Abstract

Ultra-high-resolution optical position sensing is important for applications ranging from lithographic alignment to complex optical systems. Traditionally, large area position sensors based on the lateral photovoltaic effect have been developed for long distance (several centimeters) applications. Relatively few results have been reported on ultra-high-resolution applications with resolution better than the optical spot size. Here, we report on nanometer scale position sensing using back-to-back Ni–Si–Ni Schottky diode structures. One- and two-dimensional structures with gap dimensions ranging from 3 to 100 μm have been fabricated with a simple, three level, lithographic process and lift-off metalization techniques on bulk Si wafers. The short-circuit photocurrent is monitored as these sensors are scanned under a focused (~4 μm FWHM) laser beam (λ = 334 and 633 nm). The photoresponse is linear across the gap width, and resolution to ±6 nm is demonstrated, limited by vibrational stability. Substantially improved resolutions are possible based on the electronic noise sources. The maximum position sensitivity is 8.5 μA/μm (1 mW incident power) for laser spot sizes on the order of the gap dimensions. A simple model based on the device symmetry and built-in junction fields is presented.

© 1992 Optical Society of America