Nanostructured barium strontium titanate (BST) thin-film varactors on sapphire

摘要

Varactor shunt switches (10) based on a nonlinear dielectric tunability of Ba_xSr_(1-x)TiO₃ (BST)thin-film on a sapphire substrates (100) are presented. Nanostructured BST thin-films with dielectric tunability as high as 4.3:1 can be obtained on sapphire substrates (100), with very low loss-tangents below 0.025 at zero-bias and 20 GHz.;The large capacitance of the varactor at zero bias can shunt the input signal to ground isolating the output port, resulting in the OFF state. When applying a bias voltage of approximately 10 V ( a dc electric field of -250 kV/cm), the varactor's capacitance can be reduced to a minimum, allowing maximum transmission to the output resulting in the ON state. The microwave switching performance of the varactor shunt switch (10) can be compared with the RF MEMS switches for potential applications at microwave and millimeterwave frequencies. Other applications of such BST varactors include tunable filters, phase shifter circuits and impedance matching circuits.