The Bank of Japan's staff made two proposals; one to expand the bank's massive asset-buying program and another to add negative interest rates to asset purchases, at the January rate review, minutes of the meeting showed on Friday.
The BOJ eventually decided to adopt the negative interest rate policy after several members argued the move would help forestall the risk of external factors delaying the eradication of Japan's "deflationary mindset," the minutes showed.
The BOJ unexpectedly deployed the negative interest rate policy in January to stimulate the economy, although four of the nine board members dissented the decision, which drew criticism from lawmakers for failing to boost stock prices or arrest an unwelcome rise in the yen.
The central bank kept policy settings unchanged at a subsequent meeting in March but offered a bleaker view on the economy, signalling its readiness to roll out further stimulus if needed to hit its ambitious 2 percent inflation target.