5 ms·

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 a

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_advantages https://en.wikipedia.org/wiki/Gallium_arsenide#GaAs_advantag...

duaneb 10y ago
> 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.
GregBuchholz 10y ago
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_presentations/publications/2012_10_15_Oct_rodwell_CSIC_talk.pdf 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/NORTHROP-GRUMMAN_311014.shtml http://www.semiconductor-today.com/news_items/2014/OCT/NORTH... ...for a >1THz circuit using InP HEMTs.
- raverbashing 10y ago
  Wow that's crazy. I wonder how you even test a 1THz amplifier. Also what kind of natural noise might exist in those bands
  - GregBuchholz 10y ago
    >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 10y ago
      And how do you get the 1THz signal in the 1st place? Maybe upconvert as well?
  - jpmattia 10y ago
    > 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_presentations/publications/2012_10_15_Oct_rodwell_CSIC_talk.pdf 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.
- pbhjpbhj 10y ago
  Does 'Heisenberg' or some other theory limit the top frequency, if so, what's the limit?
klodolph 10y ago
"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.
buserror 10y ago
I, for one, have a Germanium transistor in my 1964 Accutron Bulova watch. So there! http://www.decadecounter.com/accutron/history.htm http://www.decadecounter.com/accutron/history.htm
- jpmattia 10y ago
  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 10y ago

> 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.

GregBuchholz 10y ago

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_presentations/publications/2012_10_15_Oct_rodwell_CSIC_talk.pdf 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/NORTHROP-GRUMMAN_311014.shtml http://www.semiconductor-today.com/news_items/2014/OCT/NORTH... ...for a >1THz circuit using InP HEMTs.

raverbashing 10y ago
Wow that's crazy. I wonder how you even test a 1THz amplifier. Also what kind of natural noise might exist in those bands
- GregBuchholz 10y ago
  >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 10y ago
    And how do you get the 1THz signal in the 1st place? Maybe upconvert as well?
- jpmattia 10y ago
  > 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_presentations/publications/2012_10_15_Oct_rodwell_CSIC_talk.pdf 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.
pbhjpbhj 10y ago
Does 'Heisenberg' or some other theory limit the top frequency, if so, what's the limit?

klodolph 10y ago

"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.

buserror 10y ago

I, for one, have a Germanium transistor in my 1964 Accutron Bulova watch. So there! http://www.decadecounter.com/accutron/history.htm http://www.decadecounter.com/accutron/history.htm

jpmattia 10y ago
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.)