Metal Oxide Semiconductor

Metal Oxide Semiconductor

The MOS tube is a metal (metal)-oxide (oxide)-semiconductor (semiconductor) field effect transistor, or a metal-insulator (insulator)-semiconductor. The source and drain of the MOS tube can be reversed, and they are all N-type regions formed in the P-type backgate. In most cases, the two regions are the same, even if the two ends are reversed, it will not affect the performance of the device. Such devices are considered symmetrical.

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Basic Information

Name: Metal Oxide Semiconductor

Abbreviation: MOS

Model: Voltage/Current Package

Metal Oxide Varistor Specifications / Definition

Field Effect Transistor (FET), which converts changes in input voltage into changes in output current. The gain of a FET is equal to its transconductance, defined as the ratio of a change in output current to a change in input voltage. N-channel and P-channel are commonly found on the market. For details, refer to the picture on the right (P-channel depletion MOS transistor). The P channel is commonly used as a low-voltage mos tube.

Field effect transistors affect the current flowing through the transistor by projecting an electric field on an insulating layer. In fact, no current flows through this insulator, so the GATE current of the FET tube is very small. The most common FET uses a thin layer of silicon dioxide as an insulator under the GATE. Such transistors are called metal-oxide-semiconductor (MOS) transistors, or, metal-oxide-semiconductor field-effect transistors (MOSFETs). Because MOS transistors are smaller and more power efficient, they have replaced bipolar transistors in many applications.

Construction of Field Effect Transistor:

A field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current. MOSFETs are a type of FET that use a metal oxide semiconductor as the insulating layer between the gate and the channel. The construction of a MOSFET involves depositing a layer of oxide on a silicon substrate, followed by the deposition of metal to create the source, drain, and gate electrodes. The gate electrode is separated from the channel by the oxide layer, and the gate voltage controls the channel conductivity.

Detailed Introduction

First examine a simpler device - a MOS capacitor - to better understand the MOS tube. The device has two electrodes, one metal and the other extrinsic silicon, separated by a thin layer of silicon dioxide. The metal pole is the GATE, and the semiconductor terminal is the backgate or body. The insulating oxide layer between them is called gate dielectric (gate dielectric). The device shown in the figure has a backgate made of lightly doped P-type silicon. The electrical characteristics of this MOS capacitor can be explained by grounding the backgate and connecting the gate to different voltages. The GATE potential of the MOS capacitor is 0V. The difference between metal GATE and semiconductor BACKGATE on WORK FUNCTION creates a small electric field on the dielectric. In the device, this electric field causes the metal pole to have a slightly positive potential and the P-type silicon to have a negative potential. This electric field attracts electrons from the bottom layers of the silicon to the surface, and it simultaneously repels holes from the surface. This electric field is too weak, so the change of the carrier concentration is very small, and the influence on the overall characteristics of the device is also very small.

What happens when the GATE of the MOS capacitor is positively biased with respect to the BACKGATE. The electric field across the GATE DIELECTRIC is strengthened, and more electrons are pulled up from the substrate. At the same time, holes are repelled out of the surface. As the GATE voltage increases, there will be more electrons on the surface than holes. Due to the excess electrons, the silicon surface looks like N-type silicon. The inversion of doping polarity is called inversion, and the inverted silicon layer is called channel. As the GATE voltage continues to rise, more and more electrons accumulate on the surface, and the channel becomes a strong inversion. The voltage at which the channel is formed is called the threshold voltage Vt. When the voltage difference between GATE and BACKGATE is less than the threshold voltage, no channel will be formed. When the voltage difference exceeds the threshold voltage, the channel appears.