Anomalous spatial response of transverse thermoelectric thin-film devices under localized thermal excitation

Localized thermal excitation is ubiquitous in practical heat-flux sensing but deviates from the uniform-heating assumption underlying conventional transverse thermoelectric (TTE) models. Here, we demonstrate that TTE thin-film devices exhibit an intrinsic spatial response under point-like heating, where the output voltage depends strongly on the excitation position. Finite-element simulations reveal that the cross-plane temperature difference remains nearly invariant, while the in-plane temperature gradient varies significantly with heating location. This lateral gradient introduces an additional thermoelectric contribution that can enhance, suppress, or even reverse the output signal. The same spatial-dependence mechanism is further reproduced in finite-element simulations of Cu-Constantan multilayer devices, showing consistent behavior without polarity reversal. These results establish that the TTE response arises from the coupling of cross-plane and lateral thermal gradients, extending the conventional ΔTz-dominated interpretation to localized-heating conditions and providing a physical basis for position-dependent calibration and spatial-error assessment in localized heat-flux sensing.