[nutschig]

Silicon is not the best transistor material ever. For example, gallium arsenide can run at a switching frequency of 250 GHz thanks to faster electron velocity and higher electron mobility. https://en.wikipedia.org/wiki/Gallium_arsenide#GaAs_advantag...

[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?

[buserror]

I, for one, have a Germanium transistor in my 1964 Accutron Bulova watch. So there!

http://www.decadecounter.com/accutron/history.htm

[jpmattia]

Old joke: It's not that Germanium has a bad bandgap, it's just that room temperature is wrong.

[As it turns out, having a decent native oxide is also a winner.)

[duaneb]

> thanks to faster electron velocity and higher electron mobility.

How does this effect energy transfer? This is the metric I assume most people care about as it is typically much faster than an electron can move.

[klodolph]

"Best" is a funny word, because it means different things to people who care about different things. Silicon can be built with better gates / insulators than gallium arsenide, so if that's what you care about, silicon is better.