Mn3Ag(1-)Cu()N antiperovskite thin films with ultra-low temperature coefficient of resistance

Abstract

• First report on the reactive sputter deposition and post-deposition heat treatment of Mn 3 Ag (1- x ) Cu ( x ) N thin films for ultra-low TCR application. • Increasing Cu doping concentration in Mn 3 Ag (1- x ) Cu ( x ) N controls stabilization of the manganese oxide upper surface layer. • The extent of upper surface oxidation and crystallization of the underlying thin film are competing events to fine tune the electrical properties. • Optimising the post-deposition heat treatment temperature results in TCR values better than ±5 ppm/°C and resistance stability of less than 1%. We demonstrate the first successful attempt to partially substitute Cu into the Mn 3 AgN-antiperovskite system to form Mn 3 Ag (1- x ) Cu ( x ) N thin films with an ultra-low temperature coefficient of resistance (TCR) for fabrication of ultra-precise passive components. Films were grown by reactive magnetron sputtering on alumina and glass substrates and were found to be amorphous in nature with highly negative TCR of -233 to -351 ppm/°C in their as-grown state. Increasing Cu alloying from x =0 to 1, resulted in increased sheet resistance, a negative shift of TCR and a change of grain morphology from spherical to elongated. Post-deposition heat treatment at 300-375 °C, resulted in a positive shift of TCR and an ultra-low TCR of -4.66 ppm/°C for films with x =0.6. The heat treatment induces grain growth, surface roughness and the formation of a manganese oxide upper surface layer up until temperatures of 350 °C, after which surface oxidation begins to dominate. The growth rate of the surface layer is controlled by the Cu concentration and heat treatment temperature, which both play a central role in the development of these novel ultra-low TCR Mn 3 Ag (1- x ) Cu ( x ) N thin film structures.