Quaternary alloy films for thin film resistors

In this study, we fabricated the quaternary alloy films of Ni-Cr-Al-Cu for thin film resistors using five different target compositions. Thin films were deposited by a DC/RF magnetron sputter and patterned for the measurement of temperature coefficient of resistance (TCR). The TCR of the Ni-Cr-Al-Cu thin films with composition contents and the effects of annealing in air atmosphere up to 400degreesC were examined. The TCR decreased as the O-2 content decreased in film. We chose 5 mTorr as an optimum pressure. Transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis of a thin film with a composition confirmed that the sharp increase in the TCR of films annealed at 400degreesC in air is due to the formation of the rhombohedral NiO phase in the film. The TCR decreased as the Cr content increased or the impurity (Al, Cu) content increased. Above 38 wt% of Cr, the TCR changed to a negative value. The result of XRD analysis revealed that the decrease in the TCR was due to the presence of microcrystalline microstructures in these thin films. The optimal composition was determined to be 51 wt%Ni-41 wt%Cr-4 wt%Al-4 wt%Cu (target #3) and the optimal annealing condition 250degreesC/3.5 h in air. We obtained thin film resistors of low TCR under +/- 10ppm/degreesC.