Abstract
The hafnium doping effects on the performance of the Bi1.5Zn0.92Nb1.5O6.92 (BZN) varicaps are explored by means of impedance and signal power spectroscopes in the range of 10-1800 and 1000-3000 MHz, respectively. The Hf content that was varied in accordance with the Bi1.5Zn0.92-2xHfxNb1.5O6.92 formalism was observed to reach the solubility limit at the Hf content of 0.06. The free carrier concentration in the devices systematically increased with the increasing Hf content. The impedance spectral analysis revealed a series and parallel resonance exchange above 1000 MHz. The critical frequencies of resonance are observed to shift from 1638 to 1585 and reach 1476 MHz as the Hf content increases from 0.00 to 0.03 and reaches 0.06, respectively. It was also observed that the hafnium doping significantly increases the respective dielectric constant of BZN from 268 to 290 and to 470. In addition to the negative dielectric property that is useful in applications where the cancelation of parasitic capacitance is needed, the wave power spectral analysis revealed the microwave band-reject filter properties with the respective notch frequencies of 1580, 1845, and 2040 MHz. While the undoped ceramic filters can detect the signals of power down to 40 nW, the doped ones are functional for the signals of microwatt power.