Microwave Performance Dependence of BST Thin Film Planar Interdigitated Varactors on Different substrates

This paper investigated the RF and microwave characterization dependence of BST (BaSrTiO₃) planar interdigitated (PID) varactors on different substrates, such as MO (MgO), LAO (LaAlO₃) and STO (SrTiO₃). Double-layer Ba_0.6Sr_0.4TiO₃/ Ba_0.4Sr_0.6TiO₃ thin film was deposited using reactive pulsed laser deposition (PLD) and then varactors were fabricated. The results show that the capacitance, tunability and Q-factor of the PID varactors are strong dependent upon the properties of the substrates. The capacitance of the PID varactor on STO is much higher than those on MO and LAO substrates, and so its self-resonant frequency is the lowest. The tunability of the PID varactors on MO, LAO and STO are 45%, 50% and 30% respectively at 40V DC bias. The Q-factors of three PID varactors on MO, LAO and STO are different, i.e., MO>STO>LAO.