Electrical and piezoresistive properties of TaN-Cu nanocomposite thin films

Although sputtered tantalum nitride film is commonly used as thin film resistor (TFR), it has the disadvantage of having negative temperature coefficient of resistivity (TCR). It is therefore thought that the incorporation of Cu can result in near-zero TCR TFRs. TaN-Cu nanocomposite thin films with copper as the nano-particles dispersed in tantalum nitride matrix were fabricated by d.c. reactive co-sputtering. After deposition, thin films were annealed using rapid thermal processing at 400°C for 2, 4, and 8 min in Ar atmosphere, causing the emergence and growth of the Cu nano-particles. It is found that the emergence of Cu nano-particles can decrease or increase the TCR of TaN, depending on the particle size and Cu content. Strain gauge factors were evaluated on the films showing near-zero TCR behavior. The gauge factor was found affected by annealing and Cu concentrations. X-ray diffractometry (XRD), transmission electron microscopy (TEM), and high temperature four-point probe were used to characterize the microstructure and electrical properties of both as-deposited and annealed TaN-Cu thin films.