This article presents a standard case of transmission line: the microstrip structure. First, the structure is described and then the results extracted from QUEST are compared with measurements. We thank STMicroelectronics (Crolles-R&D) for experimental data support.

1. Microstrip Structure

This structure represents a line screened from the silicon substrate by a metallic plate. Figure 1 shows the microstrip structure used for the simulation in QUEST.

Figure 1. The microstrip structure.

The plate and the line are 100 ?m and 4 ?m wide respectively. Though the substrate is screened, it must be defined for simulation purpose. Figure 2 shows the definition of the parameterized materials in QUEST in the Process menu, whereas Figure 3 shows the mesh parameters in the Field Solver menu.

Figure 2. Definition of the materials

Figure 3. Mesh generation.

The number of Z-slices in the 'pass1' layer is adjusted to take into account the skin effect in the metal line.

2. Results

In order to compare simulated results with measurements, attention should be paid on the current return path. In QUEST, the reference is the substrate by default whereas the experiments have been performed in such a way that the reference is the plate. The default in QUEST has to be changed by selecting a flag setting the plate as the reference for the current return path.

Figures 4, 5 and 6 reports respectively the line resistance R, the self-inductance L and the capacitance C per unit length as measured and calculated by QUEST.

Figure 4. Ccomparison of measured and simulated resistance.

Figure 5. Ccomparison of measured and simulated self-inductance.

Figure 6. Comparison of measured and simulated capacitance.

Concerning the R and L, the simulated data are closed to the experimental ones. For the capacitance, the average difference is greater than 5%. This difference can be explained by the difference in topology between the simulated structure and the experimental one.

Conclusion

Simulated results have been compared to experimental data on a microstrip structure. A good agreement is obtained between simulated and experimental data. This comparison shows that QUEST is a reliable tool to extract the lumped elements of a microstrip line. The reader will find other comparison in [1].

Reference

Performance Characterization of Advanced Interconnects on High Speed VLSI Circuits, C.Bermond, ESSDERC 2000.