Ein MOSFET ist ein aktives Bauelement mit mindestens drei Anschlüssen (Elektroden): G (gate, dt. Steuerelektrode), D (drain, dt. Abfluss), S (source, dt. Quelle). Bei einigen Designs, an additional port B (bulk, substrate) to the outside. In most cases, the bulk is internally connected to the source.
Like other field-effect transistors affects the MOSFET as a voltage-controlled resistor, that is, the gate-source voltage UGS, the resistance between drain and source RDS and thus the current IDS (simplified ID) can be changed by several orders of magnitude by RDS . The key to understanding this change in resistance of a MOS structure is the origin (enrichment types) and destruction (depletion type) of a conducting channel under the gate (see below).
basic types [edit]
Like the bipolar transistor is also the MOSFET in the two basic variants of p-type (also p-type or PMOS) and n-type (also n-type or NMOS) each. If, for example in digital integrated circuits, using both types together, it is called CMOS (English: Complementary MOS). In addition, there are two versions of two forms that differ in their internal structure and the electrical characteristics:
depletion (English: depletion) - also conducting themselves, normal-to normal-conducting
enhancement type (English: enhancement) - also self-locking, normally-off, blocking normal
In practice, used by a large majority enrichment types.
General structure and physical function [Edit]
An example is given of the normally off n-channel MOSFET.
serves as the base material is a weakly p-doped silicon (substrate). In this substrate, two heavily n-doped regions admitted that generate the source and drain connection. Between the two areas is still the substrate, resulting in a npn structure which allows for the time being, no current flow (see npn transistor: Without the transistor base current blocked). Just above the remaining space is now a very thin, durable insulating (dielectric, usually silicon dioxide) is applied. The dielectric separating the overlying gate electrode from the silicon (or more precisely from the canal area). As gate material was bi
s used mid-1980 aluminum, which for n + and p + doped (degenerate) polysilicon (polycrystalline abbreviation Silicon has been replaced).
form by this structure gate terminal, bulk terminal dielectric and a capacitor that is charged when a voltage between the gate and bulk. By the electric field migrate in the substrate minority carriers (electrons in p-silicon) to the boundary layer and recombine with the majority carriers (defect electrons in p-silicon). This affects how a displacement of the majority carriers and is "poverty" is named. At a certain voltage Uth (engl. threshold voltage, threshold voltage) is the displacement of the majority charge carriers such that they are no longer available for recombination stand. There is an accumulation of minority carriers, thereby actually p-doped substrate n close to the insulating-conducting. This condition is called strong "inversion". The resulting thin n-type channel now connects the two n regions the source and drain, which charge carriers (almost) to flow freely from source to drain can.
operation areas of an n-channel MOSFET
In principle, source and drain initially equivalent, usually the structure is not symmetrical, a better behavior to achieve. Moreover, in most types, bulk internally connected to Source as a potential difference between source and bulk properties of the transistor (in particular the threshold voltage) negatively affected (body effect). On the basic function, the connection control. However, this will create an additional diode between source and drain, which is parallel to the actual transistor (with the bulk p-doped substrate and drain connected to the n region form the pn junction). This so-called body diode is shown as an arrow in the symbol for a MOSFET and shows the n-channel MOSFET of the bulk terminal to the channel. If the application is the body diode is usually biased in the reverse direction, with some switching applications However, it can be used to prevent reverse operation. You can run the full drain current of MOSFETs on but relatively slowly, so that used for quick switch external diodes See well. Field-effect transistor
variations in the structure [change]
addition to the conventional MOSFET variants exist several special variants with altered structure. The goal is a better circuit behavior, which is associated with some cases significantly increased manufacturing costs. Examples are the VMOS FET or the FinFET, the latter has the advantage of an increased channel region; because of the channel areas often referred to as dual (tetrode) or tri-gate. [2] [3] They are used for example in RF circuits (RF amplifiers, mixers multiplicative).
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Luis Fernando Cantor B.
Electronica de Estados Solidos
Seccion 2
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