Impact of additives and processing on microstructure and dielectric properties of willemite ceramics for LTCC terahertz applications

LTCC and Bulk Zn4B6O13–Zn2SiO4 Composites for Submillimeter Wave Applications

“…A higher willemite contribution caused an excessive increase in the sintering temperature. In previous studies [ 23 , 26 ], it was proved that both Zn 4 B 6 O 13 and Zn 2 SiO 4 ceramics do not react with silver, although the resolution, smoothness, and sharpness of the edges of the conductive patterns screen printed on the willemite-based substrates were better than those deposited on the zinc borate ceramics. Considering the requirements of a low sintering temperature suitable for cofiring with Ag-based commercial thick film pastes and the good quality of the printed conductors, the maximum preferred fraction of willemite in the Zn 4 B 6 O 13 - Zn 2 SiO 4 composites is limited to 60 wt %.…”

“…For bulk ceramics, the fabrication procedure comprised solid-state synthesis of the components, milling of batches, uniaxial pressing of pellets, and sintering at 920–950 °C for 4 h. The starting components of the composites, Zn 4 B 6 O 13 and Zn 2 SiO 4 powders, were obtained via calcination at 900 °C and 1150 °C [ 23 , 26 ], respectively, followed by ball milling for 8 h (Pulverisette 5, Fritsch, Germany). The phase compositions of the powders after the synthesis and sintering processes were examined by the X-ray diffraction method, using Cu K α1 radiation within a 2Ɵ range of 5 to 90° (Empyrean, PANalytical, Almelo Netherlands The quantitative phase analysis and the crystal structure refinement were performed using the Rietveld method.…”

“…In addition, for the 87% Zn 4 B 6 O 13 –13% Zn 2 SiO 4 composite, the influence of the temperature changing in the 30–150 °C range was studied at THz frequencies. The THz measurements procedure has been described previously [ 23 , 26 ].…”

“…The requirements for such new materials include a low dielectric constant to minimize the signal propagation delay, a low dielectric loss to ensure frequency selectivity and to restrict power consumption, and a low sintering temperature to enable the use of multilayer LTCC/ULTCC (low/ultralow temperature cofired ceramics) technology. Along with the modification of materials with a low dielectric constant, such as silica, borosilicate glasses, cordierite, mullite, forsterite, diopside, willemite, and aluminates [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], which have been well-known for decades, less popular ceramics have been explored recently, such as borates, tungstates, molybdates, vanadates, and phosphates [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. The use of ceramic-ceramic or glass–ceramic composites is an effective way to tailor microstructure, electric, and thermal properties of functional materials for microwave substrates.…”

“…To decrease the high sintering temperature of the willemite ceramics (above 1300 °C), various low melting glasses and sintering aids were added. However, publications devoted to the microwave applications of this material fabricated using LTCC technology are not numerous [ 23 , 24 ].…”