Ultra-sensitive shape sensor test structures based on piezoresistive doped nanocrystalline silicon

This paper describes the manufacture of a thin skin-like piezoresistor strain-sensing membrane and the miniaturization of dense piezoresistive sensor arrays based on n-type hydrogenated nanocrystalline silicon thin-films (nc-Si:H) deposited on flexible polyimide substrates (PI). The nc-Si:H thin-films, prepared by hot-wire chemical vapor deposition, have a piezoresistive gauge factor of −32.2. Six of the sensors batch-processed on the 15-μm thick membrane, were used in a test structure to track the simulated movement of the head of a bedridden patient. The sensors were glued to both sides of a 3-mm thick acrylic rectangular plate, to collect strain data from the tensile and compressive surfaces of the plate upon bending. The electrical output signal of the sensor was obtained by inserting the sensors into Wheatstone bridge circuits and recording the output voltage of the bridge as a function of the sensor/plate deformation. The results using quarter-, half-, and full-bridge configurations were compared. In order to give a further step toward a shape sensitive electronic textile, nine sensors were glued and interconnected using a machine-sewed conductive thread and preliminary tests on their output response under random loading conditions were performed.