Low‐Temperature Sintering of Low‐Loss Millimeter‐Wave Dielectric Ceramics Based on Li‐Kosmochlor, LiCrSi2O6

Abstract

Ceramic dielectrics with particularly low levels of dielectric loss and low permittivity are of growing interest toward millimeter-wave applications. Based on composition and structural considerations, lithic kosmochlor is expected to meet these requirements while exhibiting low densification temperatures, allowing its integration also in co-fired circuits. Herein, it is found that the spark plasma sintering of LiCrSi2O6 ceramics facilitates densification at temperatures more than 200 °C lower than conventionally processed materials in only a fraction of the time. A spark plasma sintering duration of 10 min is necessary in order to achieve a controllable process with a repeatable high-performance product material exhibiting a fine-grained microstructure. Characterization millimeter-wave frequencies reveal that LiCrSi2O6 materials produced in this manner exhibit excellent dielectric properties (Qf = 80 700 GHz and εr = 7.5 at 134.24 GHz) following densification at only 950 °C with a relative density of 97.4%. These results represent an unprecedented combination of low dielectric losses and processing temperatures for ceramics processed without the addition of sintering aids. The materials and methods explored here present a promising pathway toward high-performance millimeter-wave and co-firable systems.