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In this paper, the physical and electrical characteristics of low-temperature-processing hafnium oxide (HfO2) films are studied. A simple cost-effective room-temperature process was introduced to prepare high-k HfO2 dielectrics. A novel technique of direct oxidation of an ultrathin Hf metal by nitric acid, followed by rapid thermal annealing in N2 is demonstrated. The prepared HfO2 gate dielectrics show good uniformity, low leakage currents, high breakdown field, and superior reliability under electrical stressing. The long-term ten-year lifetime was also evaluated by a time-dependent-dielectric-breakdown analysis to project the maximum operation voltage of -1.8 V for HfO2 gate stacks. This low-temperature oxidation technology for preparing high-quality high-k HfO2 dielectrics is promising for flat-panel-display applications.