Performances of an optical ruler based on one-dimensional hydrogenated amorphous Si position-sensitive detectors produced using different metal contacts

The aim of this work is to determine the role of different metal contacts o n the performances of one-dimensional thin-film position-sensitive detector s produced by plasma-enhanced chemical vapour deposition, to be used in opt ical rulers for alignment applications. The device consists on an indium ti n oxide/p-i-n structure where the metal contacts used were based on Al, Al + Cu and Ag. The results achieved show that the contact mainly influences t he final sensor range by limiting the magnitude of the analogue signals rec orded. In spite of soldering problems the AI contact was the contact that l ead to better discrimination of the sensor, with a nonlinearity of +/-0.8% and a fall-off parameter of 3.2 x 10(-3) cm(-1). The Al + Cu contact also e xhibits good performances (nonlinearity, of +/-1.1%; fall-off parameter, 1. 4 x 10(-2) cm(-1)) and should be chosen since it is much easier to solder b ut requires protection against oxidation. The integration of these sensors on the optical ruler lead to the production of a system with a response tim e below 0.5 ms, an accuracy better than +/-1% and a mechanical precision of better than 0.25 mm in 100 mm, with a full-scale noise below +/-0.1%.