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.