![]() Another case is when the input gate voltage becomes high enough, the channel increases the depletion layer width and behaves like a resistor. Conversely, when the gate voltage exceeds this threshold, the channel becomes conductive, and the transistor is in the "on" state. When a low voltage is applied below the threshold voltage, the channel remains non-conductive, and the transistor is in the "cut-off" state. The ability to control the conductivity of the channel region with the gate voltage is the fundamental principle that allows MOS transistors to function as electronic switches. The conventional current flows from source to drain, opposite to the flow of electrons. The channel, also called an inversion layer, becomes conductive and enables the flow of current between the source and drain terminals. The p-type channel under the gate terminal becomes more like an n-type region. This electric field induces a change in the electrical properties of the channel region. Since electrons are the majority charge carriers in the N-regions, they move towards the metal under the gate terminal. The polarity of the induced capacitor due to the dielectric SiO2 layer attracts negative charge carriers towards the gate terminal. The silicon dioxide layer enables the production of a capacitance “C” that later goes on to create a conducting channel inside the device. When a voltage is applied to the gate terminal, an electric field is generated across the insulating oxide layer. These regions, known as the source and drain, are separated from each other and are in direct contact with the semiconductor region. The semiconductor material is made up of typically silicon and is doped with impurities to create distinct regions with different electrical properties. Source: WikiCommons- MOSFET four terminals This oxide layer plays a vital role in the operation of the transistor, as it prevents the flow of current directly between the gate and the semiconductor. The gate terminal is separated from the semiconductor material by an insulating oxide layer, usually made of silicon dioxide (SiO2). The basic structure of a MOS transistor consists of three terminals: the gate, source, and drain. 1.1 MOS Transistor Structure and OperationĪlso known as MOSFET, there are two types of MOS transistors- depletion mode and Enhancement mode. In this section, we will explore the structure and operation of MOS transistors, discuss the differences between N-Channel MOS (NMOS) and P-Channel MOS (PMOS) transistors, and examine the key characteristics that define their performance in electronic circuits. ![]() MOS Transistor BasicsĪn understanding of MOS transistor basics is crucial to grasp the operation and applications of these devices in modern electronics. The development has led to significant advancements in technology and enabled the miniaturization of even more electronic components. A trillion MOSFETs are fabricated on a single chip. The most significant use of MOSFET transistors is in VLSI design due to their small size. These transistors provide the basic building blocks for a wide range of devices, from microprocessors to memory chips. MOS (Metal-Oxide-Semiconductor)- NMOS (N-Channel MOS) and PMOS (P-Channel MOS) transistors play a crucial role in modern electronics.
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