# question about floating gates and tunneling

Discussion in 'General Electronics Chat' started by magnet18, Dec 15, 2011.

1. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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OK, as I understand it from 5 minuets on wikipedia, a solid state hard drive has the general layout of a mosfet, but with a secondary floating gate between the primary gate and the depletion region. When voltage is applied to the gate, it pulls electrons towards it and the floating gate. Fet turns on and the electrons begin flowing through the absence of holes along the oxide. Then, since the electrons are pulled towards the primary gate, some of them... tunnel through the oxide, losing energy and becoming trapped there, keeping a "permanent" voltage on the floating gate.

I have two questions.

1, if the electrons are on the floating gate, wouldn't the voltage be negative, keeping the FET off?.

2, WTF if tunneling?
I know it's Heisenberg uncertainty principle and stuff, and that some electrons can get to the other side by... trading energy for motion or something?
What do they actually do?
slide through the lattice structure?
teleport?

(feel free to move this to physics if you want)

2. ### JDT Well-Known Member

Feb 12, 2009
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Well I'm not an expert on this but you are correct that a flash memory cell uses a mosfet with a floating gate as well as a control gate. Charge is put on the floating gate by quantum tunneling. This does not switch the mosfet on or off but changes the threshold voltage of the transistor. Then when a certain voltage is applied to the gates of an array of these transistors, some will switch on and some will not.

http://en.wikipedia.org/wiki/Flash_memory#Floating-gate_transistor

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

magnet18 likes this.
3. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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OK, thanks, I think that makes sense.
On power up, a certian voltage is applied to the FET's to see which ones have charge in the floating gate, and should be switched fully on?

4. ### crutschow Expert

Mar 14, 2008
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2. Tunneling is a quantum effect where there is a certain probability of an electron going through a thin insulator or barrier that classical physics says it cannot. Here's a further explanation.

5. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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so... it just appears?
no jumps, no crashes, nothing... it just ceases to exist on one side and then exists on the other?

6. ### crutschow Expert

Mar 14, 2008
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Yes. The quantum world is a place of weird and strange happenings, many of which don't seem to make much sense based upon the macro world we know. For example light photons directed through two small parallel slits cut in a plate will generate an interference pattern on the opposite side of the plates on photographic film. This is attributed to the wave nature of the light. But you will get the same interference pattern if you just put one photon at a time through one of the slits. But if you cover one slit, the interference pattern goes away!.

7. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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yea, double slit experiment...
I don't get that either
the light interferes with itself... mind blown

8. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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It goes back to the quote by some scientist:

"There's only maybe 3 people that fully understand quantum mechanics, myself, and I forgot the other two"

Now there is string theory to counterpoint quantum mechanics and all sorts of stuff.

Knowing fully the interactions and details of both will pretty much guarantee you won't marry a supermodel.

9. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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psh, gave up on that a long time ago... decided I could settle for a rich lawyer or something