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I must be missing sone fundamental law of electronics. Why does the gate voltage of a MOSFET travel into the main “body”. Aren’t oxides insulators? If so, how do the electrons pass into the body of the MOSFET?

My guess: The gate creates an electromagnetic field that can pass through the oxide.

(You don’t have to answer this below)

(Everything below 5:35 is irrelevant) (Image at 5:40) video

My point of the question was to try to figure out what the oxide did (5:40). In this video, Prashant Jain made an optical transistor using a nano crystal film on top of an oxide layer with gate voltage below that. The nano crystals had charges inside of them to make them “behave like a semiconductor”. They voltage would pull these charges out. But where would the charges go?

Is the use of oxide here similar to that of a MOSFET? Or what does it do here? (I’m a little confused about how this optical switch works)

gbe
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    Electric fields pass through insulators. In fact, there is no electric field in a perfect conductor. – Hearth Oct 22 '22 at 00:18
  • Would you say that is the same reason they have an oxide in 5:40 of the video? – gbe Oct 22 '22 at 00:23
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    I haven't watched the video, and can't right now. The oxide is essential for a transistor to function as a MOSFET, but you can do without it if you need a MESFET. But those are rare, and have some weird limitations (though they're apparently good for RF stuff). – Hearth Oct 22 '22 at 00:26
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    The diagram in the video is, I think, just that: a diagram. It isn't meant to indicate anything beyond the idea of an "optical transistor" (read: a device which passes or blocks flow depending on applied voltage/current), namely one that uses nanoparticles of some sort to facilitate such a function. A real device would be made of many more components. – Tim Williams Oct 22 '22 at 00:32
  • @TimWilliams Do you have any resources you know of that I can access for free? I am not in college and am a hobbyist. – gbe Oct 22 '22 at 00:36
  • An internet search of the terms would be a good start. The Wikipedia article is an okay overview. You can likely find papers that show how they are made, though understanding their components and methods will take graduate level studies. So, further reading would be basically everything in a curriculum to that point. A lot to take in, to be sure, but surprisingly freely available. – Tim Williams Oct 22 '22 at 00:42
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    For a hobbyist, I would note: other than purely for curiosity, it is a technology which will probably never affect you, nor does its understanding affect almost anything you are likely to do, so it doesn't matter. Regular transistors however are just as rich, and much more tangible and available, if I might suggest an alternative curiosity. – Tim Williams Oct 22 '22 at 00:44

1 Answers1

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Your key problem is here:

how do the electrons pass into the body of the MOSFET?

They don't. The individual electrons on the gate stay on the gate, and the ones in the body stay in the body (or go out the drain or source, depending on circuit conditions). Unlike the potentially-more-familiar BJT, there is no steady-state current into the gate of a MOSFET.

A MOSFET is controlled by the electric field, which pulls electrons toward or pushes them away from the region of semiconductor right below the gate. It's not unlike how your hair can be attracted to a static charged balloon; there's no path for the electrons to get to the gate, but they're still pulled towards it anyway (or, again, pushed away from it, depending on the polarity of the applied voltage).

Hearth
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