Google Brain team homepage is a good general source of information [0], and the HotChips [1] conference is perhaps the best source for research information regarding latest ML ASIC designs from Google [2], Intel, ARM, Wave, IMG and others. Google TPU3 systems are discussed extensively, here [3].
[0]: https://ai.google/research/teams/brain [1]: https://www.hotchips.org [2]: https://www.hotchips.org/wp-content/uploads/hc_archives/hc29... [3]: https://www.nextplatform.com/2018/05/10/tearing-apart-google...