Chenhao Zhang

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.

Frequency tunable microstrip patch antenna using ferroelectric thin film varactor

A novel frequency tunable microstrip patch antenna using ferroelectric BST thin film varactor is presented. The resonant frequency of this reconfigurable antenna is controlled by tuning the capacitance of the RF varactor which is used as part of the antenna feedline in this design. Since the varactor uses the coplanar waveguide (CPW) transmission line, tapered microstrip line between the antenna and the varactor are employed to ensure proper transitions. Experimental results demonstrate that a high tuning range can be achieved for the reconfigured microstrip patch antenna with a lower variation of the DC biasing voltage applied on the ferroelectric varactor.

Frequency agile microstrip patch antenna using ferroelectric thin film varactor technology

This work demonstrates a useful application of the ferroelectric thin film varactor technology in the design of reconfigurable microstrip patch antennas. Results show that the resonant frequency of the microstrip patch antenna can be tuned by varying the applied DC voltages on the ferroelectric varactor. A resonance frequency shift from 12.4 GHz to 13.8 GHz was observed for a small dc bias voltage of only 2.5 V.

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.

Linearity and temperature dependence of large-area processed high-q barium strontium titanate thin-film varactors [Correspondence]

Ba0.6Sr0.4TiO3 (BST) thin-films with large dielectric tunability as high as 4:1 were obtained using a large-area pulsed laser deposition process, with low loss-tangents below 0.01 at zero-bias and 10 GHz. This paper summarizes experimental results obtained on large-area processed BST thin films on 100-mm-diameter sapphire substrates characterized using a varactor shunt switch test structure. Varactors with 0.25-μm-thick BST films exhibited large dielectric tunability, the relative dielectric permittivity at zero bias of 990 tuned to 250 at an electric field of 320 kV/cm. The leakage current through the BST film was below 2 nA up to 6 V dc bias. The quality factor (Q) exceeded 300 at relatively low 6 V dc bias for the BST varactors at 1 GHz. These results confirm that large-area processed BST thin films are ready to compete with semiconductor varactors for commercial applications at RF, microwave, and millimeterwave frequencies.

THICKNESS DEPENDENT PROPERTIES OF BARIUM STRONTIUM TITANATE THIN-FILM VARACTORS

ABSTRACT Ba0.6Sr0.4TiO3 (BST) thin-films with large dielectric tunability as high as 5.8:1 were obtained using a large area pulsed laser deposition process, with low loss-tangents below 0.01 at zero-bias and 10 GHz. This paper summarizes experimental results obtained on large area processed BST thin film varactors. Varactors with 0.6 μm thick BST films exhibited large dielectric tunability, the relative dielectric permittivity at zero bias of 1280 tuned to 220 at 20 V, at an electric field of 333 kV/cm. The leakage current through the BST film was below 1 nA up to 10 V dc bias. The Quality factor (Q) exceeded 500 at relatively low 10 V dc bias for both 0.6 and 1 μm thick BST varactors.

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.

Design of high voltage tunable Shunt Interdigitated resonator based on Barium Strontium Titanate thin film

This paper reports a design methodology of tunable Coplanar Waveguide Shunt Interdigitated Capacitor (IDC) which is fabricated on a Barium Strontium Titanate (BST) thin film deposited on a sapphire substrate. The Shunt IDC can be utilized to develop a microwave resonator, a tunable notch filter or other promising applications. The designed resonant frequencies of resonators are in the range from 11.53GHz to 17.51GHz with a notch depth of −27.72dB (S21). The measured bandwidth is around 2GHz at −10dB. The tunable range of center frequency under bias voltage is 0.3GHz for bias voltage change from 0V to 50V. The EM structure and equivalent circuit model were developed for comparison with experimental data to find out the relationship of the capacitance, and parasitic inductance and resistance.

A comparison of doped biopolymers using a coplanar waveguide based resonant bio-chemical sensor

This paper compares the effect of doped and un-doped biopolymers when the polymers are used as the sensing layer in a resonant chemical sensor. In addition to biopolymers, other polymers were doped as well for reference. The biopolymers used in this study were DNA-CTMA and Silk. The regular polymers used in this study were PMMA and Nafion. PMMA was doped with the metals nickel and iron. DNA-CTMA was doped with the metals manganese, nickel, and iron. Nafion and Silk were left un-doped for all of the tests. The above polymers were tested with DI water, humidity, ethanol, and isopropanol. All of the above polymers showed a resonant frequency change when subjected to the analyte of interest.