  Heat flux sensors (HFS) have attracted significant interest for their
potential in managing waste heat efficiently. A recently proposed HFS, that
works on the basis of the anomalous Nernst effect (ANE), offers several
advantages in its simple structure leading to easy fabrication, low cost, and
reduced thermal resistance. However, enhancing sensitivity through traditional
material selection is now challenging due to a small number of materials
satisfying the required coexistence of a large transverse Seebeck coefficient
and low thermal conductivity. In this study, by utilizing composite structures
and optimizing the device geometry, we have achieved a substantial improvement
in the sensitivity of an ANE-based HFS. We developed composite structures
comprised of a plastic substrate with an uneven surface and three-dimensional
(3D) uneven TbCo films, fabricated using nanoimprint techniques and sputtering.
This approach resulted in a sensitivity that is approximately four times
greater than that observed in previous studies. Importantly, this method is
independent of the material properties and can significantly enhance the
sensitivity. Our findings could lead to the development of highly sensitive HFS
devices and open new avenues for the fabrication of 3D devices.
