Robert R. Romanofsky

Epitaxial ferroelectric Ba0.5Sr0.5TiO3 thin films for room-temperature tunable element applications

Perovskite Ba0.5Sr0.5TiO3 thin films have been synthesized on (001) LaAlO3 substrates by pulsed laser ablation. Extensive x-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of 〈100〉BSTO//〈100〉LAO. Rutherford backscattering spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield χmin of only 2.6%. The dielectric property measurements by the interdigital technique at 1 MHz show room-temperature values of the relative dielectric constant, er, and loss tangent, tan δ, of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba0.5Sr0.5TiO3 films can be used for development of room-temperature tunable microwave elements.

(YBa2Cu3O7−δ,Au)/SrTiO3/LaAlO3 thin film conductor/ferroelectric coupled microstripline phase shifters for phased array applications

We report on the design, fabrication, and testing of novel YBa2Cu3O7−δ/SrTiO3/LaAlO3 (YBCO/STO/LAO) and Au/SrTiO3/LaAlO3 (Au/STO/LAO) coupled microstrip line phase shifters (CMPS). These CMPS were tested at frequencies within the Ku and K bands (12–20 GHz), at temperatures from 24 to 77 K, and at dc voltages (Vdc) from zero to 350 V. A relative insertion phase shift (Δφ) of 390° was measured for an eight-element YBCO/STO/LAO CMPS at Vdc=350 V, 16 GHz, and 40 K. At 77 K, a Δφ ∼260° was obtained for the CMPS at the same bias and frequency. Both results correspond to an effective coupling length of 0.33 cm. At both temperatures, the phase shifter exhibits a figure of merit of ∼30°/dB. To our knowledge, these are the best results published so far at these frequencies where miniaturization, insertion loss, and phase delay are key considerations.

Design and development of ferroelectric tunable microwave components for Kuand K-band satellite communication systems

Integration of a high-temperature superconductor with a nonlinear dielectric ferroelectric such as strontium titanate, i.e., SrTiO/sub 2/ (STO), has created a new class of electrically tunable low-loss microwave components. We have designed and fabricated frequency and phase agile components using a conductor/ferroelectric/dielectric two-layered microstrip configuration. Some examples of these components are: microstrip ring resonators, local oscillators, edge coupled filters, and phase-shifter circuits. These structures have been fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// or gold conductor-based microstrip lines fabricated on lanthanum aluminate (LaAlO/sub 3/) or magnesium oxide (MgO) substrates coated with an STO thin film. Frequency and phase agility are achieved using the nonlinear dc electric-field dependence of the relative dielectric constant of STO ferroelectric thin him (E/sub rSTO/). In this paper, we will present an assessment of the progress that our group has achieved thus far toward integration of this technology into wireless and satellite communication systems.

K-band phased array antennas based on Ba/sub 0.60/Sr/sub 0.40/TiO/sub 3/ thin-film phase shifters

This paper summarizes the development of a prototype 23.675-GHz linear 16-element scanning phased array antenna based on thin ferroelectric film coupled microstripline phase shifters and microstrip patch radiators. A new type of scanning reflect array antenna is introduced.

Thin film multilayer conductor/ferroelectric tunable microwave components for communication applications

Abstract A study of Au/SrTiO3/YBa2Cu3O7-δ/LaAlO3 and(Au,YBa2Cu3O7-δ)/BaxSr1-xTiO3/LaAlO3 (x=0, 0.50, and 0.40) multilayered structures is presented. At 1.0 MHz, the largest tuning of Au/SrTiO3/YBa2Cu3O7-δ parallel plate capacitors corresponded to single-phased, epitaxial 300–500 nm thick SrTiO3 thin films deposited at 800 °C. For SrTiO3/LaAlO3 structures having SrTiO3 films of similar quality, we observed that at 1.0 MHz and 77 K, interdigital capacitors exhibit higher tunabilities and lower losses than parallel plate configurations, but required higher dc voltage. For a 300 nm thick SrTiO3 film, a 25 Ω YBa2Cu3O7-δ/SrTiO3/LaAlO3 phase shifter exhibited a phase shift ∼2.6 times larger than its Au/SrTiO3/LaAlO3 counterpart. At 19 GHz and 32 V, a 360°phase shift could in principle be achieved with coupled microstripline sections only 7.0 mm long. At 14 GHz, 77 K and 260 V, for 1.0 μm and 300 nm thick SrTiO3 films, 25 Ω 360° Au/SrTiO3/LaAlO3 phase shifters would be nominally 4.0 mm and 12 mm long, respectivel...

Ferroelectric thin film and broadband satellite systems

There are several microwave applications where tunable ferroelectric devices could play a key role in improving system performance, or they could provide the key technology that enables a system to be deployed. This article focuses on the Ka-band phased array antennas, but tunable filters, oscillators, and switches could also utilize these materials.

Advances in Scanning Reflectarray Antennas Based on Ferroelectric Thin-Film Phase Shifters for Deep-Space Communications

Though there are a few examples of scanning phased array antennas that have flown successfully in space, the quest for ldquolow costrdquo high-efficiency large-aperture microwave phased arrays continues. Fixed and mobile applications that may be part of a heterogeneous exploration communication architecture will benefit from the agile (rapid) beam steering and graceful degradation afforded by phased array antennas. The reflectarray promises greater efficiency and economy compared to directly radiating varieties. Implementing a practical scanning version has proven elusive. The ferroelectric reflectarray, under development and described herein, involves phase shifters based on coupled microstrip patterned on films that were laser ablated onto substrates. These devices outperform their semiconductor counterparts from X- through and K-band frequencies. There are special issues associated with the implementation of a scanning reflectarray antenna, especially one realized with thin-film ferroelectric phase shifters. This paper will discuss these issues, which include relevance of phase shifter loss; modulo 2 effects and phase shifter transient effects on bit error rate; scattering from the ground plane; presentation of a novel hybrid ferroelectric-semiconductor phase shifter; and the effect of mild radiation exposure on phase shifter performance.

Structural and dielectric properties of epitaxial Ba1−xSrxTiO3/Bi4Ti3O12/ZrO2 heterostructures grown on silicon

We report on the dielectric properties of an epitaxial heterostructure comprised of Ba1−xSrxTiO3, Bi4Ti3O12, and (ZrO2)0.91(Y2O3)0.09 grown on silicon substrates for potential use in microwave devices. Careful x-ray analysis indicates crystallographic alignment of all layers and transmission electron microscopy and Auger analysis reveals high quality epitaxy with minimal interdiffusion. The viability of using such heterostructures in actual microwave devices was assessed by incorporating the films in a coupled microstripline phase shifter design. The phase shifter devices, operating in the Ku band, had losses of less than 4 dB with a maximum phase shift of nearly 40° at 40 V. We compare this performance with a (Ba, Sr)TIO3/MgO phase shifter. These results presented represent significant progress towards integrating ferroelectric films with conventional silicon technology.

Small-Size X-Band Active Integrated Antenna With Feedback Loop

A small-sized active integrated antenna (AIA), consisting of a transmission feedback oscillator loaded with a microstrip antenna is presented in this paper. The oscillator antenna, which consists of a NEC super low noise high frequency field effect transistor (HF FET) integrated into the center of a segmented patch antenna, was designed for X-band at 8.50 GHz, and occupies a 5 times 6 mm2 area. The active integrated antenna demonstrates stable oscillations and excellent radiation patterns at X-band design frequencies. When biased using a single 1.5 volt battery connected between the source and drain and with the gate terminal open, the antenna effective isotropic radiated power (EIRP) and direct current (DC)-to-radiated radio frequency (RF) conversion efficiency are +11.2 dBm and 10.5%, respectively. The radiated power level and directivity are +4.5 dBm and 6.7 dBi, respectively. The phase noise at 100 kHz offset from the carrier is -87.5 dBc/Hz, which is a notable improvement over existing AIA designs. The AIA features compact size and simple geometry, yet provides radiated power levels and radiation efficiencies that are comparable to values typically obtained using circuits that occupy larger areas, and use thicker substrates with much lower dielectric constant values.

Analysis and Optimization of Thin-Film Ferroelectric Phase Shifters

Microwave phase shifters have been fabricated from (YBa2Cu3O(7-delta) or Au)/SrTiO3 and Au/Ba(x)Sr(1-x)TiO3 films on LaAlO3 and MgO substrates. These coupled microstrip devices rival the performance of their semiconductor counter-parts parts at Ku- and K-band frequencies. Typical insertion loss for room temperature ferroelectric phase shifters at K-band is approximately equal 5 dB. An experimental and theoretical investigation of these novel devices explains the role of the ferroelectric film in overall device performance. A roadmap to the development of a 3 dB insertion loss phase shifter that would enable a new type of phased array antenna is discussed.