Analytical estimation of high-frequency properties of RF micro-inductors prepared by direct-write techniques

In this work, the high-frequency characteristics of micron size, square spiral-type RF thin film air-core inductors prepared by direct-write supersonic jet deposition of laser ablated nanoparticle were estimated by a software package. The important parameters that are determined by direct-write process, such as the materials, the cross-section shape, the thickness, and the conductivity of the coil, were varied systematically to estimate the trend of the inductors’ performances. The area dimensions of RF inductors utilized and the number of coil turns were 1.3 mm × 1.3 mm and 3, respectively. The 96 wt% Al₂O₃, SiO₂-coated Al₂O₃, and SiO₂-coated Si wafers were used as the substrate material. The high-frequency characteristics of the inductance (L) and quality factor (Q) of the utilized inductors were simulated using a Maxwell three-dimensional field simulator (HFSS 8.5), which employs the finite element method. The used inductors, which have silver metal (Ag) coils, the trapezoid shaped cross-section of the coil, the coil thickness of 30 μm, and the coil conductivity of 70% of Ag bulk value, exhibit L of 8 to 9 nH. They also exhibit a maximum Q of 35.5 near the frequency of 750 MHz and a self-resonant frequency of 5.14 GHz. The simulated high-frequency data of the inductors were agreed well with those obtained from the equivalent circuit model of the utilized inductors.