摘要:

The ferroelectric lens is a new type of phased array antenna. It uniquely incorporates bulk phase shifting using bulk ferroelectric ceramics to reduce the cost of the phased array. This paper presents the latest X band (8-12 GHz) results with improved ferroelectrics; the loss due to these ferroelectrics is less than 2 dB for obtaining 360° differential phase shift at 10 GHz. The antenna pattern of an interferometer built with ferroelectrics and demonstrating electronic scanning at 10 GHz is presented. A brief review of the ferroelectric lens concept is also included.

ISSN:1058-4587    

DOI:10.1080/10584580008222226

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The microstructural properties of (Ba0.5Sr0.5)TiO3(BSTO) thin films (300, 700, and 1400 nm thick) deposited on LaAlO3(LAO) substrates were characterized using high-resolution x-ray diffractometery. Film crystallinity was the parameter that most directly influenced tunability, and we observed that a) the crystalline quality was highest in the thinnest film and progressively degraded with increasing film thickness; and b) strain at the film/substrate interface was completely relieved via dislocation formation. Paraelectric films such as BSTO offer an attractive means of incorporating low-cost phase shifter circuitry into beam-steerable reflectarray antennas.

ISSN:1058-4587    

DOI:10.1080/10584580008222227

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Today's phased-array antennas use hundreds of radiating elements that use relatively high-loss phase shifters that operate over a limited bandwidth. The number of elements and the phase shifter losses affect the overall cost of the antenna system. Ferroelectric RF phase shifters have the potential to meet the low-loss, low-cost requirements driving many phased-array applications. Some of the issues affecting the development of ferroelectric phase shifters include ferroelectric tunability, dielectric losses, conductor losses, and impedance mismatch. We used the measured tunability (250 kHz, room temperature), dielectric constant, and loss tangent (10 GHz, room temperature) of Ba1-xSrx/TiO3(0.4x0.6) with various amounts of MgO additive, 0 to 60 wt.%, to estimate the device performance of microstrip phase shifters. The electromagnetic model of the microstrip (which uses a standard 3-mil-wide 1-oz. copper line, 3-mil-thick BST/MgO composite and the bias criteria of 2 V/μm) has produced performance benchmarks for a number of composites providing 360° of phase shift. While the accuracy of the electromagnetic model used to evaluate these materials has limitations, the results do provide some insight as to which materials may be better suited for 10-GHz phase shift devices.

ISSN:1058-4587    

DOI:10.1080/10584580008222228

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Oxide ferroelectric thin films for frequency-tunable microwave devices, in which the dielectric constant of the non-linear dielectric is varied by application of electric fields, have been deposited using PLD. We have fabricated single phase epitaxial Ba0.6Sr0.4TiO3and KTaO3thin film capacitors for applications at 300K and 77K, respectively. Single phase KTaO3films were obtained only with excess potassium source in the target along with KTaO3perovskite phase. The films have been characterized for structure and morphology by X-ray diffraction and AFM. The dielectric properties were measured in the low frequency range from 100 kHz to 10 MHz, using interdigitated capacitors. Low loss tangents (0.002 at 300K) were observed for highly oriented Ba0.6Sr0.4TiO3films. The importance of low losses for various devices is discussed and the dielectric constants, loss tangents and tunability of these films are reported in this paper.

ISSN:1058-4587    

DOI:10.1080/10584580008222229

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

It is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductiveoxide electrodes that are ferroelectric in naturethe polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3thin films with stoichiometric composition on SrTiO3single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppresses the size effects.

ISSN:1058-4587    

DOI:10.1080/10584580008222230

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We present a comparative study of broadband electrodynamic properties of coplanar waveguides made from nonlinear dielectric single-crystal and thin-film SrTiO3(STO) with high-temperature superconducting thin-film YBa2Cu3O7-δelectrodes. The waveguides that use single-crystal STO exhibit a monotonic increase in refractive index, dielectric nonlinearity, and dissipation with decreasing temperature (from 80 K to 20 K), whereas those based on thin-film STO show similar but weaker effects with increasing temperature. Under dc bias, both types of waveguides show reduced refractive index, but dissipation increases in the case of single-crystal STO, while it decreases in the case of STO thin-films.

ISSN:1058-4587    

DOI:10.1080/10584580008222231

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Pulsed-laser deposition (PLD) is a very powerful and rapid deposition technique, which can produce exceptional-quality thin films. Although PLD has tremendous versatility and potential, PLD capabilities are still constrained by a lack of process control. At the Air Force Research Laboratory on-site at Wright-Patterson AFB, we are developing in-situ/real-time control methodologies for PLD and other thin-film deposition processes. We have identified appropriate sensors for closed-loop feedback control and utilized them with YBa2Cu3O7-x(YBCO) to identify critical process control parameters. Control instrumentation has recently been improved by the addition of moveable fixed-position plume-emission sensors. The reproducibility of YBCO film quality increased significantly when process control was applied to PLD processing.

ISSN:1058-4587    

DOI:10.1080/10584580008222232

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A review is presented of approaches to integrate thin film Pb(Zr, Ti)O3-based ferroelectric capacitor structures on a filled poly-Si plug, which is a critical requirement for a high-density memory technology. Key materials issues relevant to the development of conducting diffusion barrier layers for integration of these materials on Si wafers are discussed. Specific attention in this paper is on the use of conducting perovskite oxide electrodes to contact the ferroelectric thin film. The second part of this review focuses on some novel materials that we have investigated for use as diffusion barriers. Finally, we present data on the scaling of ferroelectric properties with lateral dimensions of the capacitor.

ISSN:1058-4587    

DOI:10.1080/10584580008222233

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We present results from experiments which measure the local dielectric response of ferroelectric thin films driven by microwave-frequency electric fields. The repetition rate of a mode-locked Ti:Sapphire laser is used to generate a microwave drive signal that is phase-locked to an optical probe pulse and applied to the ferroelectric thin film. The induced polarization change in the ferroelectric film is measured stroboscopicallyviathe electro-optic effect. Polarization images are acquired by scanning the laser beam across the sample in a confocal geometry. Time resolution is achieved by changing the delay between the electrical pump and the optical probe. Initial results show large local phase shifts in the ferroelectric response of closely separated regions of a Ba0.5Sr0.5TiO3thin film. This new experimental technique may help to understand the physical mechanisms of dielectric loss in these materials.

ISSN:1058-4587    

DOI:10.1080/10584580008222234

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Ferroelectric Ba(1-x)SrxTiO3(x = 0.5 and 0.25) thin films were grown on (001) LaAlO3by using pulsed laser ablation. Extensive x-ray diffraction and selected area electron diffraction reveal that the as-grown films were (001) oriented with a good in plane relationship of <100>BSTO// <100>LAO. Rutherford Backscattering Spectroscopy ion-channeling studies suggested that the films had excellent epitaxial quality and crystallinity with an ion beam minimum yield χminof only 2.6%. Atomically sharp interfaces were seen by cross-sectional high-resolution electron microscopy, indicated that the density of misfit dislocations was consistent with the lattice mismatch from the theoretical calculation.

ISSN:1058-4587    

DOI:10.1080/10584580008222235

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor