High Quality Factor, Ultralow Sintering Temperature Li₆B₄O₉ Microwave Dielectric Ceramics with Ultralow Density for Antenna Substrates

Abstract

Dense Li6B4O9 microwave dielectric ceramics were synthesized at low temperature via solid state reaction using Li2CO3 and LiBO2. Optimum permittivity (r) ~ 5.95, quality factor (Qf) ~ 41,800 GHz and temperature coefficient of resonant frequency (TCF) ~ −72 ppm/ o C were obtained in ceramics sintered at 640 o C with a ultra-small bulk density ~ 2.003 g/cm 3 (~ 95% relative density, the smallest among all the reported microwave dielectric ceramics). Li6B4O9 ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li3AlB2O6 and Li2AlBO4 secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ~ 279 εHz at −10 dB transmission loss (S11) in agreement with simulated results. The Li6B4O9 microwave dielectric ceramic possesses similar microwave dielectric properties to the commercial materials but much lower density and could be good candidate for both antenna substrate and low temperature co-fired ceramics (LTCC) technology.

Cold‐Sintered C0G Multilayer Ceramic Capacitors

“…3D integration demands the sintering temperature of the ceramic layers to be lower than the melting temperature of (and chemically compatible with) the metallic electrode . These requirements have led to four typical categories of dielectrics based on their sintering temperature: i) high‐temperature cofired ceramics (HTCC, 1200–1800 °C); ii) low‐temperature cofired ceramics (LTCC, 900–1000 °C); iii) ultralow temperature cofired ceramics (ULTCC, 400–700 °C), and more recently iv) cold‐sintered cofired ceramics (CSCC, 20–200 °C) . The major drawback of HTCC systems is the need to use high melting temperature metallic electrodes, such as Pt, Pd, Au, or related alloys.…”

Tunable microwave dielectric properties in SrO‐V2O5 system through compositional modulation

“…The developments of commercial wireless technologies, especially the fifth‐generation (5G) telecommunication, Internet of Things (IoTs) and military radar systems, have expanded the operating frequency to the millimeter‐wave range. This new technological paradigm brings out the increasing demands of high‐speed signal propagation at high‐frequency regions . For ceramics used as substrates, low permittivity ( ε r < 15) is required for fast signal transmission and minimizing the crosscoupling between the substrates and the conductors .…”

“…To date, a number of promising low‐permittivity materials ( ε r < 15) have been reported. All of those materials have tetrahedral unit cell, such as borates, silicates, phosphates, and vanadates . Among them, vanadates have attracted considerable attention due to cheap raw materials, simple synthetic process, and good microwave dielectric properites .…”

“…All of those materials have tetrahedral unit cell, such as borates, silicates, phosphates, and vanadates. 3,[12][13][14] Among them, vanadates have attracted considerable attention due to cheap raw materials, simple synthetic process, and good microwave dielectric properites. [15][16][17][18] For example, alkaline earth orthovanadates, M 3 (VO 4 ) 2 (M = Mg, Ba, Sr) are promising candidates with low dielectric loss and low-ε r for high-frequency application.…”

Structure and microwave dielectric properties of ALn4(MoO4)7 (A = Ba, Sr, Ca, Ln = La, Pr, Nd, and Sm) ceramics

“…Multilayer co‐firing technology enables large scale size reduction of the modern wireless communication devices. LTCC technology finds applications in electronic packaging, substrates for RF front ends, substrate integrated waveguides, implantable antennas, antenna substrates for 5G applications, etc . LTCC substrates offer excellent low loss medium for the microwave signal propagation.…”