_______________________________________________________________________ Special Devices
Figure 3-52. MOSFET Symbols
3-90. Figure 3-53 shows the construction of an N-channel MOSFET. Heavily doped
N-type regions (indicated by the N+) are diffused into a P-type substrate or base. A
channel of regular N-type material is diffused between the heavily doped N-type regions.
A metal oxide-insulating layer is then formed over the channel and a metal gate layer is
deposited over the insulating layer. There is no electrical connection between the gate and
the rest of the device. This construction method results in the extremely high input
impedance of the MOSFET. Another common name for the device, derived from the
construction method, is the insulated gate field-effect transistor.
Figure 3-53. Construction of an N-channel MOSFET
23 June 2005