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The paper aims to report on fabrication procedure and present microstructure and dielectric behavior of multilayer porous low-temperature cofired ceramic (LTCC) structures…
The paper aims to report on fabrication procedure and present microstructure and dielectric behavior of multilayer porous low-temperature cofired ceramic (LTCC) structures based on glass-cordierite and glass-alumina.
The LTCC structures were created as multi-layered composites with dense external layers and inner layers with intentionally introduced porosity. Two preparation methods were applied – subsequent casting of both kinds of slurries and conventional isostatic lamination of dried green tapes arranged in the designed order. Optical microscope observations were carried out to analyze the microstructure of green and fired multilayer structures and pore concentration. To evaluate the adhesion strength of the composite layers, pull test was performed. Dielectric behavior of the composites was studied in the frequency range 50 kHz-2 MHz.
The fabricated porous LTCC structures showed dielectric constant of 3-5.6. The lowest dielectric constant was attained for glass-cordierite composite made by the conventional tape casting/lamination/firing method from slurry with 50 per cent graphite content. The samples prepared using multiple casting were of worse quality than those fabricated in conventional process, contained irregular porosity, showed tendency for deformation and delamination and exhibited a higher dielectric constant.
Search for new low dielectric constant materials applicable in LTCC technology and new methods of their fabrication is an important task for development of modern microwave circuits.
The purpose of this paper is to report on fabrication procedure and present microstructure and dielectric behavior of willemite ceramic material with addition of 5% Li2CO3…
The purpose of this paper is to report on fabrication procedure and present microstructure and dielectric behavior of willemite ceramic material with addition of 5% Li2CO3 as a sintering aid.
The samples were fabricated by ball milling of the ceramic powders, preparation of granulate and pressing and co-firing using temperature profile based on heating microscope observation. The dielectric properties of the material were measured by impedance spectroscopy (Hz-MHz), transmission method (GHz) and time domain spectroscopy (THz). The composition and microstructure of the material were investigated using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy analysis. Ceramic powder was used to fabricate a green tape and low temperature co-fired ceramics (LTCC) multilayer structures, which in the next steps of the research were examined at the angle of cooperation with conductive pastes, strength and geometric repeatability.
The fabricated material showed low sintering temperature (920°C–960°C), low dielectric constant 6.2–6.34 and low dissipation factor at the level of 0.004–0.007. As LTCC material, willemite with 5% Li2CO3 addition showed good compatibility with AgPd conductive paste.
Search for new materials with low dielectric constant, applicable in LTCC technology, and development of their fabrication procedure are important tasks for the progress in modern microwave circuits.