Investigation of Tunable Cu–Ni Alloy Resistors Sintered in Air

This study successfully achieved, for the first time, the sintering and fabrication of base-metal Cu–Ni alloy resistors in an air environment. The resistor layer consists of a base-metal Cu–Ni alloy, while highly conductive silver is used as the terminal electrode to ensure low contact resistance with the Cu–Ni resistor layer. In addition, a zinc protective layer is coated on the surface of the Cu–Ni resistor layer to effectively prevent oxidation during air sintering, thereby enabling the fabrication of high-performance Cu–Ni alloy resistors sinterable in air. Another key outcome of this study is that the resistor value can be adjusted without adding oxides to modify the material composition. In this work, using the same Cu–Ni alloy resistor material, the resistance value was adjusted by controlling the length ratio between the zinc protective layer and the Cu–Ni resistor layer, which altered the degree of oxidation during sintering and thus achieved resistance tuning for air-sinterable base-metal Cu–Ni alloy resistors. Using zinc protective layers of different lengths, this study fabricated silver-electrode Cu–Ni alloy resistors (180 mΩ and 3 Ω) that can be sintered in air (850 °C/10 min) and compared them with a 180 mΩ Cu–Ni alloy resistor with copper electrodes sintered in nitrogen (900 °C/10 min) and a 180 mΩ Ag–Pd alloy resistor with silver electrodes sintered in air (850 °C/10 min). All four types of resistors exhibited comparable short-time overvoltage and long-term reliability test results, clearly demonstrating that, by employing a zinc protective layer and silver terminal electrodes, this study successfully developed high-functionality base-metal Cu–Ni alloy resistors sinterable in air.