Probable electron field emission switch

[sondreL]

Hi again , i did some reading about this topic on google and there were only a few articles about it , so I would like to ask you for some advice.I ask this from a previous thread i asked about electrons in vacuum. Could electron field emission technology be used as a high voltage switch were semiconductor device limits are far exceeded ?

as far as I undersand it now the pluses are that vacuum is a good insulator and the control voltage to turn on the field emission is not the full voltage applied between the cathode (tip) and anode (plate) of the field emission device , but only the amount of voltage shortly before the threshold of the field emission and slightly abive it as to reach the level at which a electron current path forms and then again lower the voltage below the threshold to stop the electron emission. Any info on the subject is much appreciatted.

 

[Nugatory]

How familiar are you with the vacuum tube technology that was used before the invention of the transistor?

 

[sondreL]

Well , I have read about vacuum tube technology , the most widly used types of tubes were thermionic ones , were the electrons came from a low voltage heated cathode , probably that explains why the old TV sets usually took about 30 seconds to get to the picture after switch on , te tubes were heating up to the point were normal electron emission could occur. I also understand how these tubes were used as switches even in the first computers , with a middle mesh type plate being altered between ground and negative potential which would repel the incoming electrons from the cathode.So I recetly came upon field emission , I understand the basic concept , that the E field strength is dependent on the amount of charge in a given surface , since a small very sharp tip has a very tiny surface applying a large potential difference across the tip and a plate some distance away from it causes an extremely large E field to develop at the end of the tip and around it , large enough to push of electrons.Now I guess this vacuum tube method is much more robust because there is no hot cathode that burns out with time.

My question is how precisely this can be used as a high voltage switch or any voltage switch , I would like to understand the details. Like for example do you apply a large PD across the tip and the plate and then use a much smaller voltage to either overcome the threshold for electron emission or go below it which would either start a current between the tip and plate or cut it off? Or maybe one uses some kind of middle electrode with which to repel the incoming electrons if the current needs to be swithed off ?

 

[sondreL]

Anyone interested, please?

 

[berkeman]

Well , I have read about vacuum tube technology , the most widly used types of tubes were thermionic ones , were the electrons came from a low voltage heated cathode , probably that explains why the old TV sets usually took about 30 seconds to get to the picture after switch on , te tubes were heating up to the point were normal electron emission could occur. I also understand how these tubes were used as switches even in the first computers , with a middle mesh type plate being altered between ground and negative potential which would repel the incoming electrons from the cathode.So I recetly came upon field emission , I understand the basic concept , that the E field strength is dependent on the amount of charge in a given surface , since a small very sharp tip has a very tiny surface applying a large potential difference across the tip and a plate some distance away from it causes an extremely large E field to develop at the end of the tip and around it , large enough to push of electrons.Now I guess this vacuum tube method is much more robust because there is no hot cathode that burns out with time.

My question is how precisely this can be used as a high voltage switch or any voltage switch , I would like to understand the details. Like for example do you apply a large PD across the tip and the plate and then use a much smaller voltage to either overcome the threshold for electron emission or go below it which would either start a current between the tip and plate or cut it off? Or maybe one uses some kind of middle electrode with which to repel the incoming electrons if the current needs to be swithed off ?

Vacuum tubes are actually still used for some HV, high power applications like radio transmission towers and high-power radars. The Wikipedia article is a good introduction to how they are configured for different electrical component functions:

http://en.wikipedia.org/wiki/Vacuum_tube

:-)