Design and optimisation of an npn silicon bipolar phototransistor for optical position encoders

We describe an activity aimed at developing npn silicon bipolar phototransistors to be used in optical position encoders. Extensive numerical process and device simulations have been carried out, providing the guidelines for the definition of the phototransistor fabrication process. Results from the electrical and optical characterisation of manifactured devices are shown. With respect to the designed fabrication process, only a little adjustment of the technological parameters has proven to be necessary to achieve a final product suitable for the intended application.