Japan Short Term Long Term Bond Spread

Earlier today I posted a chart of the flattening US yield curve.  I thought for reference it might be interesting to look at Japan's yield curve over the last few decades.  The curve hasn't ever quite inverted, but has gotten to a 0.5% spread on a few occasions.

It's important to note that it's not clear what the maturity of the short term bond is from the data source that I pulled this from, so this isn't necessarily an apples to apples comparison to the US chart.  It looks to me like the short term chart may be more equivalent to a fed funds rate than a 2 yr bond.  It's an interesting chart in its own right and is posted below.

Japan has been in ZIRP for over a decade.  There remains no empirical evidence that ZIRP is effective in stimulating economic growth.