Determination of Work Function in Single-Crystalline and Polycrystalline TiN Films

Titanium nitride (TiN) has emerged as a key material for metal gate electrodes in complementary metal–oxide semiconductor (CMOS) devices. The work function is a fundamental material property that plays a critical role in the design and performance of electronic devices. However, reported values of the work function of TiN are different (ranging from 3.8 to 5.3 eV) among studies, and an experimental investigation of the work function on single-crystalline TiN films is rarely reported. Here, we report the work function of high-quality single-crystalline (111)-oriented and (001)-oriented TiN films as well as polycrystalline TiN films. The crystal and electronic structures were characterized by X-ray diffraction, atomic force microscopy, X-ray photoemission spectroscopy, and electrical transport measurements. The intrinsic work function of TiN films was around 4.3 eV, extracted from ultraviolet photoelectron spectroscopy (UPS). It is noteworthy that the work functions of single-crystalline (111)-oriented and (001)-oriented TiN films, as well as polycrystalline TiN films, are almost the same. This suggests that the work function of TiN is independent of crystal orientation and quality. Our work clarifies the intrinsic work function of high-quality TiN films and highlights its independence from both crystal orientation and quality. This comprehensive understanding of the work function of TiN benefits the design and optimization of advanced materials and devices.