CMOS PHOTODETECTORS FOR INDUSTRIAL POSITION SENSING

The properties of a CMOS-compatible pn-photodiode, phototransistor, an d one-dimensional lateral-effect photodiode (LEP) for position-sensing applications are characterized. The photodiode and phototransistor se em to have properties that are comparable to typical commercial photod etectors despite the quite large variations in their spatial and spect ral responses and the lower responsivity in the near-infrared band. In addition to the above properties the LEP's show excellent linearity, but 3-4 times larger NEP than corresponding commercial LEP's due to lo w resistance of the current dividing layer. The responsivity variation s have no effect on the linearity of the LEP, and the slightly lower r esponsivity at near-infrared has only a negligible effect on the achie vable resolution (SNR). These properties, usually considered as weak p oints of CMOS-compatible photodetectors, are believed to have little o r no effect on the properties of a position sensor, if the diameter of the light spot is small (< 100 mum). CMOS-compatible photodetectors a re therefore believed to be very suitable for industrial position-sens ing applications.