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)