Microcrystalline silicon: Strain gauge and sensor arrays on flexible substrate for the measurement of high deformations

This paper presents strain sensor arrays on flexible substrates able to measure local deformation induced by radii of curvature of few millimeters. Sensors use n-type doped microcrystalline silicon (μc-Si) as piezoresistive material, directly deposited on polyimide sheets at 165 °C. Sensitivity of individual sensors was investigated under tensile and compressive bending at various radii of curvature, down to 5 mm. A Transmission Line Method was used to extract the resistivity for each radius. The devices exhibited longitudinal gauge factors of −31 and longitudinal piezoresistive coefficients of −4.10−10 Pa−1. Reliability was demonstrated with almost unchanged resistances after cycles of bending (standard deviation of 1.7%). Strain gauge arrays, composed of 800 resistors on a 2 cm2 area, were fabricated with a spatial resolution of 500 × 500 μm2. Strain mapping showed the possibility to detect local deformation on a single resistor or to detect larger objects. These strain sensor arrays can find applications when high sensitivity and high spatial resolution is required. This paper also showed that μc-Si can be a relevant semi-conductor candidate for flexible electronics.