Experimental comparison of piezoresistive MEMS and fiber bragg grating strain sensors

Abstract

We report on the experimental comparison of piezoresistive MEMS sensors and optical fiber BRAGG grating sensors (FBGS) for strain measurements in force sensors. To our knowledge, this is the first direct comparison of piezoresistive and FBG transducers as force sensors. Cantilevers are used as deformation elements. The sensors are bonded on top and bottom side of the cantilever using a heat-curing epoxy adhesive. The piezoresistive ones are micro machined silicon chips with decoupled adhesive areas, and four ion implanted piezoresistive areas (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sq</inf> = 125 Ωcm, (1 × 2)mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ×350 µm). The FBGS are draw-tower-gratings (0.78mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 9 mm). The measured values are compared by analyzing nominal strain, sensitivity, resolution, measurement uncertainty and thermal behavior. The MEMS sensor is more sensitive than the FBGS (0.28%, /N ≫ 0.004%/ N), its measurement uncertainty is lower (2% ≪ 5%) and the resolution Δ∈ = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> µm /m is 100 times higher than in case of FBGS Δ∈ = 1.38 µm / m.