High Q dielectric resonator material with low dielectric constant for millimeter-wave applications

Abstract

Al 2O 3 TiO 2 ceramics has great promise as a dielectric resonator material for millimeter-wave use. The Al 2O 3 TiO 2 MnO system provides low dielectric constant and high quality factor ( Q). TiO 2 and Al 2O 3 can compensate each other's temperature coefficient of resonant frequency. It is important to suppress the appearance of Al 2TiO 5 phase for obtaining high Q-value. In this study, dense Al 2O 3 TiO 2 mixed ceramics without Al 2TiO 5 phase was synthesized by lowering the sintering temperature. The addition of MnO decreases the sintering temperature from 1400 to 1300 °C. In this temperature range, Al 2TiO 5 phase is hardly formed. X-ray powder diffraction (XRD) patterns show that the ceramics is composed of Al 2O 3 and TiO 2 phases only. Dense and well dispersed mixture of Al 2O 3 and TiO 2 grains is observed by scanning electron microscopy (SEM). The 0.9Al 2O 3 0.1TiO 2 ceramics doped with 0.4 mol% of MnO has dielectric constant of 12.4, Q × f of 274,000 GHz at 76 GHz, and temperature coefficient of resonant frequency of +0.4 ppm/°C. The dielectric constant and the temperature coefficient of resonant frequency can be controlled by TiO 2 content. This ceramics is suitable for millimeter-wave applications because of its low dielectric constant, high Q-value, and small temperature coefficient of resonant frequency.