The electromagnetic properties of Cu-substituted garnets with low sintering temperature

Yttrium iron garnet ceramics are used as non-reciprocal materials in circulators because they present low dielectric and magnetic losses, and their magnetic properties can be engineered in order to optimise the material for specific applications. The main drawbacks of circulators are their size and cost, due to complex mechanical assembling of different materials. A possible solution would be to adapt the different materials to a common LTCC process in order to produce circulators with a multilayer process. We showed that Cu substitutions enable us to decrease considerably the sintering temperatures of garnets, from about 1450 °C to about 1070 °C, and our more recent results show it will be possible to decrease this temperature to 1000 °C, which would be a suitable temperature for co-firing with gold. We present new microwave characterizations (the dielectric constant and losses, the different magnetic line-widths: ΔHeff, ΔHK) of Cu-substituted garnets. The important impact of these characteristics on the properties of circulators is explained, and their variations versus composition and microstructure of the materials are shown.