V-MOS

VMOS (V-MOSFETS)

A VMOS is an enhancement MOSFET that can handle much higher drain currents than standard E-MOSFETS (Enhanced-MOSFETS). The "CURRENT" capability of a VMOS transistor results from its physical make-up or construction. The V-MOSFET has a "WIDER CHANNEL" than other E-MOSFETS. The "WIDER CHANNEL" allows a higher "DRAIN CURRENT" to be generated at a given value of Vgs or "source gate voltage" Also, another advantage of the VMOSFET is that it is not susceptible to thermal runaway. The VMOS has a positive temperature coefficient, which means that the channel resistance increases when temperature increases.

Therefore V-MOSFETS can be used in high-power applications where standard MOSFETS cannot be used.

VMOS (pronounced /ˈviːmɒs/), is an acronym for Vertical Metal Oxide Semiconductor (Transistor). Vmos is also used to describe the V-groove shape vertically cut into the substrate material metal oxide semiconductor transistor.

The "V" shape of the MOSFET's gate allows the device to deliver a higher amount of current from the source to the drain of the device. The shape of the depletion region creates a wider channel, allowing more current to flow through it.

The device was used as a power device until more suitable geometries, like the UMOS (or Trench-Gate MOS) were introduced in order to lower the maximum electric field at the top of the V shape and thus leading to higher maximum voltages than in case of the

VMOS Field Effect Transistor

VMOS field effect transistor or FET, electronics components used in many applications to give higher power performance than traditional FETs.

VMOS field effect transistors or FETs are a form of power MOSFET and these electronics components are used for a variety of applications where medium powers are required. The VMOS FET gains its name from the fact that it is "Vertical Metal Oxide Silicon". From this it can be imagined that the VMOS FET has many similarities to MOS technology, but the structure is arranged with a V-groove which also adds another dimension to the name VMOS.

When VMOS FETs were first introduced they out-performed bipolar semiconductor technology in many respects making the design of amplifiers much cheaper and easier. Since their introduction VMOS FETs have become firmly established as useful power MOSFET electronics components that can be used for a variety of power MOS applications ranging from power supply switching applications through to medium power RF amplifiers. They are also incorporated into many integrated circuits as they are able to switch very quickly.

VMOS FET structure

VMOS FETs are able to overcome many of the problems which prevented FETs being used in power applications. Their new structure enabled much higher powers to be handled than was previously possible with bipolar transistors of an equivalent size and cost.

The reason for this great improvement lies in the structure of the device. To show the advantages of a VMOS FET a traditional MOS device. Here it can be seen that the drain and source are separated by the gate. Current flows horizontally between the source and drain, controlled by the potential on the gate. As the current only flows through a relatively small area, resistance values can be high reducing the efficiency of the device.

The VMOSFET uses a different structure. The most striking point about the new device is the V groove in the structure which is the key to the operation of the device. It can be seen that the source is at the top of the device, and the drain is at the bottom. Instead of flowing horizontally as in the standard FET, current in this device flows vertically giving the device its name - Vertical Metal Oxide Silicon, VMOS.

VMOS field effect transistor structure:

The device uses two connections for the source and accordingly there is a much large area through which the current can flow. This reduces the ON resistance of the device allowing it to handle much higher powers than conventional FETs.

The gate consists of a metallised area over the V groove and this controls the current flow in the P region. As the gate is fabricated in this way it means that the device retains the exceptionally high input resistance typical of the MOS family of devices.

DEMERIT:

· Structure is more complicated than a traditional FET

· More expensive.