We have demonstrated the basic operation of a vacuum diode based on the negative electron affinity polycrystalline AlN thin film emitters. The AlN films, both undoped and Ge doped, were deposited by ion beam assisted deposition (IBAD). The IBAD process utilizes thermal evaporation from either electron-beam or resistance heated sources with ion bombardment from Kaufman-type ion sources at energies from 50 to 1500 eV. Films were post-annealed by rapid thermal annealing and long-time tube furnace annealing in a N2 atmosphere to test improvements in crystallinity. The electrical and transport properties of the films were tested by DC l-V measurements. The structure of the AlN films was investigated by TEM, SIMS, optical absorption, and RBS as a function of growth parameters and annealing. The field emission was tested for films with different Ge doping concentrations, film thickness, diode voltage, and post annealing conditions. Field emission was observed for the undoped AlN films with a thickness of approximately 10 nm.