Electronics & Software – Tips & Guide


Why MOSFETs are voltage-controlled devices?

MOSFETs are voltage-controlled devices.

The basic principle of the operation of a mosfet involves the accumulation of a charge carrier near the semiconductor boundary, and the concentration of the carrier is determined by the strength of the external electric field directed at the semiconductor. this field is made using the applied stress on metal plates separated from the bulk semiconductor through the most common, silicon dioxide insulating layer. then the name of mos, ie the metal oxide semiconductor.

According to the electrostatic law, the electric potential is nothing but the integral line of the field along the distance. because the field strength determines the carrier concentration at the semiconductor-oxide edges, it is applicable, decided by the voltage applied to the metal plate. further, because the oxide isolator, there is no possibility of current flowing between the metal and the semiconductor.

Field-gate effect transistors (igfet), also known as metal oxide field effect transistors (mosfet), are derivatives of field effect transistors (fet). today, most of the transistors are mosfet type as a component of integrated digital circuits. although discrete bit more than discrete MOSFET. the number of mosfet transistors in integrated circuits can approach hundreds of millions. dimensions of individual mosfet devices are below microns, decreasing every 18 months. a much larger mosfet capable of switching nearly 100 amperes of current at low voltages; some handle almost 1000 v at a lower current. this device occupies a fraction of the square centimeter of silicon. MOSFETs find applications that are much wider than jfet. However, mosfet power devices are not widely used as transistors of current bipolar connections.

Mosfet has source, gate, and terminal disposal like fetus. However, the gate gate does not make a direct connection to silicon compared to the case for the fetus. the mosfet gate is a metal or poly silicon layer above the silicon dioxide insulator. this gate has a resemblance to the metal oxide semiconductor capacitor (mos) in the image below. when charged, the capacitor plates take the polarity charge of each battery terminal. the bottom plate is a p-type silicon from which the electron is rejected by the negative battery terminal (-) to the oxide, and is attracted by the positive top plate (+). the excess electrons near the oxide create an inverted channel (excess electrons) below the oxide. this channel is also accompanied by a depletion region that isolates channels from mass silicon substrates.

A mosfet, like a fet, is a voltage controlled device. the input voltage to the gate controls the current flow from the source to flow. the gate does not draw a continuous current. though, the gate draws current spikes to fill the gate capacitance.