A few years ago, Paul Krugman had a similar suggestion of having $1 trillion coins minted from 1-oz of platinum as a way to deal with the debt ceiling. But since platinum isn't worth anywhere near $1 trillion/oz, the coins could also be made from anything else that isn't worth $1 trillion/oz either -- wood, plastic, copper, paper...
But whatever is used to mint those coins, each one would mean an additional $1 trillion of currency put into circulation. Hyper-inflation anyone?