Flexible magnetic tunnel junction-based strain sensor with over 100 000-cycle endurance

We report a flexible mechanical sensor based on a magnetic tunnel junction (MTJ) with a CoFeB/MgO/CoFeB structure integrated on a polyimide substrate. The device exhibits a clear magnetoresistance response to uniaxial tensile strain and maintains its sensing performance under high-cycle mechanical loading. To demonstrate this durability, we utilized a custom-developed system to apply over 100 000 repetitive tensile strain cycles with up to 1.25% strain. Throughout the test, the MTJ maintained its zero-strain resistance and strain-resistance characteristics without significant degradation or delamination. Structural analysis revealed partial oxidation within the bottom Ta layer and suggested that the relatively thick bottom electrode stack (Ta/Ru/Ta) functions as a strain buffer layer. These features are considered contributing factors to the observed high durability, although the robustness is likely rooted in the intrinsic properties of the nanoscale thin film. This study provides direct experimental evidence that MTJ-based mechanical sensors can offer both high sensitivity and exceptional endurance, demonstrating their potential as practical strain sensors in flexible and deformable systems for next-generation, high-performance physical sensing.