Google is getting deeper into silicon, both datacenter and device. That R&D has substantial capital costs which I think are still included in R&D top line.
The silicon would be to save money compared to general purpose compute. The savings should overcome any fixed cost. Doubt it's having that great an impact to R&D cost growth.
whereas revenue went 65,118,000,000 to 69,092,000,000. Somewhat less of an increase.
You'd assume R&D is mostly fully loaded costs of engineers, but I suppose someone who really knows the financials could tell us for sure.