Multi-chip module interconnections at microwave frequencies: electromagnetic simulation and material characterisation

In this work both the interconnections and materials used in multi-chip modules (MCMs) at microwave frequencies have been investigated. The electrical behaviour of the
interconnections was studied using commercially available 2.SD and 3D electromagnetic simulators (HFSSTM, MDSTM and Momentum™). State-of-the-art conductive and dielectric
film materials used in the fabrication of multi-layer MCM structures were characterized using microstrip/wave guide resonator techniques.
The models chosen for simulation of interconnections are commensurate with those in current use in MCM technology. Crosstalk between microstrip conductors in multi-layer
MCM structures was simulated and new knowledge leading to new design rules was obtained.Typical elements in MCM interconnect structures, such as vias, bends and airbridges were also investigated. The principal features of these elements were simulated and the results were obtained in S-parameter form. Based on the simulated results, these parasitic elements were modelled in terms of their equivalent circuits which can be used in circuit simulators to aid more rigorous MCM circuit design.
A microstrip ring resonator, fabricated using the newly developed conductive material from Heraeus, was employed to measure the line loss.
New techniques have been developed to measure the permittivity and loss tangent of thin dielectric films. In the previous methods for the measurement of these films, the accuracy in measuring the relative permittivity is limited and there is no available technique to measure the loss tangent. A novel cavity perturbation method was developed to accurately measure both the relative permittivity and loss tangent of the films deposited on a supporting substrate.
An additional independent technique, derived from transmission line theory, for measuring the relative permittivity of dielectric film was also established. A particular feature of the new teclmiques, which led to high accuracy in measuring dielectric constant and loss tangent was the positioning of the dielectric film in the region of maximum electric field strength, thereby ensuring maximum interaction between the electric field and the film material. A rigorous error analysis was performed on the new techniques, which led to the establishment of practical measurement correction factors.
A simple and rigorous method has also been developed to accurately measure the loss tangent of dielectrics with known dielectric constant using a resonant cavity. The novel
method eliminates the need for any physical measurement of the dielectric sample. The new technique should permit the development of techniques for very high frequency
characterisation of dielectric materials.