Characterization and dielectric behavior of willemite and TiO2-doped willemite ceramics at millimeter-wave frequency

Willemite ceramics (Zn2SiO4) have been successfully prepared in the temperature range from 1280 to 1340 °C. It is found that willemite ceramics possess excellent millimeter-wave dielectric properties: a dielectric constant ɛr value of 6.6, a quality factor Q × f value of 219,000 GHz and a temperature coefficient of resonant frequency τf value of −61 ppm/°C. By adding TiO2 with large positive τf value (450 ppm/°C), near zero τf value can be achieved in a wide sintering temperature range. With 11 wt% of TiO2, an ɛr value of 9.3, a Q × f value of 113,000 GHz, and a τf value of 1.0 ppm/°C are obtained at 1250 °C. The relationships between microstructure and properties are also studied. Our results show that willemite with appropriate TiO2 is an ideal temperature stable, low ɛr and high Q × f dielectric for millimeter-wave application.