Construction of enhancement type N channel MOSFET

Enhancement mode :

When the gate voltage is negative with respect to source, the depletion type MOSFET (metal oxide semiconductor field effect transistor) operates with an enhancement mode.

The construction of N channel enhancement type MOSFET (metal oxide semiconductor field effect transistor) is shown in above figure. Onto a lightly doped P type substrate, two heavily doped N regions separated by about 25 µm are diffused. These N regions will act as a source and drain. A thin layer of insulating SiO₂ is developed over this surface and holes are cut into the oxide layer through which aluminum contacts for the source and the drain are made. A conducting layer of aluminum which will act as gate is overlaid on SiO₂ over the entire channel region. The construction of enhancement type N channel MOSFET is different from the depletion type MOSFET in the sense that it has no physical channel. It may be noted that the P type substrate extends the SiO₂ layer completely.