Some important charts at the st louis fed. In 2008 "Interest On Reserves" IOR was introduced, which allowed banks that held their money at the federal reserve to receive interest payments at this rate.
Casually added a new mechanic as a result of the gigantic reserve injection from financial crisis
IOR - https://fred.stlouisfed.org/series/IORB#:~:text=The%20interest%20rate%20on%20reserve%20balances%20(IORB%20rate)%20is%20the,important%20tool%20of%20monetary%20policy.
Federal Funds Rate - https://fred.stlouisfed.org/series/FEDFUNDS
Reserve Balances - https://fred.stlouisfed.org/series/WRESBAL