Cold sintering of microwave dielectric ceramics and devices

Abstract

Microwave (MW) dielectric ceramics are used in numerous electronic components for modern wireless communication systems, including antennas, resonators, capacitors and filters. However, to date, MW ceramics are manufactured by an energy-intensive, conventional high-temperature (> 1000 °C) sintering technology and thus cannot be co-sintered with low melting point and base electrodes (Ag, Al, etc., < 1000 °C), nor directly integrated with polymers (< 200 °C). Cold sintering is able to densify ceramics at < 200 °C via a combination of external pressure and a transient liquid phase, reducing the energy consumed and facilitating greater integration with dissimilar materials. This review outlines the basics of MW ceramics alongside the mechanism of cold sintering. Recent developments in cold sintering of MW ceramics, composites and devices are described, emphasizing new materials and progress towards component/device fabrication. Future prospects and critical issues for advancing cold-sintered MW materials and devices, such as unclear mechanism, low Q × f values and poor mechanical properties, are discussed. Graphic abstract

Insights Into the Microstructure and Dielectric Properties of Cold Sintered NaCa2Mg2V3O12 Based Composites

“…During the preliminary stage of cold sintering, particle rearrangement takes place through the liquid medium. The second stage is associated with the dissolution of particles with the presence of pressure and temperature, which leads to the development of a supersaturated phase, followed by nucleation and densification of the ceramic composites (Yu et al, 2019;Wang et al, 2021). Hence optimum time and temperature are necessary for proper densification of composites by cold sintering.…”

“…In the present case, even though (1 − x) NCMVO-xNaCl (x = 0.4, 0.5, 0.6, and 0.7) composites show a higher density with increase in volume of NaCl, its Q u × f is slightly lower beyond 0.5 volume fraction of NaCl, which could be due to decreased quality factor of NaCl compared with NCMVO ceramics. It was reported that cold sintered NaCl possess a quality factor in the range 12,000-49,600 GHz depending on the processing conditions, while that of NCMVO has a reported value of around 50,600 GHz (Hong et al, 2018;Wang et al, 2021;Fang et al, 2013). The quality factor of a two phase composite can be determined by…”

“…During the first stage of CSP, the powder in the die prompts particle rearrangement under a uniaxial pressure with the help of solvent. As temperature increases from 100 to 300 • C, the solid forms a dense ceramic by a dissolution-precipitation mechanism (Wang et al, 2021). Bouville and Studart (2017) reported that when the pressure increases above 100 MPa in CSP, a phenomenon named as plastic deformation happens and is demonstrated by Hong et al (2018) in their experiment on cold sintering of NaCl.…”

A low‐permittivity microwave dielectric ceramic BaZnP2O7 and its performance modification

“…The past few decades have witnessed an ever‐growing scholarly interest in microwave dielectric ceramics with the rapid development of telecommunication 1‐4 . Recently, there is a strong ongoing search for dielectric ceramics with a dielectric constant ( ε r ) less than 15, a low dielectric loss (tan δ = 1/ Q ), and a near‐zero temperature coefficient ( τ f ) to meet the demands for microwave substrate applications 5,6 .…”

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The past few decades have witnessed an ever-growing scholarly interest in microwave dielectric ceramics with the rapid development of telecommunication. [1][2][3][4] Recently, there is a strong ongoing search for dielectric ceramics with a dielectric constant (ε r ) less than 15, a low dielectric loss (tan δ = 1/Q), and a near-zero temperature coefficient (τ f ) to meet the demands for microwave substrate applications. 5,6 Although traditional inorganic substrates such as Al 2 O 3 possess excellent dielectric properties, the exploration for novel materials with superior dielectric properties and sintering behaviors continues today.Pyrophosphates belong to typical low-permittivity compounds, in which M 2 P 2 O 7 possesses two kinds of structure according to the ionic radius of M that is a divalent cation.

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