Accurate transmission line characterisation on high and low-resistivity substrates

Abstract

Differences in probe-tip-to-line geometry and substrate permittivity between measurement and calibration wafers decrease measurement accuracy. This is especially the case when measurements are performed on lossy silicon substrates. Two novel general techniques are presented which characterise the discontinuities near the probe tip, based on the measurement of two lines with different lengths. The equivalent elements representing the discontinuity are extracted at each frequency point, together with the propagation constant and the characteristic impedance of the line. The results obtained are superior to previous methods with a reduced number of measurements. The validity of the method is demonstrated by measurements of CPW lines on low and high resistivity silicon and on GaAs.