Do main paths reflect technological trajectories? Applying main path analysis to the semiconductor manufacturing industry

It has been proposed that main path analysis can be used to identify technological trajectories in patent-citation networks. In this paper, the method is applied to a network composed of one million US patents and eight million citations in order to trace the backbone of the technological trajectory of the semiconductor manufacturing industry. An in depth discussion of the method is presented, focusing on the many parameters that can be adjusted while applying it and on the consequences of adjusting any of them. Moreover, and differently from other papers on the subject, the result of the algorithm is analysed to determine if it indeed represents the most important technological contributions to the trajectory or if it is merely a collection of relevant and connected patents. This is made easier by the fact that the semiconductor industry has a clear and widely known technological trajectory that spans more than 50 years, Moore's law.