Structure and Electrical Properties of Co/Ta Multilayered Thin Films

RF sputtered Co/Ta multilayered thin films (MLF) are studied by means of X-ray diffraction, transmission electron microscopy (TEM), and a standard four-terminal method for resistivity measurement (77 to 300 K). With increasing Co layer thickness (t(Co)), the resistivity of the total MLF increases monotonously up to a maximum at t(Co) = 1.5 nm and gradually decreases thereafter, while the temperature coefficient of resistivity (TCR) shows quite an opposite trend with a minimum also located at t(Co) = 1.5 nm. The TCR passes through zero at t(Co) = 0.8, 1.9 nm and takes negative values between them. The zero TCR can be attributed to a balance in TCR among the, Co and Ta layers with positive TCR and the amorphous interfaces with negative TCR, from which the interface thickness is estimated to be around 1.5 nm