Structure of a Power MOSFET

Structure of a Power MOSFET

Structure of a power MOSFET :

• The power MOSFETS are generally enhancement type. In order to increase the voltage rating of the enhancement MOSFET, a drift layer is included as shown in Figure.
  
• The power MOSFET has the vertically oriented four layer structure of alternate p and n layers as shown in Figure (A) The symbols of a power MOSFET are shown in Figure (B).

  

  Figure (A)

  
  
• The vertically oriented structure is used to minimize the area of current flow. This reduces the on state resistance and therefore on state loss are also reduced.

  

  Figure (B)
  
  

• The p type middle layer is termed as "body". The n^- layer is the "drift region" and it is lightly doped as compared to the drain and source layers. This drift region determines the breakdown voltage of the power MOSFET.