<p>Heterogeneous thin films inherently exhibit directional adhesion, where the peeling force increases when peeled in the soft-to-stiff direction and decreases when peeled in the opposite direction compared to their homogeneous counterparts. This unique property offers a basis for designing smart adhesion systems requiring both strong attachment and easy detachment. However, heterogeneous thin films with sharp interfaces suffer from poor adhesion stability and robustness. The maximum peeling force is highly sensitive to the cohesive zone between the thin film and substrate, reducing adhesion robustness. Moreover, a sudden big drop in peeling force happens immediately after the sharp interface, reflecting its poor adhesion stability. Inspired by the gradient designs in adhesive microstructures of beetles and geckos, we propose a bioinspired gradient-interface design for the heterogeneous thin films. A theoretical model is developed to describe the peeling behavior of the gradient-interface heterogeneous thin films. Our results show that gradient interfaces maintain the directional adhesion property while significantly mitigating the impact of cohesive zones on the maximum peeling force, thus enhancing adhesion robustness. With analogy to the redundant design in engineering, three indices are introduced to quantitatively characterize the adhesion strength and stability of practical interest: the half-peak peeling force, the half-peak peeling-zone length, and the half-peak fracture energy. Comparative analysis reveals that the optimal gradient magnitude depends on the gradient form and interface energy. This study uncovers the mechanisms behind robust and stable directional adhesion with gradient-interface heterogeneous thin films and provides valuable insights for the design of smart adhesion systems with strong attachment and easy detachment.</p>