Improvement of the dielectric properties of rutile-doped Al2O3 ceramics by annealing treatment

The microwave dielectric properties of alumina (Al2O3) ceramics were studied. The objectives were to improve the large negative temperature coefficient of the resonant frequency (τf) of Al2O3 ceramics and to obtain a relatively large quality factor (Qf) through the addition of rutile (TiO2), which has a large positive τf, and an annealing treatment. A near-zero τf (+1.5 ppm/°C), excellent Qf (148,000 GHz) and ɛr (12.4) were obtained in 0.9 Al2O3–0.1 TiO2 ceramics sintered at 1350 °C for 2 h, followed by annealing at 1100 °C for 12 h in air.