Text Box: RESEARCH
Text Box: Signal integrity affects all levels of microelectronics packaging for high-speed circuits. Signal integrity research attempts to identify and avoid any effect that causes signal distortion and energy loss at high frequency range. Signaling rates are expected to exceed 10 Gb/s in a few years, which makes imperative the improved understanding of the off-chip loss due to metal surface roughness. Ever-increasing edge rates will raise the likelihood of cross-talk, ground bounce, resonance, attenuation and other signal discontinuities among squeezed signal lines. These are important issues for high speed circuit design and modeling. To model the surface-roughness effect of the signal integrity in interconnects on high-speed packages and boards, we characterized the rough surface by a stochastic process with spectral density function. From 3-D roughness profiles of atomic force microscope (AFM) measurements, the spectral densities were extracted. We considered the problem of a plane wave incident on a rough dielectric-metal surface and also the problem of a source in a metallic waveguide with a rough interface. To solve Maxwell equations for the problem, the analytic small perturbation method and numerical methods were used (the Method of Moments (MoM) and the transfer operator matrix (T-Matrix)). The simulation shows that a rough surface interface can cause up to 100% more power loss than a smooth surface interface. We are now extending 3D full wave method to more complicated configurations such as 3D waveguide roughness problems.
Text Box: (Left) A side view of the rough interface between the printed transmission line and the substrate, taken at the polished cross-section. (Right) A top view of the rough interface between the printed transmission line and the substrate taken by the atomic force microscope.