Understanding IGBT Structure:

           For better understanding of the IGBT structure it is recommended to read the IGBT Basics

• The generic n-channel IGBT structure is shown in the above figure.
• This structure is similar to the structure of MOSFET except the presence of  p+ layer( which is connected to the drain terminal).
• The doping levels of each IGBT layers are similar to the doping levels of each layer of MOSFET except the body region.
• As mentioned in the figure, the IGBT structure has a parasitic thyristor. Turn off of this SCR is undesirable.
• Similar to MOSFET structure, the IGBT does retain the extension of the source metallization over the body region.
• The body source short in the IGBT helps to minimize the possible turn-on of the parasitic thyristor.
• The n+ buffer layer between the p+ drain contact and the n- dirft layer is not important for the operation of the IGBT.
• Some IGBTs are made without this layer which is called as Non-Punch-Through (NPT - IGBT)
• IGBTs manufactured with this buffer layer is called as Punch-Through (PT-IGBT)