It has been suggested that Uses of jfet be merged into this article or section. (Discuss)

Electric current flow from source to drain in a p-channel JFET is restricted when a voltage is applied to the gate.

The junction gate field-effect transistor (JFET or JUGFET) (not to be confused with Jango Fett) is the simplest type of field effect transistor. Like other transistors, it can be used as an electronically-controlled switch. They are also used as voltage-controlled resistances. An electric current flows from one connection, called the source, to a second connection, called the drain. A third connection, the gate, determines how this current flows. By applying an increasing negative (for an n-channel JFET) bias voltage to the gate, the current flow from source to drain can be impeded by pinching off the channel, in effect switching off the transistor. Image File history File links Please see the file description page for further information. ... It has been suggested that this article or section be merged into JFET. (Discuss) The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... This diagram of a junction gate field effect transistor (JFET) was created and uploaded by User:Rparle on September 19, 2004. ... This diagram of a junction gate field effect transistor (JFET) was created and uploaded by User:Rparle on September 19, 2004. ... Electric current is the flow (movement) of electric charge. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Jango Fett is a fictional character from the Star Wars universe. ... Large power N-channel field effect transistor The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ... Electronics is the study of the flow of charge through various materials and devices such as, semiconductors, resistors, inductors, capacitors, nano-structures, and vacuum tubes. ... Electrical switches. ... Electric current is the flow (movement) of electric charge. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ...

Structure

Circuit symbol for an n-Channel JFET

Circuit symbol for a p-Channel JFET

The JFET consists of a long channel of semiconductor material. This material is doped so that it contains an abundance of positive charge carriers (p-type), or of negative charge carriers (n-type). There is a contact at each end; these are the source and drain. The third control terminal, the gate, surrounds the channel, and is doped opposite to the doping-type of the channel.Then, a pn junction is formed at the interface of the two types of the material and one has to make sure that the terminal made with the semiconductor are usually made Ohmic. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... A semiconductor is a fuckin solid whose electrical conductivity is in between that of a metal and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... In semiconductor production, doping refers to the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor in order to change its electrical properties. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... An electrical connector is a device for joining electrical circuits together. ... Doping is generally the practice of adding impurities to something. ... Categories: Possible copyright violations ... An ohmic contact is a region on a semiconductor device that has been prepared so that the current-voltage (I-V) curve of the device is linear and symmetric. ...

Function

The operation of a JFET can easily be understood by considering a garden hose. The flow of water through a garden hose can be controlled by squeezing it and reducing its cross section; the flow of electric charge through a JFET is controlled by constricting the cross section of the current-carrying channel. Look up hose in Wiktionary, the free dictionary. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... A 3-D view of a beverage-can stove with a cross section in yellow. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ...

About the drawing symbols

Sometimes the JFET gate is drawn in the middle of the channel instead of at the drain/source electrode as in these examples. This symmetric variation is hinting at that the channel is indeed symmetric in sense that drain and source are interchangeable physical terminals. So this symbol variation should be used only for JFETs where drain and source indeed are interchangeable, which is not true for all JFETs.

Traditionally, the US style of the symbol was drawn with the whole component inside a circle, although this has been simplified in favor of the European style to draw it without a circle.

In every case the arrow head indicates the polarity of the P-N-junction of the gate in relationship to the channel. (As with a diode, the arrow points from P to N, indicating the direction of current flow when forward-biased.) In order to pinch off the channel, one must produce a certain voltage in reverse direction (V_GS) of that junction. The precise value of this pinch off voltage varies with individual JFETs, even with JFETs of the same type, typical values ranging between 0.5 to 10 V. Types of diodes. ...

The appropriate voltage bias can be remembered easily, since the n-channel device requires a negative gate-source voltage (V_GS) to switch off the JFET, while the p-channel device requires a positive gate-source voltage (V_GS) to switch off the JFET.

Comparison with other transistors

The JFET gate presents a small current load which is the reverse leakage of the gate-to-channel junction. The MOSFET has the advantage of extremely low gate current (measured in picoamperes) because of the insulating oxide between the gate and channel. However, compared to the base current of a bipolar junction transistor the JFET gate current is much lower, and the JFET has higher transconductance than the MOSFET. Therefore JFETs are used to advantage in some low-noise, high input-impedance op-amps and sometimes used in switching applications. A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. ... The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ... Current can be measured by a galvanometer, via the deflection of a magnetic needle in the magnetic field created by the current. ... A bipolar junction transistor (BJT) is a type of transistor. ... Transconductance, also known as mutual conductance, is a property of certain electronic components. ... In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ... A 741 operational amplifier in a TO-5 metal can package An operational amplifier, usually referred to as an op-amp for brevity, is a DC-coupled high-gain electronic voltage amplifier with Differential Inputs and, usually, a single output. ...

The JFET had been predicted as early as 1925 by Julius Lilienfeld, and the theory of operation of the device was sufficiently well known by the mid 1930's for a patent to be issued for it. However, technology at the time was not sufficiently advanced to produce doped crystals with enough precision for the effect to be seen until many years later. In 1947, researchers John Bardeen, Walter Houser Brattain, and William Shockley were attempting to construct a JFET when they discovered the bipolar junction transistor. The first practical JFETs were thus constructed many years after the first bipolar junction transistors, in spite of having been invented much earlier. Julius Edgar Lilienfeld (18 April 1881 – 28 August 1963) was born in Lemberg in Austria-Hungary (now called Lviv in Ukraine). ... Year 1947 (MCMXLVII) was a common year starting on Wednesday (link will display full 1947 calendar) of the Gregorian calendar. ... John Bardeen (May 23, 1908 – January 30, 1991) was an American physicist and electrical engineer. ... Walter Houser Brattain (February 10, 1902 – October 13, 1987) was a physicist at Bell Labs who, along with John Bardeen and William Shockley invented the transistor. ... William Bradford Shockley (February 13, 1910 – August 12, 1989) was a British-born American physicist and inventor. ... The schematic symbols for pnp_ and npn_type BJTs. ...

Mathematics

Current in N-JFET due to a small voltage V_DS is given by:

where

• 2a = channel thickness
• W = width
• L = length
• Q = electronic charge = 1.6 x 10^-19 C
• μ = electron mobility

In saturation region: This does not adequately cite its references or sources. ...

In linear region

External links

• Physics 111 Laboratory -- JFET Circuits I pdf
• Interactive Explanation of n-channel JFET