[GregBuchholz]

You can create some pretty high frequency transistors (BJTs) with Indium Phosphide (InP) (ft > 600GHz, fmax > 1THz). See page 33 of:

http://www.ece.ucsb.edu/Faculty/rodwell/publications_and_pre...

...for examples of some 600 GHz circuits, and:

http://www.semiconductor-today.com/news_items/2014/OCT/NORTH...

...for a >1THz circuit using InP HEMTs.

[raverbashing]

Wow that's crazy.

I wonder how you even test a 1THz amplifier. Also what kind of natural noise might exist in those bands

[jpmattia]

> I wonder how you even test a 1THz amplifier.

The usual schtick is to measure the S-parameters a slower speeds and extrapolate out to the cutoff. (see chart 21 from the link above: http://www.ece.ucsb.edu/Faculty/rodwell/publications_and_pre...)

For the digital people, building a ring oscillator with N stages will cause the output to divide by N, and just make sure that f/N is in the range of your oscilloscope.

To actually measure things up in the THz range directly, there are more exotic methods: Superconducting bolometer is one that I've been involved with. But those are a PITA for a bunch of reasons.

[GregBuchholz]

>I wonder how you even test a 1THz amplifier.

Most likely using a mixer or some other non-linearity to down convert into the frequency range of your spectrum analyzer.

[raverbashing]

And how do you get the 1THz signal in the 1st place? Maybe upconvert as well?

[pbhjpbhj]

Does 'Heisenberg' or some other theory limit the top frequency, if so, what's the limit?