High‐quality RF Inductors in LTCC

Low temperature cofired ceramics (LTCCs) combine the advantages of both multilayer substrates with excellent high‐frequency properties and a high‐conductivity metallisation. The possibility to realise passive components embedded in the glass ceramics increases the scale of integration. Inductors are designed as single‐layer (planar spiral) or multilayer (3D) arrangements of narrow conductive traces with useful values up to a few hundred nanohenry. This range makes them useful for high‐frequency applications. Although the conductor pastes used have a low resistance, the maximum quality factor of these coils seldom exceeds 60. The decisive parameter in this regard is the line thickness which is normally 10–15 μm. A novel technique based on laser scribed canals permits conductor patterns with an almost square cross‐section, thus reducing the line resistance by a factor up to 10. Coils manufactured by this method have a considerably improved quality and are able to withstand high currents. This property widens the range of applications for LTCCs into the field of high‐power electronics.