Dual mode cross slotted filter realized with double-sided Tl2Ba2CaCu2O8 films grown by MOCVD

We report on the realization of dual mode microwave filters based on Tl2Ba2Ca1Cu2O8 (Tl-2212) double-sided superconducting films. The Tl-2212 samples have been grown ex situ on 10 x 10 mm(2) LaAlO3 (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.