Long-range displacement mini-sensor with submicrometric resolution

Miniature high-resolution sensors are required in integrated systems. In the field of high resolution sensors, available sensors can be separated into two categories: small size sensor but having a limited range and high range sensor but with prohibitive size. This paper describes a long-range miniature position sensor. We propose to use two optical probes (1 mm diameter, 15 mm length for each) in front of a silicon grating (size : 20 times 20 mm² ; thickness < 1 mm ; teeth length : 653 mum ; teeth height : 96 mum) in order to measure on a millimetric range with a submicrometric resolution. First, the principle of the sensor is given. Then, the grating sizing method is described with the best limit of resolution as the main criterion. After that, the silicon grating fabrication is explained : it was fabricated by photolithography and anisotropic wet etching solution (KOH:H₂O). Measures on a 2.9 mm range with a quasi-linear sensitivity of (0.92 plusmn 0.01) mV/mum are obtained. On this range, the limit of resolution is 163 nm rms.