![]() ![]() This is called carrier drift, and logically changes the charge concentration distribution within the semiconductor.įigure 4: Carrier Drift in Semiconductors The free electrons, evenly distributed throughout the semiconductor, are attracted to the electric field’s point of entry (in the case of a MOSFET with a positive gate voltage this is the gate electrode), whereas the holes will be dragged in the direction of the electric field opposite to the electrons (see Figure 4). When an electric field is applied to a semiconductor, it acts upon the device’s free charge carriers. holes or electrons), and pulls them up close to the gate to form a channel or pushes them away to destroy the channel. This electric field has an effect on the free charge carriers in the substrate semiconductor (e.g. Therefore, when a voltage is applied to the gate, an electric field is generated from the metallic gate, through the oxide, to the silicon substrate (metal-oxide-semiconductor). The gate pin is connected to a conductive electrode, which is separated from the substrate by a layer of silicon oxide or another dielectric material. MOSFETs get their name from the structure through which they are controlled. ![]() Conversely, if the substrate is N-type, the channel will be P-type, so the MOSFET is called a P-channel MOSFET, or PMOS transistor.įigure 3: MOSFET Structure Enhancement vs. These are called N-channel MOSFETs, or NMOS transistors. MOSFETs can be built to have a P-type substrate and an N-type drain and source regions, which means that in order for current to flow from the drain to the source the channel will also have to be N-type. The simplest MOSFET structure is comprised of a substrate, which can be P-type or N-type, and two areas of silicon of the opposite polarity to the bulk, which make up the drain and the source (see Figure 3). Figure 2 shows the difference between P-type and N-type semiconductor dopants, and the effect they have on the silicon structure.įigure 2: Dopants – Donor vs. ![]() These impurities are also called acceptor impurities. On the other hand, elements with three electrons in the valence band will be lacking an electron, which is equivalent to contributing a hole, meaning the overall charge will be positive (P-type). Since they contribute an electron, these impurities in the silicon are called donor impurities. ![]() If an area of silicon has been doped with ions that have five valence electrons (group 5 in the periodic table) then there is an extra electron that is set free into the semiconductor, so the charge will be overall negative (N-type). The difference between these two silicon types is the charge stored by the dopant ions, which are charged particles that are injected into the silicon to create charge instability, making the element useful for electronic purposes. MOSFETs are semiconductor-based devices, and are mostly built using either P-type or N-type silicon. In most cases, the MOSFET’s bulk is connected to the source, which is why MOSFETs are commonly referred to as 3-pin devices.įigure 1: MOSFET P-Channel MOSFETs vs. When the MOSFET is turned on, current flows from the drain to the source of the MOSFET, through a channel created in the bulk (also called the body). The MOSFET is controlled by applying certain voltage conditions to the gate. These devices act as voltage-controlled current sources, and are mainly used as switches or for the amplification of electrical signals. Lattice Semiconductor Reference DesignsĪ metal-oxide-semiconductor field-effect transistor (MOSFET) is an electronic device that falls under the category of field-effect transistors (FETs).Switching Converters and Controllers AECQ Grade.BLDC Pre Drivers and Integrated Solutions.Digital Isolators with Integrated Power.Multi Phase Controllers & Intelli-Phase. ![]()
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