Transistor Tutorial MOSFETs

Posted on Feb 5, 2014

The Metal-Oxide-Semiconductor Field-Effect Transistor, or MOSFET for short, is similar in many ways to the junction FET (JFET). Both are voltage-driven unipolar devices that depend on either electron or hole movement-but not both, as does the bipolar transistor. However, there is a fundamental structural difference between the two field-effect tr

Transistor Tutorial MOSFETs
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ansistors: The JFET has three layers while the MOSFET has two. The MOSFET`s simpler construction has give it a performance edge over the JFET, and made it the world`s most popular transistor style. Earlier articles in this series stated that the MOSFET`s controlling gate voltage is applied directly to its channel region across a thin layer of insulating oxide, as shown in Fig. 1-a. This geometry contrasts with that of the JFET, which is controlled by switching an internal PN junction. The MOSFET will work from lower power that the JFET, and its simpler design is reflected in lower production costs. That is why it has become the basis for all CMOS digital logic IC families. Part 9 and Part 11 in this series discussed FET`s. The basic principles of JFET`s and MOSFET`s were explained in the first article of (Electronics Now, February 1993) and the words that describe them were defined. The second article (Electronics Now, March 1993) focused on JFET`s, and included practical JFET circuit schematics. This article concentrates on the enhancement-mode MOSFET, and it includes practical MOSFET circuit schematics base upon small-signal MOS transistors available in a low-cost CMOS integrated circuit. You might wish to review the first two articles to refresh your general knowledge of FET`s before reading this article. There are both N- and P-channel MOSFET`s just as there are both N- and P-channel JFET`s. In the cross-section view of...

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