has input impedance around 1 megohm
MOSFET (metal oxide semiconductor),
also known as IGFET (insulated gate),
has a layer of insulation above a transistor junction.
very high input impedance, around 1E12 ohm.
most mosfets are enhancement mode (naturally off).
when MOSFET is off, electrons flow from N to P, and then are stopped by a reverse biased junction, from P to N.
voltage on gate creates electric field, causing electrons to migrate toward gate.
electron density sufficiently high that the P material changes to N material in the neighbourhood of gate, creating an N channel.
the N channel means the device is on, and on fully (no junction drop).
true ohmic connection (unlike current mode of BJT)
digression into how a transistor works, depletion mode FET,
IGFET (MOSFET), etc.,
historical context: diode, triode, ...