness of the depletion regions, represent full tricolorimetric information. The upper two photodiodes are integrated in the 1.2 μ thick SEG silicon, which is grown on the conventional epilayer where the lower photodiode is placed. High-quality SEG silicon with pattern-insensitive growth has been achieved. Diodes formed in SEG silicon show an ideality factor close to 1, provided the edges are oriented in the [100] directions. The first prototypes of the colour sensor have been fabricated, and measured spectral responses give reasonable agreement with simulation. Using the SEG process together with low-temperature deposited masking oxide (TEOS), maintains compatibility with standard bipolar processing and enables the integration of read-out circuitry to realize a truly smart sensor.