Rational selection of the oxygen source for atomic layer deposition Al2O3 insulators

Insulating gate dielectric is an important component of thin film transistors (TFT) and non-volatile memories, whose properties directly affect the electrical performance of the devices. In this study, the Al2O3 insulators were prepared by atomic layer deposition (ALD) using different oxygen sources and their properties were systematically studied. Based on the two-step oxidation method (H2O + O3), the Al2O3 thin films exhibited a small gate leakage current and a big breakdown field of 9 MV/cm. However, the use of the O3 increased the C-related impurities causing a large sweep hysteresis voltage of the TFTs, i.e., 8.65 V and 4.66 V for that with Al2O3 (O3) and Al2O3 (H2O + O3), respectively. Attributed to a small amount of impurities in the Al2O3 (H2O) insulators as well as the appropriate amount of Al element diffusion at the Al2O3/ZnO interface, the TFTs using Al2O3 (H2O) as insulators presented a high mobility of 36.1 cm2V−2s−1, a subthreshold swing of 0.25 V/dec and a small sweep hysteresis voltage of 0.42 V. Therefore, the properties of the ALD-Al2O3 films can be easily controlled by changing the type of the oxidizer. The Al2O3 thin films with H2O as oxidant can be used as the insulators of the TFTs, while the Al2O3 thin films based on O3 have great potential as the charge trap layer of the memories.