Thin‐Film Batteries for On‐Chip and Wearable Applications: Advances, Challenges, and Future Perspectives

Thin-film batteries (TFBs) are vital for powering miniaturized electronics and Internet of Things(IoT) devices, offering compact size, long cycle life, and high safety. Utilizing solid-state electrolytes and thin-film deposition, TFBs integrate seamlessly with microelectronic systems. Advances in fabrication methods such as magnetron sputtering and atomic layer deposition, adapted from semiconductor manufacturing, have enhanced scalability, ionic conductivity, and electrochemical performance. Direct on-chip integration simplifies design and boosts energy efficiency, making TFBs key for next-generation electronics. Coupling TFBs with energy-harvesting technologies like solar cells or thermoelectrics enables self-sustaining systems. However, challenges remain, including low areal energy density and limits to further miniaturization. Progress in materials science, electrochemistry, and microfabrication is needed to overcome these barriers. This review summarizes recent TFB advances, classifying and analyzing materials, and detailing deposition processes and their refinements. It also addresses issues in processing, packaging, and operation, and describes analytical tools for evaluating structural and chemical stability. Finally, it highlights future application prospects and unresolved questions, providing a blueprint for ongoing research and guiding innovation toward wider adoption of TFB technology.