Nearly one in five German companies has faced being charged for parking cash at its bank as a result of the European Central Bank's negative rate policy, the Ifo economic institute said today.

Only 8% of all companies eventually accept the charge, with most others escaping it through negotiations or by switching banks, Ifo's survey of 4,000 companies showed.

Alternatively, they use the cash to pay off debt or invest.

An International Monetary Fund report found that negative interest rates imposed by central banks had generally worked as a tool to boost inflation

While likely to stoke frustration among German entrepreneurs, the findings partly vindicate the ECB's policy, whose aim was indeed to stimulate investment and ease the deleveraging process.

"In particular, the last reaction (investing) is interesting from a macroeconomic perspective because it has not only a monetary, but also a real-economic impact," Christa Hainz, one of the authors of the study at Munich-based Ifo, said.

An International Monetary Fund report earlier this month found that negative interest rates imposed by central banks, including the ECB, had generally worked as a tool to boost inflation, pulling down yields and sometimes weakening currencies.

Germany has been stepping up its calls on the ECB to start winding down its stimulus policy of negative or ultra low rates and massive bond purchases in light of a rebound in inflation in recent months.

But ECB President Mario Draghi has emphasised price growth is still below the ECB's target of almost 2% and several rate setters are reluctant to withdraw their monetary support.

The Frankfurt-based central bank is likely to postpone a decision on the future of its bond-buying programme until October, rate-setters told Reuters after their July 20 policy meeting.