Wolfgang Hartung

Integration of crossed anisotropy magnetic core into toroidal thin-film inductors

A new approach to RF thin-film inductors with an integrated magnetic core has been investigated. A toroidal inductor design was realized in thin-film technology aiming at small-signal applications in the frequency range from 10 MHz to 1 GHz. The magnetic core consists of a multilayer of sputter deposited soft magnetic FeCoBSi. The individual magnetic films were deposited in a way to realize a crossed magnetic anisotropy in the core. High-frequency measurements of the multilayers already illustrated the advantages of the unique magnetic geometry. The influence and benefit of such a magnetic core on the toroid microinductor is discussed. The results show that such crossed anisotropy microinductors are a very promising alternative to common planar spiral inductors in the RF range.

High frequency performance of laminated soft magnetic films (NiFe, FeAlN, and amorphous CoFeBSi) in external fields

Thin film multilayers of different compositions (NiFe, FeAlN, and amorphous CoFeSiB) were prepared by sputter deposition. The ultrahigh frequency performance was studied using rf fields perpendicular to the in-plane easy axis. By applying external bias fields either along or perpendicular to the easy axis (perpendicular to the rf field excitation), the cutoff frequency of the different alloys can be shifted significantly to higher frequencies (>1 GHz) according to theory. On the other hand, it is possible from these measurements to identify different phenomenological damping of the material systems due to structural effects. Although FeAlN exhibits the highest saturation magnetization compared to NiFe and CoFeBSi, it shows a higher damping which is explained by nonideal structure.

A high-performance trench capacitor integrated in a passive integration technology

The requirements for the electrical characteristics of passive on-chip devices become more and more important. The electrical performance of RF circuits is predominantly restricted by the passives. New technologies and new device concepts are necessary to meet the demands. In this work, a trench capacitor developed for RF applications is presented for the first time. This so-called SilCap (silicon capacitor) device features very high capacitance density, extreme low-voltage dependence, excellent temperature stability, good RF performance and a high breakthrough voltage. First, the device function and the technological concept are introduced. The concept is realized without implementing cost-intensive high-k materials. This trench capacitor is integrated in the front end of line of a passive integration technology. The achieved specific capacitance density is compared to a standard planar capacitor. Performance of the SilCap in terms of quality factor and breakthrough voltage is shown. Finally, reliability data of this trench capacitor are presented with special focus on extrinsic and dielectric lifetime.