In this study, we develop a flexible lead-free BiFeO3 (BFO) film sensor that can be applied on complex surfaces of devices. This sensor is fabricated by depositing BFO thin film on a polyimide (PI)-coated copper substrate. The sol–gel (SG) method and spin-coating method are utilized to prepare the BFO piezoelectric film. Two different spin-coating processes under three different sets of parameters and two different annealing temperatures are used in the fabrication. X-ray diffraction (XRD) and scanning electron microscopy are used to examine the crystallinity and surface topography of the BFO thin films, respectively. A lifetime test is performed on the device to validate the robustness of its piezoelectric properties, and a linear scaling relationship between the force and output response is obtained. We propose suitable conditions for preparing the piezoelectric film and demonstrate the reliability of this sensor.