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Background: I have a circuit for a FGMOS and they are describing the Fowler-Nordheim Tunneling (FNT) mechanism. The picture features two transistors: the main (FG)MOS and a secondary MOS to encapsulate the FNT mechanism. The MOSFET responsible for FNT has the Drain, Source and Bulk all connected to a source, V_Tunn. The gate of this transistor is then connected to the gate of the (FG)MOS.

enter image description here

Image source: Ochoa-Padilla et. al. Floating-Gate MOS Charge Programming Using Pulsed Hot-Electron Injection. Oct. 2013.

Question: Why is the MOSFET connected this way? Does this make the FNT MOSFET act as a Two-Terminal Semiconductor/diode? See the attached picture.

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  • \$\begingroup\$ They can bee used as a Memory element,As FG is kept highly insulated, the previous gate voltage is stored in FG and it has a good tendency to maintain that charge,I wont yet say its a 2 terminal device,we used these in Flat panel displays,as they acted as cold cathode,but we dont use them now as their Temp range is limited. \$\endgroup\$
    – MaMba
    Jul 15 '15 at 4:33
  • \$\begingroup\$ Thank you for responding. However, I'm not so much asking what an FGMOS is as I am asking what is the MOSFET connected to V_tunn doing for the FGMOS in a general sense. If the transistor is there to maintain a floating node, why not just make it a capacitor connected to V_tunn instead of a transistor? \$\endgroup\$
    – DTaerts
    Jul 15 '15 at 17:35
  • \$\begingroup\$ It acts like a memory element and stores the previous gate charge,even when the bus is tri-stated,ie in high impedance form(can be said floating),hence they help to be a non-volatile memory,also the whole setup is called FGMOS,as you have FNT connected to a MOS,capacitor cannot be used as they lose the charge , for those you need to refresh the logic value(charge stored) using a extra strobe in your Machine cycles,as you have to keep it within a range,or you get error,you dont need this in FG cells as they have a very high order resistance isolation.It is charged using the tunneling effect. \$\endgroup\$
    – MaMba
    Jul 16 '15 at 13:05
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That is a mosfet used to make a very small capacitor. This is often done so that cmos process variation affect the active transistor and the "capacitor" equally. It also takes up fewer metal layers. What they are using the capacitor for is beyond me.

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