Programmable Crack Networks for Wide‐Range and Reversible Strain Sensing in Vertically Oriented van der Waals Molybdenum Disulfide Thin Films

ABSTRACT Although employed in various electronics, flexible crack‐based strain sensors often exhibit limited reversibility and narrow operating ranges owing to uncontrolled and irreversible crack formation. This study presents a mechanically programmable crack network‐based strategy for achieving wide‐range and reversible strain sensing with vertically aligned van der Waals (vdW) polycrystalline molybdenum disulfide (MoS 2 ) thin films deposited onto flexible polyimide (PI) substrates. Layered vdW crystallites are preferentially oriented perpendicular to the film plane in the microstructure of the MoS 2 film, providing abundant weak interfaces for controlled crack formation. The first large‐strain loading cycle primarily forms the crack network, whereas subsequent programming cycles condition and stabilize the programmed electrical response. After mechanical programming, small‐strain sensing cycles are governed primarily by repeated crack opening and closing rather than further crack multiplication. Consequently, the MoS 2 /PI system combines large‐strain mechanical programmability with reversible small‐strain sensing and a high gauge factor. A gradual baseline resistance drift, likely associated with substrate viscoplasticity and interfacial or contact relaxation, remained during cyclic sensing, whereas the resistance modulation amplitude was maintained over 1000 cycles. This study establishes a facile design principle for crack‐based sensors by decoupling crack formation from reversible operation, providing new opportunities for robust, high‐performance flexible strain sensing applications.