Low operating electric field and stable emission current have been achieved in IrO(2) nanocrystal-coated carbon nanotube bundle arrays (CNTBAs). Patterned vertically aligned CNTBAs were synthesized using thermal chemical vapor deposition followed by the deposition of IrO(2) nanocrystals by reactive radio-frequency magnetron sputtering using an Ir target. The structural and spectroscopic properties were characterized by field emission scanning and transmission electron microscopy, and Raman spectroscopy. The current density versus electric field measurements yielded a low turn-on field of 0.7 V microm(-1) at a current density of 0.1 microA cm(-2), a low threshold field of 2.3 V microm(-1) at a current density of 1 mA cm(-2) and a high field enhancement factor of 1 x 10(4) for the IrO(2)-coated CNTBAs. Long-term stability was also demonstrated. The enhancement of field emission characteristics is attributed to the combined effects of the geometrical structure of the IrO(2)-coated CNTBAs, and the natural conducting and enhanced resistance to oxidation properties of IrO(2).