What are VIAs in VLSI?
- To connect between different metal layers, we need poly layer along with the metal layers that we are going to connect. These are basically called as VIAs. From the below picture we can see that green metal is horizontal and blue is vertical, and a poly has been placed in between these two which has been highlighted in yellow. Now, if we have a connection between blue and green, then we will use this via.
Types of VIAs
- There are basically two types of VIAs:
- Single cut via
- Multi cut via
Single Cut Via
Single cut via is a type of via where we have only one poly connection between the two connecting metal layers. Below picture will explain better.
Multi Cut Via
A multi cut via is a type of VIA where there is multiple poly connections between the metal layers and poly.
Note: There are advantages of using multi cut vias over single cut vias. So, we prefer using multi cut vias. They are as follows:
1. More number of connections through vias are safer than one connection. If one connection broke, then other connections present in the via will help.
2. As we know the resistance in parallel makes final resistance lower, so multiple connections in multi cut via results into lower resistance.