A 150-200 degreesC atomic layer deposition (ALD) process has been developed for advanced gap and tunnel junction applications for thin films heads. The primary advantage of the ALD process is the near 100% step coverage with properties that are uniform along the sidewall. This process provides smooth (R-d = 2 Angstrom), pure (impurities <2 atom %), AlOx films with excellent breakdown strength (9-10 MV/cm). The process uses trimethylaluminum (TMA) as the aluminum source and water as the oxidant. The optimal precursor/oxidant delivery methods for high breakdown strengths were found to be vapor draw for the TMA and a bubbler for the water. For both reagents, a sweep gas is used to reduce the transit time to the wafer. The ALD AlOx films are continuous and exhibit excellent insulating characteristics even down to 5-10 making them a potential candidate for tunnel barriers for magnetic tunnel junctions. By plasma annealing the films in situ every 25-50 Angstrom, the as-deposited tensile stress becomes slightly compressive and the breakdown field exceeds 10 MV/cm. ALD provides a relatively low deposition rate of 0.8 Angstrom /cycle. A small chamber volume that allows the cycle time of 5 s is the key to meeting production throughput requirements of 4-6 w h(-1) for a 100 Angstrom film.