Cryotron circuits? - RF Cafe Forums
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Post subject: Cryotron circuits? Posted: Mon Nov 17, 2008 1:10 pm
Joined: Tue Dec 26, 2006 5:39 pm
Anyone here ever use a Cryotron? Ever seen one? I am curious when (if) they fell out of use.
When did "the transistor" become faster than a cryotron?
When did "the transistor" become cheaper than a cryotron?
Do you know of any interesting applications of these things other than as logic / memory devices?
These were not ever RF circuits (were they?). However, I thought I would check here to see if anyone has any experience or stories about these things.
Post subject: Posted: Tue Nov 18, 2008 11:48 am
Joined: Thu Sep 25, 2003 1:19 am
The following information is just off of the top of my head. I did not find this is on Wikipedea.
The cryotron is a switch that operates using superconductivity. The cryotron works on the principle that magnetic fields destroy superconductivity. This simple device consists of two superconducting wires ( e.g. tantalum and niobium) with different critical temperature (Tc). A straight wire of tantalum ( having lower Tc) is wrapped around with a wire of niobium in a single layer coil. Both wires are electrically isolated from each other. When this device is immersed in a liquid helium bath both wires become superconducting and hence offer no resistance to the passage of electric current. Tantalum in superconducting state can carry large amount of current as compare to its normal state. Now when current is passed through the niobium coil (wrapped around tantalum) it produces a magnetic field, which in turn reduces (kills) the superconductivity of the tantalum wire and hence reduces the amount of the current that can flow through the tantalum wire. Hence one can control the amount of the current that can flow in the straight wire with the help of small current in the coiled wire. We can think tantalum straight wire as a "Gate" and coiled niobium as a "control".
A planar cryotron was invented in 1957, made of thin films of lead and tin. This was one of the first integrated circuits, although using superconductivity rather than semiconductivity. In the next few years a demonstration computer was made and and arrays with 2000 devices operated. A short history of this work is in the newsletter of the IEEE History Center, number 75, November 2007.