Flexible thin film thermopiles based on in situ metal growth on polyimide substrate

Deformable thermoelectric sensors are required for more and more applications such as wearable devices, soft robotics, aerospace, and other flexible electronics. This paper presents the design, fabrication, and characterization of flexible thin film thermopiles (TFTPs) based on in-situ metal growth on polyimide substrate. The TFTPs are composed of silver and nickel thin film electrodes and utilize three-dimensional structure enabled by laser drilling technology. The resulting thermocouple exhibits a highly linear response with a Seebeck coefficient of 5.76 μV/K within a temperature difference range of 0-50 °C. We also investigated the effect of electrode width on the Seebeck coefficient of the fabricated TFTPs, revealing that wider width enhances the Seebeck coefficient of the sensors, thereby improving the output thermoelectric potential. Furthermore, the TFTPs demonstrate remarkable flexibility, maintaining a stable Seebeck coefficient of approximately 40 μV/K over 1000 bending cycles, which is attributed to the strong adhesion between electrodes and polyimide substrate due to the in-situ metal growth on polymer substrate. Long-term stability tests show minimal fluctuations in the output thermoelectric potential over a 2-hour period under various temperature differences. These results demonstrate the great application potential of these sensors for flexible temperature sensing, thermoelectric power generation, and flow rate measurements.