High Q, tunable thin film capacitors and geometrical effects on device performance at microwave frequencies

Low loss, tunable capacitors were fabricated by RF magnetron sputtered high-k Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films. The dielectric properties were extracted by de-embedding procedure up to 20 GHz by means of reflection coefficients measurements. The extracted dielectric properties of BZN thin films were that permittivity was ∼180 and tunability was ∼30%. On vycor glass substrates, the Q factor including dielectric- and electrode-loss was more than 200 up to several GHz for 64 μm device. There was no indication of onset of dielectric relaxation for the measurement frequency ranges. Q factor dependency on device geometry was also analyzed. The series resistance of the electrodes dominated the device Q factor at microwave frequencies. The electrode resistances were modeled by the sum of area-, periphery-, and conductor-dependent terms. The periphery-dependent series resistance was the most affected by the changes of device changes. Based on the analysis, improved device performance at microwave could be expected by increasing device perimeter. The BZN thin film capacitors with the high Q factor, electric field dependent permittivity, and refined device layout can be the alternative microwave passive components.