The metal-oxide semiconductor FET (MOSFET) offers a higher input impedance than a JFET. A section view of an N-channel MOSFET is shown in Fig. 1a. An insulating layer of silicon dioxide is grown on top of the region between the N-type source and the N-type drain. The gate is electrically isolated from the source and gate contacts and the source to-drain channel beneath it. The schematic symbol for an N-channel MOSFET is shown in Fig. 1b. The two kinds of MOSFETs are enhancement mode and depletion mode. The depletion-mode MOSFET has a lightly doped source-to-drain channel, whereas the enhancement-mode version does not.
Figure 1 Metaloxide semiconductor FET (MOSFET): (a) section view, and (b) symbol.