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Homework Help: Floating gate potential of a MOSFET

  1. Feb 10, 2010 #1

    First of all, I posted a similar question in [1] but I think it is the wrong forum and wrong question (maybe the reason why I get no answer...).

    I have to solve this (I think easy?) exercise:

    http://img705.imageshack.us/img705/8241/floatingmosfet.png [Broken]

    I think (3.1) is easy and I solved it. I also solved (3.2) but my solution is so primitive that I think it is wrong.

    In (3.2) I should express [tex]\phi_F[/tex] as a function of [tex]t[/tex] if I apply a ramp function (i.e. switch on with a high voltage [tex]V_{pp}[/tex]).

    If I look at it, the one parameter dependent on the gate voltage is [tex]V_g[/tex] (which is just replaced by [tex]V_{pp}[/tex]) and [tex]Q_F[/tex].

    The current which flows from/to the floating gate is given by the formula in the problem statement but I think it is NOT dependent on time ... What do you think?!

    If this is the case I just integrate [tex]I[/tex] from [tex]0[/tex] to [tex]t[/tex] in order to get the total charge but of course this is only linear behavior which also grows without stopping!

    So my total solution would be:

    [tex]\phi_F(t) = \frac{C_1 V_{pp} + t \cdot A \cdot E^2 \cdot e^{-\frac{B}{E}}}{C_1 + C_2}[/tex]

    Do you think this is true or am I on the wrong way?

    Best regards,

    [1] https://www.physicsforums.com/showthread.php?t=376713
    Last edited by a moderator: May 4, 2017
  2. jcsd
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