Independent control of the thermoelectric parameters in titanium nitride thin films via crystal preferred orientation control using the combinatorial sputter coating

Abstract To clarify the effect of deposition conditions on crystallographic orientation and thermoelectric properties at room temperature (300 K), titanium nitride (TiN) thin films were systematically fabricated via combinatorial reactive sputtering while varying the Ar/N 2 gas mixing ratio over a wide range of 0%–100%. Although the overall film composition remained nearly constant except for the N-free condition, significant changes in crystallographic orientation, grain growth behavior, and transport properties were observed as a function of nitrogen partial pressure. X-ray diffraction (XRD) analysis revealed two characteristic trends in orientation evolution with inflection points at N fractions of approximately 70% and 40%. The Seebeck coefficient increased monotonically with decreasing nitrogen fraction and exhibited a weak correlation with the crystallographic orientation. In contrast, electrical resistivity exhibited a strong correlation with orientation-dependent XRD peak intensity changes, resulting in the partial decoupling of the conventional trade-off between the Seebeck coefficient and resistivity. Consequently, the power factor was optimized without significant compositional modification. Thermal conductivity also exhibited obvious dependence on crystallographic orientation and grain structure, contributing to thermoelectric performance optimization. Consequently, a maximum dimensionless figure of merit of 0.025 was achieved. These results demonstrate that crystallographic orientation and microstructural control via deposition process optimization is an effective strategy for mitigating the correlations between thermoelectric parameters in TiN thin films. This approach provides useful design guidelines for nitride-based thin-film thermoelectric materials operating at room temperature.