Low‐temperature‐sintered MgO‐based microwave dielectric ceramics with ultralow loss and high thermal conductivity

Abstract

With the development of 5G/6G communication, the requirements of portable devices for miniaturization and multifunction make low‐temperature co‐fired ceramic (LTCC) more and more important. In the area of high‐frequency high‐density passive integration, microwave dielectric ceramics with a low dielectric loss and high thermal conductivity are urgently needed to ensure the effective signals transmission and system reliability. However, most microwave dielectric ceramics with a low dielectric loss were not applicable for the LTCC technology due to the high sintering temperature. In this work, a series of MgO‐based ceramics [(100 − x) wt.% MgO–x wt.% (0.2SrF2–0.8LiF) (x = 5,7,10)] were prepared by solid‐state reaction method. The addition of sintering aid 0.2SrF2–0.8LiF (S2L8) decreased the sintering temperature below 880°C without degrading the microwave dielectric properties of ceramics. Microwave dielectric properties of ceramics, including quality factor Q × f, relative permittivity εr, and temperature coefficient of resonant frequency τf, were investigated to find the optimum composition and sintering temperature. In general, MgO–7 wt.% S2L8 ceramic sintered at 860°C exhibits outstanding properties of Q × f = 180 233 GHz, εr = 9.11, τf = −40.33 ppm/°C, and a high thermal conductivity of 24.02 W/(m K). This series of ceramics are suitable to be co‐fired with Ag electrodes. With all those great properties, this series of MgO‐based ceramics are expected to be the candidates for LTCC applications in 5G/6G technology.

2D Nanosheet Spray Coating for Scalable Processing of High‐Energy‐Density Dielectric Polymer Films

“…However, the low energy density of current dielectric polymers makes capacitors bulky and heavy, which cannot meet the requirements of compact and efficient power systems. [ 10–14 ] For example, the most advanced commercially available dielectric polymer, biaxially oriented polypropylene (BOPP), has an energy density of only 2 J cm −3 . [ 15,16 ]…”

“…However, the low energy density of current dielectric polymers makes capacitors bulky and heavy, which cannot meet the requirements of compact and efficient power systems. [10][11][12][13][14] For example, the most advanced commercially available dielectric polymer, biaxially oriented polypropylene (BOPP), has an energy density of only 2 J cm −3 . [15,16] The discharged energy density (U e ) of the dielectric films can be calculated using U e = ∫ E dD, where E and D represent the applied electric field and electric displacement, respectively.…”

Modulation of the Microwave Dielectric Properties of Si-Based Olivine Structured Ceramics Through the Variation of A-Site Ions

“…Moreover, good thermal performance allows the ceramics to stably operate in high-temperature environments. [8][9][10][11][12][13][14][15][16][17][18] Microwave dielectric ceramics with an olivine structure and the general formula A 2 BO 4 (A = Mg, Zn, Ca, Ba; B = Si, Ge) have attracted much interest due to their thermal, mechanical, pyroelectric, and dielectric properties. There are two main types, Si-based and Ge-based olivine structured ceramics, with the space group Pbmn.…”

Hierarchical porous (Ta 0.2Nb 0.2Ti 0.2Zr 0.2Hf 0.2)C high-entropy ceramics prepared by a self-foaming method for thermal insulation

“…The distorted lattices of these ceramics also lead to sluggish diffusion, resulting in excellent oxidation resistance [9]. Therefore, porous high-entropy ceramics can achieve the integration of thermal insulation, load-bearing, and high-temperature resistance, making it a promising thermal insulation material in ultrahigh temperature applications [10,11]. Generally, porous highentropy carbide ceramics have been fabricated using various methods such as template [12], direct foaming [13], and partial sintering [14].…”