Research done as part of High Productivity Computing Systems DARPA project.
[1] Partially funded by a $50 million award from the Defense Advanced Research Projects Agency.
Comparing traditional area ball bonding, proximity communication has one order smaller scale, so it can be two order denser (in terms of connection number/PIN) than ball bonding.
This technique requires very good alignment between chips and very small gaps between transmitting (Tx) and receiving (Rx) parts (2-3 micrometers), which can be destroyed by thermal expansion, vibration, dust, etc.
Proximity communication can be used with 3D packing on chips in Multi-Chip Module, allowing to connect several MCM without sockets and wires.