describe construction ,working principle  and transfer characteristics of FET transistor and JFET transistor ?FET is Fild effect transistor AND JFET is junction Type Field Effect transistor

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valentin68 eNotes educator| Certified Educator

In the following we will describe the construction, working principle  and characteristics of a MOSFET transistor. The JFET transistor is similar in many aspects to the MOSFET transistor.

A MOSFET transistor is usually made on a silicon P substrate by making two separated N regions, thus obtaining two PN junctions. The P region that separates the two N regions is called the channel, and has a layer of SiO2 insulator deposited on it. Metallic contacts are made on the two N regions (the drain and source) and over the insulator deposited over the channel (the gate). The working principle is the following: normally when a voltage is applied between drain and source, there is one (of a total of two) pn junction reverse biased. The transistor does not conduct. When a positive voltage is applied to the region gate-source, it will attract electrons just under the insulator layer creating a conducting layer on the surface of the p semiconductor between the n regions. Thus the transistor will open and begin to conduct. The resistance of the channel can be varied by varying the width of the channel (the gate-source voltage) until a saturation regime is attained.

The I-V characteristic of the MOSFET is made up of a cut-off region (1), when the channel is closed and the transistor does not conduct, a linear region when the transistor is just opened and the conductivity of the channel is proportional to the voltage applied between gate and source (2) and a saturation region, when the channel is widely open (3).  The saturation current and voltage increases with increasing the applied voltage between gate and source.

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reddynagaraju1 | Student

describe construction ,working principle  and transfer characteristics of FET transistor and JFET transistor ?


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