Multi-VT Cells:

• By implanting dopants in different concentration Different threshold voltages are achieved.
• Need Multi-VT Library
• Sub-threshold leakage varies exponentially with VT compared to the weaker dependency of delay over VT
• If the optimization target is power performance, first use the HVT cells library and then try LVT cells 
• If the optimization target is to meet timing then first use LVT cells and then HVT cells
• If you swap the capture flop from SVT to LVT or HVT, there will be very minimal setup/hold impact in most flops, it is of zero impact for hold
• If you swap the launch flop from SVT to LVT or HVT, Setup will be improve and hold will be impacted correspondingly
• High Voltage Threshold (HVT )
• Use in non-timing critical paths
• Use in power critical paths
• Has low leakage and low speed
• Low Voltage Threshold (LVT )
• Use in timing critical paths
• Use in non-power critical paths
• Has high leakage and high speed
• Standard Voltage Threshold/ Regular Voltage Threshold (SVT/ RVT)
• Medium delay and medium power requirement