Paper-based anisotropic magneto-resistive thin film sensor for educational applications

The reduction in the cost of sensors, e. g., through the use of low-cost materials, remains necessary for the implementation of the trillion sensor world at a global scale. Meanwhile, paper is recently being investigated as a functional material for low-cost sensors. In this work, the design, fabrication and characterization of a paper-based anisotropic magnetoresistive sensor were investigated empirically and computationally. The intrinsic properties of conventional paper, such as high surface roughness, porosity, stochastic fibrous surface, mechanical bendability and limited hygro-thermal budget, constitute the scientific challenge behind the implementation of a reproducibly-sensitive anisotropic magneto-resistive thin film sensor. Through empirical observations, it was found that the mechanical properties of paper are most decisive in determining the magnetic quality of the permalloy thin film. With increasing permalloy film thickness, the magnetic and electromagnetic properties of the paper-based permalloy were found to improve. It was also found that the maximum pore size on the paper surface is the key parameter in determining production yield as well as the lower bound of resolution for patterned paper-based permalloy thin films. A computational model is developed which suggests that the stochastic fibrous nature of the paper induces a consistent shift in angular anisotropy of the ferromagnetic coating of the order of 45°. Ultimately, a sensor with a maximum anisotropic magneto-resistive effect of 0.4% for a permalloy thickness of 900 nm on a paper platform with average surface roughness of 2.04 µm was realized.