The influence of the transit-time effect on propagation delay measurements by electron and photon beam techniques

Abstract

Propagation delay measurements of high-speed digital devices require high accuracy and excellent stability. At the same time, long-range phase shifts are necessary because signals in these circuits may have very long periods. This can be achieved with a newly developed phase shift method, where a blanking capacitor acts as a gate to select one out of a larger number of pulses. A delay of several hundred nanoseconds with picosecond accuracy was demonstrated with this technique. Ultimately, the resolution of propagation delay measurements is limited by variations in the secondary electron transit time. This leads to a shift of the measured waveform, depending on the test point geometry. Errors then result if the propagation delay is measured between points of different dimensions. This effect was evaluated theoretically and experimentally. A difference in conductor width between two test points of a factor of 2 was found to lead to an error of 3ps for propagation delay measurements.