GaAs submicron ring oscillators characterized by electron-beam testing

Process technology and internal electron-beam test measurements of fast GaAs ring oscillators in buffered FET logic (BFL) are described. Specifically, the authors fabricated a series of 15-stage BFL ring oscillators consisting of MESFETs with 0.5- mu m gates defined by electron-beam lithography. The precise phase shift control of the electron beam sampling system used was the basis for an excellent 3.5-ps resolution of propagation delays. This made it possible to observe not only the time delay effected by individual oscillator stages but even the delay by single transistors. It is shown that the full width of the propagation time distribution comprising circuits on a number of different wafers is already completely reflected by the scatter between neighboring inverters in a single circuit. It is concluded that this result proves the importance of electron-beam measurements to the analysis of which mechanisms influence the behavior of fast digital ICs.<>