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Show 19 ·The coupling capacitance between second metal and poly with first metal shielding is Ca = 17.3 aF/JJm2, Cp = 15.3 aF/JJm, Cs (shielding) = 10.5 aF/JJm, and Ctotal = 17.3 aF/pm2 (1000)(0.7) + 2 * 15.3 (1000 + 0.7)- 10.5(1000 + 0.7) = 32.2 fF. The tables require four pages for all permutations of planes above and below, traces, and whether the interconnect is sparse or dense. Generating these tables from numerical analysis is the most intensive part of preparing for this approach to circuit analysis. This approach does take neighboring geometries into some account by dividing the possibilities of permutations into sparse and dense layout combinations, where sparse coupling values are typically higher than dense values by 1 0°/o. This would be due to the interference of neighboring geometries cutting the lines of flux that would otherwise extend farther into the layout. A Numerical Determination of Capacitance to Ground The third set of equations is from research done at the University of Illinois at Urbana-Champaign, and the two equations were empirically derived by fitting two-dimensional numerical data. 14 The pair of formulae is suitable for calculating capacitance to ground with an accuracy stated as 6°/o. w is the width of the conductor, h is the height of the conductor to ground plane, a the angle of the slant sidewall, and t is the thickness. a is taken as 90 degrees for a vertical edge. |
