I can't recall ant CB going negative on their cash rate. .25% is...

I can't recall ant CB going negative on their cash rate. .25% is more a mechanism than a real rate. Maybe it's CB psychology that the cash rate should always remain positive. Imagine a bank having to pay to have billions of required reserve funds on deposit with the RBA!!! But then there would be the discouragement to lodge excess funds which is a good thing. Except that the bank could start messing around with risk on trading.

Desirable? Because a CB has unlimited access to funds then I'd say bond buying would be the weapon of choice to drive rates down into negative territory.