Klaus Koller

Simulation and modelling of a high-performance trench capacitor for RF applications

The necessity for exact modelling and simulation data of the electrical characteristics of passive on-chip devices has become more and more important. The electrical performance of RF circuits is predominantly restricted by the passives. In this work the RF simulation and characterization for a new trench capacitor in a low loss environment are presented for the first time. The excellent accordance of the modelling data with the measured RF characteristics of this so-called SilCap (silicon capacitor) is shown. An analytical model has been developed which permits the exact circuit simulation of all relevant electrical quantities. The device simulation enables the optimization of the SilCap device geometries.

Stress induced metallurgical effects in Ti/TiN/AlCu/TiN metal stacks

Integrated circuits with aluminum metallization for products with high current densities need a metal stack with liner and antireflective coating (ARC) which can fulfill several requirements (e.g. low sheet resistance, high reliability, smooth surface, good adhesion, thermal stability, etc.). In this work different multilayer metal stacks are investigated and several phenomena which can be observed after thermal annealing of Ti/TiN/AlCu/TiN stacks are described and discussed. Metallurgical, electrical and mechanical properties of different layer combinations are investigated after thermal annealing and stress tests are done to compare the electromigration and life time behavior of each metal stack. For all investigated metal stacks it is shown that an interface reaction between Ti and aluminum will form TiAl3 phase. Even with very thick TiN layers on top of titanium or with only TiN liner the phase formation occurred. Explanations and models for the formation of different phenomena (hillocks, depressions ...

A New Process for On-Chip Inductors with High Q-Factor Performance

A novel technological method to improve the quality factor (Q) of RF-integrated inductors for wireless applications is presented in this paper. A serious reduction of substrate losses caused by capacitive coupling is provided. This is realised by removing the oxide layers below the coils with optimized underetching techniques. This special etching procedure is used to establish an environment in the inductor substructure with very low permittivity. A set of solid oxide-metal-columns placed below the metal windings stabilize the coil and prevent the hollowed out structure from mechanical collapse. The oxide capacitance is lowered significantly by the reduction of the permittivity 𝜀r from values around 4 to nearly 1. Capacitive coupling losses into substrate are decreasing in the same ratio. The resulting maximum Q-factors of the new designs are up to 100% higher compared to the same devices including the oxide layers but shifted significantly to higher frequencies. Improvements of Q from 10 up to 15 have been obtained at a frequency of 3 GHz for a 2.2 nH inductor with an outer diameter of 213 𝜇m. The resonance frequency (𝑓res) and frequency at maximum Q (𝑓(𝑄max)) are shifted to higher frequencies, caused by the shrunk total capacitance of the structure. This enables the circuit designer to use the inductors for applications working at higher frequencies. Coils with different layouts and values for inductance (L) were verified and showed similar results.