Book Description

Radio frequency (RF) and microwave passive devices are indispensable elements in wireless communication applications. The integrated passive components such as inductors, capacitors, and resonators have played a vital role in the development of high performance, low cost, and smaller size microwave circuits. This dissertation developed tunable integrated passive devices by using thin film vanadium dioxide (VO2) and barium strontium titanate (BST), and first demonstration of a novel tunable integrated resonator by using VO2 thin film based tunable inductor and BST varactors. The topics discussed include design, modeling, fabrication, testing, and analyses. Two types of reconfigurable tunable inductors, tunable meander line inductor and tunable spiral inductor, integrated with vanadium dioxide (VO2) thin film on coplanar waveguide (CPW) transmission line are proposed. The tunable inductance is achieved by using the reversible, thermally controlled VO2 thin film. VO2 is one of the metal to insulator phase transition (MIT) materials, which can be a potential solution for reconfigurable RF/microwave wireless communication systems. The VO2 based tunable inductors were fabricated on sapphire substrates. The equivalent circuit models were used to characterize the behavior of tunable inductors and extract the equivalent component values, which show excellent matching to the measured scattering parameters. The measured results have shown an inductance tunability of 35.24% (3.856 nH - 2.498 nH) at 4 GHz, as well as an improved Q factor compared with our group's previous design. Tunable coplanar waveguide interdigital capacitors (IDC) designed with VO2 thin film are presented in this dissertation. Two different configurations, series IDC and shunt IDC, are proposed. Tunable capacitance can be implemented by the thermally controllable VO2 thin film. The tunability of IDC structures are 95.6% and 85.4% corresponding to the series IDC and shunt IDC, respectively.The novel contributions of this dissertation include improved tunability and Q of the VO2 based tunable inductors, and development of tunable filters by integrating the tunable inductors and BST based varactors on coplanar waveguide transmission line structures. The capacitive component of BST varactors can be tuned by applying a DC bias voltage. Moreover, the tunable inductive component can be tuned by a thermal controlled VO2 based inductor. The tunable filters exhibit adjustable characteristics of center frequency, bandwidth, and rejection. This study represents the potential for VO2 and BST based RF/microwave reconfigurable devices.