We have developed a new fabrication process forAlN barriers with excellent reproducibility and controlcompared to previous work, enabling the use of thesebarriers in SIS mixers. We report results with niobiumaluminumnitride-niobium superconductor-isolatorsuperconductor(SIS) mixers for 700 GHz, demonstrating awide bandwidth behavior with Fourier TransformSpectrometer (FTS) measurements. These measurementshave been performed in air and reveal that the bandwidth isno longer limited by the tuning circuit but by theatmospheric absorption of radiation. We also present noisetemperature measurements of AlN SIS mixers thatcomplement the FTS results.