[Baeocystin]

I appreciate the links.

Here's a more recent link, specifically regarding terahertz research, you might find interesting.

http://iopscience.iop.org/article/10.1088/1361-6463/50/4/043...

I want to emphasize an important distinction: that vacuum-based amps have higher potential switching speeds than semiconductors is not a novel thing, nor is it early stage research. It is part and parcel of the nature of semiconductors. What is cutting-edge is miniaturization of vacuum-based systems using conventional fab processes. That's the exciting stuff!