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

Al2O3TiO2 ceramics has great promise as a dielectric resonator material for millimeter-wave use. The Al2O3TiO2MnO system provides low dielectric constant and high quality factor (Q). TiO2 and Al2O3 can compensate each otherʹs temperature coefficient of resonant frequency. It is important to suppress the appearance of Al2TiO5 phase for obtaining high Q-value. In this study, dense Al2O3TiO2 mixed ceramics without Al2TiO5 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, Al2TiO5 phase is hardly formed. X-ray powder diffraction (XRD) patterns show that the ceramics is composed of Al2O3 and TiO2 phases only. Dense and well dispersed mixture of Al2O3 and TiO2 grains is observed by scanning electron microscopy (SEM). 9Al2O30.1TiO2 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 TiO2 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.