ZrN thin film field emitter arrays were fabricated by the ion beam assisted deposition technique. The work function of ZrN is controlled by the selection of the deposition parameters. We investigated the relationship between the work function and the emission stability, and the influence of the ambient gas on the emission stability by introducing the gases of N-2 and O-2 into the measurement chamber. It was found that the emission stability depended on the work function : the emitters with a lower work function were more stable than those with a higher work function. The dependence is explained qualitatively by the analysis of the Fowler-Nordheim equation. Emission noise increased with the increase of the ambient gas pressure. However, difference in the increase of noise between N-2 gas and O-2 gas was seen. O-2 gas severely affected the emission stability of the ZrN emitter.