Varactor Shunt Switch Research Articles

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

Ba(0.6)Sr(0.4)TiO(3) (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-mumthick 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.

FERROELECTRIC VARACTOR SHUNT SWITCHES FOR BROADBAND PHASE CONTROL APPLICATIONS

ABSTRACT Our research group has recently demonstrated the operation of ferroelectric varactor shunt switches. The device operation is based on the nonlinear dielectric tunability of a barium strontium titanate (BST 60/40) thin-film sandwiched between two metal layers in a parallel plate configuration. A 4:1 change in the varactor capacitance has been achieved with a bias voltage < 10 V, through optimization of the nanostructured BST thin-film fabrication process on high resistivity Si substrates. In this work, we investigated the varactor shunt switches for broadband phase control applications. Varactor shunt switches and cascaded shunt switches were used for phase control circuits, due to the large phase shifts possible as a result of the dc bias dependent tunability of the varactor. The differential phase shift can be defined as the difference between the phase of S21 at a dc bias voltage and zero-bias. The measured differential phase shift for a single varactor shunt switch was 30 ± 2 degrees between 8 and 26 GHz at 8 V dc bias. A cascaded varactor shunt switch resulted in a differential phase shift of 110 degrees ± 10 degrees over the bandwidth of 20 and 31 GHz.

A New Method for Electrical Characterization of Ferroelectric Thin Films at Microwave Frequencies

In this work, varactor shunt switches (VSS) are utilized as test structures for characterization of ferroelectric thin films. The varactor shunt switch consists of coplanar waveguide input and output feed lines, and a shunt parallel plate varactor. The simplicity of the device structure and the ease of modeling the device allow one to match the experimental scattering parameters (S parameters) to the modeled results, and hence characterize the dielectric properties of the ferroelectric thin-film accurately. This paper illustrates the precise characterization of the ferroelectric thin-films using the VSS as a test structure.

DESIGN CONSIDERATIONS FOR A NOVEL COPLANAR WAVEGUIDE BASED FERROELECTRIC VARACTOR SHUNT SWITCH

ABSTRACT Novel ferroelectric variable capacitor (varactor) shunt switches have been designed, and experimentally verified recently. The varactor shunt switches are designed for microwave and millimeterwave switching applications, based on the nonlinear dielectric tunability of the Ba0.6Sr0.4TiO3 (BST) thin-films. Nanostructured BST thin-films with dielectric tunability as high as 350% were used in this study. The device consists of a coplanar waveguide line loaded by a ferroelectric varactor. The large capacitance of the varactor at zero bias shunts the input signal to ground, thus isolating the output port, resulting in the OFF state of the device. When one applies a bias voltage corresponding of approximately 10 V (a dc electric field of ∼ 250 kV/cm), the varactor's capacitance is reduced to a minimum, allowing maximum transmission to the output, thus resulting in the ON state of the device. The microwave switching performance of the varactor shunt switch is compared with the RF MEMS switches for potential applications at microwave and millimeterwave frequencies.

A Si MMIC compatible ferroelectric varactor shunt switch for microwave applications

This letter describes a ferroelectric thin-film based varactor shunt switch, for microwave and millimeterwave switching applications. Our implementation is based on a coplanar waveguide transmission line shunted by a ferroelectric varactor. The concept of switching ON and OFF is based on the dielectric tunability of the ferroelectric barium strontium titanium oxide (BST) thin-films. From experimental verification, the isolation of a switch with a varactor area of 75μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was approximately 20dB at 35GHz and the insertion loss was below 4.5dB up to 35GHz. This letter addresses the design and experimental verification of the first ferroelectric varactor shunt switch with an Si monolithic microwave integrated circuit compatible process.

RF performance evaluation of ferroelectric varactor shunt switches

This paper addresses experimental RF performance evaluation, and electrical-parameter extraction of different-size ferroelectric varactor shunt switches. Ferroelectric varactor shunt-switch operation is based on the nonlinear dielectric tunability of a Ba0.6Sr0.4TiO3 (BST) thin film sandwiched between two metal layers in a parallel-plate configuration. Coplanar-waveguide implementation of the varactor shunt switch results in a high-speed RF switch, through a simple two-metal layer Si MMIC compatible process on high-resistivity Si substrates. The experimental RF performance of the switches shows low insertion loss for smaller-area devices, with good isolation for larger-area devices. To optimize the device design, the rf performances of multiple devices are tested, and the electrical parameters are extracted. The capacitance of the varactor shunt switches tested are tunable by more than 4:1 for bias voltages below 12 V. The switching speed of the devices tested is approximately 43 ns, based on the step-response measurements. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 370–374, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21172

A New Ferroelectric Varactor Shunt Switch for Microwave and Millimeterwave Reconfigurable Circuits

Abstract : This paper presents a ferroelectric varactor shunt switch which can be useful for microwave/millimeter wave switching as well as for the design of reconfigurable circuits. The device operation is based on nonlinear dielectric tunability of a ferroelectric thin-film sandwiched between two metal layers in the parallel plate configuration. A CPW based design allows for MMIC compatible shunt switches with low insertion loss and high isolation. Experimental performance of the varactor shunt switch indicates good switching performance with ^24 dB isolation 41 GHz, and insertion loss below 7 dB up to 45 GHz.