Metal Oxide Semiconductor Field-Effect Transistors
Metal oxide semiconductor field-effect transistors (MOSFETs) are incredibly popular transistors that in some ways resemble JFETs. For instance, when a small voltage is applied at its gate lead, the current flow through its drain-source channel is altered. However, unlike JFETS, MOSFETs have larger gate lead input impedances (≥1014 Ω, as compared with 109 Ω for JFETs), which means that they draw almost no gate current whatsoever. This increased input impedance is made possible by placing a metal oxide insulator between the gate-drain/source channel. There is a price to pay for this increased amount of input impedance, which amounts to a very low gate-to channel capacitance (a few pF), through the gate and destroy the MOSFET. (Some MOSFETs are designed with safeguards against this breakdown-but not all.) Both enhancement-type and depletion-type MOSFETs come in either n-channel or p-channel forms. MOSFETs are perhaps the most popular transistors used today; they draw very little input c