Dustin Brown

Miniaturized and Reconfigurable CPW Square-Ring Slot Antenna Loaded With Ferroelectric BST Thin Film Varactors

A novel miniaturized and reconfigurable coplanar waveguide (CPW) square-ring slot antenna is presented in this paper. The miniaturization is achieved via a hybrid approach including ferroelectric varactor loadings, high dielectric constant materials, and tuning stub for impedance matching. For the first time, nine shunt ferroelectric (FE) BST (Ba_(1-x)Sr_xTiO₃) thin film varactors are integrated with the CPW antenna structure achieving both antenna miniaturization and reconfiguration at the same time. The size of the miniaturized antenna is reduced to 0.067λ₀ 0.067λ₀ without ground, and 0.1λ₀ 0.1λ₀ with ground. The resonant frequency of the miniaturized antenna can be reconfigured from 5.3 GHz to 5.8 GHz by applying a DC voltage. Measured E-plane and H-plane co-polarized patterns are presented.

Miniaturized and reconfigurable CPW square-ring slot antenna using thin film varactor technology

Ferroelectric (FE) Barium Strontium Titanate (Ba<inf>(1−x)</inf>Sr<inf>x</inf>TiO<inf>3</inf>, BST) thin film varactor technology is applied to the antenna miniaturization and reconfiguration successfully. CPW square-ring slot antenna is used as a design example, and antennas with and without integrated BST varactors were fabricated and characterized. Including the total ground, the size of miniaturized antenna is 0.12λ<inf>0</inf>×0.12λ<inf>0</inf> which is reduced by 31% compared with antenna without the BST varactors. Moreover, the frequency of the miniaturized antenna with the BST varactors is reconfigurable from 5.8GHz to 6.1GHz with a low DC biasing voltage of 3V. Both E-plane and H-plane patterns were measured for the antennas. Fabrication details and measurement setup are also presented.

Thermally controlled vanadium dioxide thin film microwave devices

Vanadium dioxide (VO2) thin films have unique insulator to metal transition above the critical temperature of 68 °C. In this study, VO2 thin films were deposited on a sapphire substrate for thermally controllable RF/microwave devices such as switches, limiters and resonators. The selectively deposited VO2 thin film based devices showed ~2 kΩ at room temperature and less than 2 Ω at 70 °C. These thermally controlled varistors were utilized in shunt as well as series configurations for microwave switching and in resonant structures. Switching devices designed using a VO2 shunt varistor showed good isolation (>20 dB) and low insertion loss (<;1 dB) up to 20 GHz. This paper presents two types of shunt varistor devices designed and fabricated on sapphire substrates.

A Reconfigurable Coplanar Waveguide Bowtie Antenna Using an Integrated Ferroelectric Thin-Film Varactor

A novel printed antenna with a frequency reconfigurable feed network is presented. The antenna consists of a bowtie structure patch radiating element in the inner space of an annulus that is on a nongrounded substrate with a ferroelectric (FE) Barium Strontium Titanate (BST) thin film. The bowtie patch is fed by a coplanar waveguide (CPW) transmission line that also includes a CPW-based BST shunt varactor. Reconfiguration of the compact 8 mm × 8 mm system has been demonstrated by shifting the antenna system’s operating frequency 500 MHz in the 7–9 GHz band by applying a DC voltage bias.

Vanadium dioxide thin film series single-pole single throw switch

Vanadium dioxide (VO2) thin films have unique insulator to metal transition above the critical temperature of 72 °C. In this research, VO2 thin films were deposited on a sapphire substrate for thermally controllable RF/microwave switching devices with integrated heating coil. The VO2 thin film based devices showed insulator performance at room temperature and metallic state (low resistive phase) at 80 °C. Switching devices designed using a VO2 series varistor showed good isolation (<; -30 dB) and low insertion loss (> -5 dB) up to 20 GHz.

Thin film Barium-Strontium-Titanate Parallel-Plate varactors integrated on low-resistivity silicon and saphhire substrate

Barium-Strontium-Titanate (BST) thin film based ferroelectric varactors are designed at specific capacitances under 0V dc bias on CMOS compatible low-resistivity silicon substrate. The BST varactor device operation is based on the nonlinear dielectric tunability of BST thin film sandwiched between two metal plates in a revised conductor-backed coplanar waveguide (CBCPW) transmission line configuration. The varactor capacitance at 0V dc bias is determined by the overlap area between the CPW signal line in the top metal electrode and a tapered shunt line in the bottom electrode. Therefore a series of devices with unbiased capacitances ranging from 0.8pF to 4.8pF were designed and fabricated based on changing their corresponding overlap areas according to the generic parallel plate capacitance equation. A schematic model was also utilized to extract the designed and measured capacitances. The relationships between the sizes of overlap areas and the extracted capacitances from the electromagnetic and schematic models are demonstrated by a reasonable agreement with the experimental measurements from fabricated devices. Devices were also designed and fabricated on sapphire substrate with three layout variations aiming to modify the parasitic resistance.

Ferroelectric thin-film characterization through use of coplanar waveguide varactors

This paper investigates the implementation of a least squares estimation of varactor capacitance values across a wafer for reasons of characterizing thin-film ferroelectric Ba0.6Sr0.4TiO3, barium strontium titanate (BST). The varactor design utilized for this characterization as well as an equivalent schematic representation of the device used will be presented. Comparisons between the estimated thin-film performance and those of previously presented results will also be discussed.

Coplanar waveguide varactors with bottom metal trenched in silicon

This paper reports the effects of embedding the bottom metal of a thin-film ferroelectric varactor into the wafer substrate. By embedding the bottom metal to a height flush with the surrounding dielectric, a smooth surface remains for the ferroelectric and top metal layers. This parallel stack of layers reduces the coupling between the two metal layers and the resulting capacitance. The design of the device and measured data of etched and non-etched varactors is also presented.

Frequency tuning of CPW bowtie antenna by ferroelectric BST thin film varactors

The main objective for this research is to develop an antenna that can shift its frequency over a broadband. A coplanar waveguide (CPW) antenna was designed with the center conductor of the CPW transmission line connected to a bowtie patch. The size of the antenna is 6mm × 6 mm. The antenna is tuned with a barium strontium titanate (BST) thin film varactor which can tune the device from 5.75 GHz to 6.1937 GHz by adjusting the DC bias from 0 to 10V.

Modeling and analysis of coplanar waveguide (CPW) based multilayer on-chip inductors

CPW based multilayer inductors which can provide higher frequency band and Q factor value are studied and characterized so that a new microwave Equivalent circuit model may be found. In order to study the correlation between the inductance and the length, width and thickness of the conductor, EM structures of multilayer inductors are designed and compared of electrical models. Data analysis and graphic comparison of inductance, S-parameter will be collected and shown.