V-FET and SIT
The static induction transistor (SIT) is a three-terminal semiconductor device. Similarly to other active devices (like the bipolar-junction transistor (BJT) or the junction field-effect transistor (JFET), in a SIT the current flow between two terminals (the source and the drain) can be controlled through the third terminal (the gate).
Static induction transistor (SIT) was invented by Y. Watanabe and Professor Junichi Nishizawa of Tohoku University in 1950 with a multichannel structure; it controlled current flow by means of the static induction or electrostatic field surrounding two opposed gates. Many years passed before transistor fabrication technology was sufficiently developed to take advantage of this concept. In 1975, however, experimental SITs were fabricated and the source-drain current of this device was shown to follow the predicted space-charge injection model.
A FET amplifier is an amplifier that makes use of one or more field-effect transistors (FETs). The most common kind of FET amplifier is the MOSFET amplifier that uses MOSFETs. Using FET for amplification gets high input impedance while low output impedance. The FET can be a 2N5486, 2N4416 or any general purpose FET. Allison Parent, KB1GMX, wrote the following email after suggesting a correction to the circuit: 'I've used the circuit from VLF (100khz) to UHF (432mhz) with good success. I've even used it for a low power amp (20 milliwatts) to drive diode mixers. THE FM3954 monolithic-dual gives us an ideal low-offset and acts as low-drift buffer function for the LM101A op amp.
Static induction transistor (SIT) shows non-saturating I-V character and high-frequency and high-efficiency characteristics as the result of the reduction of the series channel resistance. SIT has a caged type gate electrode similar to the grid in vacuum tube triode and the electro-static potential around the gate electrode control the flow of majority carriers).
The idea was so innovative that the current establishment in the solid state electronics community had difficulty understanding and accepting this discovery.
The IEEE Transactions on Electron Devices the leading IEEE periodical had difficulty finding proper reviewers and as a result the reviewing process continued for years.
Japan was the only country where static induction family devices were successfully fabricated.
As said the SIT has been originally conceived as a solid-state analog of the vacuum-tube triode. The device is normally on, and a reverse bias applied to the gate is used to modulate the drain-source current. In this mode of operation the steadystate current drawn from the gate is negligible, and the SIT can be considered as a voltage-controlled device, like the JFET.
A SIT, however, can also be designed to operate with a forward bias applied to the gate terminal (in this case, the device is called bipolar-mode SIT or BSIT). In this mode of operation a significant current flows through the gate of the SIT and the device becomes current-controlled, similar to a BJT. The BSIT is generally designed as a normally off device and is characterized by a much larger current-handling capability with respect to SIT.
SITs are a class of transistors with a short-channel FET structure in which a current flowing vertically between source and drain is controlled by the height of an electrostatically induced potential energy barrier under the source. This electrostatic barrier develops at pinch-off when negatively charged opposing gate depletion layers coalesce to completely deplete the source-drain channel of mobile charge carriers.
Analogous to the vacuum triode, both the gate (grid) voltage and the drain (anode) voltage affect the drain (anode) current because, in the SIT, the height of the induced electrostatic barrier is influenced by both these potentials.
By 1969, it became a complete device having non-saturating type voltage/current characteristics. One of the main advantages of the SIT device is its high speed switching characteristics. Since no carriers are injected from the gate, switching can be performed at an extremely high speed (without storage effects) and a small gate resistance (rg) is used for minimum high frequency signal loss.
SIT have high input impedance and is a voltage controlled device and therefore low drive power is required at the gate. The absence of electric current concentrations for very high breakdown voltage resistance can be explained by the negative temperature coefficient of the drain current, due to some residual channel resistance, which makes it difficult for thermal runaway to occur. Thus SITs are highly suited for high power applications. The non-saturating current/voltage characteristic is based on the SIT exponential function characteristics due to their reduced negative feedback capacitance. SITs can be defined as a type of V-channel field effect transistor (FET) in which the distance between the source and depletion layer of the drain is so reduced that the negative feedback of the channel resistance will not affect the direct current characteristics. SITs require a negative voltage signal in order to turn off as they are normally-on devices.
They can operate as a unipolar or bipolar device (BSIT). Generally, the unipolar mode is used for high frequency applications whereas the bipolar mode is utilized for circuits handling high power. Reason being, the bipolar mode requires the removal of minority carriers from the bulk substrate, which takes more time, thus maximum frequency is reduced.
However static induction transistors presented here are normally-ON devices, meaning they require the application of a negative gate voltage signal (respect to the positive main voltage Vds) (Vds and Vgs may be opposite) in order to turn the device OFF. In the SIT structure, the gate voltage controls the current flow through the means of depletion regions that extend from the gate junctions into the n-type channel, extending deeper as an increase in the magnitude of the negative gate-to-source voltage. When the device has zero gate voltage or a small negative gate voltage, a small depletion region forms between the p+ / n- interface, and the channel that forms has a width of the distance between the two depletion regions. With a positive drain-source voltage, majority carrier electrons flow from the source to the drain. With large applied voltages and currents, a resistive voltage drop occurs along the length of the channel, causing a distortion in the width of the depletion layers. If the pinch-off voltage Vp is applied to the gate and a large drain to source voltage is applied to the device, full pinch-off does not occur, and current will continue to flow. In order to guarantee full pinch-off under high Vds operation, a voltage must be applied to the gate that is more negative than the rated pinch-off voltage of the device. The requirement of a negative gate voltage is essential to proper device operation.
This latter characteristic is usefully exploited in the production of audio amplifiers in class B or AB because unlike other devices it virtually never turned off completely and therefore also in this mode of operation does not pass completely by the on-state to the off one with all benefits on the sound for the failure to produce artifacts due to oscillations that otherwise would be generated by switching between the aforementioned states.
So a Static Induction Transistor (SIT) is basically a power JFET with a buried gate, as shown in Figure b. Construction as well as operation is reminiscent of a vacuum tube.
V-FET is a V-groove JFET. SIT has an embedded meshlike grid
Other SIT construction and electrical symbol. Typical output characteristics of SIT (n channel) Output characteristics of Yamaha 2SJ24 (p channel)
I became interested in SIT (Static Induction Transistor) since 1985, when an Italian magazine (ELETTRONICA OGGI) did an interesting article about these new devices and their excellent characteristics that promised incredible performance in the field of industrial electronics, telecommunications to very high frequency and in the field of the electronics of low-frequency (audio-frequency amplifiers). In particular for the latter use was captured by the dream of one day come into possession and build around the magnificent power amplifiers for use Hi-Fi. Advantages of using audio could be seen for three main characteristics:
output curves similar to triodes with high linearity and absence of the phenomenon of saturation characteristics;
parasitic capacities significantly lower than other devices of similar power that would have resulted in a much higher operation band.
the device, as mentioned above, unlike all others, never turned off completely, so it exhibits a significant advantage in the realization of class B and AB amplifiers, because here the distortion switching is absent.
I could list other prerogatives, as the increased stability of operation when the temperature varies or the low output impedance, but from the point of view of audio, these three points described above are fundamental, all the rest is a more.
By whom were products such devices? from Japanese TOKIN.
Who saw them? Perhaps anybody in Europe, much less in Italy.
And Internet? At that era Internet do not existed or were very little information around. For a while the mystery behind the VFET was obscured by lack of data and curves. However since then I have done continuous researches without find anything about. After several years of unsuccessful attempts, finally begins to find some news about it. People began to realize that SIT and V-FET had a lot in common. Indeed they could be considered synonyms as they had the same operating principle and the same type of curves (triode like), as well as the same inventor.
In the audio field such devices were known as V-FET (mainly by Sony) referring to the construction technology, the 'V-shaped vertical channel' (see diagram above), while in industry were known as SIT stands for Static Induction Transistor referring to the physical principle relative to the 'ELECTROSTATIC' field which with its 'INDUCTION' governs the operation.
At the end with the names V-FET, VJFET and SIT we intend the same class of devices.
If we thinking about applications for which they are intended, today there may be a subdivision:
Fet Amplifier Circuit Diagram
Англо-русский словарь технических терминов. 2005.
Fet Amplifier Pdf
Смотреть что такое 'planar FET' в других словарях:
Fet Amplifier Calculator
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