Dual mode cross slotted filter realized with double-sided Tl₂Ba₂CaCu₂O₈films grown by MOCVD

Abstract

We report on the realization of dual mode microwave filters based on Tl 2 Ba 2 Ca 1 Cu 2 O 8 (Tl-2212) double-sided superconducting films. The Tl-2212 samples have been grown ex situ on 10 × 10 mm 2 LaAlO 3 (100) substrates by a combined approach of metal-organic chemical vapour deposition (MOCVD) and thallium vapour diffusion. Their morphological, compositional and structural natures have been investigated by scanning electron microscopy, energy dispersive x-ray analyses and x-ray diffraction characterization. Both sides of the films are smooth, homogeneous in thickness and composition and show epitaxially-grown Tl-2212 phases. Typical values of T c = 100 K and J c = 0.05 MA cm −2 at 77 K have been inductively measured for both sides. Microwave measurements have been performed at 20 GHz by using a dielectric resonator.Two planar superconducting single-stage dual mode filters operating in the C-band with 1% and 10% fractional bandwidth have been realized. The basic element of the device is a square patch resonator diagonally crossed by unequal slots providing both a size reduction and a simple and controllable way to couple the two degenerate modes. Device response has been studied at different temperatures, performing power and intermodulation measurements. In view of practical applications, the results are compared with those obtained by a filter based on high-quality YBCO films.

A Novel Approach to Synthesizing Calcium Copper Titanate Thin Films with Giant Dielectric Constants

“…The LaAlO 3 substrate was chosen because it is among the most suitable substrates for perovskite mixed-oxide films, and has been widely used for the growth of HTc perovskite superconducting films. [23,24] The X-ray diffraction spectrum (Fig. 1a) of a typical CCTO film deposited on a LaAlO 3 (001) substrate shows peaks due to (00l) planes, thus indicating that the CCTO films have their c axis normal to the substrate surface.…”

MOCVD of LaAlO3 Films from a Molten Precursor Mixture: Characterization of Liquid, Gas, and Deposited Phases

“…The multi-component La/Al precursor DSC curve shows a lower temperature peak (72.8 C) associated with melting of the La-(hfa) 3 d diglyme component, while the broad endothermic peaks in the temperature range 85±160 C may be likely associated with the Al(acac) 3 partial dissolution. Note that, in this case, the endothermic peak (198.6 C) expected for the Al(acac) 3 melting, is not observed. Optical microscope, polarized light data, and sublimation under reduced pressure of the two component mixture are in agreement with these conclusions.…”

“…Individual La and Al precursors show endothermic peaks due to melting (74.9 C for La(hfa) 3 d diglyme, and 198.6 C for Al(acac) 3 ) and to evaporation from melts (250±280 C and 260±290 C, respectively). The multi-component La/Al precursor DSC curve shows a lower temperature peak (72.8 C) associated with melting of the La-(hfa) 3 d diglyme component, while the broad endothermic peaks in the temperature range 85±160 C may be likely associated with the Al(acac) 3 partial dissolution. Note that, in this case, the endothermic peak (198.6 C) expected for the Al(acac) 3 melting, is not observed.…”

“…under experimental conditions similar to those used in the MOCVD process. The mass loss as a function of time has been recorded for a La(hfa) 3 d diglyme:Al(acac) 3 1:1 mixture, in the temperature range 100±140 C, under nitrogen flow. Note that the mixture is molten in the entire temperature range under investigation, and the vaporization shows a linear behavior (Fig.…”

“…Lanthanum aluminate with a perovskite-type structure (LaAlO 3 ) [2] is a very appealing material because it has quite interesting dielectric properties. It has been widely applied as a substrate for high T c superconducting microwave devices, [3,4] and is among the most suitable insulator for SQUIDs fabrication. [5] Moreover, the growing demand for fabrication of multilayer superconductor±insulator± superconductor (SIS) arrays, has spurred, over the past few years, intense scientific investigation on the growth of buffers, interlayers or overlayers suitable for high T c oxide films.…”