Low-Temperature Sintering and Microwave Dielectric Properties of Zn2SiO4 Ceramic Added with Crystalline Zinc Borate

Abstract

The physical and dielectric properties of composites of known microwave materials, Zn 2 SiO 4 and Zn 3 B 2 O 6 , prepared by solid-state reaction, were investigated with the purpose of developing a low-loss dielectric material for low-temperature co-fired ceramic applications. An off-stoichiometric phase of Zn 2 SiO 4 with extra SiO 2 was used to avoid the occurrence of unreacted ZnO. During sintering, zinc borate was found to partially react with residual SiO 2 to form Zn 2 SiO 4 . The residual zinc borate was converted to a boron-rich glassy phase which helped to reduce the sintering temperature of the composite. Good relative sintering density (>90%) at temperatures below the melting temperature of zinc borate is indicative of a sintering mechanism of diffusion-based mass transfer. Composites containing 15 wt.% zinc borate, 2.5 wt.% lithium carbonate and 20 wt.% zinc borate in zinc silicate had dielectric constants of 6.8 and 6.1, quality factors (Q9f) of 48,800 and 94,300 GHz when sintered at 900°C and 950°C, respectively. These quality factor results are close to the best values reported for zinc silicate at these sintering temperatures.

LTCC and Bulk Zn4B6O13–Zn2SiO4 Composites for Submillimeter Wave Applications

“…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 ].…”

Synthesis and Microwave Dielectric Properties of BBSZ-Zinc Silicate Based Material for LTCC Applications

“…Pure ZS formation by calcining the mixture of ZnO and SiO 2 powders at 1150°C has been previously reported. 14 The XRD pattern of BBSZ glass powder confirms its amorphous nature. The XRD patterns of sintered zinc silicate-glass pellets confirm the absence of any chemical interaction between the glass and the ceramic phase.…”

“…Similarly, d 1 and d 2 are the theoretical densities of zinc silicate and BBSZ glass, respectively. Here, the density of zinc silicate was taken as 4.23 gm/cc from a previous report, 14 while the density of BBSZ glass, as measured using the Archimedes principle, was 6.85 gm/cc. This value of density matches with that reported in the literature.…”

“…It possesses a low dielectric constant ($ 6.1) and low dielectric loss, in the range of 10 À5 . 13,14 However, its sintering temperature is high ($ 1350°C), which needs to be reduced using appropriate additives for its use as LTCC host material. There are several reports for reducing the sintering temperature of zinc silicate using lowmelting-point oxides and glasses, such as B…”