AMP's banking division generated significantly higher cash account and term deposit inflows through superannuation funds than through retail distribution during the June half.AMP Bank's super fund net inflows were A$804 million during the six months to June, compared with retail net inflows of $626 million.In its financial report, AMP said: "The proportion of deposits sourced from superannuation and investment fund platforms continues to grow as customers continue to increase their allocation to cash."Last year, AMP Bank added its term deposits and cash accounts to the North and Summit superannuation platforms, which formed part of AMP's acquisition of Axa. Since then the two platforms have generated more than $400 million in deposits.Overall, deposits grew by 20 per cent to $8.6 billion. The bank's mortgage book grew by eight per cent to $12 billion. AMP Bank reported operating earnings of $29 million for the six months to June - down from $30 million in the December half. Revenue was down one per cent. Strong mortgage growth was tempered by lower net interest margins.AMP Bank's net interest margins for the June half was 1.45 per cent - down from 1.55 per cent in the December half. The contraction in NIM was due to higher funding costs. The cost-to-income ratio rose from 33 per cent in December to 36 per cent in the latest half.The bank has a total of $3.5 billion of residential mortgage-backed securities on issue. Its most recent issue was a $650 million RMBS in May this year.