The insulating layer of SiO 2 is the reason why this device is called the insulated gate field effect transistor. Metal contacts are made to drain and source and the contact to the metal over the channel area is the gate terminal.The metal area of the gate, in conjunction with the insulating dielectric oxide layer and the semiconductor channel, forms a parallel plate capacitor. Then the gate metal area is overlaid on the oxide, covering the entire channel region. A thin layer of insulation silicon dioxide (SiO 2) is grown over the surface of the structure, and holes are cut into oxide layer, allowing contact with the source and drain. These n+ sections, which will act as source and drain. The N- channel MOSFET consists of a lightly doped p-type substance into which two heavily doped n+ re gions are diffused as shown in the Fig. As with JFET an arrow pointing in represents an N-channel device, while an arrow pointing out represents P-channel device. In the symbol for the MOSFET, the arrow is placed on the substrate. This material is represented in the schematic symbol by the center line that is connected to the source. The foundation of the MOSFET is called the substrate. Since the gate is insulated from the rest of the component, the MOSFET is sometimes referred to as an insulated gate FET or IGFET. Thus going from gate to substrate, we can have metal oxide semi-conductor which is where the term MOSFET comes from. The gate material is made up of metal conductor. This insulating layer is made up of SiO 2, a glass like insulating material. It depends on the gate voltage to form a channel between the source and the drain terminals.īoth MOSFETS have an insulating layer between the gate and the rest of the component. The E-MOSFET on the other hand has no such channel physically. The construction difference between the two is shown in the fig given below.Īs we can see the D-MOSFET have physical channel between the source and The primary difference between them is their physical construction. (1) Depletion type (2) Enhancement type MOSFET.ĭ-MOSFETS can be operated in both the depletion mode and the enhancement mode. E MOSFETS are restricted to operate in enhancement mode. (a) Depletion type MOSFET (b) Enhancement type MOSFET The circuit symbols used by several manufacturers are indicated in the Fig below. Most MOSFETS however are triodes, with the substrate internally connected to the source. We now turn our attention to the insulated gate FET or metal oxide semi-conductor FET which is of greater commercial importance than the junction FET.
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