Planar inductors on an LTCC substrate realized by the gravure-offset-printing technique

The fabrication and properties of planar inductors on a low-temperature co-fired ceramic (LTCC) substrate are studied together with computational simulations of their properties. One- and two-layer inductors with both square and spiral shapes were fabricated with and without a ground plane. The narrowest line width of conductors was 60 μm and the size of the inductors was limited to 2.5×2.5 mm². Inductors were printed on the LTCC sheet by the gravure-offset printing. Via holes needed in the two-layer structures were made by excimer and Nd-YAG lasers. The layers were aligned and laminated at 70°C with a pressure of 20 10⁶ N/mm² for 15 min, and the laminated layers were co-fired at a peak temperature of 850°C. The dependence of the electrical values on the geometrical dimensions and material properties of the inductor structures was studied both experimentally and by simulation. The electrical measurements were made by an LCR meter and a network analyzer, and the dimensions of the printed conductors were measured by a surface profilometer. The measured inductance values varied from a few nH to hundreds of nH depending on the structure and the resonant frequencies of the coils ranged from 300 MHz for the microstrip coils up to several GHz for the one-layer inductor structures. The measured inductance values were higher than the calculated ones and the variation of the measured electrical values was in the range of ±10%