Why Did the U.S. Stop Using Silver Certificate Currency?

By GovMint :

Silver certificates were once a popular form of U.S. currency, representing a promise to pay the bearer a specific amount of silver on demand. However, the U.S. Treasury Secretary announced such certificates would stop being redeemable for silver in 1964 with issuance stopping soon thereafter. Today such certificates can be redeemed for their face value rather than an equivalent amount of silver. The phasing out of Silver Certificates was largely due to the rising value of silver which made it impractical to continue backing currency with the precious metal. Additionally, the shift towards a fiat currency system, where money is not backed by physical commodities, further diminished the need for silver certificates.

Sources Used:

https://www.investopedia.com/terms/s/silver-certificate.asp